A SYSTEMATIC TREATISE ON THE OCULAR MUSCLES, 
 
 BY 
 
 G^c. SAVAGE, M.D., 
 
 Professor of Ophthalmology (Defects of the Eye) in the Medical Department of Vanderbilt 
 
 University, Author of " New Truths in Ophthalmology," and " Ophthalmic Neuro- 
 
 Myology," Ex-President of the Nashville Academy of Medicine, Ex-Presider.t 
 
 of the Tennessee State M.edical Association, Ex-President of 
 
 the Southern Medical Association. 
 
 EIGHTY-FOUR ILLUSTRATIVE CUTS AND SIX PLATES 
 
 SECOND EDITION 
 
 PUBLISHED BY 
 THE AUTHOR, 137 Eighth Avenue, North, Nashville, Tenn. 
 
 PRINTED BY 
 McQuiDDY PRINTING COMPANY, Nashville, Tenn. 
 
 1911. (i)
 
 o 
 
 Entered, according to Act of Congress, in the year 1902, 
 
 BY THE AUTHOR, G. C. SAVAGE, 
 In the Office of the Librarian of Congress, at Washington. 
 
 Revised, reprinted, and re-copyrighted 
 
 BY THE AUTHOR, G. C. SAVAGE, 
 
 July, 1911. 
 
 (ii)
 
 PREFACE TO THE SECOND EDITION. 
 
 The bringing 1 out of this edition has been delayed two 
 years longer than the author had intended, the first 
 edition having been practically exhausted three years ago. 
 He trusts that the delay has served to make this book 
 both more interesting and more convincing. The first 
 chapter has been enlarged by the addition of ninety-one 
 pages; but one hundred and thirty of the one hundred and 
 forty-five pages of this chapter have been newly written. 
 This chapter has been enriched by the addition of 
 twenty-three new illustrative cuts, every one of which 
 helps to make the light of truth, as the author sees 
 it, shine the more vividly. 
 
 For twenty years the author has been at a disadvan- 
 tage in that his teaching, concerning the fundamental 
 principles of ocular rotations, has not been in accord 
 with that of the immortal Helmholtz. The contrast is 
 shown in the parallel columns on pages 32 to 34. The 
 whole of the difference between the teaching of Helm- 
 holtz and that of the author hinges on the correct 
 answers to the following four questions: (1) Is the cen- 
 ter of the cornea always the anterior pole? (2) Is the 
 
 (iii)
 
 iv PREFACE. 
 
 central point of the macula always the posterior pole of 
 the eye? (3) Do all secondary visual lines cross the vis- 
 ual axis at the nodal point? (4) Do all secondary visual 
 lines cross the visual axis at the center of retinal curva- 
 ture the center of rotation? To question (1) Helmholtz' 
 answer was "yes," but the author's answer is "no;" 
 to question (2) the author's answer is " yes," but Helm- 
 holtz' answer was "no;" to question (3) Helmholtz' an- 
 swer was "yes," but the author's answer is "no;" to 
 question (4) the author's answer is "yes," but Helm- 
 holtz' answer was "no." 
 
 The unbiased reading- of the first chapter of this 
 edition will convince the most skeptical that the central 
 point of the macula is the posterior pole of every eye, 
 whether it be the ideal or the nonideal eye; that the cen- 
 ter of the cornea is the anterior pole of the ideal eye only. 
 
 All related principles of ocular rotations stand out 
 clearly in the light of the demonstrated fact that the cen- 
 tral point of the macula is the posterior pole of the eye. 
 
 The so-called "optic axis " of Helmholtz, when not the 
 visual axis, as in the ideal eye, is nothing more nor less 
 than one of the secondary lines of vision. 
 
 The mastery of the fundamental principles, set forth 
 in the first chapter, can be easily accomplished with the 
 aid of the Muscle Indicator, five times depicted in this 
 chapter. There is no condition of a single ocular mus-
 
 PREFACE. V 
 
 cle, or any combination of the ocular muscles, normal, 
 abnormal, or pathologic, which this device will not show; 
 and its construction is based on the following 1 two facts: 
 (1) The center of the macula is the posterior pole of the 
 eye; (2) all indirect visual lines cross the visual axis at 
 the center of retinal curvature, which is the center of 
 rotation. 
 
 No book on the ocular muscles, except this one and its 
 companion volume. "Ophthalmic Neuro-Myology, " has 
 been based on the fundamental principles set forth in 
 the first chapter of this book. If these principles are 
 not correct, this book and its companion volume are 
 worthless. The author has no doubt but that the final 
 verdict of the scientific world will be: " These princi- 
 ples are veritable truths." 
 
 The practical chapters, II. to XII., have had such cor- 
 rections and additions made to them as appeared neces- 
 sary in order to make them clearer and stronger. This 
 is especially true of Chapter III., to which four pages 
 have been added. Everything taught in these chapters 
 is based on the fundamental principles set forth in Chap- 
 ter I.; and the value of every procedure advocated has 
 been established by abundant practical experience.
 
 PREFACE TO THE FIRST EDITION 
 1902 
 
 ART cannot succeed when principles are unknown or 
 ignored. The mechanical or surgical art of readjusting 
 the ocular muscles, when there is maladjustment or im- 
 balance, should be based on the scientific principles un- 
 derlying ocular rotations, else such art should not be 
 practiced. These principles, as simple as they are en- 
 during, are discussed in Chapter I. of this volume, and 
 with sufficient clearness, the author hopes, to enable the 
 reader to fully comprehend them. Without a clear un- 
 derstanding of these principles, it will be impossible to 
 grasp the teaching of subsequent chapters; but in the 
 light of the teaching of Chapter I., the remainder of 
 the book may be easily understood. 
 
 Whenever it has been possible, in the interest of truth, 
 the author has been glad to agree with writers who have 
 preceded him; when forced to dissent from their teach- 
 ings, he has done so cautiously and respectfully, invari- 
 ably giving his reasons for so doing. 
 
 If the aim of the critic and the author hopes that 
 every reader will be a critical reader who may review 
 this volume, shall be the establishment of truth and the 
 
 (vi)
 
 PREFACE. Vll 
 
 dethronement of error, he will not become an object of 
 terror to the author; for he himself has been laboring 1 , 
 through a period of fifteen years, for the accomplishment 
 of the same end, as it relates to the ocular muscles. He 
 believes that what he has taught in this book is true, 
 and that practice based on what he has taught will be 
 correct. He would not promulgate nor perpetuate error 
 if he knew it; therefore the reviewer who, in his own 
 way, points out what he may find to be erroneous is as 
 much his friend as the one who may give emphasis to 
 what he finds to be true. 
 
 In the body of the book the author has given due credit 
 to every writer and thinker on the subjects discussed, 
 whom he had an opportunity to consult, and it only re- 
 mains for him to acknowledge here the helpfulness he 
 has derived from their labors. 
 
 For the mechanical excellencies of the volume, the 
 author, who is also the publisher, is indebted to the 
 printing establishment whose inscription can be found 
 on the title-page.
 
 ILLUSTRATIONS. 
 
 FIG. i. Illustrating rotation of a sphere 3 
 
 FIG. 2. The plane and axis of a rotation 1 1 
 
 FIG. 3. The left monocular spacial pole and field of vision 18 
 
 FIG. 4. The right monocular spacial pole and field of vision 18 
 
 FIG. 5. Rotation of the eye in its orbit 23 
 
 FIGS. 6, 7. Erroneous teaching as to poles of the eye and lines of direc- 
 tion 28 
 
 FIG. 8. True teaching as to poles of the eye and lines of direction ... 28 
 
 FIG. 9. The Le Conte 1882 horopter 36 
 
 FIG. 10. The Le Conte 1898 horopter _ 37 
 
 FlG. II. The equator and the two axes of rotation 44 
 
 FlG. 12. For calculating false torsion in oblique conjugate rotations ... 47 
 
 FlG. 13. Professor Daniel's figure for calculating false torsion 49 
 
 FIG. 14. The fixed vertical and horizontal planes of the head, the two 
 
 eyes in ideal orbits and Listing's plane 72 
 
 FIG. 15. The conjugate and fusion brain centers 93 
 
 FlG. 16. Isogonal circle of the author 97 
 
 FIG. 17. A section of a wooden body representing the surface of binoc- 
 ular single vision 100 
 
 FlG. 18. The primary and secondary isogonal circles 103 
 
 FlG. 19. The Muscle Indicator showing the eyes in their primary posi- 
 tion 112 
 
 FlG. 20. The Muscle Indicator showing the right cardinal secondary 
 
 position of the visual axes 1 16 
 
 FIG. 21. The Muscle Indicator showing the upward cardinal secondary 
 
 position of the visual axes 1 18 
 
 FlG. 22. The Muscle Indicator showing an oblique secondary position 
 
 of the visual axes without torsion (normal) 120 
 
 (viii)
 
 ILLUSTRATIONS. IX 
 
 FIG. 23. The Muscle Indicator showing an oblique secondary position 
 
 of the visual axes with torsion (unreal j 122 
 
 FIG. 24. The field of binocular single vision 124 
 
 FIG. 25. The field of binocular view 124 
 
 FIGS. 24, 25. Both show the binocular spacial pole, meridians and 
 
 parallels 124 
 
 FIG. 26. Binocular spacial meridians and parallels, groups of, and the 
 
 primary isogonal circle 131 
 
 FIG. 27. Shows that a binocular spacial pole, meridians and parallels, 
 would be impossible if the maculas are not the posterior 
 
 poles of the eyes 138 
 
 FIGS. 28, 29. The Stevens phorometer 149, 150 
 
 FIG. 30. The Wilson phorometer 151 
 
 FIG. 31. The monocular phorometer 155 
 
 FiG. 32. The cyclo-phorometer 162 
 
 FiG. 33. The Stevens clinoscope 164 
 
 FIG. 34. The Stevens tropometer 170 
 
 FiG. 35. Showing the retinal areas of binocular fusion 175 
 
 FiG. 36. The Stevens scissors 249 
 
 FIGS. 37, 38. The Stevens forceps 249, 250 
 
 FiG. 39. The Stevens hook 250 
 
 FiG. 40. The Stevens needle holder 250 
 
 FIG. 41. The Price tendonometer 254 
 
 FiG. 42. Retinal fusion areas 289 
 
 FIG. 43. Showing malformation of left Orbit 343 
 
 FiGS. 44, 45, 46. Showing malformation of both orbits 344, 345, 346 
 
 FiG. 47. Hyperphoric exercise set 373 
 
 FiGS. 48, 49, 50, 51. Illustrating cyclophoria 391 
 
 FiG. 52. Illustrating orthophoria of the obliques 391 
 
 FiG. 53. Perry's device for taking cyclo-duction 399 
 
 FiG. 54. Showing frames containing exercise cylinders 411 
 
 FiG. 55. A square, illustrating the changes by non-oblique astigmatism 421
 
 X ILLUSTRATIONS. 
 
 FIG. 56. A rectangular parallelogram, illustrating the changes by non- 
 
 oblique astigmatism 425 
 
 FIG. 57. A square, showing changes by oblique astigmatism 426 
 
 FIG. 58. Showing the shape of a fused square by one who has oblique 
 
 astigmatism, most curved meridians diverging 427 
 
 FIG. 59. Showing changes caused in lines not parallel with chief me- 
 ridians of astigmatic corneas 429 
 
 FIG. 60. A photograph of a rectangle, made by a non-astigmatic lens 431 
 
 FIG. 61. A photograph of a rectangle, made by an oblique astigmatic 
 
 lens 432 
 
 FlG. 62. A photograph of a rectangle, made by a vertical astigmatic 
 
 lens 433 
 
 FIG. 63. A photograph of a rectangle, made by an oblique astigmatic 
 
 lens 434 
 
 FlG. 64. A photograph of a rectangle, made by a horizontal astigmatic 
 
 lens 435 
 
 FIG. 65. Same as Fig. 61, except that the sensitized plate was not at 
 
 the focal interval 436 
 
 FIG. 66. Showing the retinal images of an arrow, when there is no as- 
 tigmatism, or when the astigmatism is vertical or horizontal 437 
 
 FIG. 67. Showing one horizontal image and one oblique image of an 
 
 arrow 441 
 
 FlG. 68. Showing how the arrow would be doubled, except for compen- 
 sating cyclotropia 441 
 
 FIG. 69. Showing the minus cyclotropia that has occurred for fusing the 
 
 two images shown in Fig. 68 443 
 
 FlG. 70. Showing one horizontal image and one oblique image of an 
 
 arrow 444 
 
 FIG. 71. Showing the plus cyclotropia that has occurred for fusing the 
 
 images shown in Fig. 70 445 
 
 FIG 72. Showing two oblique images of the arrow, the obliquity up in 
 
 one eye and down in the other 445
 
 ILLUSTRATIONS. Xl 
 
 FIG. 73. Showing the minus cyclotropia that has fused the images 
 
 shown in Fig. 72 446 
 
 PLATE I. Showing images and object in non-oblique astigmatism and 
 
 in hyperopia and myopia 448 
 
 PLATE II. Showing object and images in diverging oblique astigmatism 453 
 PLATE III. Showing the minus cyclotropia that has fused the dissimilar 
 
 images 457 
 
 PLATES IV., V., VI. Showing arcs of distortion by cylinders. 472, 477, 485 
 FlG. 74. Representing compensating vertical and lateral heterotropia 491 
 
 FIG. 75. The amblyoscope of Worth 546 
 
 FlG. 76. Illustrating the first step of the Fox operation for exotropia . 577 
 
 FlG. 77. Illustrating the second step of the Fox operation 578 
 
 FlG. 78. Illustrating the third step of the Fox operation 579 
 
 FlG. 79. Illustrating paralysis of the right-vertors 606 
 
 FlG. 80. Illustrating paralysis of the left-vertors 607 
 
 FiGS. 81, 82. Illustrating paralysis of the sub-vertors 608 
 
 FiGS. 83, 84. Illustrating paralysis of the supervertors 609
 
 CONTENTS. 
 
 CHAPTER I. PAGES. 
 
 The Fundamental Principles of Ocular Rotations 1-145 
 
 CHAPTER II. 
 Orthophoria 146-179 
 
 CHAPTER III. 
 Heteropboria 180-272 
 
 CHAPTER IV. 
 Esophoria 273-313 
 
 CHAPTER V. 
 Exophoria 314-340 
 
 CHAPTER VI. 
 Hyperphoria and Cataphoria 341-381 
 
 CHAPTER VII. 
 Cyclophoria 382-416 
 
 CHAPTER VIII. 
 Compensating Cyclotropia 417-488 
 
 CHAPTER IX. 
 Compensating Heterotropia 489-496 
 
 CHAPTER X. 
 
 Comitant Esotropia, Exotropia, Hypertropia, Catatropia, and Cyclo- 
 tropia 497-594 
 
 CHAPTER XI. 
 Paralysis and Paresis of the Ocular Muscles 595-622 
 
 CHAPTER XII. 
 Muscles of the Iris and of the Ciliary Body 623-661 
 
 Index 662-684 
 
 (xii)
 
 OPHTHALMIC MYOLOGY. 
 
 CHAPTER I. 
 
 THE FUNDAMENTAL PRINCIPLES OF 
 OCULAR ROTATIONS. 
 
 A SPHERE, in rotation around its center as a fixed 
 point, has on its surface two points, and only two points, 
 that do not move. These two points must be 180 apart, 
 and the straight line that connects them must be a 
 diameter of the sphere. This diameter is the axis of 
 a given rotation. Every point on the surface of the 
 sphere, other than the two fixed points, moves in a plane 
 at right-angles to the axis of rotation, describing the 
 circumference of a circle larger or smaller, on the sur- 
 face of the sphere. The size of any one of these circles 
 is determined by the distance of the given rotating point 
 from the nearer of the two fixed points up to 90. A 
 point 90 from the two fixed points describes the circum- 
 ference of a great circle, while all other rotating points 
 describe circumferences of small circles. The planes of 
 all the circles thus created are rotation planes, and each
 
 2 THE FUNDAMENTAL PRINCIPLES 
 
 one is parallel with all the others. The planes of all 
 these circles, except the plane of the one great circle, 
 may be ignored, for the plane of any given rotation is 
 the plane of the one great circle. This plane alone cuts 
 the axis of rotation at its center the center of the 
 sphere while the planes of all the small circles cut the 
 axis at varying 1 points from the center. 
 
 Only one of the infinite number of points lying* on the 
 great circle should be studied in any given rotation, but it 
 should not be forgotten that all points on this great circle 
 bear an unalterable relationship to the one chosen point. 
 The line extending- from the chosen point back through 
 the center of rotation the center of the sphere to an- 
 other point on its surface just 180 distant, is the rota- 
 ting line, and all other moving lines, whether diameters 
 or not, may be ignored, for all these lines must bear a 
 fixed relationship to this one chosen line. Both the ro- 
 tating line and the axis of rotation are diameters of the 
 revolving sphere. They lie in the plane of the same 
 great circle, and each is at right-angles to the other. 
 This is always true, regardless of the point of applica- 
 tion and the direction of the force effecting the rotation. 
 A change in the direction of the force only means a new 
 axis of rotation, a new rotating point and rotating line, 
 and a new rotation plane. 
 
 A careful study of Fig. 1 will serve to fix in the
 
 OF OCULAR ROTATIONS. 
 
 mind the truths that have been taught above. In this 
 figure, A-B-D represents the cross-section of a concave 
 hemisphere whose center is c\ in which is set the con- 
 
 Fig. i. 
 
 vex sphere whose cross-section is a-d-b-e. and whose 
 center is also c. The lines a-b and d-e are diameters 
 of this sphere, at right-angles to each other and in
 
 4 THE FUNDAMENTAL PRINCIPLES 
 
 a plane common to the two. Since this sphere is loose 
 in the concave hemisphere, any point on its surface may 
 be chosen as the point for rotation. If a is to be rotated 
 into the position of I), it must move in the plane of the 
 great circle of which a-b is the diameter. The two fixed 
 points on the surface of the sphere in this rotation are 
 d and e, and the line connecting- them is the diameter 
 d-e, which is the axis of this rotation. It lies in the same 
 plane with a-b and also in the plane of the great circle 
 which is equally distant at all points from both a and b. 
 The force so applied as to make a the rotating point and 
 a-b the rotating 1 line, fixes the axis of rotation as d-e, for 
 d and e are the only two fixed points on the surface in 
 this rotation. Any point on the surface between a and 
 // and between a and n will rotate in a plane parallel 
 with a-b, each circle growing" smaller as the point re- 
 cedes toward h or n. Likewise circles for revolving 
 points between h and </and between n and c grow small- 
 er as the rotating points recede from h or n, until at d 
 and e the circle has become infinitely small, or, in other 
 words, d and e do not move at all. The tangents at d 
 and e are parallel with a-b, therefore these two points 
 are 90 from both a and b. 
 
 Again referring to Fig'. 1, it will be seen that the un- 
 broken line a-b is the diameter of the great circle de- 
 scribed by the rotating point a, the dotted line h-m is
 
 OF OCULAR ROTATIONS. 5 
 
 the diameter of the small circle created by the moving 
 secondary point h, and n-i is the diameter of the small 
 circle generated by the moving secondary point n. 
 These three lines are parallel, and they all cut the axis 
 of rotation, d-e, at right-angles. In like manner, an} T 
 point between a and d or between a and c might be 
 studied. The point a moves most rapidly, while the 
 points d and e do not move at all. 
 
 The force may be so applied to the loose sphere as to 
 make n the rotating point and n-m the rotating line. 
 Thus h and i would become the two fixed points, and 
 h-i would be the axis of this rotation. By changing the 
 point of application and the direction of the force on this 
 loose sphere, any^ point on its exposed surface may be 
 made the rotating point. The diameter extending from 
 this point would become the rotating line, and the diam- 
 eter at right-angles to this revolving line and in the 
 plane with it would become the axis of rotation. 
 
 In any rotation of a sphere there are three points on 
 its surface to be considered viz., the rotating point and 
 the two fixed points. There are two lines, each a di- 
 ameter, to be considered viz., the rotating line and the 
 axis of rotation. There are three planes to be studied 
 viz.: (1) the rotation plane, a fixed plane, in which move 
 the rotating point and the rotating line; (2) the rotating 
 plane, in which lie the three points and the two lines
 
 6 THE FUNDAMENTAL PRINCIPLES 
 
 (diameters); and (3) the plane containing- the two fixed 
 points and the axis of rotation, which also is a rotating 
 plane. These three planes are each at right-angles to 
 the other two, and the only point within the sphere com- 
 mon to all of these planes is the center of rotation. 
 The intersection of the rotation plane (1) and the rota- 
 ting plane (2) is the rotating line. The intersection of 
 the two rotating planes (2 and 3) is the axis of rotation. 
 The eye is spherical, the posterior half, at least, be- 
 ing a perfect hemisphere. (See Fig. 5.) It is not 
 loosely set in the concavity in the anterior part of the 
 bed of fat designed to receive it, but it is movably 
 confined therein by the capsule of Tenon and the mus- 
 cles in which reside the power for rotating it with 
 mathematical precision and with wonderful frictionless 
 speed. In the eye, as in the loose sphere studied, every 
 rotation plane is the plane of a great circle, and these 
 planes may be many. The eye, unlike the loose sphere 
 studied, has only one rotating point, and this point is 
 not anterior, but posterior it is the central point of the 
 macula. The eye, having only the one primary rotating 
 point, can have only one primary rotating line (diame- 
 ter), and this line is the one extending from the central 
 point of the macula forward through the center of rota- 
 tion to the cornea at, or not far removed from, its cen- 
 ter, thence to be prolonged into space. This is the
 
 OF OCULAR ROTATIONS. 7 
 
 direct line of vision, or the visual axis. In the study of 
 the loose sphere, the primary rotating 1 point was in the 
 front, or in view, and the rotating- line extended back- 
 ward throug-h the center of rotation. In the eye the 
 primary rotating- point is behind is unseen and the 
 primary rotating- line comes forward throug-h the center 
 of rotation to the cornea, where it does not stop, but ex- 
 tends on into space. 
 
 As in the loose sphere studied, so in the eye, there are 
 two fixed points on the surface in any cardinal rotation, 
 and these are connected by that diameter which is the 
 axis of that rotation. All other points on the surface 
 of the eye, not in the rotation plane, are rotated in 
 planes of small circles that are parallel with the rota- 
 tion plane, as shown in the study of Fig-. 1. All second- 
 ary points on the retinal surface bear an unalterable 
 relationship to the one primary rotating- point, the cen- 
 ter of the macula, whether the eye be at rest or in mo- 
 tion; hence in the study of ocular motion, all points 
 except the central point of the macula and one secondary 
 point may be ig-nored. All secondary diameters of the 
 eye bear a fixed relationship to the visual axis (the pri- 
 mary diameter), and all move in perfect harmony with it. 
 
 The diameters of the eye are divisible into two class- 
 es, the rotating and the fixed. The rotating- diameters 
 are divisible into two classes, the primary and the sec-
 
 8 THE FUNDAMENTAL, PRINCIPLES 
 
 ondary. To the primary class belongs only a single di- 
 ameter, and it lies in the plane of every meridian is the 
 line of intersection of all the meridional planes and it 
 alone connects the two poles of the eye. To the second- 
 ary class belong- all other rotating- diameters, each lying 
 in the plane of only one meridian, but cutting the planes 
 of all other meridians at the center of rotation. The 
 fixed diameters are two, and they both lie in the equato- 
 rial plane of the eye. One of the two also lies in the 
 plane of the horizontal meridian and is the axis of verti- 
 cal rotations; the other lies in the plane of the vertical 
 meridian and is the axis of lateral rotations. 
 
 The primary rotating diameter is the visual axis; all 
 other rotating diameters are secondary lines of vision. 
 The fixed diameter, always in the equatorial plane, is 
 the axis of a cardinal rotation, and it, too, always lies in 
 that meridional plane which is at right-angles to the ro- 
 tation plane of a given cardinal rotation. 
 
 Secondary rotating lines are divisible into two classes: 
 first, diameters which are secondary lines of vision, 
 each bearing its own relationship, in degrees, to any 
 given rotation plane; second, the lines that connect any 
 two directly opposite points on the surface, lying on the 
 same side of the rotation plane and equally distant from 
 it, but on opposite sides of the equatorial plane. These 
 two points, if they do not lie in the plane common to the
 
 OF OCULAR ROTATIONS. 9 
 
 visual axis and the axis of rotation, must be on opposite 
 sides of this plane and equally far removed from it. Such 
 lines are always bisected by the axis of rotation and are 
 at right-angles to it, and each lies in the plane of its 
 own small circle, which plane is always parallel with 
 any given rotation plane. These planes of small cir- 
 cles, like the rotation plane with which they are paral- 
 lel, are fixed planes in a cardinal rotation. 
 
 Lines connecting surface points not 180 apart on 
 either a great or a small circle, should not be considered 
 as either primary or secondary rotating lines. Rotating 
 lines of whatever class are lines bisected by the axis of 
 rotation, but only those lines that are bisected at the 
 center of rotation are lines of vision. All visual lines, 
 whether direct or indirect, and the axis of any rotation 
 mutually bisect each other, and hence all are diameters. 
 
 The author's method of finding the axis of any cardi- 
 nal rotation as set forth in the study of Fig. 1 is simple, 
 and is applicable to all eyes. Helmholtz' method of find- 
 ing the axis of rotation is not so simple, nor can it apply 
 to all eyes. It was only in the ideal eye that Helmholtz 
 found the visual axis and his so-called ' ' optic axis ' ' to co- 
 incide; He taught that, in the larger number of eyes, 
 the visual axis intersects his so-called "optic axis" at the 
 nodal point. Since such a visual axis could not be a di- 
 ameter, it could not become the primary rotating line, in
 
 10 THE FUNDAMENTAL PRINCIPLES 
 
 the Helmholtz method of finding the axis of rotation. 
 As will be shown further on, Helmholtz made a funda- 
 mental mistake in his selection of the center of the cornea 
 as the anterior pole of the eye, constructing 1 therefrom 
 his optic axis, which he carried backward through the 
 center of rotation to a point on the retina, usually be- 
 tween the macula and the optic disc, which point he 
 named the ' ' posterior pole. " He should have selected the 
 center of the macula as the posterior pole; and if he had 
 done so, his so-called ' ' optic axis ' ' would have been the vis- 
 ual axis of all eyes, and the anterior pole would have 
 been that point on the cornea cut by the visual axis, 
 whether it were its center or some other point slightly 
 removed from the center. His method of finding the axis 
 of rotation is proof of the error he made, for his method 
 could apply only to that eye whose visual axis cuts the 
 center of rotation. 
 
 Helmholtz' method of locating the axis of any rotation is 
 fairly illustrated in Fig. 2. In this cut, a-b is the first 
 position of the visual axis and a'-b' is the second position 
 of the visual axis. The plane a-a'-b-b' is constructed 
 through five fixed points the first point of view b and its 
 image a, the second point of view b' and its image a, and 
 the center of rotation c. With b as the primary or di- 
 rect point of view, a-b is the visual axis, a being the cen- 
 ter of the macula. With b as a secondary or indirect
 
 OF OCULAR ROTATIONS. 
 01 
 
 11 
 
 00,
 
 12 THE FUNDAMENTAL, PRINCIPLES 
 
 point of view, a'-b' is a secondary or indirect line of vi- 
 sion, a being- the retinal image of b' '. The lines a-b and 
 a'-b', each connecting- two points lying- in the plane, and 
 crossing- each the other at the common point c in the 
 plane, must, therefore, lie wholly in the plane. The ret- 
 inal images a and a are the same distance apart in de- 
 grees as are the spacial points b-b ', for the arc a-a and 
 the arc b-b' subtend ang-les that are equal, for they are 
 opposite, as shown at c. That b' ma}^ become the direct 
 point of view, the macula must move from a to a and the 
 visual axis must rotate from b to b' , to take the place or 
 position of what was an indirect line of vision before the 
 rotation began. This turning has been about the point 
 c. The former direct point of view b has become an in- 
 direct point of view, and its image a is on the retina to 
 the left of the new position of the macula. The line a-b 
 is a new indirect line of vision. Truly the first position 
 of the visual axis was a-b, but this position is now occu- 
 pied by an indirect line of vision which followed the visual 
 axis from right to left through an arc equal to the arc 
 b-b' . Just as truly the second position of the visual axis 
 is a'-&', for b' is now the direct point of view; but it now 
 occupies the position of what was an indirect line of vi- 
 sion before the rotation began, which line has been ro- 
 tated to the left through an arc equal to that connect- 
 ing b' and b. The new and the old indirect visual lines
 
 OF OCULAR ROTATIONS. 13 
 
 have been rotated around the point c in perfect har- 
 mony with the rotation of the visual axis. If the plane 
 a-a'-b-b' were extended right and left, .it would include 
 the line that was the indirect visual line a'-b' before 
 the rotation began, and that other line which has become 
 the indirect visual line a-b, as a result of the change of 
 point of direct view from b to b' . The rotation of all 
 lines has been around the common point c, and in the 
 plane a-a'-b-b' . This point is the rotation center and 
 this plane is the rotation plane. 
 
 Helmholtz found the axis of this rotation by construct- 
 ing 1 two other planes, each at right-angles to the plane of 
 rotation, one of them including the visual axis in its 
 first position, the other including the visual axis in its 
 second position. The first of these two planes, as shown 
 in Fig". 2, is a-b-f-e, and the second is d-b'-h-g. The 
 line of intersection of these two planes is c-d, and this 
 line is the axis of rotation. Since the planes a-b-f-c and 
 a'-b'-h-g- are at right-angles to the plane a-a'-b-b', their 
 line of intersection c-d must be at right-angles to the ro- 
 tation plane, and, as shown in the figure, if extended up- 
 ward, would cut the center of rotation. 
 
 In Fig. 2 the horizontal retinal meridian of the eye is 
 represented as lying in the rotation plane a -a'-b-b' , with its 
 center of curvature at c. In the first position of the vis- 
 ual axis the solid line curve representing the cornea
 
 14 THE FUNDAMENTAL PRINCIPLES 
 
 shows the eye looking- at b; in the second position of the 
 visual axis the broken line representing- the cornea shows 
 the eye looking- a.t b '. In either case the visual axis gfoes 
 from the central point of the macula, throug-h the center 
 of rotation, c, on to the point of direct view. 
 
 Fig-. 2 represents the rotation of Helmholtz' ideal eye, 
 one in which the visual axis and the optic axis coincide. 
 If Helmholtz had constructed Fig-. 2 and had g-iven it a 
 close and clear stud} r , he would have seen that, at least in 
 the ideal eye, all indirect lines of vision must cross the 
 visual axis at the center of retinal curvature, which is the 
 center of rotation, and not at the nodal point; that they 
 are radii of retinal curvature prolong-ed, and not the axial 
 rays of cones of light. He would have seen that, in the 
 
 non-ideal eye the eye whose visual axis cuts the optic 
 
 
 
 axis at N, with the macula at o the line a-b could not 
 be the visual axis in the first position, nor could the line 
 a-b' be the visual axis in the second position. The vis- 
 ual axis in the first position would be a line drawn from 
 o throug-h N to p, a point in space 5 to the rig-ht of b, as 
 shown by the unfinished dotted line o-p; and the visual 
 axis in the second position would be a line drawn from 
 o throug-h N' to p', a point 5 to the rig-ht of b', as shown 
 by the incomplete dotted line o-p'. He would also have 
 seen that, according- to his own teaching-, the lines a-b 
 and a-b' must be indirect lines of vision, as well as optic
 
 OF OCULAR ROTATIONS. 15 
 
 axes, for each crosses its respective visual axis at the 
 nodal point. He would have seen that in this non-ideal 
 eye there could be no point on the visual axis that would 
 be stationary in any rotation except the one directly up 
 or down, for only in such a rotation would the misplaced 
 visual axis cross the axis of rotation; and even in the ver- 
 tical rotation that part of the visual axis within the eye 
 would not be bisected by the axis of rotation. Such a 
 visual axis could not be called a " rotating 1 line " for there 
 is no fixed point on the line around which it can turn. 
 All lines bisected by the axis of rotation have on them a 
 point around which they can rotate, and that point lies 
 on the axis of rotation. Only those lines that are bisect- 
 ed by the axis of rotation at its center mutual bisection 
 can be lines of direction, or visual lines lines connect- 
 ing- objects in space with their retinal images. 
 
 Reverting again to the study of Fig. 2, Helmholtz could 
 have seen that the plane of the horizontal retinal merid- 
 ian, being in the rotation plane, itself became the plane 
 of rotation, for the rotation plane in this figure is noth- 
 ing more nor less than the plane of the horizontal retinal 
 meridian extended. He would also have seen that the 
 axis of the given rotation, at right-angles to the merid- 
 ional plane and cutting it at the center of rotation, must 
 lie in the equatorial plane. 
 
 Reversing Fig. 2 so that a shall be directly above a
 
 16 THE FUNDAMENTAL PRINCIPLES 
 
 on the retina, and that b' shall be directly below b, in 
 space, then the part of the figure representing- the ideal 
 eye will be the vertical meridian, and its plane extended 
 would be the rotation plane from b to b ' . Then the di- 
 rect and the indirect lines of vision, lying in the plane of 
 the vertical meridian, would cross each other at the cen- 
 ter of rotation, as they are shown to de when lying in 
 the plane of the horizontal retinal meridian; and the axis 
 of rotation, at right-angles to the rotation plane and cut- 
 ting it at the center of rotation, would be horizontal and 
 in the equatorial plane. 
 
 The author's method of finding the axis of a cardinal 
 rotation of the eye, as shown in the study of Fig. 1, dif- 
 fers in every respect from the method of Helmholtz, as 
 illustrated in Fig. 2. The author's method found the 
 fixed points on the surface which determined the axis of 
 rotation; Helmholtz' method found the axis of rotation 
 which located the two fixed points. By each method it 
 was found that the two fixed points on the globe are in 
 a plane with the rotating point and with the center of 
 rotation; that the two fixed points are each 90 from the 
 rotating point and 180 from each other, the three points 
 lying on the same great circle; and that the line con- 
 necting the two fixed points is a diameter at right-angles 
 to the rotating line, which is also a diameter. In each 
 case the rotating point is the center of the macula. The
 
 OF OCULAR ROTATIONS. 17 
 
 rotating 1 line is the visual axis, and that diameter lying 
 in the rotating- plane"with the visual axis and at rig-ht- 
 ang-les to it is the axis of rotation. By each method the 
 visual axis is found lying- in the plane of two great cir- 
 cles at rig-ht-ang-les to each other, and is the line of in- 
 tersection of these two planes, the rotating plane and 
 the rotation plane, each being- a meridional plane; and 
 the axis of rotation is found to lie in the plane of a great 
 circle at rig-ht-ang-les to these two planes, which plane 
 is undeniably the equatorial plane. 
 
 For every eye there must be a spacial pole, and it must 
 be on the extended line which connects the two poles of 
 the eye. Throug-h the spacial pole must pass the spa- 
 cial meridians, which must be in planes with correspond- 
 ing- retinal meridians and concentric with them. Fig-. 3 
 represents the spacial pole and spacial meridians for the 
 left eye and its field of vision, and Fig-. 4 shows the same 
 for the rig-ht eye. The true spacial pole is always the 
 direct point of view, therefore it must lie on the visual 
 axis. It can be on the visual axis only when the center 
 of the macula is the posterior pole; but, as has been 
 shown, and will be shown ag-ain in the study of binocu- 
 lar rotations, the center of the macula is ahvays the pos- 
 terior pole ', a truth never grasped by Helmholtz and his 
 followers. 
 
 A g-lance at Fig-. 3 will show that if the point of cross-
 
 18 
 
 THE FUNDAMENTAL, PRINCIPLES
 
 OF OCULAR ROTATIONS. 19 
 
 ing of all the spacial meridians the spacial pole for the 
 left eye is the direct point of view, any and all second- 
 ary points of view, in the outlined field, must lie on some 
 spacial meridian. The point of direct view has its image 
 on the central point of the macula. Secondar} T points of 
 view on the vertical spacial meridian will have their 
 images on the vertical retinal meridian, and every point 
 and its image will correspond in relationship with the 
 spacial and posterior poles; and the spacial points will 
 be connected with their respective retinal images by 
 straight lines lying in the plane of the vertical meridian 
 and cutting the center of rotation. The same is true of 
 points and images lying on any other meridian. A 
 change of the point of view is a change of the spacial 
 pole. This change in the position of the spacial pole is 
 accompanied by a corresponding change in position of the 
 posterior pole of the eye, the latter coming under the 
 image of the new point of view the moment the spacial 
 pole has reached that point. In this rotation the visual 
 axis moves in the plane of that meridian on which are 
 located the two points of view and their two images. 
 The direct point of view and its image are connected by 
 the visual axis which lies in the planes of all the merid- 
 ians; a second point of view and its image are connected 
 by a line which lies in the plane of only one meridian, and 
 this line is a secondary line of vision. In any rotation
 
 20 THE FUNDAMENTAL PRINCIPLES 
 
 the direct line of vision moves into the position of an indi- 
 rect line of vision around the point common to the two 
 lines, the center of rotation, and along the plane of that 
 meridian on which were located the secondary point and 
 its image; therefore every rotation plane is a meridional 
 plane extended. 
 
 The center of the macula is the rotating point of the eye 
 By means of the wonderful muscular mechanism of the 
 eye, the macula may be rotated in any direction, but always 
 in the plane of a great circle. For this to be possible, 
 all the great circles whose planes can become planes of 
 rotation must intersect each other at the central point 
 of the macula and at a corneal point 180 removed. 
 Great circles thus related to each other are meridians, 
 and the points of their intersection are the poles; hence 
 the center of the macula in all eyes is the posterior pole 
 of the eye, and the point on the cornea, whether its cen- 
 ter or not, distant from the center of the macula 180, 
 must be the anterior pole. The line connecting these 
 two poles must cut the center of rotation, hence is a di- 
 ameter, and it must be the line of intersection of the 
 planes of all the meridians. This line connecting the two 
 poles becomes the antero-posterior axis of the eye; and 
 since the center of the macula is the posterior pole, the 
 antero-posterior axis is none other than the visual axis. 
 
 In the study of a given rotation of the eye, in either
 
 OF OCULAR ROTATIONS. 21 
 
 one of the four cardinal directions, there are three sur- 
 face points to be considered: the center of the macula 
 (the rotating 1 point) and the two fixed points lying- in the 
 plane with it and removed from it 90. There are two 
 lines to be studied: the visual axis (the rotating 1 line) 
 and the axis of rotation, which connects the two fixed 
 points, and is, therefore, at right-angles to the rotating 
 line, the two lines always lying- in the same meridional 
 plane. There are three planes to be kept in mind: (1) 
 the plane of rotation, a meridional plane, in which move 
 both the rotating- center of the macula and the visual 
 axis, the plane itself being fixed; (2) the rotating- plane, 
 a meridional plane, in which lie the center of the macula 
 and the two fixed points, also the visual axis and the 
 axis of rotation; (3) the rotating- plane which contains 
 only the two fixed points and the line connecting- them 
 the axis of the rotation. These three planes are at 
 rig-ht-ang-les to each other, and the common point within 
 the eye through which they all pass is the center of ro- 
 tation. The planes (1) and (2) are the horizontal and 
 vertical meridional planes; and since plane (3) cuts the 
 center of rotation and is at right-angles to planes (1) 
 and (2), it can be none other than the equatorial plane. 
 Any meridional plane may be a plane of rotation; but 
 the axes of oblique rotations will be studied later in this 
 chapter.
 
 22 THE FUNDAMENTAL PRINCIPLES 
 
 The correctness of what has been taught already about 
 ocular rotations may be made clearer by a study of Fig-. 
 5, which is a modification of Fig. 1, in that the oblique 
 diameters have been omitted and the curve s-r has been 
 added to represent the cornea. A-B-D represents the 
 concavity in the anterior part of the orbital fat in which 
 the eye either rests or moves. The globe is represented 
 by d-s-r-x-e-b. The center of the concavity and that of 
 the eye is c. The posterior pole is at b, the center of the 
 macula. The true anterior pole is at , but for conven- 
 ience of study may be considered as at r, which in this 
 figure is the center of the corneal curve. The line ex- 
 tending from b to r is the antero-posterior axis, which, 
 when prolonged into space, becomes the visual axis. In 
 every rotation the moving point is b and the moving line 
 is b-r. The points d and e are each 90 from b and lie 
 on the horizontal meridian. The line d-e is a diameter and 
 lies in the same plane with b-r and is at right-angles to 
 it. In Fig. 1 any diameter could become the rotating 
 line, but in Fig. 5 the only diameter that can be the ro- 
 tating line is the visual axis b-r. Let d-a-e-b be the hor- 
 izontal meridian of the eye. If the point of view is to be 
 changed from the primary position to a point in space 
 directly below, then the image of the latter point must 
 be on the vertical retinal meridian as many degrees above 
 the center of the macula as the secondary point in space is
 
 OF OCULAR ROTATIONS. 
 
 23 
 
 Fig- 5-
 
 24 THE FUNDAMENTAL, PRINCIPLES 
 
 below the first point. In changing- the point of view, the 
 macula will move upward in the plane of the vertical 
 meridian until it gets beneath the second image, and at 
 the same time the visual axis will rotate on the point c 
 until its spacial end has reached the second point of view. 
 In this rotation d and e have not moved and the rotation 
 has been around d-e as an axis. In this rotation the only 
 fixed plane has been the plane of the vertical meridian, 
 while the two rotating planes have been the plane of 
 the horizontal meridian and the plane of the equator. 
 Throughout the rotation these three planes have been at 
 right-angles, each to the other two. 
 
 THE POSTERIOR POLE. 
 
 What has already been written in this chapter in jus- 
 tification of the selection of the central point of the mac- 
 ula as the posterior pole of the eye should be enough 
 to convince the most skeptical. Truth looked at from 
 many points of view will always appear as truth; error 
 may appear to be the truth when viewed from one or two 
 standpoints, but it is sure to become manifest under the 
 clearer light of many-sided investigation. Truth is al- 
 ways simple, and the greatest truths are the simplest. 
 When an investigator finds himself beset with difficulties, 
 he may be sure that error, either of his own creating" or 
 that has been handed down to him, shadows his path-
 
 OF OCULAR ROTATIONS. 25 
 
 way. Fundamental errors, until discovered and discard- 
 ed, are dangerous thing's, for out of these come many 
 other errors of greater or less magnitude. Helmholtz' 
 fundamental error in his study of ocular motions was 
 the selection of the center of the cornea as the anterior 
 pole of all eyes. Because of this fundamental error, he 
 was not able to write clearly and consistently about ocu- 
 lar rotations. He must have recognized the murkiness of 
 his own teaching on this subject when he said to Her- 
 man Knapp, "Leave this chapter aside," promising "a 
 different, shorter, and more comprehensive presentation " 
 of the subject, at which task he was then engaged. This 
 task was never finished, and for the simple reason that 
 he was never able to rid himself of the fundamental er- 
 ror pointed out above, though he lived and labored for 
 twenty-five or more years after his conversation with 
 Knapp. With the consent of Arnold Knapp, the well- 
 known son of Herman Knapp, the author reproduces on 
 page 26 a part of a letter received by him from Dr. 
 Knapp soon after the latter had read his smaller book, 
 "Ophthalmic Neuro-Myology," which had just come 
 from the press (1905), a companion volume to "Ophthal- 
 mic Myology." 
 
 If Helmholtz had grasped the truth that the center of 
 the macula is the posterior pole of every eye, his funda- 
 mental error would have flown, and the other errors
 
 26 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 ft. 
 
 r*W1-. 
 
 /f ,
 
 OF OCULAR ROTATIONS. 27 
 
 growing out of it would have been supplanted by beau- 
 tiful truths. Then his chapter on ' ' movements of the 
 eyes" would not have been misty, nor would Knapp 
 have complained that there were difficulties in this chap- 
 ter. 
 
 In further refutation of Helmholtz' erroneous teach- 
 ings which have been perpetuated in all books on the eye, 
 except this book and its companion volume, " Ophthalmic 
 Neuro-Myology, " it will be profitable to study Figs. 6, 
 7, and 8. Fig. 6 represents the non-ideal eye of Helm- 
 holtz, in which o, the center of the cornea, is the ante- 
 rior pole, and a, between the macula and the disc, is the 
 posterior pole, and o-c-a is the optic axis. PP is the 
 primary point of view, whose retinal image is at m. The 
 so-called "visual axis" of Helmholtz, connecting object 
 and image, crosses the optic axis at the nodal point N. 
 SP is the secondary point of view, whose retinal image, 
 according to Helmholtz, is at x. The indirect visual 
 line, SP-x, connecting this secondary point of view and 
 its image, crosses the visual axis at the nodal point N. 
 Motionless objects in space and their retinal images bear 
 an unalterable relationship to each other. For this re- 
 lationship to be maintained, when the point of view is 
 changed, the visual axis must assume the position of the 
 indirect visual line that connected the secondary point of 
 view with its image before the rotation began. Since
 
 28 
 
 THE FUNDAMENTAL PRINCIPLES
 
 OF OCULAR ROTATIONS. 29 
 
 in Fig 1 . 6 the visual axis, PP-m, lies to the outer side of 
 the center of rotation, c, while the indirect visual line, 
 SP-x, lies to the inner side of the center of rotation, c, the 
 former can never be made to assume the position of the 
 latter. To show the confusion that would occur when 
 such an eye is rotated, the figure must be complicated 
 by drawing 1 a line from PP through c to n. This line, 
 PP-c~n, a radius of retinal curvature prolonged, will 
 have its relationship with PP-m unaltered in any rota- 
 tion of the eye. When the eye rotates from PP to the 
 point SP, the position of the prolonged radius is SP-n', 
 and that of the visual axis SP-m '. The visual axis in 
 space has reached the secondary point SP, but has not 
 reached the retinal image at x, for even SP-n has 
 stopped short of x, and m is just as far behind n as ;, 
 in the primary position, was distant from n. The mac- 
 ula m may be rotated under the secondary image at x\ 
 but when this is done, the prolonged radius PP-n will as- 
 sume the position ri'-c-e-r, and the visual axis will take 
 the direction x-d-r. Since, in monocular vision, any 
 point whose image is on the macula appears to lie on the 
 visual axis, the secondary point of view would appear to 
 be at r in space, removed nearly twice as far from the 
 primary point as it was before the rotation began. The 
 images have remained the same distance apart, but the 
 motionless objects in space have apparently become more
 
 30 THE FUNDAMENTAL, PRINCIPLES 
 
 widely separated. This is out of harmony with human 
 experience. 
 
 In the next place, study the ideal eye of Helmholtz, as 
 shown in Fig-. 7. In this figure the visual axis PP-m 
 cuts the center of the corneal curve, Helmholtz' ante- 
 rior pole, and therefore coincides with his optic axis, the 
 macula becoming- the posterior pole. The secondary 
 point of view is SP, and its imag-e is supposed to be at x, 
 the two being- connected by the indirect visual line 
 SP-N-x. As in Fig-. 6, PP and SP are motionless 
 points in space; therefore they and their imag-es must 
 bear a fixed relationship the one with the others. Hence, 
 when the eye rotates from one point of view to the other, 
 the visual axis PP-m should assume the position of SP-x; 
 but since the one passes throug-h the center of rotation 
 and the other does not, the former can never become the 
 latter. To show what would take place, we must extend 
 a line from SP throug-h the center of rotation, c, to the 
 retina at m'. When the eye is rotated from PP to SP, 
 the visual axis PP-m assumes the position SP-ni '. The 
 spacial end of the visual axis has reached the secondary 
 point, but the retinal end has fallen short of its imag-e. 
 The macula, m, can be rotated under the imag-e at x; but 
 when this has been done, the motionless point SP will ap- 
 pear in the direction x-c-d-r. This, too, is contrary to 
 all experience.
 
 OF OCULAR ROTATIONS. 31 
 
 Many years ago the author announced as a fact that 
 the central point of the macula is the posterior pole, and 
 that the anterior pole may or may not be the center of 
 the cornea. He also announced, at the same time, that all 
 lines of direction are radii of retinal curvature prolonged, 
 and not axial rays of light. Fig. 8, representing a non- 
 ideal eye that is, an eye whose true anterior pole is to 
 the nasal side of the center of the corneal curve proves 
 conclusively that he discovered the truth. In this figure 
 PP is the primary point of view and SP is the secondary 
 point of view. The image of the former is on the macula 
 at m, while the image of the latter is on the retina at m . 
 The visual axis is PP-m, and the secondary visual line 
 is SPm '. Since these lines cross each other at the center 
 of rotation and are radii of retinal curvature prolonged, 
 the one can be made to assume the position of the other 
 when the point of view is changed, and that, too, without 
 disturbance, either apparent or real, of the fixed relation- 
 ship of the two motionless points in space and their re- 
 spective retinal images. This is in accord with human 
 experience. 
 
 Returning to the ideal eye, shown in Fig. 7, the image 
 of SP is not at x, but at m\ and the real secondary vis- 
 ual line is SP-c-m , whose position the visual axis takes 
 when the eye rotates from the primary to the secondary 
 point of view. Thus Fig. 7 may be made to teach the
 
 32 THE FUNDAMENTAL PRINCIPLES 
 
 truth, after erasing the continuous line SP-N-x and the 
 dotted line d-r to the left. 
 
 In Fig. 8 is shown Helmholtz' so-called "optic axis" 
 o-a, and on it his nodal point "useless each e'en with 
 the other." The sooner they are forgotten, the better; 
 and the angle g"amma should be included in the forget- 
 ting-. The true posterior pole is the central point of the 
 macula; the true optic axis is the visual axis; and the 
 true anterior pole is that point of the cornea cut by the 
 visual axis, whether it be the center of the cornea or not. 
 An undeniable evidence that the central point of the 
 macula is the posterior pole is the fact that all retinal 
 meridians cross at this point at the crossing 1 of the me- 
 ridians is the -pole. There is no longitude there; and, 
 likewise, there is no latitude for adverse argument. 
 
 The discovery of the true locations of the posterior and 
 anterior poles of the eye was a fortunate one, and the au- 
 thor must be pardoned for feeling some joy in the achieve- 
 ment. On this discovery is based the law of monocular 
 and binocular rest and motion, and the law of direction. 
 
 Before passing to the study of binocular rotation, it may 
 be profitable to the reader to review in parallel columns 
 the conflicting teachings of Helmholtz and the author. 
 
 HEI,MHOI/rz. 
 
 (1) The center of the cornea is 
 always the anterior pole, and the 
 
 THE AUTHOR. 
 
 (1) The center of the macula is 
 always the posterior pole, and the
 
 OF OCULAR ROTATIONS. 
 
 33 
 
 center of the macula is the pos- 
 terior pole only in ideal eyes. 
 
 (2) The optic axis begins always 
 at the central point of the cornea, 
 passes backward through the center 
 of rotation to the retina, rarely at 
 the central point of the macula, but 
 usually to a point between the mac- 
 ula and the optic disc. 
 
 (3) The optic axis is the visual 
 axis only in the ideal eye, and only 
 then does the visual axis cut the 
 center of rotation. Usually the 
 visual axis misses the center of ro- 
 tation by passing to the outer side 
 of it, crossing the optic axis at the 
 nodal point, and lying in only one 
 meridional plane. 
 
 (4) Visual lines are axial rays of 
 cones of light, as is also the visual 
 axis, and all these cross the optic 
 axis at the nodal point. Even in 
 ideal eyes the visual lines do not 
 cross the visual axis at the center of 
 rotation. 
 
 (5) In passing from one point of 
 view to any other, the visual axis 
 of a non-ideal eye cannot move in 
 a plane of a meridian except when 
 the rotation is directly to the right 
 or left. 
 
 (6) In cardinal and oblique rota- 
 
 center of the cornea is the anterior 
 pole only in ideal eyes. 
 
 (2) The optic axis always begins 
 at the center of the macula, passes 
 through the center of rotation and 
 cuts the cornea, rarely at its center, 
 but usually to the nasal side. 
 
 (3) The optic axis in all eyes is 
 the visual axis and is the line of 
 intersection of all meridional planes, 
 hence it lies in the plane of every 
 meridian. 
 
 (4) Visual lines are not axial rays 
 of light, but are radii of retinal 
 curvature prolonged, all of them 
 crossing the visual axis at the center 
 of rotation, which is the center of 
 retinal curvature. 
 
 (5) In monocular motion every 
 rotation plane is a meridional plane 
 extended, and the visual axis always 
 moves in this plane. 
 
 (6) The axis of every rotation,
 
 34 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 tions starting from the primary point 
 of view or returning to it, the axis 
 of any rotation lies in Listing's 
 plane; the axis of rotation from one 
 secondary point to another second- 
 ary point lies in a plane bisecting 
 the angle between Listing's plane 
 and the equatorial plane. 
 
 (7) The object in space and its 
 retinal image are connected by a 
 straight line which crosses all simi- 
 lar lines at the nodal point, and 
 never at the center of rotation. 
 
 (8) Thespacial pole, if on the same 
 straight line with the two poles of 
 the eye, cannot be the direct point 
 of view for non-ideal eyes. 
 
 whether cardinal or oblique, whether 
 from a primary to secondary point of 
 view, or vice versa, or whether from 
 one secondary to another secondaiy 
 point of view, lies in the equatorial 
 plane. 
 
 (7) The object in space and its 
 retinal image are always connected 
 by a straight line which crosses all 
 similar lines at the center of rota- 
 tion and at no other point. 
 
 (8) The spacial pole is on the same 
 straight line with the two poles of 
 the eye and is the direct point of 
 view for all eyes. 
 
 In drawing- the above parallel, no attempt has been 
 made to quote the exact language of Helmholtz, or any 
 of his followers, on either of the eight points of difference; 
 but that he has been fairly represented as to his teach- 
 ings, no one will deny. His two fundamental errors were: 
 (1) In not taking the central point of the macula for his 
 posterior pole, and (2) in his axial-ray theory of direction. 
 To be in agreement on the location of the posterior pole 
 and on the law of direction would mean agreement every- 
 where. If on these points Helmholtz is right, the au- 
 thor is wrong; if the author is right on these points, then 
 Helmholtz is wrong. The teaching of the one who is
 
 OF OCULAR ROTATIONS. 35 
 
 correct in the location of the posterior pole and in his con- 
 ception of the law of direction will stand. 
 
 LINES OF DIRECTION. 
 
 One of these times some one will read this language 
 in Le Conte's book on "Sight:" "For every retinal 
 point there is a corresponding spacial point;" and "the 
 rods and cones see end-on." Having read it, he will be 
 ready to claim that Le Conte was first to discover the 
 true law of direction; for the first quotation would mean 
 that the retinal and spacial curves are concentric and 
 that lines connecting the corresponding points would cut 
 this common center; and the second quotation would 
 mean the same thing, for do not rods and cones all point 
 toward the center of the retinal curve? In a letter to 
 the author, in reply to one he had written him, Le Conte 
 said that he had used the language quoted above only in 
 a rough sense, for he certainly believed that Helmholtz' 
 axial-ray theory of direction was correct, and that all 
 lines of direction cross at the nodal point. In his first 
 edition of " Sight," his figure representing the horopter 
 shows the lines of direction crossing each other at the 
 nodal point, while the horopteric curve cuts the centers 
 of rotation. Fig. 9 is an exact copy from his book (first 
 edition, 1882). In his second edition of "Sight," the 
 figure representing the horopter has been changed, but
 
 36 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 not in respect of the point of crossing of the visual lines, 
 for these are made to cross at the nodal point. The 
 change, as shown in Fig. 10, reproduced from the second 
 edition of "Sight" (1898), is shown in the horopteric 
 circle which has been constructed through the two nodal 
 
 Fig. 9. 
 
 points and the point of fixation; whereas, in the first 
 edition, the same circle had been constructed through 
 the two centers of rotation and the point of fixation. 
 L/e Conte had written the author that one result of our
 
 OF OCULAR ROTATIONS. 
 
 37 
 
 correspondence would be a change in the construction of 
 the horopter in the second edition of his book. 
 
 Extracts from some of Le Conte's letters are photo- 
 graphically reproduced on page 38 and will be interesting- 
 
 Fig. 10. 
 
 reading 1 in this connection. What he denies so emphat- 
 ically in the reproduced letter is that the lines of di- 
 rection cross at the center of retinal curvature. 
 
 The fig-ure referred to in the seventh line of the
 
 38 THE FUNDAMENTAL PRINCIPLES 
 
 'V***-**'-
 
 OF OCULAR ROTATIONS. 39 
 
 Le Conte letter was on page 80 of the author's "New 
 Truths in Ophthalmology " (first edition). The thing 
 represented in that figure, and declared not true, is the 
 crossing of the visual lines at the center of retinal curva- 
 ture the center of rotation for this was the one truth 
 taught by that illustration. 
 
 The reproduced figures of the horopter will be re- 
 ferred to again in the discussion of that subject fur- 
 ther on. 
 
 Monocular rotation differs enough from binocular ro- 
 tation to justify the study of each separately. The 
 same muscles are concerned in each, but the innervations 
 are not identical throughout. The volitional brain cen- 
 ters, with one exception, are alike concerned in each, but 
 with monocular rotations the fusion centers have nothing 
 to do. In the study of monocular rotation one eye must 
 be considered as not existing, as blind, or as obscured. 
 It has been shown conclusively that the spacial pole of 
 one eye is the direct point of view for that eye, and that 
 the image of that point of view is on the center of the 
 macula, which is the posterior pole of the eye. It has 
 also been shown that every secondary point of view in 
 the field of vision must lie on some one spacial meridian; 
 if not on the vertical meridian, then either to the right 
 or to the left of it; and if not on the horizontal meridian, 
 then either above or below it. The image of every sec-
 
 40 THE FUNDAMENTAL PRINCIPLES 
 
 ondary point of view must lie on a corresponding* retinal 
 meridian; but if the object be above the horizontal spa- 
 cial meridian, its image must be below the horizontal ret- 
 inal meridian, and vice versa', if the object be to the right 
 of the vertical spacial meridian, its image must be to the 
 left of the vertical retinal meridian, and vice versa. The 
 secondary object and its image bear the same relationship, 
 in degrees, to the primary object and its image, and vis- 
 ual lines connecting them cross each other at the center of 
 rotation. The purpose of any rotation is to make the di- 
 rect line of vision, the visual axis, take the place of an 
 indirect line of vision. To do this, the spacial pole, which 
 is the point of crossing of all spacial meridians, must move 
 along that spacial meridian on which lies the second 
 point of view, until it reaches that point; and the center 
 of the macula, which is the point of crossing of all retinal 
 meridians, must move, in the direction opposite to the mo- 
 tion of the spacial pole, along that retinal meridian on 
 which lies the image of the second point of view, until it 
 gets under that image. The visual axis is thus rotated 
 in the plane of that retino-spacial meridian on which are 
 lying the two spacial points and their respective retinal 
 images. 
 
 To effect all possible monocular rotations, the four 
 straight muscles and the two obliques are essential. A 
 single muscle can effect a given rotation only when that
 
 OF OCULAR ROTATIONS. 41 
 
 muscle is bisected by the rotation plane (always a merid- 
 ional plane) from its origin to its insertion. If two mus- 
 cles, one of which is always an oblique muscle, are re- 
 quired to effect a cardinal rotation, the resultant action 
 of these two muscles would be the same as the action of 
 one imaginary straight muscle which would be bisected 
 from origin to insertion by the real plane of rotation. If 
 three muscles are required for any oblique rotation (more 
 than three muscles are never active in any rotation), the 
 resultant action of these three, one of which is an oblique 
 muscle, is not the same as would be effected by a single 
 imaginary muscle which would be bisected throughout 
 its length by the rotation plane. As will be shown later, 
 oblique rotations are not effected around a fixed single 
 axis at right-angles to the rotation plane, but around 
 two moving axes at right-angles to each other and to the 
 visual axis, thus insuring against that torsion which 
 would result if such rotation were around a single fixed 
 axis. 
 
 If there were only as many rotation planes as there are 
 minutes on one-half of the equator of the eye, and two in- 
 dividual muscles existed for every rotation plane, there 
 would have to be twenty-one thousand and six hundred 
 muscles, and an equal number of voluntary innervation 
 centers, for effecting all possible monocular rotations, 
 each around a fixed axis. In the wonderful mechanism of
 
 42 THE FUNDAMENTAL PRINCIPLES 
 
 monocular motions only six muscles are needed, the four 
 straight muscles and the two obliques, and only eight 
 voluntary centers are requisite, one center for each 
 straight muscle and two for each oblique muscle. Only 
 one muscle and one innervation center are needed for a 
 cardinal motion either toward the temple or toward the 
 nose, provided the lateral recti are bisected by the plane 
 of the horizontal retinal meridian. Two muscles and 
 two innervation centers are necessary if the visual axis 
 is to be rotated in the plane of the vertical meridian. If 
 the visual axis is to be rotated in the plane of any oblique 
 meridian, this must be done by the simultaneous and 
 harmonious action of three muscles under impulses 
 from three volitional brain centers. One of the three 
 muscles, an oblique, will prevent any rotation on the vis- 
 ual axis while it is being rotated in the rotation plane 
 by the other two muscles (recti), around two moving 
 axes, these axes being always the transverse and verti- 
 cal axes of the eye. That the prime object of the ob- 
 lique muscles is to prevent torsioning in vertical and 
 oblique rotations, regardless of whether it helps or hin- 
 ders a rectus muscle in effecting its rotation around the 
 transverse or vertical axis of the eye, is shown by the fact 
 that, if the rotation of the right eye is up and to the 
 right, the superior oblique acts with the superior and ex- 
 ternal recti, hindering the former, but helping the latter.
 
 OF OCULAR ROTATIONS. 43 
 
 The same rotation of the left eye would be effected by 
 the inferior oblique acting 1 with the superior and internal 
 recti, helping- the former, but hindering the latter. In 
 either case the oblique, by preventing- rotation on the 
 visual axis, enables the superior rectus to rotate the eye 
 on the transverse axis as if it were going straight up, 
 and at the same time enables the externus of the right 
 eye, or the internus of the left, to rotate the eye on the 
 vertical axis, as if the eye were being- turned directly to 
 the right. These three forces combined (not converted 
 into one force in the sense of creating a fixed axis at 
 right-angles to the plane of rotation) rotate the eye in 
 an oblique plane without torsioning, just as if the eye 
 had been rotated first on the vertical axis to a point in 
 the horizontal plane directly beneath the secondary 
 point, and thence directly up around the transverse axis 
 of the eye to that point. 
 
 Listing's law was quoted correctly in the first edition 
 of this book as follows: "When the line of fixation 
 passes from its -primary to any other position, the angle 
 of torsion of the eye in this second position is the same as 
 if the eye had arrived at this second position by turning- 
 about a fixed axis perpendicular to the first and second 
 positions of the line of fixation. ' ' Immediately following 
 this quotation the author said: "Certainly it is around 
 such an axis [but it isn't] that the eye rotates from the
 
 44 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 primary point of view to the obliquely placed secondary 
 point of view. It is equally certain that there would be 
 a torsioning unless a preventive force were called into 
 action." The obliques were given the credit for the force 
 that prevents torsioning in both vertical and oblique 
 rotations. To the obliques belong" this power, and 
 without them the torsioning would be inevitable in ob- 
 lique rotations, even around two axes. 
 
 J. 
 
 Fig. ii. 
 
 In oblique rotations the oblique muscles make impossi- 
 ble the existence of a fixed axis of rotation at right- 
 angles to the rotation plane. There are only two axes of 
 rotation, around one or both of which every possible oc- 
 ular motion takes place. These axes are fixed and at 
 right-angles to the rotation plane only when the rota- 
 tions are in the four cardinal directions, and then the 
 motion is around only one axis. There is no torsion in
 
 OF OCULAR ROTATIONS. 45 
 
 such a cardinal rotation. In Fig-. 11 these two axes are 
 shown. The circle a-d-b-e represents the equator of the 
 eye, the line a-b is the vertical axis, and the line d-e is 
 the transverse or horizontal axis of the eye. These are 
 at right-angles to each other, the one in the plane of the 
 vertical meridian and the other in the plane of the hori- 
 zontal meridian, and both lie in the plane of the equa- 
 tor. They are both at right-angles to the visual axis. 
 Around a-b the visual axis rotates directly to the right 
 or left and without torsion. Around d-e the visual axis 
 moves directly up or down and without torsion. These 
 cardinal rotations can be shown easily by means of a 
 rubber ball to represent the eye, and two knitting nee- 
 dles, one to represent the visual axis and the other to rep- 
 resent one or the other of these two axes of rotation. The 
 rubber ball and the knitting- needles are worthless in the 
 study of oblique rotations, for the reason that there can 
 be no fixed axis for any one of these rotations. Any and 
 every oblique rotation is around both the vertical and the 
 horizontal axes, a-b and d-e, which are always at right- 
 angles to the visual axis, but not at right -angles 
 to any oblique rotation plane. These axes are not 
 fixed, but are themselves in motion as the eye rotates 
 around them in any oblique plane. As in cardinal rota- 
 tions, so in oblique rotations, the rotation plane is a fixed 
 plane. The duty of each of the three muscles concerned 
 in an oblique rotation is well defined, and each does its
 
 46 THE FUNDAMENTAL, PRINCIPLES 
 
 duty well in the interest of correct orientation. The 
 oblique muscle prevents the loss of parallelism of the 
 vertical axis of the eye with the median plane of the 
 head. The superior rectus elevates the eye by rotating 
 it on the transverse axis, d-e\ while the external rectus, 
 acting- simultaneously and harmoniously with the other 
 two muscles, rotates the eye to the rig-fat around the 
 vertical axis, a-b. As these two rotations beg-in, the axis 
 of each is made to move by the power that is making the 
 eye rotate around the other, hence they cannot be fixed 
 axes. At the end of such an oblique rotation (up and to 
 the right), there is no more torsion than if the eye had 
 been first rotated outward on the fixed axis a-b, and then 
 directly upward on the fixed axis d-e. In every possible 
 monocular rotation the vertical axis of the eye must be 
 kept parallel with the median plane of the head, and this 
 is the task that is set for the oblique muscles. 
 
 The study of torsion in oblique rotations on a fixed 
 axis, at right-angles to the rotation plane, as it appeared 
 in the first edition, is reproduced in the four following 
 pag-es as matter of mathematical interest, but not as a 
 physiolog-ical truth. 
 
 The accompanying' cut, Fig. 12, was designed by Mad- 
 dox for solving "false torsion." It is taken from his 
 very interesting book on "The Ocular Muscles," pub- 
 lished in 1898. The following is the solution in his own 
 words:
 
 OF OCULAR MOTIONS. 
 
 47 
 
 Fig. 12. 
 
 4 'Taking VC as unity - 
 
 Since OV = sin I 
 
 and 2 = cosR, 
 
 .-. OM = sinIcosR. 
 Moreover OC = cos I; 
 
 OM = sin i cos R = tan I cos R. 
 
 OC cos I 
 
 But ^ = tan(I X); 
 
 . '. tan (I X) = tan I cos R. 
 
 Or X = I tan" 1 (tan I cos R) 
 
 "Putting this into language: The false torsion is 
 equal to the angle from the vertical, or from the hori-
 
 48 THE FUNDAMENTAL PRINCIPLES 
 
 zontal, of the axis about which the eye rotates, less the 
 angle whose tangent is the multiple of the tangent of 
 the inclination of the axis of motion with the cosine of 
 the angle traversed by the line of fixation. 
 
 "The short table overleaf will give an idea of the 
 amount of false torsion which takes place on looking in 
 any diagonal direction midway between any two of the 
 cardinal directions. 
 
 "Since the greatest false torsion of which the eye is 
 capable occurs at the extremity of these diagonals, we 
 may see at once that it does not ever much exceed 10." 
 
 Rotation about an axis 45 from the Jiorizontal. 
 
 Degrees | 5 
 
 10 
 
 15 | 20 
 
 25 
 
 80 
 
 35 
 
 40 
 
 4o 
 
 Torsion | 6^' 
 
 26' 
 
 1 |1 47' 
 
 2 49' 
 
 4 6' 
 
 5 40' 
 
 733 / 
 
 9 44' 
 
 The above table was taken from Maddox. 
 
 At the author's request, Prof. John Daniel, of Van- 
 derbilt University, designed Fig. 13 with the view of 
 determining the amount of torsion that would occur as 
 the result of oblique rotation of the eyes, if it were not 
 prevented by the oblique muscles. The following is the 
 solution by Professor Daniel:
 
 OF OCUIvAR MOTIONS. 
 
 49 
 
 Fig- i3- 
 Make vo = unity. 
 
 I = angle between the vertical and the 
 
 axis of rotation, 
 = ocv. 
 R = angle through which the eye is turned 
 
 on said axis, 
 vot. 
 Then X = angle of torsion, vcm. 
 
 R \ rfnr in thpfrian{r1p7y/-> wphavp 
 ot 2 !/ sinX -vm = sinoz'c-^- me). 
 
 COS I vers R 
 
 cos 2 R-|-c 
 "XT* * vin /c\r\o T\ "vnt 
 
 sin X. = sin ovc = sin (90 I) c 
 
 cos I vers R cos I vers R 
 
 ' cos R+ cot 2 I 
 
 = sn 
 
 m~V c s * v^ R \ 
 \ i/ cos* R+ cot 2 1 /
 
 50 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 " That is, starting from a primary position, when the 
 eye is rotated R degrees on axis inclined I degrees to the 
 vertical (or horizontal) the resulting torsion, X, is an 
 angle whose sine is equal to cos I times the vers R, di- 
 vided by the square root of the sum of the squares of 
 cos R and cos I. The numerical value of the torsion, X, 
 when the inclination of the axis is 45, is as follows for 
 angles of rotation, R, as follows: 
 
 Angle of rotation = 
 R 
 
 5 
 
 10 
 
 16 
 
 20 
 
 25 
 
 30 
 
 35 
 
 40 
 
 45 
 
 
 
 
 
 
 
 
 
 
 
 Torsion 
 
 fi'4' 
 
 ?6' 
 
 1 
 
 147' 
 
 249' 
 
 46' 
 
 540' 
 
 733' 
 
 944' 
 
 
 
 
 
 
 
 
 
 
 
 " This was worked out independently of the simpler 
 formula given in Maddox, but the two are equivalent." 
 
 The mistake made by Maddox was in supposing that 
 no effort was made by the obliques to correct the tor- 
 sioning that otherwise would occur. 
 
 The work of mastering the study of ocular rotations is 
 greatly simplified by a knowledge of the fact that a car- 
 dinal rotation is around one of two axes, and that oblique 
 rotations are around both these axes simultaneously, and 
 that no other axes are possible. Rotation planes are in- 
 numerable, but the axes of rotations are only two, the 
 vertical and the transverse axes of the eyes. Although 
 every vertical motion is effected by two muscles, and 
 every oblique rotation by three muscles, nevertheless it 
 will be profitable to study each muscle and its plane.
 
 OF OCULAR ROTATIONS. 51 
 
 THE INDIVIDUAL MUSCLE AND ITS PLANE OF 
 ROTATION. 
 
 If the nine conjugate innervations were never defective, 
 and if there were no such thing as heterophoria, there 
 would be but little need for studying the ocular muscles 
 as to their separate action or in the light of synergism 
 and antagonism. In paralysis and paresis of an ocular 
 muscle, a diagnosis can be made easily and quickly only 
 when one knows what would be the result of unopposed 
 action of the affected muscle. 
 
 The reader is supposed to be fully acquainted with the 
 extrinsic ocular muscles, as to their origin, course, inser- 
 tion, and nerve supply. With this knowledge already ac- 
 quired it is easy to pass to the study of the result or re- 
 sults of the contraction of any single muscle. The axis 
 of rotation of the eye by any one muscle must be at right- 
 angles to the plane of rotation for this muscle. This plane 
 must bisect the muscle at its origin and at its attachment, 
 and must also pass through the center of rotation of the 
 eye. As to the internus or externus, the relationship 
 that the muscle plane bears to the horizontal plane of the 
 eye indicates the exact rotation that will result from its 
 action. If the rotation plane of the internus coincides 
 with the horizontal plane of the eye, then this muscle 
 will have only one result from its contraction; that is,
 
 52 THE FUNDAMENTAL PRINCIPLES 
 
 the eye will be turned directly in (ad version), the rota- 
 tion taking- place around the vertical axis of the eye. 
 This action of the internus may be termed its principal 
 action; and under such condition there can be no subor- 
 dinate action of the muscle. Some may prefer the terms 
 used by Dr. Maddox, viz., pre-eminent and subsidiary 
 action. 
 
 If the plane of rotation of the internus does not coin- 
 cide with the horizontal plane of the eye, the simple ro- 
 tation is impossible. Let this muscle plane be inclined 
 down and out, as it must be when the internus is attached 
 too high, then the axis of rotation cannot be the vertical 
 axis of the eye, for the former must bear the same rela- 
 tionship to the latter that the muscle plane bears to the 
 horizontal plane of the eye. The unopposed action of 
 this muscle cannot rotate the eye directly in, but associ- 
 ated with the adversion there will be superversion and in- 
 ward torsion or declination, both of which are subordi- 
 nate actions. Let the internus be attached too low on 
 the globe, then its plane of rotation will have an inclina- 
 tion down and in, forming- a definite angle with the hor- 
 izontal plane of the eye. The axis of rotation will form 
 the same angle with the vertical axis of the eye. Unop- 
 posed, the internus thus attached cannot rotate the eye 
 directly inward, but, associated with the adversion (prin- 
 cipal), there will be sub-version and an outward torsion
 
 OF OCULAR ROTATIONS. 53 
 
 or declination. It is reasonable to suppose that the plane 
 of rotation of the internus does not always coincide with 
 the horizontal plane of the eye. Thus H is shown that, 
 by error of attachment (too high or too low), an internus 
 may be one factor in a hyperphoria or a cataphoria, and 
 in a minus or a plus cyclophoria. 
 
 In like manner rotation by the external rectus muscle 
 may be studied. If the plane bisecting the origin and in- 
 sertion of this muscle, and passing throug~h the center of 
 rotation, coincides with the horizontal plane of the eye, 
 its action will result in abversion (principal, without any 
 kind of subordinate, action). If the muscle be attached 
 too high, its plane of rotation must be inclined down and 
 in, its axis of rotation making the same angle with the 
 vertical axis that its plane makes with the horizontal 
 plane. The action of the externus thus attached will 
 have a triple result: (a) abversion (principal); (Z>) super- 
 version (subordinate); and (c) an outward torsion or dec- 
 lination (subordinate). 
 
 If the externus be attached too low, its plane of rota- 
 tion will be tilted down and out, forming a definite angle 
 with the horizontal plane, and its axis of rotation will 
 form an equal angle with the vertical axis. In contract- 
 ing, the eye will be abverted (principal action); it will 
 also be sub-verted, and there will be an inward torsion 
 (subordinate actions). Thus it is shown that an externus
 
 54 THE FUNDAMENTAL, PRINCIPLES 
 
 attached too high or too low will be one factor in the pro- 
 duction of a hyperphoria or a cataphoria, and just as cer- 
 tainly a factor in the production of a plus or a minus 
 cyclophoria. 
 
 It will be observed, from the foregoing, that either an 
 internus or an externus attached in greater part above 
 the horizontal plane, will have the superverting effect of 
 a superior rectus; and that either muscle attached in 
 greater part below the horizontal plane of the eye, will 
 have the sub-verting effect of the inferior rectus. The 
 torsioning effect of an internus attached too high will be 
 in, while that of an externus with a too high attachment 
 will be out. An internus attached too low will produce 
 a plus cyclophoria, while an externus attached too low 
 will cause a minus cyclophoria. Thus it will be seen that 
 an internus will have the same kind of verting and tor- 
 sioning effects as the superior or inferior rectus towards 
 which its attachment is displaced. The external rectus 
 will have the superverting or sub-verting effect of the su- 
 perior or inferior rectus towards which its attachment is 
 displaced, but the opposite torsioning effect. The prac- 
 tical nature of these observations will be shown in the 
 study of operations on the lateral recti muscles. 
 
 The correctness of what has been said about the action 
 of the internus or externus, when the plane of rotation 
 does not coincide with the horizontal plane of the eye, can
 
 OF OCULAR ROTATIONS. 55 
 
 be easily demonstrated by the use of the rubber ball and 
 the knitting needles, and in the same way can be studied 
 the individual action of the superior and inferior recti 
 and that of the obliques. The rotation plane of an indi- 
 vidual muscle bisects the muscle and cuts the center of 
 rotation. Only in properly attached lateral recti mus- 
 cles does this plane correspond with a meridional plane, 
 hence the axes of rotations by the other four muscles can- 
 not lie in the equatorial plane. 
 
 The origin, course, and insertion of the superior rectus, 
 also of the inferior rectus, make it impossible for the 
 plane of rotation for either one of these muscles to coin- 
 cide with the vertical antero-posterior plane of the eye 
 when in the primary position. The plane of rotation for 
 either one of these muscles is made to pass through the 
 center of the origin of the muscle, the center of rotation 
 of the eye, and the center of the insertion of the muscle. 
 It is only when either muscle has a very definite attach- 
 ment that its plane of rotation can be vertical. A dis- 
 placement in or out of the attachment of either the 
 superior or the inferior rectus will not change the kind 
 of rotation to be effected, but it would modify the ex- 
 tent of the three effects of its contraction. For sim- 
 plicity of study, it may be considered, therefore, that 
 there is a common plane of rotation for both the supe- 
 rior and the inferior recti, and that the plane is ver- 
 tical, forming an angle of 27 with the vertical antero-
 
 56 THE FUNDAMENTAL PRINCIPLES 
 
 posterior plane of the eye. The axis of rotation must 
 be at 'right-angles to the muscle plane, and consequently 
 must form an angle of 27 with the transverse axis, but 
 in the horizontal plane with it. The superior rectus 
 unopposed has for its principal effect superversion, and 
 for its subordinate results, adversion and an inward 
 torsion or declination. The inferior rectus will have for 
 its principal action sub-version, and for its secondary ac- 
 tions, adversion and outward torsion. Thus the superior 
 rectus, while being the chief factor in a hyperphoria, 
 may be also a secondary factor in the production of an 
 esophoria, and of a minus cyclophoria. The inferior 
 rectus, while the chief factor of a cataphoria, may also 
 be a secondary factor both in esophoria and in a plus 
 cyclophoria. 
 
 An oblique muscle, when unopposed, is incapable of a 
 simple rotation. Its plane of rotation must be constructed 
 in the same way as have been constructed the planes for 
 the recti. In the case of the superior oblique, the point 
 of origin through which the plane must pass is the pulley 
 at the upper-inner angle of the orbit, and not at its real 
 origin at the apex of the orbit. Since the inferior oblique 
 arises beneath this pulley, and since the superior oblique 
 may be supposed to pass directly above, while the inferior 
 passes directly beneath, the center of motion of the eye, to be 
 inserted directly opposite each other in the outer-posterior
 
 OF OCUIvAR ROTATIONS. 57 
 
 quadrant, they may be said to have a common plane of 
 rotation, which means, also, that they have a common 
 axis, around which each must revolve the eye when un- 
 opposed by any other muscle. This plane is at an angle 
 of 39 with the vertical transverse plane of the eye. The 
 axis must be, therefore, at an angle of 39 with the visual 
 axis. When the superior oblique contracts, its principal 
 action is to tort the eye in; but always accompanying- this 
 are the subordinate actions, sub-version and abversion. 
 When the inferior oblique is unopposed and unaided, its 
 principal action is outward torsion, and its secondary ef- 
 fects are superversion and abversion. Thus it may be 
 seen that the obliques may be a factor in three forms of 
 heterophoria: (a) cyclophoria, (Z>) hyperphoria and cata- 
 phoria, (c) exophoria. 
 
 LAW OF MONOCULAR MOTION. 
 
 The law g'overning' monocular rotations may be formu- 
 lated as follows: (1) The visual axis, which is the line of 
 intersection of the planes of all meridians, must be rotated 
 in the plane of that meridian on which lie the first and sec- 
 ond points of view and their retinal images. (2) In the 
 plane of the horizontal, or that of the vertical, meridian, 
 the rotation must be effected around a sing-le fixed axis, 
 at rig-ht-ang"les to the rotation plane and cutting- it at the 
 center of rotation if in the horizontal plane, around the
 
 58 THE FUNDAMENTAL PRINCIPLES 
 
 vertical axis of the eye; if in the -vertical plane, around the 
 transverse axis of the eye. (3) In the plane of an oblique 
 rotation, 'whatever the degree of obliquity, the rotation 
 must be accomplished around two moving- axes by two 
 forces acting simultaneously, these axes being the trans- 
 verse and vertical axes, both at right-angles to the visual 
 axis, but neither one at rig"ht-angles to any oblique ro- 
 tation plane; while a third force prevents any rotation 
 around the vistial axis. 
 
 The only part of the above law open to controversy 
 pertains to oblique rotations. These rotations are ac- 
 complished by three forces; and they are so applied as to 
 make it impossible for such a rotation to be around a re- 
 sultant fixed axis, as would be the case if only two forces 
 were acting". If a resultant axis for the three forces be 
 possible, the axis would be a moving" one, for, in any ob- 
 lique rotation of the eye, there are no two fixed points, 
 directly opposite or otherwise related, on its surface, 
 hence there could be no fixed diameter. If there be a 
 resultant moving axis for an oblique rotation, it would 
 be hard to locate. It is so easy to grasp the thoug-ht 
 that, in an oblique rotation, one oblique muscle prevents 
 rotation around the visual axis, while one rectus muscle 
 is moving" the eye around the vertical axis and one other 
 rectus muscle is moving- the eye around the transverse 
 axis, it seems to the author that the wording 1 of the third 
 section of the law of monocular rotation must be correct.
 
 OF OCULAR ROTATIONS. 59 
 
 The purpose of the above law is that, while the visual 
 axis is being- rotated in a fixed plane, the vertical axis of 
 the eye shall never lose parallelism with the median 
 plane of the head, for on this parallelism depends correct 
 orientation. 
 
 A single muscle can obey this law only when the rota- 
 tion is in the horizontal plane, and then only when the 
 externus or the internus is bisected by this plane. In 
 vertical and oblique rotations, an oblique muscle pre- 
 vents rotation around the visual axis, hence performs the 
 task of keeping 1 the vertical axis of the eye parallel with 
 the median plane of the head, while one rectus (as in 
 vertical rotations), or at most two recti (as in oblique ro- 
 tations), moves the visual axis from point to point in 
 space. 
 
 In the light of this law the six extrinsic ocular muscles 
 should be studied as they are related to each other in 
 performing their tasks. 
 
 The helping of one muscle by other muscles is s} r ner- 
 gism; the opposing of one muscle by other muscles is an- 
 tagonism. The old method of studying these is set forth 
 in the following 
 
 TABLE. 
 
 I Superior rectus } 
 
 f Synergists . . . -I [ Tonicity. 
 
 ( Inferior rectus ) 
 
 Internus 
 
 External rectus . 
 
 I Antagonists < Superior oblique '- Tonicity. 
 
 ( Inferior oblique )
 
 60 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 { Superior oblique 1 
 
 Synergists . . . 4 > Tonicity. 
 
 ( Inferior oblique ) 
 
 Externus . 
 
 i Internus ', 
 
 Antagonists . . -< Superior rectus [ Tonicity. 
 
 ( Inferior rectus ) 
 
 I Inferior oblique Contractility 
 
 Synergists . . . ] A too high internus, or } Trmi _: tv 
 
 e / A too high externus . f * 
 
 Superior rectus in 
 
 superversiou , , nterior rectl]s - 
 
 Antagonists. | l^?^^,,,; or P"-^ 
 
 [ A too low externus . . . . j 
 
 i. Superior oblique Contractility 
 
 f Synergists . . . 4 A too low internus, or j T>nni+ 
 
 , , . ( A too low externus ....?.* 
 
 Inferior rectus in 
 
 sub-version ... f Supertor retus , 
 
 ! An^gonists. | ngrnus, or 
 
 [ A too high externus . 
 
 ( Superior rectus } 
 
 f Synergists . . . ] A too high internus, or > Tonicity. 
 
 (( A too low externus . . . . ) 
 [Inferior oblique... 
 Antagonists ItoTfo^ernus, or 
 [ A too high externus . 
 
 {Inferior rectus ....... } 
 A too low internus, or > Tonicity. 
 A too high externus . . . ) 
 
 Inferior oblique Superior oblique 1 
 
 Antagonists. ^n^'Sernus, or ["^- 
 [ A too low externus . . . . j 
 
 It will be noticed that in the above table each ocular 
 muscle has one more antagonistic muscle than syner- 
 gistic.
 
 OF OCULAR ROTATIONS. 61 
 
 Another point to be noted in the study of the table is 
 that synergism more often comes from tonicity than from 
 contractility, and that the antagonism shown comes 
 entirely from tonicity. In this table the synergistic 
 muscle, either by tonicity or contractility, aids a con- 
 tracting" muscle in the performance of its principle func- 
 tion only; and the antagonistic muscle, by its tonicity, 
 hinders the contracting muscle in the performance of its 
 principal function only. 
 
 A single muscle may be both synergistic and antago- 
 nistic. To illustrate: Rotation directly up is accom- 
 plished by two muscles, the superior rectus and the in- 
 ferior oblique. The principal action of the superior rec- 
 tus would be to elevate the eye, but the secondary re- 
 sults would be to tort the eye in and to turn it in. The 
 inferior oblique, in its principal function, prevents the 
 intorting, and the subsidiar} T result is to prevent the in- 
 turning and to help in the upturning. The inferior ob- 
 lique is, therefore, both synergistic and antagonistic to 
 the superior rectus. 
 
 In the truest sense, a synergistic muscle, by contrac- 
 tility, should be one helping another muscle in the per- 
 formance of its task of rotating the visual axis correctly; 
 while an antagonistic muscle, by contractility, should be 
 one to prevent an error in the relationship of the verti- 
 cal axis of the eye with the median plane of the head.
 
 62 THE FUNDAMENTAL PRINCIPLES 
 
 It would seem, therefore, that a new table of syner- 
 g-ism and antagonism should be constructed, in which no 
 mention of muscles not contracting- should be made. Since 
 this is a study of monocular rotation, the following- table 
 may be considered a study of the rig-ht eye: 
 
 TABLE. 
 
 ( Synergist: None. 
 
 (1) Rotation directly to the right: Externus -j 
 
 ( Antagonist: None. 
 
 ( Synergist: None. 
 
 (2) Rotation directly to the left: Internus. . ] 
 
 / Antagonist: None. 
 
 ( Synergist: Inferior oblique. 
 
 (3) Rotation directly up: Superior rectus . . -j 
 
 ( Antagonist: Inferior oblique. 
 
 ( Synergist: Superior oblique. 
 
 (4) Rotation directly down: Inferior rectus . < 
 
 ( Antagonist: Superior oblique. 
 
 ( Synergist: Superior oblique. 
 f Externus < 
 
 (5) Rotation obliquely] ( Antagonist: Superior oblique, 
 up-and-right - and 
 
 ( Synergist: None. 
 (_ Superior rectus . -J 
 
 ( Antagonist: Superior oblique. 
 
 i Synergist: None. 
 ( Internus < 
 
 (6) Rotation obliquely I ( Antagonist: Superior oblique, 
 down-and-left -I and 
 
 ( Synergist: Superior oblique. 
 Inferior rectus. . -| 
 
 ( Antagonist: Superior oblique. 
 
 ( Synergist: None. 
 Internus < 
 
 (7) Rotation obliquely] ( Antagonist: Inferior oblique, 
 up-and-left -j 
 
 ( Synergist: Inferior oblique. 
 ! Superior rectus . < 
 
 ( Antagonist: Inferior oblique.
 
 OF OCULAR ROTATIONS. 63 
 
 i Synergist: Inferior oblique. 
 
 f Externus - 
 
 (8) Rotation obliquely j ( Antagonist: Inferior oblique. 
 
 down-and-right -j 
 
 ( Synergist: None, 
 i Inferior rectus 
 
 / Antagonist: Inferior oblique. 
 
 BINOCULAR ROTATION. 
 
 In the human being the two eyes are so placed and so 
 adjusted as to make binocular single vision possible, in 
 obedience to the supreme law of corresponding retinal 
 points. To say that the macula of one eye must corre- 
 spond, point for point, with the macula of the other e} T e; 
 that the vertical meridian of one eye must correspond, 
 point for point, with the vertical meridian of the other 
 eye; that the horizontal meridian of the one eye, in like 
 manner, must correspond with the horizontal meridian 
 of the other eye, does not explain the fundamental fact 
 which makes binocular single vision possible. There are 
 eyes whose maculas and whose vertical and horizontal 
 meridians do not correspond eyes that have never had 
 binocular single vision and can never be made to have it. 
 This abnormal condition was known to Von Graefe and 
 was by him named "antipathy to binocular single vi- 
 sion," but he made no attempt to explain it. For such 
 eyes there is no circle (horopter or monoscopter) of single 
 seeing with the two eyes. There is no such thing as a 
 binocular spacial pole, and over such eyes the law of bin-
 
 64 THE FUNDAMENTAL PRINCIPLES 
 
 ocular rotation has no power. For these eyes, and they 
 are fairly numerous, the fundamental fact underlying- 
 binocular single vision does not exist. 
 
 "What is the fundamental fact of corresponding- reti- 
 nal points?" is a question worth the asking-. The au- 
 thor believes he uttered the truth when he taug-ht, some 
 years ag*o, that the secret of corresponding- retinal points 
 is common brain-cell connection; that one macula corre- 
 sponds, point for point, with the other macula only be- 
 cause these corresponding- points have, g"oing- from them, 
 two fibers which meet in the optic tract and go, side by 
 side, back into the same cuneus to terminate in one com- 
 mon cell in the visual center. Corresponding- points on 
 the two vertical and the two horizontal meridians, like- 
 wise corresponding points on any two oblique meridians 
 similarly related to the vertical and horizontal meridians 
 and to the maculas, must have common brain-cell con- 
 nection. This explains double impressions, yet a single 
 sensation two images, yet a single object. If the fibers 
 from the right macula should go to the right side of the 
 brain, and the fibers of the left macula should go to the 
 left side of the brain, there would be two sensations 
 excited, as certainly as that there have been two ret- 
 inal impressions* Or, if the fibers going from retinal 
 points that normally correspond, find their way back to 
 the same cuneus, but terminate each in a separate brain-
 
 OF OCUIvAR ROTATIONS. 65 
 
 cell, there would be two sensations as certainly as that 
 there have been the two retinal impressions. One or 
 the other of these anatomic faults must exist in every 
 person who has antipathy to binocular vision who has 
 never seen singly with the two eyes and who can never 
 be made to do so. A good illustration of common brain- 
 cell connection may be had by any one riding- on a street 
 car, when there are two individuals who wish to signal 
 the conductor their desire to leave the car at the same 
 crossing. The two press the button at the same moment 
 of time with but one result, the ringing of one bell, just 
 as if only one button had been pressed a double impres- 
 sion with only one bell excited. If one button were con- 
 nected with a bell at one end of the car, while the other 
 button is connected with a bell at the other end of the car, 
 or if the two bells be at the same end of the car and very 
 near to each other, the pressing of the two buttons would 
 make the two bells ring, but their sounds could not be 
 blended into one. 
 
 The law of visible direction does not explain corre- 
 sponding retinal points, for this law is violated in the in- 
 terest of binocular single vision whenever the prism is 
 placed before either of the two eyes. Duction is possible 
 only in violation of the law of direction. When there are 
 no corresponding retinal points, nothing can interfere 
 with the law of direction: Everything seen is on a line
 
 66 THE FUNDAMENTAL, PRINCIPLES 
 
 connecting* the object and its image, which line passes 
 through the center of rotation "every line of direction 
 is a radius of retinal curvature prolonged." Nor is this 
 law ever violated when there is only one eye. 
 
 A person whose eyes have not corresponding retinal 
 points is always strabismic, and while he may prefer to 
 use almost constantly one eye, the other eye does not be- 
 come blind from want of use, although mental suppres- 
 sion alone prevents diplopia. This crossing exists from 
 the day of birth to the day of death, yet the crossed eye 
 continues to see well, whenever permitted to do so by 
 the temporary obstruction of the other eye. In ordinary 
 strabismus, as is well known, the deviating eye becomes 
 mentally blind. 
 
 Nature has two methods of preventing diplopia (1) 
 fusion of the two images by bringing the two corre- 
 sponding retinal points into conjunction with the two 
 images; (2) mental suppression of one of the two images. 
 Fusion is possible only when there are corresponding reti- 
 nal points. Suppression is a necessity, (1) when there are 
 no corresponding retinal points; (2) when there are corre- 
 sponding retinal points, but mal-adjustment of the ocu- 
 lar muscles makes it impossible to correctly relate these 
 two points to the two images of the single object. 
 
 In strabismic (heterotropic) eyes, when the seeing eye is 
 being rotated in obedience to the law of monocular rota-
 
 OF OCULAR ROTATIONS. 67 
 
 tion, the other eye moves, but not in the interest of either 
 binocular single vision or correct orientation. The com- 
 itant rotation of a squinting" eye differs in nothing- from 
 the rotation of an eye that is stone-blind. 
 
 Binocular rotation, as it will now be studied, is the 
 rotation of the two eyes in the interest of binocular sin- 
 gle vision and correct orientation. Binocular rotations 
 are either cardinal or oblique. They are effected by the 
 same muscles that are concerned in monocular rotations, 
 but not wholly by the volitional brain-centers, which 
 alone are concerned in monocular rotations. Besides the 
 nine conjugate brain-centers, all under the control of the 
 will, and each connected with two muscles, one belong- 
 ing 1 to each eye, there are twelve centers controlled by 
 the fusion faculty of the mind, each center being con- 
 nected with only a single muscle. These fusion centers, 
 as their name indicates, exist in the interest of binocular 
 single vision; hence when there is a condition that would 
 cause diplopia, whether the eyes be at rest or in rota- 
 tion, one or more of these fusion centers must be in ac- 
 tion. These fusion centers must be ready to act both 
 independently of, and coordinately with, the conjugate 
 centers. The conjugate centers furnish the neuricity 
 that brings about all voluntary movements of the eyes, 
 such as verting and converging. The single centers, in 
 the sense of acting on only one muscle, are the centers
 
 68 THE FUNDAMENTAL, PRINCIPLES 
 
 that effect duction, the power that overcomes double vi- 
 sion, and planing-, the power that prevents diplopia. 
 
 Fig. 15 shows, in a schematic way, the conjugate cen- 
 ters and the single fusion centers. This figure also 
 shows the two eyes with their twelve muscles; but, in 
 its study, the imagination must make the connections. 
 In "Ophthalmic Neuro-Myology " there is a separate il- 
 lustration for each conjugate brain-center and the mus- 
 cles controlled by it, in which the connecting nerve-fibers 
 appear; and the connection of each fusion center and its 
 muscle is also shown. 
 
 As related to the volitional brain-centers which con- 
 trol them, the twelve muscles belonging to the two eyes 
 are arranged in pairs as follows: (1) The two superior 
 recti, (2) the two inferior recti, (3) the two interni, (4) 
 the right externus and the left internus, (5) the right in- 
 ternus and the left externus, (6) the two superior ob- 
 liques, (7) the two inferior obliques, (8) the right supe- 
 rior oblique and the left inferior oblique, (9) the left su- 
 perior oblique and the right inferior oblique. For each 
 of the nine groups of two muscles there is a conjugate 
 innervation center from which go fibers to be distributed 
 equally to the two muscles to be controlled by it. The 
 internal recti and the four obliques are each connected 
 with two conjugate innervation centers, while the re- 
 maining muscles are each under the control of only one 
 conjugate innervation center.
 
 OF OCULAR ROTATIONS. 69 
 
 THE INNERVATIONS. 
 
 To accomplish their work these muscles have nine 
 conjugate innervations: 
 
 (1) The one to elevate both eyes. 
 
 (2) The one to depress both eyes. 
 
 (3) The one to converge both eyes. 
 
 (4) The one to move both eyes to the right. 
 
 (5) The one to move both eyes to the left. 
 
 (6) The one to keep the vertical axes from diverging 
 above. 
 
 (7) The one to prevent their converging above. These 
 (6 and 7) are called into action by the guiding sensation, 
 when the point of view is primary or in either one of the 
 four cardinal directions. 
 
 (8) The one to maintain the parallelism of the vertical 
 axes and the median plane of the head when the point of 
 view is obliquely up and to the right, or down and to the 
 left; and 
 
 (9) The one to maintain the parallelism of the vertical 
 axes of the eyes and the median plane of the head, when 
 the point of view is obliquely up and to the left, or down 
 and to the right. 
 
 The innervations one to five are for the recti, and 
 the sixth, seventh, eighth, and ninth are for the ob- 
 liques. Each of the conjugate innervation centers con-
 
 70 THE FUNDAMENTAL PRINCIPLES 
 
 trols one of the several pairs of muscles. The first con- 
 trols the two superior recti; the second, the two inferior 
 recti; the third, the two interni; the fourth, the right ex- 
 ternus and the left internus; the fifth, the right internus 
 and the left extern us; the sixth, the two superior ob- 
 liques; the seventh, the two inferior obliques; the eighth, 
 the right superior oblique and the left inferior oblique; 
 the ninth, the left superior oblique and the right inferior 
 oblique. The verting centers act singly only in the 
 sweeping of the eyes in the horizontal plane; they act in 
 pairs only when the eyes are moved directly up or down; 
 three of these centers act together in oblique rotations 
 of the eyes. It is only in oblique rotations that nor- 
 mal ocular muscles need any other centers of nerve- 
 power than the conjugate centers already studied. 
 Eyes whose muscles are unequal in tonicity cannot have 
 binocular single vision when controlled only by the con- 
 jugate innervation centers, or even when at rest. Ob- 
 lique rotations of eyes with normal muscles, and rota- 
 tions of any character, or even rest, when muscles are 
 unequal in tone, require that there shall be emergency 
 or fusion brain-centers, one for each individual muscle. 
 These centers, twelve in number, are certainly not under 
 control of the will. They exist in the interest of binoc- 
 ular single vision, and, therefore, may be said to be 
 tinder the control of the fusion faculty of the mind.
 
 OF OCULAR ROTATIONS. 71 
 
 Their location is, probably, at the base of the brain; and 
 certainly each of these centers has power over one ocu- 
 lar muscle. Six of these fusion centers must be on 
 either side of the brain. These should be numbered in 
 harmony with the numbering- of the conjugate centers, 
 and the same number should be given to two basal cen- 
 ters, the words right and left to distinguish the one from 
 the other. The right first center belongs to the right 
 superior rectus, and the left first center belongs to the 
 left superior rectus; the right second center belongs to 
 the right inferior rectus, and the left second center be- 
 longs to the left inferior rectus; the right third center 
 belongs to the right internus, and the left third center 
 belongs to the left internus; the right fourth center be- 
 longs to the right externus, and the left fourth center 
 belongs to the left externus; the right sixth center be- 
 longs to the right superior oblique, and the left sixth 
 center belongs to the left superior oblique; the right 
 seventh center belongs to the right inferior oblique, and 
 the left seventh center belongs to left inferior oblique. 
 When one of these basal centers discharges neuricity, 
 only a single muscle responds; when a conjugate center 
 discharges neuricity, both muscles of a pair respond. 
 
 The necessity for the existence of both the conjugate 
 volitional centers and the basal fusion centers is shown 
 in Fig. 14, which will now be studied. A careful study
 
 72 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 ** 
 
 H- 
 
 bi)
 
 OF OCULAR ROTATIONS. 73 
 
 of this figure will bring- many things into the light of the 
 understanding. First of all, the figure shows three 
 planes (1) the fixed horizontal plane of the head, 
 a-b-c-d; (2) the fixed vertical plane of the head, g-h-i-j ; 
 (3) Listing's plane, or the fixed transverse plane of the 
 head, cutting the centers of the two eyes, this plane be- 
 ing k-l-m-n. Each of these planes is at right-angles to 
 the other two planes, and the three lines of intersec- 
 tion are e-f, a-b, and h-g. In the horizontal plane are 
 shown horizontal sections of the two eyes, r and s, and 
 the two visual axes are ry and s-f. 
 
 PLANES OF REFERENCE. 
 
 The extended fixed vertical and horizontal planes of 
 the head are planes of reference. With the head in the 
 primary position, if a point is not in the horizontal plane, 
 a-b-c-d, it is instantly known to be above or below it; if 
 a point is not in the vertical plane, h-i-j-k, it is certainly 
 known to be to the right or left of it; and an approxi- 
 mately correct estimate of the degrees of removal of 
 such point from these planes can be made in obedience 
 to the law of visible direction. In the primary position 
 of the head, the plane a-b-c-d is horizontal, and the eyes 
 are in their primary positions when the two visual axes 
 lie in this plane, and are converged on some point, at 
 practical infinity, lying on the line of intersection, e-f, of
 
 74 THE FUNDAMENTAL PRINCIPLES 
 
 the horizontal and vertical planes. Converged on such 
 a point, the visual axes are practically, though never 
 really, parallel. To be perfectly parallel, the visual 
 axis (r-f) of the right eye would have to be in the posi- 
 tion r-f", and the visual axis (s-f) of the left eye would 
 have to be s-f. 
 
 In locating the position of any point in viewable space, 
 the word right and left would be used in reference to the 
 vertical plane of the head, h-i-j-k; the words above and 
 below would be used in reference to the horizontal plane, 
 a-b-c-d; and the word in should be used in reference to 
 both the vertical and horizontal planes. The points/"' 
 and/" are in the horizontal plane, the one to the right, 
 the other to the left, of the vertical plane; the points z 
 and z are in the vertical plane, respectively above and 
 below the horizontal plane. All points lying on the line 
 of intersection (e-f] of the two planes would be points 
 directly ahead, and these would be primary points of 
 view. All points off this line of intersection (e-f) would 
 be secondary points of view. The four cardinal direc- 
 tions a.rzf-i,f-j,f-c, zndf-d. All points not in the line 
 c-d (or in the plane a-b-c-d) and not in the line i-j (or in 
 the plane g-h-i-j) are obliquely related to these lines (or 
 planes). The point of binocular view whether direct, 
 cardinal, or oblique is the point of intersection of the
 
 OF OCULAR ROTATIONS. ?D 
 
 visual axes, to be studied a little further on as the binoc- 
 ular spacial pole. 
 
 With the head fixed in the primary position, the point 
 of binocular view may be changed from the primary 
 point,/", to any secondary point, whether cardinal or ob- 
 lique, in obedience to the law of binocular rotation. The 
 absurdity of the claim that the axes of all binocular ro- 
 tations, from the primary to a secondary point of view, 
 or vice versa, must lie in Listing's plane, is made appar- 
 ent by even a casual study of Fig. 14. In this figure, 
 k-l-m-n represents Listing's plane, which is at right-an- 
 gles to the planes a-b-c-d and h-i-j-k. Listing's plane 
 is, therefore, a transverse vertical plane of the head, and 
 it cuts the centers of rotation of the two eyes. It has 
 been shown that the axes of all rotations lie in the plane 
 of the equator of the eye, and that the equatorial plane 
 is always at right-angles to the visual axis. Therefore, 
 with every change in the position of the visual axis, 
 there must be a change in the relationship of the plane 
 of the equator with Listing's plane. There is only one 
 point in the plane of the equator that never leaves the 
 Listing plane, and that is the center of rotation. Since 
 the transverse and vertical axes of the eyes, alone or to- 
 gether, are the only axes of rotations, the relationship 
 that these bear to Listing's plane is determined by the 
 relationship that the visual axes bear to the fixed verti-
 
 76 THE FUNDAMENTAL PRINCIPLES 
 
 cal and horizontal planes of the head. When the visual 
 axes, r-f and s-f, lie in the plane a-b-c-d, the vertical 
 axes of the eyes must be in Listing's plane. Any move- 
 ment of the eye that compels the visual axis to remain in 
 the plane a-b-c-d, as from/" to/' or from fiof", must be 
 around the vertical axis, which must lie in Listing's 
 plane. Any rotation around the transverse axis will 
 carry the point of fixation up to z or down to z', but in 
 these rotations the transverse axis of each eye forms the 
 same angle with a-b that r-f and s-f form with e-f, hence 
 the rotation from f to z or z is about an axis that does 
 not lie in Listing's plane, any more nearly than is 
 there parallelism of r-/"and s-f with e-f. If the rota- 
 tion upward were to start from/", the axis of rotation 
 of the left eye would lie in Listing's plane, for the 
 visual axis, in position of s-f , would be parallel with e-f; 
 but the axis of the right eye would form the same angle 
 with Listing's plane as its visual axis, in the position of 
 r-f , forms with e-f. In a rotation starting upward from 
 a point between /and/' or beyond/', neither of the two 
 axes of rotation would lie in Listing's plane. 
 
 The conclusion compelled by the above study of Fig. 
 14 is that Listing's plane cannot be a plane of reference, 
 nor can it be a plane containing the axes of all rotations 
 starting from, or returning to, the primary point of view. 
 The equatorial plane of the eye contains both the verti-
 
 OF OCULAR ROTATIONS. 77 
 
 cal and transverse axes of the eye, and it is around one 
 or the other or both of these that all rotations, car- 
 dinal and oblique, occur. Listing's plane, like List- 
 ing's law, should be forgotten in the interest of truth. 
 
 BRAIN-CENTERS FOR BINOCULAR ROTATIONS. 
 
 These brain-centers, volitional and fusional, have al- 
 ready been named. The study of Fig. 14 will convince 
 even a skeptic that these centers are real and not imag- 
 inary. The convergence of the visual axes, r-/"and s-f, 
 to any point on e-f, is effected by the 3rd volitional 
 center acting on both interni; turning the visual axes 
 from f to/" is accomplished by the 4th volitional cen- 
 ter acting on the right externus and the left internus; 
 sweeping the visual axes from ftof is made possible by 
 the action of the 5th volitional center on the right in- 
 ternus and the left externus. The above centers have 
 been pointed out first because they effect the simpler ro- 
 tations. 
 
 More complicated are the rotations directly up and 
 down. Elevating the visual axes from^to z is accom- 
 plished by the combined activity of two volitional cen- 
 ters (a) the 1st conjugate acting on the two superior 
 recti, and (b) the 7th conjugate acting on the two in- 
 ferior obliques. Depressing the visual axes from f to 
 z is effected by the harmonious activity of two volitional
 
 78 THE FUNDAMENTAL PRINCIPLES 
 
 centers (a) the 2nd conjugate acting on the inferior 
 rectus of each eye, and (b) the 6th conjugate acting on 
 the two superior obliques. 
 
 More complicated still are oblique rotations, for each 
 of these must be effected by the harmonious action of 
 three volitional brain-centers; and, in addition to these, 
 every oblique rotation requires activity on the part of 
 two basal or fusion centers. If the visual axes are to be 
 moved from fto any point above the horizontal plane and 
 to the right of the vertical plane, this motion must re- 
 sult from the harmonious action of the 1st conjugate 
 center on the two superior recti, the 4th conjugate on 
 the right externus and left internus, and the 8th con- 
 jugate on the right superior oblique and the left inferior 
 oblique. In the right-sweep part of this rotation, since 
 the left inferior oblique would hinder the left internus, 
 while the right superior oblique would help the right ex- 
 ternus, the hindered left internus must receive a supple- 
 mental impulse from the left 3rd basal or fusion center, 
 whose sole power pertains to that muscle. Since, in the 
 upward part of this oblique rotation, the right superior 
 rectus would be hindered by the right superior oblique, 
 while the left superior rectus would be helped by the left 
 inferior oblique, the hindered right superior rectus must 
 receive supplemental neuricity from the right 1st basal 
 center, else the right visual axis would lag behind the
 
 OF OCULAR ROTATIONS. 79 
 
 left visual axis. Whatever the degree of obliquity and 
 in whatsoever direction, the rotation must be accom- 
 plished by the harmonious action of three conjugate vo- 
 litional centers and two basal or fusion centers. 
 
 In order to bring" into view the only remaining 1 conju- 
 gate brain-center connected with the extrinsic ocular 
 muscles while studying- Fig-. 14, the rotation may be con- 
 sidered as from/" to a point above the horizontal plane 
 and to the left of the vertical plane. This point can be 
 reached only as the result of the harmonious activity 
 of the 1st, 5th, and 9th conjugate centers. The left 
 superior rectus, hindered by the left superior oblique, 
 must receive supplemental neuricity from the left 1st 
 basal center; and the right internus, hindered by the right 
 inferior oblique, must receive supplemental neuricit} r from 
 the right 3rd basal center. In like manner might be 
 studied rotations from/" to some point below the horizon- 
 tal plane and to the left of the vertical plane, or to some 
 point below the horizontal plane and to the right of the 
 vertical plane, but in every such study the fact would be- 
 come apparent that three volitional and two fusion cen- 
 ters have been acting in the interest of binocular single 
 vision and correct orientation. 
 
 In every rotation above the horizontal plane, a-b-c-d, 
 the 1st conjugate center participates; in every rotation 
 below this plane the 2nd conjugate center has a part.
 
 80 THE FUNDAMENTAL PRINCIPLES 
 
 In every rotation to the right of the vertical plane, g-h-i-j, 
 the 4th conjugate center is active, and in every rota- 
 tion to the left of this plane the 5th conjugate center 
 participates. The 3rd conjugate center is concerned 
 in the fixing of any point in space. Thus the five con- 
 jugate centers controlling the four recti muscles, become 
 more real when studied in the light of Fig. 14. 
 
 Rotation from/" to any point in space above or below 
 the horizontal plane, a-b-c-d, must call into action some 
 one of the four conjugate centers connected with the ob- 
 lique muscles. In rotations from /"to z, the 7th conju- 
 gate center keeps the vertical axes of the eyes parallel 
 with the vertical plane, g-h-i-j', and in rotations from/" to 
 z ', the 6th conjugate center maintains this parallelism. 
 In rotations up-and-to-the-right and down-and-to-the- 
 left, the 8th conjugate center prevents torsioning to- 
 ward the right; and torsioning toward the left is pre- 
 vented by the 9th conjugate center when the rotations 
 are up-and-to-the-left and down-and-to-the-right. Ac- 
 tivity of the 8th and 9th conjugate centers arouses into 
 action six of the right and left fusion or basal centers 
 belonging to the recti, but only two of these at any one 
 time. The two basal centers never excited in oblique 
 rotations of eyes whose muscles are normal, are the 
 right 4th and the left 4th. Cardinal rotations by nor- 
 mal muscles do not excite a single fusion center. Thus
 
 OF OCULAR ROTATIONS. 81 
 
 far the study of Fig 1 . 14 has demonstrated the existence 
 of all of the nine conjugate brain-centers belonging" to 
 the recti and obliques, and six of the eight right and 
 left basal or fusion centers connected with the recti. 
 
 The demonstration of the fact of the existence of the 
 right and left individual fusion centers connected with 
 the recti, and the four like centers connected with the 
 obliques, is made easy by a further study of Fig. 14. Nor- 
 mal recti muscles, in a state of tonicity, would converge 
 the visual axes at/", if that point were twenty feet distant, 
 and would keep the two visual axes in the plane a-b-c-d\ 
 and the obliques of equal tonicity would confine the two 
 horizontal retinal meridians in this plane. In such a 
 condition of equal tonicity, neither volitional nor fusion 
 brain-centers are active, when both the head and the eyes 
 are in their primary positions. Convergence of the visual 
 axes and planing these axes and the horizontal meridians 
 are conditions essential to binocular single vision; but the 
 existence of single vision with the two eyes does not 
 guarantee that all the muscles are normal in tone. If 
 tonicity cannot effect binocular single vision, this must be 
 accomplished by contractility of the muscles wanting in 
 tone. The source of the required neuricity is not con- 
 trolled by the will, but by the fusion faculty of the mind, 
 itself dominated by the desire for single vision. Every 
 ocular muscle has its individual fusion center, the neu-
 
 82 THE FUNDAMENTAL PRINCIPLES 
 
 ricity from which acts on only the one muscle. These 
 centers have already been individualized by numbers, 
 and the existence of six of the right and left fusion cen- 
 ters for the recti has been proved in the study of oblique 
 rotations, in the light of Fig. 14. By means of this fig- 
 ure the existence of all the fusion centers, eight for the 
 recti and four for the obliques, can be demonstrated 
 from two different vantage grounds viz., the tests for 
 heterophoria and the duction tests. 
 
 The proof, from the standpoint of heterophoric tests, 
 will presuppose the uncomplicated existence of each of 
 the several errors to be studied in Chapter III. One 
 eye must be taken off its guard in order that any one of 
 these errors may become manifest. The placing of a 6 
 prism, base up, before the right eye in Fig. 14, would 
 double/", the false f being thrown to the position of /. 
 The right eye now off its guard will assume the position 
 that muscle tonicity would give to it, and not a single 
 muscle belonging to this eye will receive neuricity from 
 any source, provided the mind uses the left eye for fixing 
 the true/. If the false /"be directly under the true/", it 
 thus appears because the externus and internus of the 
 right eye have equal tonicity, and the visual axis of this 
 eye, notwithstanding the prism diplopia, will be pointing 
 to the true/. By removal of the prism the diplopia is 
 made to disappear without the turning of either eye.
 
 OF OCULAR ROTATIONS. 83 
 
 If the false/", instead of being- at z\ stands directly under 
 f", it is so because the right eye, in assuming' its position 
 of rest, has its visual axis pointing to f (esophoria). On 
 removing" the prism the false / would jump into the 
 position of f" and would remain there so long 1 as the 
 right visual axis points to/'. This diplopia would not 
 be tolerated. To overcome it, the fusion faculty would 
 unlock the right 4th basal center and cause neuricity 
 to flow to the rig-ht externus, whose contraction would 
 pull the eye so as to quickly bring- its visual axis from/' 
 to/". The left eye, throughout the diplopia, and during 
 the recovery of binocular single vision, has remained sta- 
 tionary, for it has received no fusion impulse. The right 
 fourth basal center alone has acted, and only the exter- 
 nal rectus of the right eye has responded. Any impulse 
 to any muscle of the left eye would have made the vis- 
 ual axis leave the point/". In the same manner the left 
 eye could be tested, and by the test the left 4th fu- 
 sion center could be found. 
 
 Placing the prism, base up, before the right eye, the 
 false f would be thrown directly down to z'\ but instead 
 of appearing directly below/", it would seem to be under 
 f , and only because excessive tonicity of the externus of 
 the right eye (exophoria) has turned it out so that its vis- 
 ual axis points tof". On removing the prism the false/ 
 would jump to the position off and would remain there
 
 84 THE FUNDAMENTAL PRINCIPLES 
 
 if no fusion effort were made; but instantly the right 
 3rd fusion center alone would be excited, and its dis- 
 charged neuricity would compel the right internus to 
 pull the right eye so that its visual axis shall move from 
 f" to f. In this fusion effort not a muscle connected 
 with the left eye has received any impulse, else its vis- 
 ual axis would have been carried away from point f. 
 By applying the test to the left eye, the existence of the 
 left 3rd basal center could be demonstrated. 
 
 By placing a 10 prism, base in, before the right eye, a 
 false /"would be thrown to d. If the false/ appears to 
 be at d, it is because of the fact that the superior and 
 inferior recti of the right eye are equal in tonicity; and 
 notwithstanding the diplopia, the right visual axis con- 
 tinues to point to/. Removal of the prisrn makes the 
 false/ jump at once into the true/, and that, too, with- 
 out any movement of either eye. But if the false f 
 appears under d, on a level with z , it is because the right 
 superior rectus, endowed with an excess of tonicity 
 (hyperphoria),has elevated the eye so that its visual axis 
 points to z. On removal of the prism the false f would 
 jump into z' and would remain there if no effort at fusion 
 were put forth; but this effort at fusion will be made 
 and the diplopia will disappear. The power this time 
 comes from the right 2nd basal center, and it acts only
 
 OF OCULAR ROTATIONS. 85 
 
 on the right inferior rectus, which at once turns the eye 
 down so that its visual axis shall point to /. 
 
 With the 10 prism, base in, before the right eye, the 
 false f may be made to appear above d, on a level 
 with z, because of excessive tonicity on the part of the 
 right inferior rectus (cataphoria). Now the right visual 
 axis will point to z . On removal of the prism the false 
 / will jump into z and will remain there, should the right 
 visual axis continue to point to z . To overcome this 
 diplopia, the right 1st basal center calls into action the 
 right superior rectus alone, and by this action the right 
 eye is elevated so that its visual axis may point to/", the 
 diplopia disappearing at that moment. 
 
 The existence of the rig-Jit 1st and 2nd basal or fu- 
 sion centers has thus been proved from a second stand- 
 point. Placing the 10 prism before the left eye, the 
 fact of the existence of the left 1st and 2nd fusion 
 centers can be shown. The eight fusion centers, each 
 controlling a single rectus muscle in the interest of 
 binocular single vision, certainly exist. 
 
 A Maddox triple rod placed vertically before each eye, 
 with a 6 prism, base up, behind the right rod, will make 
 two streaks of light when a candle or gas jet is the test 
 object. The upper streak should be fixed. If the lower 
 streak is parallel with the upper one, it is because the 
 right superior and inferior obliques are equal in tonicity.
 
 86 THE FUNDAMENTAL PRINCIPLES 
 
 If the lower streak diverges from the upper at their left 
 ends, it is because the right inferior oblique, possessing 
 an excess of tonicity, has tilted the horizontal retinal 
 meridian down at the right (plus cyclophoria). Remov- 
 ing the 6 prism, the two streaks can be made to blend 
 throughout only because the right 6th fusional or bas- 
 al center compels the right superior oblique to restore 
 the horizontal retinal meridian to its correct position in 
 the horizontal plane, a-b-c-d. No other center has acted 
 on any other muscle connected with either eye. If, with 
 the prism behind the right rod, the lower streak has 
 lost parallelism by leaning down to the right, this would 
 be due to the fact that the right superior oblique, with 
 excessive tonicity, has torted the right eye in (minus 
 cyclophoria). On removal of the prism the two streaks 
 could blend only because of activity of the 7th basal 
 center compelling the weak inferior oblique to replace 
 the horizontal meridian in the horizontal plane, from 
 which it had been thrown when the eye was off its guard. 
 Thus has it been proved that there are right 6th and 
 7th basal or fusion centers. By placing the prism 
 behind the left rod, the fact of the existence of the 
 left 6th and 7th basal or fusion centers is also prov- 
 able. 
 
 No additional proof should be necessary in order to 
 convince even the most skeptical concerning the twelve
 
 OF OCULAR ROTATIONS. 87 
 
 fusion centers, and the tasks they are set to perform. 
 The one remaining' method of proving- their existence 
 is the duction test. This must be studied in connection 
 with Fig. 14, in order that the whole truth may be told 
 about them. 
 
 The best means for taking- the duction power of the 
 recti muscles is the rota.ry prism of the Monocular Pho- 
 rometer, but this test may be made by means of the loose 
 prism in the refraction case. With the rotary prism, the 
 fusion centers involved will discharg-e neuricity in in- 
 creasing 1 quantity, as the imag-e is being- gradually moved, 
 up to the point when fusion is no longer possible. The 
 placing- of a loose prism before the eye excites suddenly 
 and to the full extent the fusion center and the muscle 
 under its control. In the former method the eye glides 
 g-ently; in the latter method the eye jumps violently. 
 Each method is as capable as the other in proving- the 
 existence of the individual fusion centers connected with 
 the recti muscles. Since the author prefers the revolv- 
 ing- prism, that method will be made to give evidence 
 concerning the existence of these centers in the still fur- 
 ther study of Pig. 14. The phorometer, without the 
 supernumerary displacing prism, should be placed in 
 front of the right 'eye in position for taking abduction 
 and adduction. With the index at zero, the two or- 
 thophoric eyes will fix the pointy as a result of muscle
 
 88 THE FUNDAMENTAL PRINCIPLES 
 
 tonicity only. By turning- the index in the temporal arc, 
 the image of /on the right retina will be carried nasal- 
 ward that is, toward e in that eye. The only way to 
 prevent diplopia is for the macula to keep under the mov- 
 ing image. Since the image is moving nasal-ward on 
 the horizontal meridian, the macula must move directly 
 nasal-ward and in no other direction. This motion of the 
 eye is accomplished by a discharge of neuricity from the 
 right 4th basal center to the right externus alone. 
 During this revolution of the prism, no other brain-cen- 
 ter has been excited, and no other ocular muscle has 
 contracted. 
 
 When the index has been returned to zero, there is 
 easy binocular vision at the expense of muscle tonicity 
 only. Revolving the index of the prism into the nasal 
 arc will make the image of f move temple-ward that is, 
 toward a. At the very beginning of the rotation of the 
 prism the right 3rd fusion center becomes active, and 
 the neuricity from it makes the right internus move the 
 eye so that the macula may remain beneath the moving 
 image. This action of the right 3rd fusion center on 
 the right internus alone, has prevented diplopia. No im- 
 pulse has gone from any other center to any other muscle 
 belonging to either eye. Thus abduction and adduction 
 of the right eye prove the existence of the rig-Jit 4th 
 and 3rd fusion centers. In the same manner abduction
 
 OF OCULAR ROTATIONS. 89 
 
 and adduction of the left eye may be made to prove the 
 existence of the left 4th and 3rd fusion centers. 
 
 The prism should now be placed before the right eye 
 for the taking" of superduction and subduction. With 
 the index at zero, the two orthophoric eyes will have easy 
 binocular single vision at the expense of muscle tonicity 
 only. When the index is being rotated into the upper 
 arc, the image of f on the right retina is made to move 
 downward on the vertical meridian. The macula must 
 remain under the moving image, else the object/ will be 
 doubled, the false /"appearing directly above the true f. 
 This moving of the macula is made possible by the con- 
 traction of the right superior rectus, in response to an 
 impulse coming from the right 1st fusion center. No 
 other muscle contracts, nor does any other center dis- 
 charge neuricity for effecting this fusion. Returning 
 the index to zero relieves both the right 1st fusion cen- 
 ter and the right superior rectus from further activity. 
 If the index is now made to move downward, the image 
 of f on the right retina will be moved upward on the ver- 
 tical meridian. The macula must be kept under the 
 moving image or a false /"will appear directly below the 
 true f. To prevent this diplopia, the right 2nd fusion 
 center will be made to discharge neuricity to the right 
 inferior rectus alone. No other center and no other mus- 
 cle will be brought into action for maintaining this fu-
 
 90 THE FUNDAMENTAL PRINCIPLES 
 
 sion, and this center and its muscle cease activity the 
 moment the index is returned to zero. Thus the taking- 
 of right superduction and subduction proves the exist- 
 ence of the right 1st and 2nd fusion centers. By plac- 
 ing 1 the prism before the left eye in position for tak- 
 ing- left superduction and subduction, the existence of 
 the left 1st and 2nd fusion centers may be proved. 
 
 In all these duction tests it will be observed that fusion 
 has been accomplished in violation of the law of direction 
 as it applies to the rig-lit eye. As the macula moves in, 
 the visual axis moves from y 7 toward /"'; as the macula 
 moves out, the visual axis moves f rom f toward/"'; as 
 the macula moves downward, the visual axis moves 
 from f toward z; and as the macula moves upward, 
 the visual axis moves from/" toward z '. The fused point, 
 /, is on the visual axis of the eye not under test, but is off 
 the visual axis of the ducted eye. In the duction act of 
 fusion, the line connecting- the fused point and its dis- 
 placed imag-e is not a true line of direction, for it does not 
 cut the center of the retinal curve. 
 
 The existence of the individual fusion centers for the 
 obliques cannot be proved by prisms, but the Maddox 
 rods g-ive positive evidence. With a triple rod before 
 each eye, set vertically, and with no prism behind either 
 rod, the test candle will appear as a sing-le streak of 
 lig-ht. Turning- the rig-lit rod toward the temple, with- 
 in the arc of possible fusion for an oblique muscle, will
 
 OF OCULAR ROTATIONS. 91 
 
 not result in doubling- the line, but this doubling- will be 
 prevented by the rig-lit 7th fusion center acting- on the 
 right inferior oblique. This activity of center and muscle 
 places the horizontal retinal meridian under the inclined 
 streak of lig-ht. If the rig-ht rod had been turned toward 
 the nose, in the arc of possible fusion for an oblique mus- 
 cle, the diplopia would have been prevented by the dis- 
 charg-e of neuricity from the rig-ht 6th fusion center to the 
 rig-ht superior oblique. In each of these efforts at fusion, 
 only one center and one muscle have been active. By 
 these tests the existence of the right 7th and 6th fu- 
 sion centers has been proved. Leaving- the rig-lit rod 
 vertical and turning- the left rod slig-htly out and in 
 would prove, in like manner, the existence of the left 
 7th and 6th centers. 
 
 A final source of proof concerning- the existence of the 
 four fusion centers for the oblique muscles is oblique 
 astig-matism of one eye, while the astigmatism of the 
 other eye is either vertical or horizontal. In the latter 
 eye a horizontal line will have a horizontal imagfe, but in 
 the former eye the imag-e of the horizontal line will 
 be displaced toward the meridian of greatest curva- 
 ture, hence this imag-e will be oblique. To fuse the ob- 
 lique imag-e with the one that is horizontal, an oblique 
 muscle belong-ing- to the oblique-astig-matic e}*e, under 
 the influence of the 6th or the 7th fusion center on the
 
 92 THE FUNDAMENTAL, PRINCIPLES 
 
 corresponding 1 side, must force the horizontal retinal 
 meridian under the displaced image. It would be the 
 7th center and the inferior oblique if the most curved 
 meridian is in the upper nasal quadrant; it would be the 
 6th center and superior oblique if the meridian of great- 
 est curvature is in the upper temporal arc, whether it be 
 the one eye or the other. 
 
 For further, and a more comprehensive, study of the 
 ocular muscles, normal and abnormal, from the brain- 
 side of all questions that can arise, the reader is referred 
 to the author's other book, "Ophthalmic Neuro-Myol- 
 ogy," a necessary companion volume to this book. In 
 this companion volume the brain-centers, voluntary and 
 fusion, and their muscle connections, are freely and fully 
 illustrated. The origin, course, and distribution of all 
 the motor nerves of the eye are also fully illustrated. In 
 all, there are thirty-nine full-page plates, the reproduced 
 one, (Fig 1 . 15) on next page, constituting 1 the foundation 
 for all the others. Besides these full-pag'e cuts, there are 
 twelve smaller illustrations. The book contains 210 
 pages of illustrations and reading matter, all pertaining 
 to the nervous system as related to the ocular muscles, 
 extrinsic and intrinsic. In Fig. 15 the upper part rep- 
 resents, schematically, the volitional and fusional brain- 
 centers the former at the margin, the latter grouped 
 near the median line. All these centers exist in dupli-
 
 OF OCULAR ROTATIONS. 
 
 93 
 
 3 
 
 Fig. 15-
 
 94 THE FUNDAMENTAL PRINCIPLES 
 
 cate, but the volitional centers are not all active. The 
 smaller circles at the periphery represent the centers 
 unused by a right-handed man, only one of which is in 
 the left side of the brain. Conjugate and basal centers 
 10 and 11 belong to the ciliary body and iris. While 
 only half of the conjugate centers are ever used, all of 
 the basal centers stand ready for action at the command 
 of the fusion faculty of the mind. 
 
 THE HOROPTER MONOSCOPTER ISOGONAL ClRCLE. 
 
 There is now neither mystery nor complicated mathe- 
 matics connected with the circle bearing the three names: 
 Horopter, Monoscopter, and Isogonal Circle. The sim- 
 plicity of this comes as the result of the author's discov- 
 ery that the macula is the posterior pole of the eye, and 
 that the center of rotation is the point of crossing of all 
 visual lines. Fig. 16 is a photographic reproduction of 
 the first correct horopteric figure ever published, and 
 was constructed by the author in 1892, immediately after 
 his discovery of the true law of visible direction viz., 
 All lines of direction are radii of retinal curvature pro- 
 longed. Le Conte, in "Sight," first edition (1882), 
 thought he had correctly constructed Mueller's horopter. 
 This is shown in his reproduced figure, Fig. 9 (page 36), 
 in which the circle is constructed through the two cen- 
 ters of rotation and the point of fixation; but he has
 
 OF OCULAR ROTATIONS. 95 
 
 ruined the figure by constructing 1 his indirect visual lines 
 in such a way as to make them cross the visual axes at 
 the nodal points. Noyes evidently had the same concep- 
 tion of Mueller's horopter, for he said: "It is a circle 
 which passes through the center of rotation of each eye 
 and the point of fixation of the visual axes." If Noyes 
 had drawn indirect visual lines, he would have made them 
 cross the visual axes at the nodal points, as did Le Conte. 
 At any rate, there was something" that confused him, for 
 he said: " This statement is not strictly correct, but will 
 suffice for our purposes." No horopteric circle is correct 
 that does not make indirect visual lines cross the visual 
 axes at the center of rotation. 
 
 Le Conte, in his 1897 edition of " Sight," published a 
 new figure which he claimed as a true presentation of 
 the Mueller horopter. This 1897 figure is reproduced in 
 Fig. 10 (page 37). This circle is constructed through 
 the two nodal points and the point of fixation, and the 
 direct and indirect visual lines are made to cross each 
 other on the circle. Le Conte's two figures as re- 
 produced in this chapter, on pages 36 and 37, should be 
 studied in contrast with each other. In Fig. 9, the vis- 
 ual axes, under the same angle of convergence, could 
 move from point to point on the circle, each eye around 
 the point common to the visual axis and the circle; but 
 the visual axes A-c and A-c could never be made to take
 
 96 THE FUNDAMENTAL PRINCIPLES 
 
 the place of the indirect visual lines B-b and B-b' , for his 
 indirect visual lines do not cut the visual axes at the cen- 
 ters of rotation, but at n and ri , the so-called nodal points. 
 It will be further observed that the two eyes in Fig. 9 
 are ideal eyes of Helmholtz, in that the visual axes pass 
 through the centers of rotation. 
 
 As erroneous as is Fig-. 9, Fig-. 10 is still worse. If 
 the visual axes A-c and A-c should move from A to B, 
 neither eye would rotate around a point common to its 
 visual axis and the horopter, hence the points n and n 
 would be made to leave the circle; or if the circle should 
 move with the nodal points, it would be forced to leave 
 the points A and B. It is equally clear that A-c and 
 A-c could never be made to take the positions B-b and 
 B-b'. 
 
 The true horopter, in the sense that it is the circle of 
 binocular single vision, both direct and indirect, as shown 
 in Fig-. 16, is based on three great facts: (a) The macula 
 of all eyes is the posterior pole, and the visual axis is the 
 antero-posterior axis of the eye; (b) all indirect lines of 
 vision cross the visual axis at the center of rotation; (c) 
 corresponding retinal points have a common brain-cell 
 connection, and these points bear identical relationship, 
 in degrees, to their respective maculas. In this figure 
 the circle is constructed through two fixed points and 
 one changeable point, the former being the centers of ro-
 
 OP OCULAR ROTATIONS. 
 
 97 
 
 tation of the eyes, b and d, and the latter the point of 
 direct fixation. This circle is b-d-e-c-a. Any point so 
 situated on the circle as to throw light into the two eyes 
 will be seen as a single point, for the images will be on 
 corresponding retinal points. The direct point of view, 
 
 Fig. i 6. 
 
 c, and its images, h and gr, will be connected by lines 
 that cut the centers of rotation, b and d. The secondary 
 point of view a and its images, / and /, will be connected 
 by lines passing through the centers of rotation, b and 
 d; and the secondary point e will be connected with its 
 images, / and k, by lines that cut the visual axes at the
 
 98 THE FUNDAMENTAL, PRINCIPLES 
 
 centers of rotation. That all points on this circle, whether 
 direct or indirect, will be seen under the same angle, 
 is proved by the fact that each angle is measured by half 
 the arc b-d, for each is an inscribed angle, with this com- 
 mon arc. If the visual axes should be moved from c to , 
 they will take the positions of the indirect visual lines, a-j 
 and a-f; if the visual axes should be moved from c to e, 
 they will take the positions of the indirect lines, e-l and 
 e-k. The figure also shows that the direct and the indi- 
 rect points of view are related in degrees as are their re- 
 spective images. The angle c-b-a is an inscribed angle 
 and is measured by half the arc a-c. The angle h-b-j is 
 an angle at the center and is measured by the whole arc 
 h-j. But these angles are opposite and are, therefore, 
 equal. The angle a-d-c is equal to the angle a-b-c, for 
 it, too, is measured by half the same arc, a-c; therefore 
 the angle g'-d-f is equal to the angle h-b-j. Since/ and f 
 are similarly related, in degrees, to the maculas, ^and^, 
 they are corresponding retinal points, for such points 
 have common brain-cell connection. The statements 
 made above are strictly correct, and, therefore, Fig. 16 
 TV ill suffice for all purposes in the study of binocular sin- 
 gle vision and binocular rotations. 
 
 Points on the circle whose indirect visual lines cross 
 m-a at the same point are equally far removed from the 
 direct point of view. To show this, the line m-c was
 
 OF OCULAR ROTATIONS. 99 
 
 drawn. For a different purpose entirely, and one more 
 practical, the line b-d was placed in the figure. 
 
 Having 1 demonstrated the curved line of binocular sin- 
 gle vision, it was only one step to the demonstration of 
 the curved surface of binocular single vision. The au- 
 thor suggested to Dr. Manning- Brown, now of Hopkins- 
 ville, Ky., then his private student, that this surface 
 could be generated by revolving- the circular plane, 
 b-d-e-c-a, on the cord, b-d. Dr. Brown at once volun- 
 teered to have this peculiar surface of single seeing- made 
 in wood, by means of the skillful use of the turning- 
 lathe. This he succeeded in doing-. This oddly, but 
 beautifully, shaped piece of wood was then cut along- 
 a plane including- the line b-d, into two equal parts, with 
 a very delicate saw. E}ach of the two cut surfaces pre- 
 sented a plane the outlines of which were larg-e seg-ments 
 of two circles, as shown in Fig-. 17, which represents a 
 vertical section of this model. 
 
 It is clear that the parts above and below b-d are pre- 
 cisely alike. In this figure, b and d represent the cen- 
 ters of the two eyes, and b-d is the line connecting- 
 these centers. The circular planes shown on either side 
 of b-d, each represents perfectly the plane of the horop- 
 ter. A section made from any point on the surface of 
 this model, along- a plane including- the line b-d, would 
 have shown the two conjoined horopteric planes just as
 
 100 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 Fig. 17.
 
 OF OCULAR ROTATIONS. 101 
 
 depicted in Fig. 17. As on the line, so on the surface 
 generated, there is not a point so situated as to send light 
 into the two eyes but that it would be seen as a single 
 point with the two eyes. The concave area of binocular 
 single seeing is clearly shown in Fig. 25. 
 
 The section of this model should have led at cnce to 
 the making of Fig. 18, but, in fact, it was fifteen years 
 later (1907) before the author found the artist who could 
 make this complicated figure, to be studied further on. 
 
 Referring again to Fig. 16, it may be stated that, since 
 b-a-c-e-d is the line of binocular single vision, all points 
 within and beyond it should be seen double. This is lit- 
 erally true as applied to small circles; and it is alwa} T s 
 true as to near-by points, however large the circle may 
 be. If the horopteric circle has a diameter of thirty feet, 
 objects beyond will not appear as double, though points, 
 if they could be seen so far, would be double. Even the 
 double appearance of near-by objects, when the circle is 
 small or large, is not confusing, nor is it hurtful, for no 
 attempt is made by the mind or eyes to fuse such images. 
 
 In 1898, Maddox published in his book, " The Ocular 
 Muscles," a cut which he named the " Isogonal Circle." 
 This circle he constructed through the centers of rotation 
 and the point of fixation. In the cut he had no indirect 
 visual lines, but only the two visual axes, converged first 
 on the direct point on the circle, and then rotated to a sec-
 
 102 THE FUNDAMENTAL PRINCIPLES 
 
 ondary point. His purpose was to show that the angle 
 of conversance was the same for the two points. If he 
 had seen, he had not accepted, the teaching of the au- 
 thor that all points on this circle, whether direct or indi- 
 rect, were seen as single points and under a common an- 
 gle. The author, some years before, had named Fig. 16 
 "the monoscopter, " the meaning of which is "line of 
 binocular single vision." Either one of the names is bet- 
 ter than the older name, " horopter," which means " the 
 limit of seeing." Since points, to be seen as single, must 
 be seen under the same angle, and for other reasons, the 
 name " isogonal circle " is preferable to the name "mono- 
 scopter." The name "isogonal circle " may be defined 
 as follows: The circle on which all visual lines, lying in 
 a common plane and coming from corresponding retinal 
 points, converge, each two lines forming the same angle 
 as do all other two lines. This has been shown to be true 
 in the study of Pig. 16. The name " isogonal " may be 
 made to apply to the surface of single seeing as well as 
 to the circle. ' ' Isogonal surface ' ' may be defined as fol- 
 lows: The two visual lines, whether direct or indirect, 
 from corresponding retinal points, converging at any 
 point on this surface, form the same angle as the two vis- 
 ual lines converging at any other point on this surface. 
 
 The definition of the isogonal circle as given by Mad- 
 dox, in connection with his figure of the circle constructed
 
 OF OCULAR ROTATIONS. 
 
 103 
 
 through the centers of rotation and the point of fixation, 
 is as follows: " It is the curve of uniform convergences 
 and of equal lateral ductions for the two eyes." 
 
 c' 
 
 M 
 
 Fig. i 8. 
 
 In the study of Fig 1 . 18, published for the first time in 
 1907, the author accepts the name " isogonal circle " in 
 its fuller meaning, in preference to either of the two 
 other names " horopter " and "monoscopter." Equal
 
 104 THE FUNDAMENTAL PRINCIPLES 
 
 angles of all two visual lines from corresponding- retinal 
 points on a circle (isogonal) means binocular single vi- 
 sion; binocular single vision of points on a circle (mono- 
 scopteric) means equal angles. Since the two terms 
 mean practically the same thing, "isogonal" has the 
 preference over " monoscopteric " when joined with 
 "circle," because it is more easily pronounced and is 
 more pleasing to both the ear and the eye. 
 
 The spherical concavity of the retinas, corresponding 
 retinal points, and the law of visible direction, make pos- 
 sible the mathematical circle and surface of binocular 
 single vision. In the light of Fig. 18, the isogonal circles 
 will be studied as belonging to one of two classes. To 
 the first class belongs only one circle, and there is no bet- 
 ter way to distinguish it from the many members of the 
 other class, than by naming it the Primary Isogonal Cir- 
 cle. The circles of the other class should be known as 
 Secondary Isogonal Circles. 
 
 THE PRIMARY ISOGONAL CIRCLE. In Fig. 18, M-C 
 represents the extended median plane of the head, and C 
 is a point on the line of intersection of this plane and the 
 horizontal plane of the head. With C as the point of 
 fixation, the primary isogonal circle must pass through 
 it. The other two points through which this circle must 
 pass are the centers of rotation of the two eyes, D and B. 
 The primary isogonal circle, B-D-C, thus constructed,
 
 OF OCULAR ROTATIONS. 105 
 
 presupposes that both the head and the eyes are in their 
 primary positions. The distinguishing fact of this circle 
 is that in its plane lie the two visual axes and the two 
 horizontal retinal meridians, and that the visual axes are 
 converged to a point on it. On either side of the point 
 of fixation are many indirect points of view on this circle, 
 and in its plane lie twice as many indirect lines of vision, 
 for to each point belong two lines. 
 
 THE SECONDARY ISOGONAL, CIRCLES are constructed 
 through the two centers of rotation, B and D, and 
 through indirect points of view lying in the extended 
 vertical plane of the head, both above and below C, each 
 and all of these points being the same distance from the 
 point of intersection of M-C and B-D as is the point C. 
 Fig. 18 shows only one of these secondary circles, B-D-C '. 
 Lying on this circle to either side of C', itself a second- 
 ary point are many other secondary points, as E. Each 
 of these secondary circles has on it only secondary points 
 of view, and in its plane lie only indirect visual lines, two 
 for each point. The plane of no secondary isogonal cir- 
 cle contains a retinal meridian, but it intersects the 
 planes of all the retinal meridians. The number of sec- 
 ondary isogonal circles can be computed if they should be 
 considered as only 1" apart. By reference to Fig. 24, it 
 will be seen that the upper part of the field of binocular 
 single vision is 55 and the lower part of this field is 70.
 
 106 THE FUNDAMENTAL PRINCIPLES 
 
 This would give 198,000 secondary isogonal circles above 
 the primary circle, and 252,000 below it, making- a total of 
 450,000 secondary isogonal circles to one primary isogo- 
 nal circle. 
 
 All isogonal circles, whether primary or secondary, are 
 alike in the following respects: (a) They are all con- 
 structed through two common points, the centers of ro- 
 tation, B and Z?, of the two eyes; (b) they all have a 
 common cord (J3-D], the lines connecting the centers of 
 the two eyes; (c) they are all bisected b} r the extended 
 median plane of the head; (d) all points on all of the cir- 
 cles, belonging to one group, so located as to send light 
 into the two eyes, will be seen as single points; (e) the 
 two lines of vision connecting any secondary point, on 
 any circle of a given group, with its two images, have 
 the same angle as that formed by the convergence of 
 the visual axes on the point of direct view the angles 
 B-A-D, B-C'-D, and B-E-D are equal to the angle 
 B-C-D. 
 
 What has been said above in (a), (b), and (c) applies to 
 all circles of all groups. What has been said in (d) 
 and (e) applies to any single group of isogonal circles 
 circles that have the same diameter. An infinite num- 
 ber of points lie on the line of intersection of the extended 
 vertical and horizontal planes of the head, and each of 
 these points may become the primary point of view the
 
 OF OCULAR ROTATIONS. 107 
 
 point of direct fixation. For each of these points there is 
 a possible primary isogonal circle; hence the number of 
 possible primary isogonal circles is infinite, but only one 
 can exist at a time. Each new primary isogonal circle 
 creates a new group of secondary circles, all of equal 
 size. 
 
 There is no point in the space devoted to binocular sin- 
 gle vision (see Fig 1 . 24) that does not lie on some isogonal 
 circle, or in the plane of one of these circles. The field 
 of binocular rotations is a little smaller than the field of 
 binocular single vision, but any secondary point within 
 this smaller field may become the point of fixation, and 
 that, too, regardless of the size of the circle on which 
 the secondary point may be located. 
 
 The degree of convergence of the visual axes at a sec- 
 ondary point will be the same as if they were converged 
 on the direct point of that primary circle which belongs 
 to the same group. This is well shown in Fig. 18, in 
 which the visual axes can be considered as moved, first 
 from C to C', and again from C' to E. In either case 
 the visual axes have been made to take the position of 
 indirect visual lines, under the same angle of convergence. 
 
 If the point for indirect fixation is on a smaller or lar- 
 ger circle than is the primary point of view, the primary 
 circle, which must move with the visual axes, must grow 
 smaller or larger until it shall finally include the second-
 
 108 THE FUNDAMENTAL PRINCIPLES 
 
 ary point to be fixed. If, at the beginning- of a rotation, 
 the second point of view lies on the circumference of the 
 primary isogonal circle, that circle neither enlarges nor 
 does its plane move, while the visual axes move from one 
 point of view to the other. If the second point of view 
 is at a greater distance than the first point, but in the 
 plane with it, the circle enlarges, but the plane does not 
 move, as the visual axes pass from the one point to the 
 other. If the second point of view is in the plane of a 
 secondary isogonal circle, the plane of the primary circle 
 moves into the position of the secondary circle as the vis- 
 ual axes converge on the second point. No point in 
 viewable space can be fixed until the plane of the pri- 
 mary isogonal circle is made to include it, as the visual 
 axes converge upon it. 
 
 From the foregoing it will be seen that the plane of all 
 isogonal circles are movable planes, and that the common 
 axis around which they rotate is the line connecting the 
 centers of the two eyes the line B-D in Fig. 18. If the 
 visual axes rise, the primary isogonal rises with them; if 
 the visual axes must be depressed, the primary isogonal 
 circle must go down with them. As the primar} T isogo- 
 nal circle rotates, all secondary isogonal circles rotate 
 with it, in the same direction and to the same extent. 
 Thus within the limit of vertical rotations, the plane of 
 the primary circle may be made to assume the former
 
 OF OCUL,AR ROTATIONS. 109 
 
 position of the plane of any secondary circle. As the 
 plane of the primary circle rises or falls, the visual axes 
 move in the moving- plane, if the second point is obliquely 
 located, so as to converge on the second point of view at 
 the moment that the plane reaches that point. In doing 
 this the point of convergence moves along a binocular 
 spacial meridian. (See Fig. 25.) 
 
 THE LAW OF BINOCULAR REST AND MOTION. 
 
 THE TWELVE EXTRINSIC MUSCLES OF NORMAL EYES, 
 UNDER THE CONTROL OF THE NINE CONJUGATE, AND 
 THE TWELVE FUSION, BRAIN-CENTERS, MUST SO RE- 
 LATE THE TWO EYES THAT THEIR TWO VISUAL AXES 
 AND THE TWO HORIZONTAL RETINAL MERIDIANS SHALL 
 ALWAYS LIE IN THE PLANE OF THE PRIMARY ISOGONAL 
 CIRCLE, WHETHER AT REST OR IN MOTION, AND THAT 
 THE TWO VISUAL AXES SHALL CONVERGE AT SOME 
 POINT ON THIS CIRCLE, IN THE INTEREST OF BOTH BIN- 
 OCULAR SINGLE VISION AND CORRECT ORIENTATION. 
 
 The two eyes, while obeying the law of binocular ro- 
 tation, do not violate the law of monocular motion. Each 
 visual axis moves in the plane of that individual retinal 
 meridian projected into space, on which lie both the first 
 and the second points of view, during which motion the 
 vertical axis of the eye will be kept parallel with the 
 median plane of the head. The fusion centers, not used
 
 110 THE FUNDAMENTAL PRINCIPLES 
 
 in monocular rotations, are essential in binocular rota- 
 tions. Without the fusion centers, even when muscles 
 are normal in tone, all oblique rotations would be at- 
 tended by diplopia; and without them, muscles of unequal 
 tonicity would cause diplopia, whether the e} r es be at rest 
 or in motion, as shown in the study of Fig-. 14. 
 
 The cord common to all isog-onal circles the line, JB-D, 
 connecting 1 the centers of the two eyes should always 
 lie in the horizontal plane of the head; but this cannot 
 be if one eye is set lower in the orbit than is the other. 
 Even in such faulty eyes the horizontal retinal meridians 
 must lie in the plane of the laterally inclined primary isog-- 
 onal circle, when both eyes are being 1 used. Should the 
 plane be inclined 5, the vertical axes of the two eyes must 
 be inclined throug-h the same arc, toward the side of the 
 lower eye. This would be effected by activity of either 
 the 8th or 9th conjugate center, on the superior oblique 
 of one eye and the inferior oblique of the other. With one 
 eye covered, as in the work of refraction, the con jug-ate cen- 
 ter would cease its activity and the eye would then have 
 its vertical axis normally related to the median plane of 
 the head. On uncovering- the eye, the two vertical axes 
 would be tilted ag-ain toward the side of the lower eye. 
 The practical point growing- out of this observation is 
 that such eyes would require the shifting- of the axes of 
 correcting- cylinders toward the side of the lower eye,
 
 OF OCULAR ROTATIONS. Ill 
 
 through arcs corresponding- to the lateral displacement 
 of the horizontal retinal meridians. 
 
 In the interest of binocular single vision, but against 
 correct orientation, the horizontal retinal meridians of 
 uncorrected oblique astigmatic eyes must be forced out 
 of the plane of the primary isogonal circle. This sub- 
 ject will be given proper emphasis in the chapter on 
 "Compensating Cyclotropia." In that chapter the 6th 
 and 7th conjugate centers are represented, respectively, 
 as the source of power for converging and diverging the 
 vertical axes of the eyes in the interest of fusion of dis- 
 placed images. It probably would be more nearly cor- 
 rect to say that this work is accomplished by the right 
 and left 6th, and the right and left 7th, basal centers, as 
 has been pointed out in the study of Fig. 14. The fusion 
 function must be under the control of the fusion faculty 
 of the mind, and this faculty presides over the single 
 basal centers, right and left. 
 
 Emmetropia and orthophoria make it easy for the ocu- 
 lar muscles to obey the law of binocular rotation. Hy- 
 peropia and myopia interfere with the act of convergence; 
 oblique astigmatism, with meridians of greatest curva- 
 ture diverging or converging, makes it impossible for the 
 obliques to keep the horizontal retinal meridians in the 
 plane of the primary isogonal circle; hyperphoria and 
 cataphoria make it hard for the superior and inferior
 
 112 THE FUNDAMENTAL PRINCIPLES 
 
 recti to plane the visual axes; exophoria and esophoria 
 make difficult the task of converging the visual axes to 
 points on the circle, and the shifting of the visual axes in 
 
 Fig. 19. 
 
 the plane of the circle, by the lateral recti. In the 
 light of these facts, it would appear that the e} T es, not nat-
 
 OF OCULAR ROTATIONS. 113 
 
 urally so, should be made emmetropic and orthophoric 
 by art. 
 
 THE MUSCLE INDICATOR. This device is the primary 
 isogonal circle put in material form, as shown in the 
 half-tone picture, Fig-. 19. The circle o-M-N-o passes 
 through the centers of rotation, o and o, and through 
 the direct point of fixation, shown at the intersection 
 of the visual axes. The horizontal retinal meridians are 
 represented by the two circles, E and E, each passing- 
 through two vertical slots, S and S. They both lie in 
 the plane of the larg-er circle, and each is supported in 
 that position by the two clips, C and C. Each visual 
 axis, V-A, extends from the macula at E, throug-h the cen- 
 ter of rotation, o, on through the cornea, either at or 
 near its center, thence across the circle to meet its fel- 
 low-axis at the point on the circle through which passes 
 the extended median plane of the head. The two visual 
 axes, as well as the two horizontal retinal meridians, are 
 lying in the plane of the circle. The clips, C and C, 
 across the front vertical slot, S, prevent the visual axes 
 from rising above or falling below this plane. Each vis- 
 ual axis is made of two pieces of copper wire and a tube, 
 so as to make both lengthening and shortening possible, 
 as the point of view may be changed. The horizontal 
 slot, M-N, allows the moving of the point of fixation of 
 the visual axes both to the left and to the right. The 
 slot, M-N, does not quite reach the- limit of lateral rota-
 
 114 THE FUNDAMENTAL PRINCIPLES 
 
 tions, but it extends far enough to show how the visual 
 axes can be made to move in the plane of the circle, 
 around the centers of rotation, o and o. The circle is 
 supported by the upright, U, attached to the base, B. 
 At the upper end of the upright there is a screw attach- 
 ment for either fixing the circle in the horizontal posi- 
 tion, or allowing it to rotate up or down, on the cord, o-o, 
 the line that connects the centers of the two eyes. The 
 screw is worked by the sliding rod, R-R. Imagining 
 that the real circle in Fig. 19 has a diameter of twenty 
 feet, then it will not be hard to conceive that the tonicity 
 of the superior and inferior recti has planed the visual 
 axes, and that tonicity of the lateral recti has converged 
 them; nor will it be a difficult matter to understand that 
 the tonicity of the superior and inferior obliques has 
 planed the horizontal retinal meridians. The clips, C 
 and C, front slot, S, represent the power that keeps 
 the visual axes planed, and that power resides in the 
 superior and inferior recti. The four clips, C, across 
 the vertical slots through which the horizontal meridians 
 pass, represent the power that planes these meridians, 
 and this power resides in the superior and inferior ob- 
 liques. When the tonicity of either of these pairs of 
 muscles is unequal, the planing of the visual axes or the 
 horizontal retinal meridians, as the case may be, can be 
 maintained only by contractility of the weaker muscle of
 
 OF OCULAR ROTATIONS. 115 
 
 a pair. Should the lateral recti muscles be unequal in 
 tone, the visual axes would tend to cross, either within 
 or beyond the circle, and only contractility of the weaker 
 muscle of each pair would compel them to converge on 
 the direct point of view. 
 
 If tonicity keeps the horizontal retinal meridians and 
 visual axes in the plane of the primary isogonal circle, 
 when lying in the horizontal plane of the head, and con- 
 verges these axes at the direct point of view on this cir- 
 cle, the rotations will all be effected by the normal ex- 
 penditure of neuricity. That the visual axes, when ro- 
 tated from any one point of view to any other point of 
 view, assume the exact positions of the two indirect vis- 
 ual lines which connected the second point of view and its 
 two images, before the rotation began, can easily be 
 shown by a further study of Fig. 19, in connection with 
 a glance at Fig. 20. Before rotating the visual axes 
 from the primary point, shown in Fig. 19, to the sec- 
 ondary point, TV, directly to the right, two wires should 
 be made to extend from TV, directly over the right end of 
 the horizontal slot, J/-TV, the one wire back to the right 
 retina and the other back to the left retina, each passing 
 over the center of rotation, o, of its eye. These wires 
 should be firmly held in their respective positions while 
 the visual axes are rotated from the direct point of view 
 to TV, as shown in Fig. 20. At the end of the rotation it
 
 116 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 will be found that the two visual axes lie directly under 
 the two wires which were made to represent the two indi- 
 rect visual lines. 
 
 Fig. 20. 
 
 If each of the two wires representing- indirect visual 
 lines, going from TV, were carried over the nodal point
 
 OF OCUIvAR ROTATIONS. 117 
 
 of its eye, back to a point directly above the supposed 
 location of the image on its retina, and these wires 
 should be firmly held while the visual axes are rotated 
 from the direct point to JV, it would be seen that the vis- 
 ual axes do not lie directly under these wires thus placed. 
 This would show that, while the two visual axes have 
 reached the second point of view, the maculas have fallen 
 short of the two supposed images of that point. No man 
 can make these two experiments with the Muscle Indica- 
 tor and not be convinced that all lines of direction are 
 radii of retinal curvature prolonged. 
 
 Fig. 20 shows that when the second point of view al- 
 ready lies on the primary isogonal circle, the visual axes 
 move from the primary point, in the plane of that circle, 
 but the circle itself remains stationary. 
 
 Fig. 21 shows that when the second point of view is 
 in the vertical plane above the primary point of view, 
 the visual axes are carried upward in the rotating plane 
 of the primary isogonal circle, without change of posi- 
 tion in that plane, to the second point of view. The pri- 
 mary circle has been made to take the position of that 
 secondary circle on which rested the second point before 
 the rotation began, and the visual axes have been made 
 to assume the positions of the two indirect visual lines 
 which connected the second point and its two images be- 
 fore the rotation started.
 
 118 THE FUNDAMENTAL PRINCIPLES 
 
 In both Figs. 20 and 21, the point of convergence of 
 the visual axes has moved along that binocular spacial 
 meridian on which were lying both the first and second 
 
 Fig. 21. 
 
 points of view. In the two cardinal directions right and 
 left, the visual axes must move in a motionless plane; in
 
 OF OCULAR ROTATIONS. 119 
 
 the two cardinal directions up and down, the visual 
 axes must remain motionless in the moving 1 plane 
 throughout the rotation. The rotations shown in Fig's. 
 20 and 21 have been accomplished without either the hor- 
 izontal retinal meridians or the two visual axes leaving 
 the plane of the primary isogonal circle, and the visual 
 axes are still converged at a point on the circle. The 
 rotation shown in Fig 1 . 20 has been effected around the 
 vertical axis of the eye, a fixed axis throughout the ro- 
 tation. That shown in Fig. 21 has been accomplished 
 around the transverse or horizontal axis of the eye, like- 
 wise a fixed axis for that rotation. In both of these ro- 
 tations each eye has obeyed the law of monocular rota- 
 tion, and the two eyes together have obeyed the law of 
 binocular rotation. 
 
 Fig. 22 shows a rotation that has been effected from 
 the primary point of view, as shown in Fig. 19, to a sec- 
 ond point of view obliquely up-and-to-the-right. The 
 primary isogonal circle has been so elevated as to take 
 the place of that secondary circle on which rested the 
 second point of view before the rotation began; and the 
 visual axes have been made to assume the position of the 
 two indirect visual lines which connected that second 
 point with its two images while the eyes were yet fixed 
 on the first point. To fix this obliquely placed second 
 point of view, the visual axes must rise with the plane,
 
 120 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 and must move in this plane to the right, as it ascends, 
 so as to converge at the second point the moment the 
 plane reaches it. In this motion with the plane and the 
 
 Fig. 22. 
 
 other movement in the plane, the point of convergence of 
 the visual axes has moved along that binocular spacial
 
 OP OCULAR ROTATIONS. 121 
 
 meridian on which were lying- both the first and second 
 points of view. 
 
 Pig 1 . 22 shows that this oblique rotation has been ac- 
 complished with the horizontal retinal meridians still 
 tying- in the plane of the primar} T isog-onal circle; and it also 
 shows that the visual axes have remained in that plane 
 and are converged at the proper point on the circle. The 
 plane of the primary isog-onal circle has been carried up- 
 ward with the visual axes of the two eyes, which have 
 been rotated, each around its transverse axis, and the 
 visual axes have been moved in the slot toward JV by 
 an accompanying- rotation of each eye around its ver- 
 tical axis. Each of these axes, the vertical and the 
 transverse, have been themselves in motion throughout 
 the oblique rotation. The perfectness of this double ro- 
 tation about the two moving- axes has been made possi- 
 ble by the obliques preventing- any rotation of either e} T e 
 around its visual axis. The clips supporting- the two 
 horizontal retinal meridians show that these meridians 
 have not been allowed to leave the moving- plane of the 
 primary circle. Fig 1 . 22 is representative of all oblique 
 rotations. 
 
 In oblique, as in cardinal, rotations, as illustrated, 
 each eye has obeyed the law of monocular rotation, and 
 the two tog-ether have obeyed the law of binocular ro- 
 tation.
 
 122 THE FUNDAMENTAL, PRINCIPLES 
 
 If the oblique rotation, illustrated in Fig. 22, had 
 been effected around fixed axes, at right-angles to their 
 respective rotation planes, the horizontal retinal merid- 
 
 Fig. 23. 
 
 ians would have been made to leave the plane of the pri- 
 mary isogonal circle, each tilting- down-and-to-the-right,
 
 OF OCULAR ROTATIONS. 123 
 
 as shown in Fig. 23, introduced here to show ivhat docs 
 not occur in any oblique rotation. Two clips are down. 
 
 The Muscle Indicator proves the existence of corre- 
 sponding- points, in that it would not be a possibility if 
 there were no such points. It proves the correctness of 
 the law of direction, as discovered by the author viz.: 
 All lines of direction are radii of retinal curvature pro- 
 longed; for if this were not the true law of direction, 
 the Muscle Indicator could not have been made. It proves 
 that the macula is the posterior pole of the eye; for if 
 this were not true, the Muscle Indicator would be a mus- 
 cle mystifier. Of a muscle mystifier this could not be 
 said: " There is not a single phase of a single ocular 
 muscle, or any combination of ocular muscles, normal, 
 abnormal, or pathological, which the Muscle Indicator 
 will not show." It is the embodiment of truth, con- 
 densed and clarified, concerning all muscle problems. 
 With its aid the mediocre mind may become master of 
 muscle questions which were baffling to the brightest 
 intellects of other days. It is the only device that 
 teaches "the truth, the whole truth, and nothing but 
 the truth," concerning binocular rest and easy motions 
 of orthophoric eyes, and concerning binocular unrest and 
 uneasy rotations of heterophoric eyes. 
 
 In an early part of this chapter, Figs. 3 and 4 were 
 introduced to make easier the study of monocular motion.
 
 124 
 
 THE; FUNDAMENTAL PRINCIPLES
 
 OF OCULAR ROTATIONS. 125 
 
 These two figures are so familiar to all readers, having 
 been seen in practically all books on the eye, it would 
 seem superfluous to sa} T anything- more about them. In 
 other books, however, Figs. 3 and 4 only represented 
 the field of vision for the left and the right eyes respec- 
 tively, as shown within the shadings above, below, and 
 to the inner side. Heretofore the lines traversing the 
 white space were not called spacial meridians, and the 
 point of their crossing has not been known as the spacial 
 pole. 
 
 From these two figures the author has been able to 
 construct Figs. 24 and 25. He did this by dividing both 
 Figs. 3 and 4, along the vertical meridians, and then 
 pasting the divided parts together as follows: He trans- 
 posed the right half of the left and the left half of the 
 right fields, and, bringing these together, he formed Fig. 
 24, for which there is no name better than binocular 
 field of vision; then, without transposing, he brought to- 
 gether the left half of the left field and the right half of 
 the right field, thus creating Fig. 25, which he has 
 named the binocular field of vieiv. 
 
 Fig. 24, although standing separate from, is, in reality, 
 a part of, Fig. 25. Fig. 24 represents the field of binoc- 
 ular vision when both the head and the eyes are station- 
 ary and in their primary positions. In this peculiarly 
 shaped field every object is seen by the two eyes; and
 
 126 THE FUNDAMENTAL PRINCIPLES 
 
 every object within this field, further removed than the 
 point of fixation, is seen singly by the two eyes, if 
 that point is distant thirty or more feet. The measure- 
 ments of this field in the four cardinal directions are: 
 55 up, 70 down, and 60 to the right and left. In 
 the center of this field is the binocular spacial pole, and 
 passing through this pole are the binocular spacial me- 
 ridians. Encircling the pole are the parallels, located 
 10 apart. Since the field of binocular rotations is only 
 a little smaller than the field of binocular single vision, 
 as shown in Fig. 24, practically all the points in this 
 field may become points of fixation, by rotating the eyes, 
 while the head remains stationary. There cannot be a 
 point in this space which will not lie on one of the spa- 
 cial meridians, except the point of fixation the binocular 
 spacial pole which lies on every meridian, at the point 
 of their crossing. 
 
 Two points in space are to be considered in every ro- 
 tation the first point of view, which is the point of fixa- 
 tion, and the second point of view, which is the point to be 
 fixed. The changing from the one to the other is neither 
 more nor less than the moving of the binocular spacial 
 pole along that binocular spacial meridian on which lie 
 both the first and second points. If the first point of 
 view is the primary point, as in Fig. 24, the second 
 point may be the point of crossing of parallel circle
 
 OF OCULAR ROTATIONS. 127 
 
 40 and meridian 120-300, above (any other meridian and 
 parallel might have been chosen). In this case the 
 point of fixation the binocular spacial pole would 
 move along" this meridian until it reaches the point which 
 was on circle 40. In every rotation the parallel circles 
 move with the pole, so that when the pole (point of 
 fixation) reaches the second point of view, the point of 
 crossing of parallel 40 and meridian 120-300, below, 
 will have moved up to the point which was the primary 
 point before the rotation began. All points that were 
 on that meridian before the rotation began will be on it 
 when the rotation has ended, but they will be differently 
 related to both the binocular pole and the binocular 
 parallels. 
 
 In the binocular field of vision (Fig. 24), when the 
 head and eyes are in their primary positions, every point 
 will lie on three circles common, or belonging, to the two 
 eyes (1) a spacial meridian which determines the re- 
 lationship (cardinal or oblique) that the point bears to 
 the vertical and horizontal planes of the head; (2) a 
 spacial parallel which marks its distance in degrees from 
 the line of intersection of the two planes of reference; (3) 
 an isogonal circle, primary or secondary, of some group, 
 which determines the angle under which it is seen by the 
 two eyes. Any one spacial meridian and any one spacial 
 parallel can cut each other at only two points, which
 
 128 THE FUNDAMENTAL PRINCIPLES 
 
 points are in opposite directions from the spacial pole 
 and equally distant from it. 
 
 The easy coexistence of the binocular spacial pole, meri- 
 dians, and parallels depends on normal conditions of the 
 ocular muscles. There may be a binocular spacial pole 
 and parallels, but no binocular meridians; but such a 
 state can be established only by unconnected oblique 
 astigmatism, through abnormal work on the part of the 
 obliques. Normal recti and oblique muscles easily create 
 and maintain the binocular spacial pole, meridians and 
 parallels, as shown in Fig-. 24. Abnormal recti and 
 oblique muscles make it either difficult or impossible to 
 have the binocular spacial pole, meridians, and parallels. 
 The treatment, surgical and otherwise, of abnormal 
 muscle conditions has for its aim the easy creation and 
 maintenance of the binocular spacial pole, meridians, and 
 parallels. 
 
 Fig. 25 is a combination of both the field of binocular 
 vision and the field of binocular view. Objects located 
 anywhere within the white area of Fig. 25 will be seen 
 with the two eyes together if located within the space 
 corresponding in shape and size with Fig. 24, but with 
 one or the other eye only if removed further from the 
 spacial pole. Objects beyond parallel 60 to the left 
 will be seen with the left eye only, and objects beyond
 
 OF OCULAR ROTATIONS. 129 
 
 the same parallel to the right will be seen by the right 
 eye only. 
 
 The spacial pole of an eye must be on the same 
 straight line with the anterior and posterior poles of the 
 eye. The spacial pole of an eye can be the direct point 
 of view, for that eye, only because the center of the 
 macula is the posterior pole, for the center of the macula 
 and the direct point of view must be connected by a 
 straight line. If the spacial pole for each eye is the 
 direct point of view for that eye, as in Figs. 3 and 4, the 
 fixing of the two eyes on one point brings the two poles 
 into one, as in Figs. 24 and 25. The perfect fusion of 
 the two poles brings into practical fusion the spacial 
 meridians and parallels of the two eyes, also well shown 
 in Figs 24 and 25. 
 
 The monocular spacial parallel is everywhere equally 
 distant from the visual axis of the eye to which it be- 
 longs; therefore, strictly speaking, no two circles equal- 
 ly distant from the two poles could be perfectly fused, 
 for their centers could not be made the same point. In 
 the formation of the binocular pole, the two vertical 
 spacial meridians would be perfectly fused, but the two 
 horizontal spacial meridians would cross each other at 
 the binocular pole, and they would then diverge, but so 
 slightly that, at 90, they would be just that distance 
 apart corresponding with the measurement between the
 
 130 THE FUNDAMENTAL, PRINCIPLES 
 
 two eyes. At the extreme limit of lateral binocular ro- 
 tation they would be much closer together, probably 1 
 inches or less. For practical infinity, so slight a sepa- 
 ration would amount to nothing. 
 
 When the binocular spacial pole is at practical infinity, 
 a line going from this pole to a point halfway between 
 the two eyes may be considered as the binocular vis- 
 ual axis. This conception would give perfect binoc- 
 ular spacial meridians and parallels. Fig. 26 has 
 been constructed on this conception, and the mathematics 
 of the figure proves the value of the conception. 
 
 In the study of the Isogonal Circles in Fig. 18, it has 
 been stated that, for every point on the line of intersec- 
 tion of the vertical and horizontal fixed planes of the 
 head, there is a new group of isogonal circles, all the 
 members of any one of the infinite number of groups 
 having the same diameter. The point of direct fixation 
 not only creates an independent group of isogonal circles, 
 but it also creates an independent group of binocular 
 spacial meridians and an associated group of binocular 
 parallels. 
 
 In Fig. 26, the primary isogonal circle is constructed 
 through B and D, the centers of the two eyes, and the 
 point of fixation, C. The horizontal binocular spacial 
 meridian, /-C-/, for that point of fixation, has been cre- 
 ated by M-C, the binocular axis, as a radius. The ver-
 
 OF OCULAR ROTATIONS. 
 
 131
 
 132 THE FUNDAMENTAL PRINCIPLES 
 
 tical and oblique meridians of this group would be con- 
 structed with the same radius. Binocular spacial 
 meridians, constituting- any one group, are meridians 
 with the same radius. The binocular parallels created 
 by the point of fixation, C, are A'-E' ', R"-S" , V"'- W" . 
 
 If G had been chosen as the point of fixation, the pri- 
 mary isogonal circle would have passed through it and 
 the two centers of rotation, B and D. With C' as the 
 point of fixation, the binocular axis, M-C' , as a radius, 
 would generate the horizontal binocular spacial meridian, 
 2-C'-2, for that point, and all the other members of that 
 group of spacial meridians would have the same radius. 
 The parallels for this new group of meridians and par- 
 allels would be A-E, R'-S', and V"-W". 
 
 If C" had been chosen as the point of fixation, then 
 the primary isogonal circle for that point would have 
 passed through C" and the two centers of rotation, B 
 and D. M-C" would have been the binocular axis and 
 the radius of curvature for all the binocular spacial 
 meridians for that point. The circle representing the 
 horizontal binocular spacial meridian, with M-C" as 
 the radius, would be j-C"-j. The associated parallels 
 would be X-S and V- W. 
 
 If C'" had been chosen as the point of fixation, the 
 primary isogonal circle for that point would have passed 
 through C"' and the two centers of rotation B and D, and
 
 OF OCULAR ROTATIONS. 133 
 
 M-C'" would have become the binocular axis. With M- 
 C'" as a radius, the horizontal binocular spacial meridian 
 would be 4-C'"-4, and all the other meridians belonging 
 to the group created by the point C'" would have M-C'" 
 as the radius. The parallel for this group of meridians 
 and parallels would be V- W. 
 
 The equator of any one of these four groups of meridians 
 and parallels would have the same radius of curvature as 
 the meridians. The diameter of the equator of group C 
 is X-Z, that of group C v&X'-Z' , that of group C" is X"- 
 Z" , and that of group C" is X'"-Z'" . The diameter of 
 each equator is the same as that of the meridians be- 
 longing to the same group. The diameters of the par- 
 allels belonging to group C are A-E ', R"-S" , and V'"- 
 W"; the diameters of the parallels belonging to group C' 
 a,reA-J, J?'-S', and V"-W"\ those for group C" are R- S 
 and V'-W'\ and the one for group C" is V-W. 
 
 An interesting feature of Fig. 26 is that the two in- 
 direct visual lines drawn from A and E respectively, that 
 from A through D, and that from^ 1 through B, intersect 
 each other on the line M-C. Lines similarly drawn 
 from R and ,5* and from Fand W, respectively, would inter- 
 sect each other on the line M-C. Mathematically, A and 
 E are equally distant from C ', R and S are equally dis- 
 tant from C", and Fand PFare equally distant from C'".
 
 134 THE FUNDAMENTAL, PRINCIPLES 
 
 The very definition of a parallel makes apparent the 
 correctness of the above statement. 
 
 A binocular spacial parallel cuts the horizontal spacial 
 meridian (and all other meridians) at only two points, and 
 these points are equally distant from the binocular 
 spacial pole. This is true of every parallel of every 
 single group of parallels and meridians, as group C, C", 
 C", and C'". It is through a succession of such two 
 points on diminishing horizontal spacial meridians that 
 the primary isogonal circle passes, as A and , R and S, 
 and Fand W. 
 
 Three other primary isogonal circles could be con- 
 structed in Fig. 26, all of which must pass through the 
 centers of rotation, B and D. One of these, in going 
 from B, would pass through V , R ', A', thence through 
 a new point of fixation on M-C extended, and thence on 
 through ', 6", and W to D, thence to the beginning at 
 B. Another isogonal circle may start from B and go 
 through V" and R" on to a still more distant point of di- 
 rect fixation on M-C extended, thence around to S", 
 through W" and D, to the point of beginning at B. And 
 again, a still larger isogonal circle may be started at B, 
 carried thence through V"\ to a point of direct fixation, 
 still further removed, on the line M-C extended, around 
 to W" t thence through D to B, the starting point.
 
 OF OCULAR ROTATIONS. 135 
 
 Thus it is shown by Fig 1 . 26 that any two points on 
 any horizontal binocular spacial meridian cut by a 
 parallel circle may become points of binocular single 
 vision, for these two points either lie on a constructed pri- 
 mary isogonal circle or in the line of a possible primary 
 isogonal circle. 
 
 There is no point in viewable space which is not at the 
 crossing of a spacial meridian and a spacial parallel be- 
 longing to some group; and such points as lie in the ro- 
 tation field (only slightly smaller than that represented in 
 Pig. 24) are also on either the primary or some secondary 
 isogonal circle of some group the three groups of circles 
 as related to any one point of direct view constitute one 
 common triple group. 
 
 When the binocular spacial pole moves from point to 
 point on the primary isogonal circle the first point of 
 view, whether direct or indirect, is always on the primary 
 isogonal circle it moves along the intervening arc of 
 that circle, as from C to A, without change of angle of 
 convergence; or if it moves along the cord of that arc, 
 the angle of convergence increases as it moves from C to 
 the middle of the cord, and thence on decreases until 
 the pole arrives at A . The angle at the end of the ro- 
 tation is the same as at the beginning. In this rotation 
 the pole has moved from a point on the horizontal spacial 
 meridian, /-C-/, of one group, to a point on the horizon-
 
 136 THE FUNDAMENTAL PRINCIPLES 
 
 tal spacial meridian, 2-C-2 of another group, but the 
 visual axes have not left the plane common to these two 
 meridians and the retinal meridian on which were lying 
 the two images; and the macula, in passing from one image 
 to the other, has not deviated from that retinal meridian 
 on which were lying the two images before the rotation 
 began, nor does it ever deviate from such a meridian. 
 
 If the second point of view is A', it will be seen that 
 the two points, C and A\ lie on the same horizontal 
 spacial meridian, i-C-i. This rotation cannot be effected 
 without a change of angle of convergence which will 
 grow smaller, for the second point is on a larger isogo- 
 nal circle. The spacial pole, in moving from C to A', 
 may go along the arc C-A' or along the cord of this arc, 
 but in either case the angle of convergence has continually 
 changed. The maculas have moved from the images of C 
 to the images of A ', along the horizontal retinal meridian. 
 Thus might be studied rotations from any one point of 
 view to any other point of view, cardinal or oblique. 
 
 Some one primary isogonal circle passes through the 
 two points of intersection of all successively diminishing 
 horizontal binocular spacial meridians and any one of 
 the parallels belonging to the same group. 
 
 Every secondary isogonal circle cuts every parallel at 
 two points similarly related to the spacial pole and the 
 vertical and horizontal meridians; but at these points it
 
 OF OCULAR ROTATIONS. 137 
 
 cuts two different meridians which bear the same relation- 
 ship to the vertical and horizontal meridians. This is 
 made evident by the fact that the spacial part of every 
 secondary isogonal circle is wholly either above or be- 
 low the plane of the horizontal spacial meridian, while 
 one-half of every oblique meridian, and the vertical meri- 
 dian as well, is above, and the other half is below, the 
 plane of the horizontal meridian. 
 
 Since the two points of intersection of a parallel and 
 any oblique, or the vertical, meridian are on opposite 
 sides of the plane of the horizontal meridian, it would 
 not be possible for any secondary isogonal circle to pass 
 through both points. The primary isogonal circle 
 passes through a point common to all meridians of any 
 one group, which point is the binocular spacial pole, and 
 intersects the horizontal meridian of all diminishing 
 groups at two points. The spacial part of no secondary 
 isogonal circle cuts any horizontal spacial meridian at 
 any point, but every secondary circle cuts all other 
 meridians, each at only a single point. 
 
 If the maculas were not the posterior poles of the eyes; 
 if the centers of the retinal concaves were not the 
 centers of rotation; and if all lines of direction did not 
 cross each other at the centers of rotation, then Fig. 26, 
 with all of its mathematical beauties, could have no exist- 
 ence; nor would Figs. 24 and 25 have any true foundation.
 
 138 
 
 THE FUNDAMENTAL PRINCIPLES 
 
 If the macula is not the posterior pole, then the mo- 
 nocular spacial pole cannot be on the visual axis, except 
 in ideal eyes, but would be to its inner side about 5. 
 
 SO ffff' 
 
 210 
 
 Fig. 27. 
 
 The convergence of the two visual axes would leave the 
 two spacial poles 10 apart, as shown in Fig-. 27. A 
 binocular spacial pole would be impossible, and without
 
 OF OCULAR ROTATIONS. 139 
 
 a binocular pole there could be no binocular meridians 
 and parallels. As shown in Fig-. 27, the two vertical 
 meridians would be made parallel with each other, but 
 10 apart, while the two horizontal meridians seem to be 
 fused into one. If such a condition as depicted in Fig-. 
 27 were true, the point of convergence of the visual axes, 
 in rotating 1 , could not move along 1 a single meridian except 
 the horizontal. The confusion in Fig. 27, when con- 
 trasted with the clearness of Fig. 25, must conve} r a 
 forceful lesson to the mind of the searcher after the truth. 
 
 ANGLE OF CONVERGENCE. 
 
 In all binocular rotations the binocular spacial pole is 
 made to move along the plane of the binocular spacial 
 meridian in which lie the first and second points of view. 
 The spacial meridians all accompany the motion of the 
 spacial pole; but that meridian whose plane is the rota- 
 tion plane, and it alone, has a wheel-like motion. All 
 parallels also move with the rotating pole, but they have 
 no wheel-like motion. As the spacial pole rises or falls, 
 the planes of all the parallels look up or down; as the 
 pole moves to the right or left, or obliquely up or down, 
 the planes of the parallels face in a corresponding di- 
 rection, but in no case does a parallel move in its plane. 
 
 Several interesting facts have already appeared in 
 connection with the study of the isogonal circle.
 
 140 THE FUNDAMENTAL PRINCIPLES 
 
 Another important feature growing- out of the study 
 of the isogonal circle is the easy determination of the 
 angle of convergence, whatever may be the distance of 
 the point of fixation. The mathematical formula for 
 solving this problem is : As the circumference of the 
 isogonal circle is to 360, so is the arc extending- from 
 the center of one eye to the center of the other, divided 
 by 2, to the angle of convergence. 
 
 The first member of this proportion is found by multi- 
 plying the length of the diameter of the circle, which is 
 the distance of the point of fixation, by 3.1416. The third 
 member of the proportion depends on the size of the circle 
 and the distance between the centers of the two eyes. If 
 the circle is large, the arc from the center of one eye to 
 the center of the other is practically the same length as 
 its chord, which is the straight line from the center of the 
 one eye to the center of the other. If the diameter of the 
 circle is in feet, then the arc must be expressed in a frac- 
 tion of a foot, but if the one is expressed in inches, the 
 other must be also. To illustrate : Let the diameter of 
 the circle be 16 inches, and let the arc subtending the 
 angle of the visual axes be 2\ inches, then the following 
 is the formula expressed in figures : 
 
 50.26 :360::2i-2 : X. 
 
 From this it will be found that X=8.9. If the first and 
 third members of the proportion were feet and a fraction
 
 OF OCULAR ROTATIONS. 
 
 141 
 
 of a foot, and if the arc subtending the angle formed by 
 the visual axes was always 2^ inches, or i of a foot, 
 the work of determining' the angle of convergence could 
 be simplified as follows : Divide 36 (the result of multi- 
 plying 360 by | -^- 2) by the product of the distance of 
 the point of fixation (the diameter of the isogonal cir- 
 cle) and 3.1416. To illustrate: Fixation is at 1 foot. 
 Multiply 1 by 3. 1416 and the product is 3.1416; with this 
 number divide 36 and the quotient will be 11.35. For 
 any given length of the diameter of the isogonal circle, 
 the visual axes will form a greater angle if the eyes are 
 wide apart than if they are close together. For compar- 
 ison, let the diameter be 16 inches and the arc 2\ inches; 
 then the angle of convergence will be, as already shown, 
 8.9; but let the arc be 2 inches, then the angle of conver- 
 gence will be 7.16, a difference of 1.74. The following 
 table is interesting and helpful, and is approximately cor- 
 rect. The point of fixation being 16 inches, the upper row 
 of figures represents the pupillary distance and the lower 
 row the angle of convergence of the visual axes for each: 
 
 2 
 
 2K 
 
 2% 
 
 2^ 
 
 m 
 
 23/ 4 
 
 2% 
 
 3 
 
 7.16 
 
 8.06 
 
 8.5 
 
 8.95 
 
 9.4 
 
 9.85 
 
 10.3 
 
 10.74 
 
 As is well known, the metre-angle of Nagel is not 
 formed by the intersection of the two visual axes, but it
 
 142 THE FUNDAMENTAL PRINCIPLES 
 
 is the angle formed by the intersection of one visual axis 
 with the extended median plane of the head, the head in 
 the primary position, the point of fixation being 1 at a dis- 
 tance of one meter. Under these conditions, the angle 
 formed by the visual axis of the other eye and the ex- 
 tended median plane of the head, is also a metre-angle; 
 the one exactly equal to the other. The sum of the two 
 angles constitutes the angle of convergence, so that the 
 angle of convergence is two metre-angles of Nagel. Both 
 the metre-angle and the angle of convergence vary with 
 variations of the distance between the centres of the two 
 eyes. The angle of convergence is a thing to be meas- 
 ured, but not more certainly than that the metre-angle is 
 also a thing to be measured. The metre-angle, therefore, 
 cannot be taken as a standard of measurement, because a 
 standard must never vary. A yard must be 36 inches, 
 whether one is buying or selling, and whether the thing 
 bought or sold is cloth or tape. The very word standard 
 means unvarying. The unvarying standard for measur- 
 ing angles is the arc of a circle in degrees, minutes, and 
 seconds. This standard, for reasons to be shown, should 
 apply to the angle of convergence. If Nagel had taught 
 that the metre-angle is the angle formed by the intersec- 
 tion of the visual axes at a distance of one metre, and had 
 given to it twice the value in degrees that he did give it, 
 there would be less objection to it. Even then, the me-
 
 OF OCULAR ROTATIONS. 
 
 143 
 
 tre-ang-le would mean 3 20' with the distance from center 
 to center of the two eyes 58mm; while it would mean 
 3 40' with the distance from center to center of the two 
 eyes 64mm. After having- determined the value of the 
 metre-angle (the angle formed by the intersection of the 
 visual axes of the eyes at the distance of one metre, the 
 head invariably in the primary position) in any given 
 case it would be very easy to translate any fraction of a 
 metre-angle or any number of metre-angles into degrees. 
 Distances less than a metre, therefore a fraction of a 
 metre, would increase the metre-angle in inverse ratio; for 
 distances greater than a metre, the metre-angle would 
 decrease in inverse ratio. To illustrate: Fixation at 
 i a metre would give convergence of two metre-angles; 
 g metre would give a convergence of 8 metre-angles; but 
 fixation at 2 metres would give convergence of \ metre- 
 angle; fixation at 8 metres would give convergence of | 
 metre -angle. Let the value of the metre -angle be 
 3 20', then the above would be translated: 2 ma = 6 40', 
 8 ma = 26 40', \ ma = 1 40', | ma == 25'. 
 
 The value of the metre-angle (the angle of convergence) 
 for various distances between the eyes is given in the 
 accompanying table : 
 
 Distance be- 
 tween the eyes 
 in inches. 
 
 2 
 
 2!/ 8 
 
 2^ 
 
 2% 
 
 2/2 
 
 2% 
 
 2* 
 
 2-j 
 
 3 
 
 Value of one 
 metre-angle. 
 
 254'38" 
 
 35'33" 
 
 316"28" 
 
 327'23" 
 
 338'18" 
 
 349'13" 
 
 4(X8" 
 
 411'3" 
 
 421'58"
 
 144 THE FUNDAMENTAL PRINCIPLES 
 
 An interesting 1 fact developed in working- out the size 
 of the metre-angle, is that for every g of an inch in- 
 crease of the distance between the eyes there is an in- 
 crease of the angle to the extent of 10' 55". Knowing* the 
 size of the metre-angle when the base-line (distance be- 
 tween the centers of the eyes) is 2 inches, the size of the 
 angle with the base-line 2| inches is found by adding to 
 the former 54' 35", which is 5 times 10' 55". This would 
 give 2 54' 38" + 54' 35"= 3 49' 13", just the size of the 
 angle shown in the table, when the base-line is 2f inches. 
 
 To find the size of the angle of convergence in any given 
 case, when the point of fixation is less than one metre dis- 
 tant, divide the size of the metre-angle in degrees by that 
 part of a metre that measures the distance of the point of 
 fixation, which, of course, means that }~ou are to invert 
 the terms of the divisor and multiply. To illustrate: 
 Fixation at 16 inches is fixation at (1 4-, metre. Let the 
 
 i.4b 
 
 base-line be 2i inches and we have the following : 
 3 38' 18" -H tt --= 3 38' 18" X = 8 57' 1". 
 
 Again, let the point of fixation be 3 m, and the base-line 
 be 2J inches. We now have 
 
 3 38' 18" -^-3 = 3 38' 18'' X | = 1 12' 46", 
 
 the size of the angle of convergence at 3 m. The base- 
 line remaining the same, the angle of convergence at a 
 distance less or greater than one metre, is to the angle of
 
 OF OCULAR ROTATIONS. 145 
 
 convergence at one metre (the metre-angle), inversely, 
 as the distance of the point of fixation is to one metre. 
 The mathematical formula is that the tangent of half 
 the angle of convergence varies inversely as the dis- 
 tance of the point of fixation from the middle of the line 
 joining the centers of the eyes. But for small angles 
 the above rule gives approximately the same results. 
 
 The reason for suggesting that the metre-angle be the 
 angle formed by the intersection of the visual axes at one 
 metre, and not the angle formed by the visual axis and 
 the extended median plane, and that it be given a value 
 double that given it by Nagel, is that the angle of con- 
 vergence, or rather the nervous impulse from the third 
 conjugate center, necessary to make this angle, is the 
 chief factor in the formation of judgment as to distance. 
 In fixing points to the right and left on the isogonal curve 
 the angle formed by the intersection of the visual axis 
 and the median plane of the head is confined to one eye, 
 and is constantly changing in value, whereas the metre- 
 angle, which is synonymous with the angle of convergence 
 of the visual axes at one metre, remains the same every- 
 where when carried along the isogonal curve.
 
 CHAPTER II. 
 
 ORTHOPHORIA. 
 
 THE terminology introduced by Stevens for indicating 
 the relationship, normal and abnormal, between the oc- 
 ular muscles, being 1 of pure derivation, leaves no room 
 for change and but little room for addition. These terms 
 are so widely used and are now so well known, they need 
 mentioning 1 only when used in connection with the condi- 
 tions indicated by them. The Stevens nomenclature was 
 adopted as both scientific and correct, by the section of 
 Ophthalmology of the American Medical Association, at 
 the Washington meeting in 1891. 
 
 Orthophoria is the term applied to a perfect balance 
 of the ocular muscles when the head is in the primary 
 position and the eyes are looking straight forward. This 
 condition, in the strictest sense, includes the idea that 
 the twelve extrinsic muscles have all been perfectly devel- 
 oped, that each has its correct origin, pursues its proper 
 course through the orbit to the eye, and is rightly at- 
 tached to the globe; and that the orbits themselves are 
 perfectly formed. It also includes the idea that the nine 
 conjugate innervations are wanting in nothing. When 
 
 (146)
 
 ORTHOPHORIA. 147 
 
 such a state of thing's exists, the visual axes are easily 
 kept in the same plane through the first and second con- 
 jugate innervations; are always perfectly converged 
 through the third conjugate innervation; and by means 
 of the first, second, fourth, and fifth conjugate innerva- 
 tions, are made to sweep harmoniously along the hori- 
 zontal plane, in the vertical plane, and in any oblique di- 
 rection. Nor will the sixth, seventh, eighth, and ninth 
 conjugate innervations fail to keep the vertical axes of 
 the eyes parallel with each other and with the median 
 plane of the head, while the transverse axes lie in the 
 plane of the primary isogonal circle, regardless of the lo- 
 cation of the point of fixation. Such a condition would 
 also include the idea that the verting and ducting power of 
 all of these muscles is up to the standard. But for 
 these eyes, thus well balanced, to be perfect, there must 
 be no error of refraction. There are such eyes, and the 
 happy possessor of them knows of their existence only 
 for the joy they give him. The workings of such eyes 
 never add anything to the sum of human ills. 
 
 There are accurate instruments for determining the ex- 
 istence of orthophoria. The Stevens phorometer, the only 
 one in use for a few years, is represented in Figs. 28 and 29. 
 This instrument being incapable of making all the tests, 
 even for orthophoria, it was natural that others should 
 be invented, and that the evolution would go on to final
 
 148 ORTHOPHORIA. 
 
 perfection. The Stevens instrument is capable only of 
 showing- the state of balance between the different pairs 
 of muscles, and in that much can determine the existence 
 of orthophoria but not the kind, for, after all that has 
 been said, there are two kinds of orthophoria. It cannot 
 acquaint the operator with the duction power of a sin- 
 gle muscle. It cannot, nor can any other phorometer, 
 already known or hereafter to be invented, give informa- 
 tion about the verting power. One serious objection to 
 the Stevens phorometer, which applies with equal force 
 to the Wilson phorometer next to be considered, is that it 
 is a binocular instrument, and to that extent must be 
 faulty. In all phorometers, either diplopia must be pro- 
 duced by prismatic action, the images in the two eyes 
 being on non-corresponding points of the retinas, or the 
 image in one eye must be made very different from the 
 image in the other, as by the Maddox rod, so as to de- 
 prive the guiding sensation of the reins of control. In 
 the Stevens phorometer both images are displaced so that 
 neither eye can be in the primary position while under 
 test. Again, if the patient be not orthophoric, rotation 
 of the instrument to properly relate the two images, 
 moves the image in each eye, which must be a source of 
 inaccuracy. 
 
 The method of using the Stevens phorometer is simple. 
 A candle or gas jet is placed twenty feet from the pa-
 
 ORTHOPHORIA. 
 
 tient, who, in the sitting- posture, should hold his head 
 erect. Placing- the instrument before him, he looks at 
 the Jig-fat throug-h the prisms, when diplopia must become 
 
 Fig. 28. 
 
 manifest. In testing- for lateral orthophoria the lights 
 are made to appear the one above the other, by rotating 
 the instrument so that the base of one prism may be di-
 
 150 ORTHOPHORIA. 
 
 rectly up and the base of the other down. In orthopho- 
 ria a vertical imaginary line will connect the two lights. 
 If the one is not directly above the other, there is not 
 lateral orthophoria. The slightest movement of these 
 prisms will change the relationship of the images, and in 
 this way whatever error may exist is measured. 
 
 Fig. 29. 
 
 In the test for vertical orthophoria, the instrument is 
 so rotated as to place the prisms with bases directly in. 
 The two lights should now be the same height, but if 
 not, then there is not vertical orthophoria. The rota- 
 tion necessary to make the lights level shows the kind 
 and quantity of the error. 
 
 This instrument can also determine the existence of 
 oblique orthophoria. It must be rotated into the posi-
 
 ORTHOPHORIA. 
 
 151 
 
 tion for testing for lateral orthophoria; but, for the 
 light, a horizontal line must be substituted. The line 
 will be doubled by the prisms and they should be par- 
 allel with each other. 
 
 The test of the lateral muscles and of the obliques 
 should be resorted to in the near also. For the former, 
 
 Fig. 30- 
 
 a card with a dot or cross in its center must be held at 
 the reading 1 distance; for the latter, a card with a hori- 
 zontal line on it should be held in the same manner. The 
 dots and the lines should bear the same relationship as in 
 the distant test. These tests made, the Stevens phorom- 
 eter can do no more.
 
 152 ORTHOPHORIA. 
 
 The Wilson phorometer, Fig-. 30, can do all that the 
 Stevens phorometer is capable of doing; and, besides, can 
 determine the duction power of all the recti. The diplo- 
 pia with this instrument is produced by a prism of 10 
 (found in one of the opening's in the revolving 1 disc) be- 
 fore the right eye, whose base can be placed up for a test 
 of the lateral muscles, or in, for a test of the vertically- 
 acting- muscles. In lateral orthophoria the two images 
 will be in a vertical line, when the slightest turning of 
 the rotary prism constituting that part of the instrument 
 which is always before the left eye, will displace the up- 
 per (true) image either to the right or left. Should the 
 lower image not be in a vertical line with the upper, mov- 
 ing the rotary prism until the one is directly above the 
 other will show both the kind and the quantity of the 
 error. Changing the position of the disc, the 10 prism 
 will present its base towards the nose. When the im- 
 ages are found in the same horizontal plane there is ver- 
 tical orthophoria, and the slightest movement of the ro- 
 tary prism will elevate or depress the one seen by the left 
 eye. Should the false image be higher or lower than the 
 true, moving the rotary prism in the proper direction 
 will bring the true image into the horizontal plane with 
 the false, thus showing both the kind and quantity of the 
 vertical error. Thus far the workings of these two in- 
 struments practically correspond, the one being no bet-
 
 ORTHOPHORIA. 153 
 
 ter than the other. With the Stevens instrument both 
 images are moved in every rotation; with the Wilson in- 
 strument only the true image is made to change position. 
 In connection with each of these phorometers there is the 
 indispensable spirit level. 
 
 With the open space of the disc before the right eye 
 and the rotary prism in a neutral state before the left 
 eye, the prism axes being horizontal, by moving the ro- 
 tary prism, the duction power of the superior and infe- 
 rior recti can be taken, which should be 3 certainly not 
 less than 2 for each. Since this revolving prism can 
 measure 10, it can always show, practically, the duction 
 power of the vertically-acting muscles. Turning the ro- 
 tary prism again into a neutral state, so the axis may be 
 vertical, still keeping the open space before the other eye, 
 abduction can be taken, which, in orthophoria, should 
 be 8 certainly not less than 6. Rotating it in the other 
 direction, adduction can be taken only up to 10, its max- 
 imum power. To go higher than this, the disc before 
 the right eye must be revolved until the 15 prism is 
 brought into position, base out. Now, starting the ro- 
 tary prism in the adduction arc, every movement adds to 
 the 15 adduction caused by the prism before the right 
 eye, until, when the end of the arc has been reached, 25 
 of adduction is shown. The doubling just now occur- 
 ring, the conclusion is that adduction is normal; if soon-
 
 154 ORTHOPHORIA. 
 
 er, that it is below normal. It cannot be carried higher 
 by this instrument. It will be noticed that the test has 
 been applied not to one internus, but to both, and for 
 this reason cannot be reliable. 
 
 The Wilson phorometer is also capable of testing- the 
 balance and imbalance of the oblique muscles. To do 
 this, the open space in the disc is placed before the right 
 eye, while the rotary prism is before the left in the neu- 
 tral position, axis horizontal. By revolving- the prism as 
 if testing for superduction, the point is finally reached 
 when the horizontal line, which is now the test object, 
 becomes double. If these two lines are parallel, then 
 for that direction at least, there is orthophoria of the 
 obliques. Returning to the neutral position, the prism 
 should next be revolved in the direction of sub-duction. 
 Presently the line is again doubled, the false line being 
 below the true. If these lines are parallel, again there 
 is evidence of orthophoria of the obliques. Not infre- 
 quently the false line in the latter position will show an 
 insufficiency of the superior obliques, while in the former 
 position the lines may be parallel. By slowly revolving 
 the prism back towards the neutral point, whether from 
 the one direction or the other, the patient can observe 
 whether or not the fusion of the two lines is simultane- 
 ous throughout, or whether the fusion takes place at one 
 end and then gradually throughout. When the lines are
 
 ORTHOPHORIA. 
 
 not parallel, the kind of dipping- indicates the character 
 of error. This instrument is wholly incapable of testing- 
 the lifting- power of the obliques. 
 
 Neither one of these instruments is constructed on the 
 correct principle underlying the tests of the ocular mus- 
 cles, even when orthophoria exists. The principle on 
 which all the tests possible to a phorometer rest, is that 
 the imag-e in one eye, throug-hout every test, shall be un-
 
 156 ORTHOPHORIA. 
 
 disturbed; that the head shall be erect; and that both 
 eyes and the object better a white dot on a black back- 
 ground shall be on the extended horizontal plane of the 
 head. The false object must have its image thrown out- 
 side the area of binocular fusion in the eye under test, 
 while the true object will have its image on the macula 
 of the eye not under test, thus making it not only possi- 
 ble, but necessary, that this eye shall be in the primary 
 position throughout the test, for it is not to have its im- 
 age disturbed during any one of the several tests. An 
 instrument based on the principle enunciated above is 
 the monocular phorometer. It fulfills every essential 
 condition, and is wholly reliable, and, except in rare 
 cases, is invariable. The accompanying cut, Fig. 31, 
 represents its appearance, but not its capabilities. The 
 screw-and-spring arrangement, for regulating the spirit 
 level, is as good as the best. In the base of the instru- 
 ment there are slots on either side of the rotary prism, 
 in one of which, towards the patient's face, is to be 
 placed the displacing prism for causing the diplopia. If 
 the instrument has been leveled, this prism, when placed 
 in the slot, must have its axis either vertical or horizon- 
 tal, and must produce a corresponding diplopia. The 
 rotary prism differs from the one in the Wilson phorom- 
 eter in that it has a face correctl}' lettered and marked 
 in degrees, for each eye, and is easily reversible.
 
 ORTHOPHORIA. 157 
 
 With the instrument properly leveled before the right 
 eye, the axis of the rotary prism vertical, and the 6 prism 
 base up, in the slot toward the face, the false object is 
 made to appear below the true, and if directly under it, 
 there is lateral orthophoria. The rotary prism turned 
 in either direction will make the false object go either to 
 the right or to the left of the vertical line through the 
 true object, which must be, at all times, the one looked 
 at. Should the false object not be under the true, turn- 
 ing the rotary prism in the proper direction will place 
 it there. On the face of the instrument toward the op- 
 erator, can be read the kind and quantity of the error. 
 The test for lateral orthophoria, in the near, is made 
 by holding a card with a dot or cross in its center, at the 
 reading distance. To test the vertically-acting muscles, 
 the rotary prism must be turned so as to have the revolv- 
 ing screw vertical, and the axis horizontal. The 10 
 displacing prism, base in, must be placed in the slot to- 
 wards the patient's face, so as to displace the image 
 beyond the area of binocular fusion. The false object 
 should be in the same horizontal plane with the true, 
 if there is vertical orthophoria. Any movement of the 
 rotary prism will displace the false object, either rais- 
 ing or depressing it. When the false object is not 
 found on a level with the true, there is a vertical hetero- 
 phoria. Turning the rotary prism so as to bring the
 
 158 ORTHOPHORIA. 
 
 false object to a level with the true, shows, on the face 
 towards the operator, the kind and quantity of the ver- 
 tical error. 
 
 With the instrument in the adjustment for detecting- 
 vertical orthophoria, and without a displacing 1 prism, the 
 balance of the obliques is found by moving- the rotary 
 prism, first down, while the patient looks at a hori- 
 zontal line until it doubles. The lines will be parallel 
 if there is orthophoria of the obliques. Reversing- the 
 movement of the rotary prism, the false line appears 
 above the true, but should be parallel with it. If there 
 is not a perfect balance between the obliques it will 
 be shown by a want of parallelism between the false 
 and true lines. The kind of error will be indicated by 
 the direction in which the lines converge, but the quan- 
 tity cannot be measured by this instrument. 
 
 With the instrument still in the adjustment for the 
 vertical muscles, sub-duction and superduction may be 
 quickly determined, as by the Wilson phorometer. Ad- 
 justing 1 it as for testing- the lateral muscles, abduction 
 can be taken without the aid of a supernumerary prism, 
 if the patient is orthophoric. To take the adduction, 
 one or two supernumerary prisms will have to be used 
 to aid the rotary prism. If adduction is not above 25, 
 the 15 prism may be placed in the slot toward the 
 face, with its base toward the temple. Turning- the ro-
 
 ORTHOPHORIA. 159 
 
 tary prism will add to the effect of the supernumerary 
 prism up to 10. This added to 15 gives 25 of adduc- 
 tion, provided the doubling- occurs only at the end of the 
 rotation. If the adduction should be 30, or more, it can 
 be shown by placing- the 5 or 10 prism, base out, in the 
 slot in front, while the 15 prism remains behind, and 
 again moving- the rotary prism throug-h the nasal quad- 
 rant. This instrument can measure adduction only up 
 to 35. In testing- for the adduction with the monocular 
 phorometer, the only muscle to respond is the one inter- 
 nal rectus. 
 
 By reversing the instrument all of these tests can be 
 repeated on the muscles of the left eye. In every one 
 of these tests the imag-e in one eye remains undisturbed. 
 The object seen by this eye must always be seen by di- 
 rect vision, while the false object must be seen by indi- 
 rect vision. 
 
 The simpler methods of testing- for orthophoria of 
 the recti, even including- the use of the Maddox rod, are 
 "all faulty and should be discarded. The leveling- part 
 of a phorometer is an absolute necessity, for without 
 it there can be no exactness in the placing- of prisms be- 
 fore an eye. In testing- for lateral orthophoria, slight 
 errors, resulting from an improperly-placed prism, could 
 be tolerated, but not so in testing for vertical orthopho- 
 ria. The Maddox rod is objectionable in all tests of the
 
 160 ORTHOPHORIA. 
 
 recti for the reason that a part of the streak of light, 
 whether it be vertical or horizontal, will fall on the 
 field of binocular fusion, unless the error be great. The 
 false image, whatever may be its character, should nev- 
 er be on any part of this field; otherwise a greater or 
 less effort at fusion will be made. 
 
 There is a legitimate use for the Maddox rod. It is 
 in testing the oblique muscles, both as to their ortho- 
 phoria and their intrinsic strength. This instrument 
 may be called the cyclo-phorometer, though Stevens 
 has named the instrument he has invented for this pur- 
 pose the clinoscope. The first of these instruments 
 was invented by Price, in 1893, and was exhibited by 
 him before the Section of Ophthalmology, at the meet- 
 ing of the American Medical Association in San Fran- 
 cisco, in 1894. It consisted of a double prism, line of 
 bases horizontal and a rod at right-angles to this line of 
 union, placed in a circular disc to fit the rim of a trial 
 frame, and a Maddox rod only to be placed vertically in 
 the other side of the frame. Looking at a candle, the 
 patient would see two horizontal and necessarily parallel 
 lines of light with the one eye, and a single horizontal 
 line of light with the other, the latter appearing be- 
 tween the other two, and parallel with them in ortho- 
 phoria of the obliques. This was for testing the ob- 
 liques when the visual axes were approximately paral-
 
 ORTHOPHORIA. 161 
 
 lei. It was faulty in that there was no adjustment by 
 means of which the frames holding- the rods could be 
 leveled. A little later, Baxter, of Boston, and Brewer, 
 of Connecticut, each independently, invented a cyclo- 
 phorometer, with the error in the Price instrument elim- 
 inated. Brewer, not knowing of the Price invention 
 when he made claim for himself, later wrote to the 
 Ophthalmic Record as follows: "Dr. G. H. Price, of 
 Nashville, Tenn., appears in your July [1898] issue as 
 claimant to prior use of the Maddox rods in testing the 
 position of the retinal meridians. Since he very clearly 
 substantiates his claim, so far as I am concerned I tend 
 him such laurels as I may have grasped, and trust he 
 may wear them securely and gloriously." Dr. Brewer 
 named his instrument the torsiometer. Later than this 
 Stevens brought out his prism clinoscope, the construc- 
 tion of which is not very different from the instruments 
 of Baxter and Brewer. 
 
 The cyclo-phorometer must, of necessity, be a binocu- 
 lar instrument. The cyclo-phorometer, Fig. 32, made for 
 use in connection with the monocular-phorometer stand, 
 or the Wilson phorometer holder, consists of a base on 
 which rest two graduated cells (E), in each of which is 
 to be placed a triple Maddox rod (H) with the axis verti- 
 cal. Behind each of these circular cells is a rectangular 
 cell (F) for a displacing prism. There is an arrange-
 
 162 
 
 ORTHOPHORIA. 
 
 ment (D) by means of which the pupillary distance can be 
 easily regulated so that the one streak of light may be 
 brought directly under the other. There is beneath the 
 base of the instrument, a spirit level (L) for regulating 
 
 A - 
 
 Fig. 32- 
 
 the adjustment of the instrument. On each disc contain- 
 ing the rods is marked below a line continuous with the 
 axis of the central rod. The rods placed vertically, with 
 a prism of 5 base up behind one of them, will show two
 
 ORTHOPHORIA. 163 
 
 horizontal lines of light, when a candle is looked at. The 
 lower one will be seen by the eye before which is the 
 combination rod-and-prism. The lines should be paral- 
 lel, and their ends even. The latter can be regulated 
 by turning- the screw (D) that controls the pupillary dis- 
 tance. The slightest movement of either disc will cause 
 a loss of parallelism of the streaks of light. If not par- 
 allel, there is want of orthophoria of the obliques, the 
 kind and quantity of the error being shown b} r the rota- 
 tion of either disc. 
 
 By removing the displacing prism, the intrinsic power 
 the cyclo-duction of each oblique muscle can be taken 
 alone, and then the combined cyclo-duction of either both 
 superior or both inferior obliques. This is done, when 
 only one muscle is being tested, by revolving the one rod 
 in the temporal arc for a superior, and in the nasal arc 
 for an inferior oblique. If both superior obliques are 
 under the duction test, then both rods must be revolved 
 in the temporal arc; if both inferior obliques, then both 
 rods must be revolved in the nasal arc. The moment the 
 two streaks separate, the rotations must stop. On the 
 arc of the cell the extent of cyclo-duction can be read. 
 The normal cyclo-duction for a single oblique muscle is 
 somewhere between 7 and 14. The combined cyclo- 
 duction of either pair of obliques is somewhere between 
 12 and 22.
 
 164 
 
 ORTHOPHORIA. 
 
 The method of determining the perfect balance of the 
 oblique muscles, or the imbalance when it exists, by the 
 Stevens clinoscope, will be better understood after a de- 
 scription of the instrument itself. This description is 
 given in the words of the inventor: 
 
 Fig- 33- 
 
 "The clinoscope [Fig. 33] is composed essentiall}" of 
 two hollow tubes, each of which has at one end a minute 
 pin-hole opening through which the eye can look, and at 
 the other end a translucent disc on which is drawn a line, 
 in the case of one tube from the centre straight up, and 
 in that of the other tube straight down. 
 
 " These tubes are so adjusted on a standard that they 
 can be placed and maintained in the same horizontal 
 plane, which is indicated by a spirit level, but from end 
 to end the} 7 can be directed horizontally or up or down.
 
 ORTHOPHORIA. 165 
 
 They can, as above intimated, be made to converge or 
 diverge to meet certain contingencies. 
 
 "The tubes rotate on their long axes, and a pointer 
 attached to each tube indicates on a scale the extent to 
 which the tube is rotated. The small sight openings are 
 so adjustable that the distance between them may be 
 suited to the interpupillary distance of different persons. 
 For the accommodation of those who, on account of pres- 
 byopia, myopia, or any high degree of refractive error, 
 cannot see at the distance of the test objects from the 
 eyes, there are clips in which refracting glasses ma}" be 
 placed. The sight openings being very small and ex- 
 actly in the same horizontal plane, there can be no doubt 
 as to the erect position of the median plane of the head 
 when the two eyes are seeing, each through its appropri- 
 ate sight opening, any existing hyperphoria being cor- 
 rected. 
 
 "The instrument is to be so adjusted in respect to 
 height that the sight-holes will be on a level with the 
 eyes of the examined person when sitting erect. This 
 is best accomplished by the use of an adjustable table. 
 The tubes may be exactly parallel or they may, in 
 certain cases, be made to converge very slightly, thus 
 making the distant point at 8 or 10 feet instead of 
 infinite distance. Under other exceptional circum- 
 stances they may be made to diverge. The tubes
 
 166 ORTHOPHORIA. 
 
 must be brought to an exact level with each other 
 as shown by the spirit level. 
 
 "Unless the subject of the examination is unable to 
 see the test lines of the tubes, on account of presbyopia 
 or high refractive error, no glasses should be used, and 
 when glasses are necessary the weakest that will enable 
 the person to see the lines clearly should be placed in the 
 clips. A prism for the correction of hyperphoria may 
 also be required. The glasses should not be worn, since, 
 if a strong glass should not be held exactly at right- 
 angles with the axis of the tube, the lens would itself 
 induce a declination of the image. 
 
 " The examiner must be sure that the examined person 
 sees through both openings simultaneously, and that the 
 view of both images is maintained throughout the exam- 
 ination; otherwise there can be no certainty that the 
 head is precisely erect. 
 
 "When the examined person has secured a good view 
 of both the test lines, he should endeavor, if they do not 
 at once unite, to induce them to do so as in a stereoscope. 
 Some people do not succeed in this, in which cases the 
 examination may go on with the images separated, but it 
 is less satisfactory. 
 
 "When the apparent vertical position of the lines has 
 been attained, the examiner should move them more or 
 less backward and forward, in order that the true posi-
 
 ORTHOPHORIA. 167 
 
 tion may be more positively located. Few people can 
 arrive at a satisfactory conclusion regarding- the position 
 of the lines at the first trial, but after a da} 7 or two the 
 tests become, for nearly all intelligent people, remark- 
 ably uniform." 
 
 With the clinoscope thus adjusted, the head of the pin 
 with the point up should be fused with the head of the 
 pin whose point is down, and both pins should be verti- 
 cal if the oblique muscles are doing 1 their full duty if 
 the vertical axes of the eyes are parallel with the median 
 plane of the head. If the two pins are not now one ver- 
 tical line there is a cyclophoria. Whether the C} T C!O- 
 phoria is plus or minus is easily determined, and its 
 quantity is measured by revolving the tubes till the two 
 pins become one vertical line. 
 
 In determining cyclo-duction by the clinoscope, the 
 translucent discs with lines entirely across are to be 
 used instead of those that have the lines only half way 
 across. With the tubes properly adjusted the two lines 
 would be seen as one. Revolving one tube would tend to 
 displace the image of one line, which the eye would over- 
 come by torsioning, as long as possible. The conclusion 
 which Stevens has reached is that the image may be dis- 
 placed as much as 14 in one eye before doubling occurs, 
 and that the combined displacement, in opposite direc- 
 tions, of the images in the two eyes, may be as much as
 
 168 ORTHOPHORIA. 
 
 22. He also claims that a little greater displacement 
 may be overcome by the inferior obliques than by the 
 superior. 
 
 No test for orthophoria is complete until the verting- 
 power of the recti has been determined. 
 
 In the study of the field of fixation, or, better, the field 
 of rotations, it must not be confounded with the field of 
 vision which, in healthy eyes, is much larg-er than the 
 former. The rotations in the four cardinal directions 
 are those to be studied; and the best means at our com- 
 mand for this study is the tropometer, invented by Stev- 
 ens. A fair degree of accuracy may be obtained by the 
 use of the perimeter and a lighted candle, or a small 
 electric lig"ht, in a dark room. This method, though not 
 the better of the two, will be described first. The pa- 
 tient should be placed in front of the perimeter as for 
 the taking- of the field of vision. The eye to be tested 
 must be in the center of the perimeter curve. The ex- 
 tent of the outward rotation is determined by asking- the 
 patient to fix the blaze of a small candle, or a small elec- 
 tric light, as it is moved behind the arm of the perimeter, 
 toward the temporal side of the eye under test. When 
 the patient can turn the eye no further out, the operator 
 putting- his open eye (one eye should be closed) in line 
 with the candle and the center of the rotated cornea, ob- 
 serves the imag-e of the candle reflected from the center
 
 ORTHOPHORIA. 169 
 
 of the cornea, and then reads the number of degrees 
 marked at the point of location of the candle. In like 
 manner the extent of rotation of the same eve in the op- 
 posite direction is determined and noted. The arms of 
 the perimeter are now to be placed in the vertical posi- 
 tion, when the extent of the upward and downward ro- 
 tations can be measured in the same way. There is no 
 necessity for other than these measurements in the four 
 cardinal directions. Muscles found capable of making 
 these rotations reach the standard, will be fully capable 
 of doing the work of effecting any other rotation, which, 
 after all, must be a combination of the forces effecting 
 the cardinal rotations. Both eyes should be thus tested. 
 The Stevens tropometer, shown in the accompany- 
 ing cut, Fig. 34, is an instrument of greater precision 
 and is more convenient for use. The arrangement for 
 fixing the head needs no description, since it is easil} 7 un- 
 derstood. At the base of the instrument is a thumb- 
 screw by means of which the tropometer proper can be 
 placed at varying distances from the patient's eye. The 
 object of this arrangement is to so adjust the instrument 
 that the reflected image of the cornea will extend from 
 one of the darker lines in the scale, to the other one, and 
 this adjustment should be made at the beginning of 
 every examination. Near the center of the upright piece 
 there is a thumb-screw for elevating or depressing the
 
 170 
 
 ORTHOPHORIA. 
 
 Fig- 34- 
 
 mirror so that its center may be on a level with the pa- 
 tient's eye. At the top of this upright there is a flat base 
 by means of which the mirror-box of the tropometer may 
 be placed directly in front of the eye to be examined. 
 This is effected by simply sliding the tropometer in 
 either the one direction or the other. The horizontal 
 part of the tropometer is a little more difficult to under- 
 stand, and yet it is simplicity itself. It consists of a 
 square box, closed completely by metal on all sides ex- 
 cept the one facing the patient, and in the center of this
 
 ORTHOPHORIA. 17l 
 
 side is an opening* which is filled with a disc of perfectly 
 plane transparent glass, in the center of which is a 
 white dot at which the patient is directed to look, at the 
 beginning of the examination. Inside of this box is the 
 mirror, placed at an angle of 45 on a vertical axis. 
 From this mirror the patient's eye is reflected, an aerial 
 image of which is formed on the graduated disc, so that 
 the operator at the other end of the instrument may see 
 it. The sharpness of the image is regulated by the 
 thumb-screw in the center of the telescope part, by 
 means of which the lenses contained in the tube are so 
 adjusted as to enable the operator to get perfect sharp- 
 ness of outline of the aerial image. The disc containing 
 the graduated scale has been constructed with mathe- 
 matical correctness. In the center of this disc there is a 
 heavy line extending entirely across. At right-angles to 
 this base-line there extends from each side a heavy line, 
 the distance between the two being nearly 60. On 
 either side of the base-line there are lighter lines placed 
 at points 10 apart. When the handle of this disc is 
 vertical, the position is for measuring superversion and 
 sub-version. With this instrument adjusted so the pa- 
 tient's cornea extends from one heavy line to the other, 
 the base-line passing down through the center of the 
 cornea, and the image itself being sharply focused, we 
 take the superversion by asking the patient to look up as
 
 172 ORTHOPHORIA. 
 
 far as possible. In the reflected image the eye appears 
 to move downward, for the image is irverted. The po- 
 sition of the lower margin of the cornea (upper of image; 
 is now noted and the extent of the rotation is read off on 
 the scale. In a normal condition the superversion should 
 be 33. This having been noted, the patient is asked to 
 look straight forward again, when the image of the cor- 
 nea will extend from one heavy line to the other as be- 
 fore, while the base-line will pass directly down through 
 the center of the pupil. Now the patient is asked to look 
 down as far as possible. Unless the upper lid is held up 
 by external force, it will so cover the cornea that the 
 measurement cannot possibly be taken. An assistant is 
 necessary then to elevate the upper lid in order that sub- 
 version may be taken. While the patient is looking 
 down as far as possible, the position of the upper margin 
 of the cornea (lower as it appears in the image) is noted, 
 and the extent of the rotation is read off on the scale. 
 This should be about 50. The superversion and sub- 
 version having been taken, the handle connected with the 
 scale-disc is turned from the vertical to the horizontal. 
 Now the instrument must be so adjusted that the base- 
 line will coincide with the horizontal meridian of the cor- 
 nea, while the cornea itself extends from one heavy line 
 to the other. If the left eye be under test, abversion is 
 taken by asking the patient to look as far towards the
 
 ORTHOPHORIA. 173 
 
 left as possible. The location of the nasal margin of the 
 cornea, when the eye is in extreme abversion, is noted on 
 the scale and the extent of the rotation is read off. This 
 should be about 50. This done, the patient is asked to 
 look straight forward, when the instrument is adjusted 
 as before. Now he is asked to look as far towards the 
 right as possible, when the extent of the adversion can 
 easily be determined. This should be about 50. The 
 power of rotation in the four cardinal directions having 
 been found normal, it would be correct to conclude that 
 rotation in any one of the oblique directions would also 
 be normal. Any marked variations in the different ver- 
 sions from the standard, as noted above, should be con- 
 sidered a very important guide as to any surgical pro- 
 cedure to be resorted to, but this will be more clearly set 
 forth in the study of heterophoria. Both eyes should be 
 thus tested. 
 
 The candle method of simply watching the eye as it 
 rotates in each of the four cardinal directions, does not 
 commend itself as being at all accurate; and yet it is 
 better than no examination to determine the extent of 
 these rotations. Unless the temporal rotation carries 
 the outer margin of the cornea to the external canthus, 
 and the inner rotation carries the inner corneal margin 
 to the internal canthus, it would appear that these rota- 
 tions are too limited. In the upward and downward ro-
 
 174 ORTHOPHORIA. 
 
 tations there are only the lid margins, themselves mov- 
 able, to give us an approximate judgment as to their 
 extent. This method is of use in a case of paresis or 
 paralysis, but it ought never to be relied on for other 
 purposes. 
 
 The extent of these rotations, as given by different 
 authors, varies but little. L/andolt makes the standard 
 of these rotations as follows: Out, 46; in, 44; down, 
 50; up, 33. Stevens places the standard as follows: 
 Out, 48 to 53; in, 48 to 53; down, 50; up, 33. The 
 standard set by Stevens is probably more nearly cor- 
 rect. A knowledge of an excess of, or deficiency in, these 
 measurements can but be helpful when the question of a 
 muscle operation presents itself. The rotating power 
 of a muscle should never be reduced by operation below 
 the standard measurement for that muscle. 
 
 The importance of the study of the field of rotation 
 should not lead to a disregard of the field of binocular 
 fusion. The latter can be determined only by the use of 
 prisms. In this study again, it is not important to find 
 the extent of the field except in the four cardinal direc- 
 tions. Authors differ as to the extent of this, while none 
 of them sufficiently emphasize its importance, in the 
 study of heterophoria. The accompanying cut, Fig. 35, 
 shows approximately the shape and size of this field of 
 fusion. When an image is displaced by a prism to any
 
 ORTHOPHORIA. 
 
 175 
 
 point within the field, while the image in the other eye 
 is on the macula, an effort at fusion will be made, and if 
 the muscle that must respond is sufficiently strong", 
 fusion will at once take place, caused by such a rotation 
 as will bring- the macula under the displaced image. 
 When the image is thrown, by a stronger prism, entirely 
 outside of the field of fusion, the guiding sensation, 
 
 RISHT 
 
 UEFT 
 
 Fig- 35- 
 
 which seems to reside in this area only, will not call on 
 any muscle to move the eye for the purpose of fusion. 
 The nasal limit of this retinal area, as measured by 
 a prism in front of the eye, is 8; the temporal limit, 
 25; the upper limit, 3; and the lower limit, 3. The 
 line drawn through these four points marks the entire 
 boundary of the field. ' This may be considered the nor- 
 mal size of the fusion area. In some cases it mav
 
 176 ORTHOPHORIA. 
 
 appear to be smaller, while in still other cases it may 
 be larger. 
 
 It is by means of prisms which displace an image 
 within this field that we can determine the fusion power 
 of a muscle. This may be termed the intrinsic or lift- 
 ing- power of the muscle. A determination of this power 
 is important, even in the study of orthophoria, but of 
 much more importance in the study of heterophoria. 
 A knowledge of the fusion power, associated with a 
 knowledge of the verting power of a muscle, is indis- 
 pensable in the formation of a judgment as to what 
 ought, or ought not, to be done in an operative way, in 
 any given case of heterophoria. 
 
 The power of the recti muscles for fusing images, ex- 
 pressed in prism degrees, is for the internus (adduction), 
 25; for the externus (abduction), 8; for the superior 
 rectus (superduction), 3, and for the inferior rectus (sub- 
 duction), 3. A muscle that has the normal fusion power 
 should also possess the normal verting power; and when 
 the one is abnormal the other is likely to be abnormal 
 also. The standard of the fusion power of the recti 
 might safely be set a little lower than that given above, 
 for all except that of the internus. A fusion abduction 
 of 6 and a sub-duction and superduction of 2 or 2.3 
 may be considered as favorable. ' 
 
 If all the muscles respond correctly to the diplopia
 
 ORTHOPHORIA. 177 
 
 test; if the duction power of the recti and the obliques 
 reaches the standard; and if the verting- power of the 
 recti does not fail short, then there is sthenic ortho- 
 phoria. Such a patient needs no help for his ocular ad- 
 justments. 
 
 ASTHENIC ORTHOPHORIA. 
 
 There is an orthophoria that is not in strength, but in 
 weakness. The diplopia tests may elicit responses indi- 
 cating orthophoria of all the pairs of muscles, but these 
 muscles may show a want of duction power, also a want 
 of verting power. Such eyes, though orthophoric, as 
 judged by the diplopia tests, cannot be as strong as they 
 would be if the muscles were possessed of full intrinsic 
 power. If an externus perfectly balances its antagonis- 
 tic internus and there is an abduction of only 4, there 
 must be a correspondingly low adduction. If there is 
 harmony between the superior and inferior recti, and 
 they show a superduction and sub-duction of only 1, 
 there is weakness that demands attention. Such cases 
 are often met in actual practice. The treatment is ceil- 
 ingf-to-floor and wall-to-wall exercise. The method of 
 
 o 
 
 carrying out this exercise is both simple and efficient. 
 The patient is directed to stand against one wall of his 
 room, midway between the walls to the right and left. 
 Having previously fastened, by pin or tack, a piece of 
 paper on each wall to right and left, at an angle of 35,
 
 178 ORTHOPHORIA. 
 
 approximately, and on a level with his eyes; and having 
 placed some object on the floor immediately in front of 
 him and at a distance equal to his height, he must stand 
 with his head erect while he looks up at the ceiling where 
 it joins the wall in front of him, then down at the object 
 on the floor, and so on for six or eight movements in the 
 vertical plane; then he must change his movements to 
 the horizontal plane, looking first at the paper to the 
 right, then at the paper to the left, and so on for six or 
 eight movements in this plane. He then passes again to 
 the vertical plane, changing the point of view rhythmic- 
 ally every three seconds; and, at regular intervals, al- 
 ternating the vertical and horizontal movements. He 
 should stop the exercise always short of fatigue, and 
 should not continue it longer than ten minutes at a time. 
 Once a day is often enough to resort to the exercise. 
 The time of day for the exercise may be suited to the 
 convenience of the patient. The duction power should 
 be taken at intervals of a few weeks, and the exercise 
 should be continued until the recti show the normal lift- 
 ing power. In this way an asthenic orthophoria may 
 be converted into a sthenic orthophoria. 
 
 The alternate contraction and relaxation of the recti, 
 under the stimulus of the first, second, fourth, and fifth 
 conjugate innervations, if not carried to excess, can re- 
 sult only in the up-building of the muscles. Since every
 
 ORTHOPHORIA. 179 
 
 muscle is exercised in the same way and to the same ex- 
 tent as its antagonist, there is no danger of interfering 
 with the equal balance that existed between the muscles 
 before the exercise was commenced. 
 
 There are cases in which there is a sthenic lateral 
 orthophoria and an asthenic vertical orthophoria. In 
 such cases the ceiling-to-floor exercise alone should be 
 advised. There are other cases in which there is a 
 sthenic vertical orthophoria and an asthenic lateral 
 orthophoria. In these cases only the wall-to-wall ex- 
 ercise should be given. 
 
 Since the strength of opposing muscles is correspond- 
 ingly increased, there is never any danger of accomplish- 
 ing too much. A lateral orthophoria with an abduction 
 of 12 and an adduction of 36, is a better condition than 
 when the abduction is 8 and the adduction is 25. A 
 vertical orthophoria with sub-duction and superduction 
 of 5 is better than if these ductions were only 3. 
 
 The diagnosis between sthenic and asthenic ortho- 
 phoria should always be made.
 
 CHAPTER III. 
 
 HETEROPHORIA. 
 
 Heterophoria is a generic term and includes all errors 
 of tendency of all the extrinsic ocular muscles. It is the 
 disposition on the part of a muscle, or muscles, to dis- 
 obey the law governing it; that is, the supreme law of 
 corresponding- retinal points. To obey this law, the 
 recti, in the final result of their action, are concerned only 
 with the visual axes; the superior and inferior recti of 
 the two eyes keeping these axes in the same plane, the 
 external and internal recti causing- them to intersect at 
 the point of fixation. The obliques must keep the verti- 
 cal axes of the eyes parallel with each other and with 
 the median plane of the head. In orthophoria the de- 
 mands of this law are easily met; in heterophoria the de- 
 mands are met, but not with ease; there is strain or 
 overwork. 
 
 In heterophoria involving- the superior and inferior 
 recti, there is a disposition on the part of these muscles 
 not to keep the visual axes in the same plane, the visual 
 axis of one eye tending- above the plane that ought to be 
 common to the two axes, while the visual axis of the 
 
 (180)
 
 HETEROPHORIA. 181 
 
 other eye has a corresponding- tendency downward. The 
 direction of this tendency gives name to the error: up- 
 ward tendency, hyperphoria; downward tendency, cata- 
 phoria. In heterophoria involving the lateral recti, there 
 is a tendency toward intersection of the visual axes be- 
 tween the observer and the point observed, or they tend 
 to intersect beyond the point of view, or even to become 
 divergent. The tendency to cross too soon is esophoria; 
 the tendency to cross too far away is exophoria. In 
 heterophoria involving the obliques, there is either a 
 tendency on the part of the inferior obliques to cause 
 the vertical axes to diverge from each other above, or of 
 the superior obliques to converge these above. The for- 
 mer is properly termed -plus cyclop Jioria; the latter, 
 minus cyclophoria. 
 
 Heterophoria has its causes, and just as certainly has 
 its consequences. To exist in any one of its several 
 forms, one muscle must have an advantage over its an- 
 tagonist; or, what is the same thing, in reverse order, 
 one muscle must be at a disadvantage as compared with 
 its antagonist. The difference may be in the compara- 
 tive sizes of the two muscles, the one being larger, and, 
 therefore, stronger than the other. There may be a 
 difference in the insertions of the two muscles, the one 
 being too near the corneo-scleral junction and the other 
 too far back. These muscles may be of proper size, but
 
 182 HETEROPHORIA. 
 
 it is certain that the one with insertion too far forward 
 will exert more power in rotating the globe than its an- 
 tagonist not so favorably attached. It must also be 
 conceded as possible that one muscle of proper size as 
 compared with its antagonist, and with no more favor- 
 able attachment, is more powerful than its antagonist 
 because of an excess of nerve impulse sent to it. Wheth- 
 er the one cause exists alone, or whether two or more of 
 them combine in the production of heterophoria, the 
 error is corrected by an extraordinary nerve impulse 
 which is sent to the weaker muscle of a pair, and thus, 
 with the undue expenditure of nerve force, binocular 
 single vision is maintained. 
 
 ORBITAL MALFORMATIONS. 
 
 As has been claimed by Stevens, Risley, and others, 
 malformation of the orbits may be a cause of heteropho- 
 ria. Such malformation can be the direct cause of 
 vertical and lateral errors, but not of errors of the 
 obliques. As is shown in Chapter I., ideally-con- 
 structed orbits are such that the eyes they contain, 
 when in the primary positions, will have their horizon- 
 tal planes lie in the fixed horizontal plane of the head. 
 As already defined, this fixed horizontal plane must nec- 
 essarily be at right-angles to the median plane of the 
 head. It may be said always to pass through the optic
 
 HETEROPHORIA. 183 
 
 chiasm. Thence anteriorly it should pass through the 
 centers of origin of the extern! and interni of both eyes; 
 thence on through the centers of rotation of the two 
 eyes. Posteriorly this plane passes, approximately, be- 
 tween the cerebrum and cerebellum, just as the median 
 plane of the head passes between the two halves of the 
 cerebrum. 
 
 In the chapter on hyperphoria and cataphoria will be 
 found illustrations showing how an orbit that is too low 
 will contain a cataphoric eye, while an orbit that is too 
 high will contain a hyperphoric eye. 
 
 If the two orbits are neither too high nor too low, but 
 only too far apart or too close together, it is hard to see 
 how any form of heterophoria could result; yet it is pos- 
 sible that a lateral error might be thus caused: an ex- 
 ophoria when the eyes are too far apart, an esophoria 
 when they are too close together. 
 
 However interesting may be the study of malforma- 
 tion of the orbits as causative of heterophoria, the treat- 
 ment, whether operative or otherwise, must be directed 
 to the muscles; since it would be utterly impossible, by 
 manipulation or operation, to convert a malformed orbit 
 into an ideal one. It stands to reason that prisms in po- 
 sitions of rest would be the ideal treatment of hetero- 
 phorias dependent on orbital malformation, there being 
 no muscle imbalance -per se.
 
 184 HETEROPHORIA. 
 
 To Stevens, of New York, is due much credit for his 
 pioneer work in the study of the ocular muscles. Be- 
 fore him, Graefe, in his study of insufficiency of the in- 
 terni, gave us a glimpse of that light which Stevens af- 
 terwards turned on more fully. By means of the pho- 
 rometer which he invented, he found it much easier to 
 investigate the recti muscles. He prosecuted this study 
 for many years, almost alone, and under fire of most se- 
 vere criticism. The information given us by Graefe 
 about insufficiency of the recti muscles is so incomplete, 
 as compared with the results of Stevens' labors, that 
 the latter may well be looked upon as the discoverer of 
 these conditions. The remarkable feature of Stevens' 
 work is that he so long ignored any study of the oblique 
 muscles, which have a duty to perform no less impor- 
 tant and exacting than that required of the recti. It 
 has already been shown that the obliques, under the in- 
 fluence of four conjugate innervations, must keep the 
 vertical axes of the eyes parallel with each other and 
 with the median plane of the head. As far back as 
 1891,* it was shown that the obliques were not always 
 capable of accomplishing their work with ease; and a 
 little later the method of exercising these muscles so as 
 to strengthen them, was introduced. t In 1893 it was 
 
 * See Archives of Ophthalmology, Vol. XX., No. 1. 
 t See Ophthalmic Record, Vol. II., No. 1.
 
 HETEROPHORIA. 185 
 
 shown that one danger attending an advancement of a 
 rectus muscle was that its new attachment might be so 
 displaced as to throw unbearable work on one or other of 
 the obliques.* Again, in 1893, following- a suggestion by 
 Swan M. Burnett that one or more of the recti might 
 naturally be so attached that the obliques would be in- 
 sufficient for the work demanded of them, an operation 
 on a rectus for strengthening an oblique muscle was 
 suggested. t It was not until 1895 or 1896 that Stevens 
 commenced his study of the obliques. Soon thereafter 
 he invented his clinoscope, the capabilities of which will 
 be fully shown in the discussion of c} T clophoria. His 
 work in this direction, as might have been expected, has 
 been helpful; but in his paper published in the January 
 (1899) number of the Archives of Ophthalmology, he 
 claims entirely too much credit for himself, as expressed 
 in these words: "Anomalous declinations not related to 
 disabilities of the muscles had, previous to my own con- 
 tributions, t obtained no recognition as a practical sub- 
 ject, if, indeed, it had been recognized at all, although it 
 is probably one of the most practical of the various im- 
 portant phases of the adjustments of the eyes." 
 
 In the matter of nomenclature Stevens gave us per- 
 fect terms, but not a complete list. There should be a 
 
 * See Ophthalmic Record, Vol. II., No. 9. 
 
 f See New Truths in Ophthalmology, 1893, pp. 40. 41. 
 
 t Not earlier than 1897.
 
 186 HETEROPHORIA. 
 
 name for every deviating tendency, but he gave none for 
 the downward tendency. In conformity with his nomen- 
 clature, the downward tendency of an eye has been named 
 cataphoria.* 
 
 Before Stevens began the study of the obliques, the 
 name cyclophoria was given to insufficiency of the ob- 
 liques, in conformity with the nomenclature applied to 
 the recti. To distinguish insufficiency of the superior 
 from insufficiency of the inferior obliques, the term plus 
 cyclophoria has been applied to the former and minus 
 cyclophoria to the latter. Maddox, for some reason, 
 preferred the terms plus torsion and minus torsion. 
 Still later Stevens gives to these conditions the names 
 plus declination and minus declination. Unless there is 
 a very special reason for doing otherwise, there should 
 be uniformity in the nomenclature applied to the ocular 
 muscles. As there appears no valid reason against this 
 uniformity, the term cyclophoria alone will be used in 
 the chapter on errors of the obliques. 
 
 Terms should be multiplied only when there is abso- 
 lute need for them. The terms anaphoria and katapho- 
 ria added to nomenclature by Stevens a while ago, and 
 applied, respectively, to an upward tendency of both eyes 
 and the reverse, a downward tendency of both eyes, 
 would tend only to confusion. These conditions exist, 
 
 * See New Truths in Ophthalmology, 1893, page 68.
 
 HETEROPHORIA. 187 
 
 but it is far better to say double kyperphoria and double 
 cataphoria. 
 
 Maddox did good work when he offered as substitutes 
 for sursum - duction and deorsum - duction the simpler 
 and easier terms super-duction and sub-duction. But 
 even these terms should be given only a single meaning. 
 They should be made to apply only to the power the 
 superior and inferior recti have for overcoming prisms 
 in the interest of binocular single vision. Likewise ad- 
 duction and abduction should be restricted in meaning so 
 as to apply only to the interni and externi in their ef- 
 forts to overcome the lateral displacing of images by 
 prisms. 
 
 The fact that it is better to have two terms, each 
 with a single meaning, than to have one term with two 
 very different applications, must be the author's apol- 
 ogy for adopting the following nomenclature for the 
 turning of the eyes in the four cardinal directions: Ab- 
 version, turning the eye out; adversion, turning the eye 
 in; superversion, turning the eye up; and sub-version, 
 turning the eye down. These terms are shorter and bet- 
 ter than outward rotation, inward rotation, upward rota- 
 tion, and downward rotation. 
 
 Duane deserves credit for his very careful study of 
 the ocular muscles in his little brochure, ' ' Motor Anom- 
 alies of the Eye; " but the terms hyperkinesis and hypo-
 
 188 HETEROPHORIA 
 
 kinesis, introduced by him, are not nearly so simple or 
 easy as the terms sthcnic and asthenia esophoria, sthenic 
 and asthenic exophoria, and sthenic and asthenic hyper- 
 phoria, and so on for all the phorias. The meaning", 
 however, is precisely the same. 
 
 The heterophoria that is purely innervational should 
 be designated by the prefix pseudo as pseudo-esophoria, 
 a condition depending* on the relationship existing- be- 
 tween accommodation and convergence, and not depend- 
 ent on any error inherent in the interni. 
 
 The following- is a list of the heterophorias: 
 
 (1) Esophoria, of which there are two varieties, viz.: 
 pseudo-esophoria and intrinsic esophoria. Of the intrin- 
 sic variety there are two kinds, sthenic and asthenic. 
 
 (2) Exophoria, pseudo and intrinsic. Of the intrinsic 
 variety there are two kinds, sthenic and asthenic. 
 
 (3) Hyperphoria and cataphoria, which are always in- 
 trinsic when the superior and inferior recti are the only 
 factors. These errors are either sthenic or asthenic. 
 There is now and then to be found a double hyperphoria 
 or a double cataphoria. 
 
 (4) Cyclophoria, plus and minus, both pseudo and in- 
 trinsic. The intrinsic variety may be either sthenic or 
 asthenic. 
 
 Two or three of these errors may be found combined 
 in many cases; but it is probably better not to have
 
 HETEROPHORIA. 189 
 
 compound names for such combinations of errors, as it is 
 important that the quantity of each error should be 
 noted. It would be difficult to indicate the quantity of 
 the two errors if the note was made hyper-esopohria or 
 hyper-cyclophoria. 
 
 TESTS. 
 
 There are some interesting tests for heterophoria that 
 can be made, in a rough way, independent of the pho- 
 rometer. One is the cover test. If there is an error of 
 any magnitude, it will manifest itself on covering one 
 eye while the patient is looking with both eyes at a test 
 object twenty feet distant. The covered eye will imme- 
 diately place itself in a state of equilibrium. When the 
 cover is removed, it will return to the position of har- 
 mony with the fellow eye. This readjustment can be 
 easily seen, in many cases, by the observer. The direc- 
 tion in which the eye moves when uncovered indicates 
 the kind, but not the quantity, of the heterophoria. A 
 patient of keen observation will be made conscious of 
 the disturbance. This is better done by covering and 
 uncovering the eyes alternately. In high degrees of 
 heterophoria a plane red glass placed before one eye 
 will suspend, to some extent, the effort at fusion, and 
 diplopia will result. A candle should now be the test 
 object. The position of the red blaze, the patient the
 
 190 HETEROPHORIA. 
 
 while looking- at the real candle, will indicate the kind 
 of error. Only the higher errors respond to the red- 
 glass test. 
 
 The test by means of the phorometer, preferably the 
 monocular instrument, for the reasons given in the 
 chapter on orthophoria, is the only one to be relied 
 upon. By it the kind of error is quickly determined 
 and the quantity is easily measured. In testing the 
 interni and externi, the 6 prism is placed, base up, 
 in the cell next to the eye. This will throw the false 
 image above on the retina and entirely outside the field 
 of binocular fusion, so that no attempt can be made at 
 fusion. The false object will be below the true, and 
 will bear that relationship to it determined by the exist- 
 ing imbalance. The handle of the rotary prisms must 
 be horizontal, the index at zero, and the instrument per- 
 fectly level. The true object must be the one looked at. 
 If the false object is toward the opposite side, there is 
 exophoria. Turning the controlling screw, the index is 
 moved toward the corresponding side until the patient 
 says the false object is directly under the true. The 
 number at which the index stands marks the quantity of 
 exophoria for that eye. 
 
 If the false object, instead of being on the opposite 
 side, shows itself on the corresponding side, the existing 
 error is esophoria. The controlling screw is now turned
 
 HETEROPHORIA. 191 
 
 so that the index moves toward the opposite side. The 
 revolution is stopped when the patient says the false ob- 
 ject is in a vertical line with the true one. The number 
 at which the index stands shows the quantity of esopho- 
 ria for that eye. 
 
 The test having been made for the distance, it should 
 now be repeated at the reading- point. The test object 
 now should be a white card in the center of which is a 
 black dot, and the card should be held directly in front 
 of the eyes. There should be no line drawn vertically 
 throug-h the dot, as advised by Graefe, for the reason 
 that this line would cross the area of binocular fusion, 
 and would thus lead to an attempt, on the part of the 
 eye, to correct its error. The kind of error is deter- 
 mined and its quantity is measured, as in the distant 
 test. The result, not always the same as found in the 
 distant test, should be noted. 
 
 The lateral error having- been thus found and meas- 
 ured, the 6 prism should be removed and the 10 prism, 
 base toward the nose, should be placed in the cell; the 
 handle of the rotary prism should be placed vertically, 
 and the index must be made to stand at zero. It is now 
 of vast importance that the instrument shall be perfect- 
 ly level; otherwise, a vertical error may be shown when 
 none exists. The instrument thus adjusted, any verti- 
 cal imbalance may be detected and measured. As in the
 
 192 HETEROPHORIA. 
 
 test for lateral errors, the true object must be the one 
 fixed. The false image will be thrown outside the area 
 of binocular fusion, toward the nose, while the false ob- 
 ject will appear on that side of the true, corresponding 
 to the eye under test. If the false object is below the 
 horizontal line passing" through the true, there is hyper- 
 phoria of that eye, the quantity of which is determined 
 by revolving the controlling- screw so that the index 
 shall move upward. The number at which the index 
 stands when the patient says the two objects are level 
 shows the quantity of the error. 
 
 If in the test the false object is above the horizontal 
 line passing through the true, there is cataphoria of 
 that eye. The screw is now turned so that the index 
 shall move downward. The number at which the index 
 stands, when the patient says the objects are level, 
 shows the quantity of the cataphoria. The test for ver- 
 tical imbalance need not be repeated at the near point. 
 
 The one eye having been tested thus for imbalance of 
 all the recti, the instrument should now be turned into 
 position before the fellow eye, that the lateral and ver- 
 tical imbalances it may have may be found and measured. 
 Usually, if there is esophoria of one eye, the other will 
 also show esophoria; the amount in the one is about 
 equal to that in the other. Occasionally, however, there 
 will be a difference of 1 or even more. The same may
 
 HETEROPHORIA. 193 
 
 be said of exophoria. When there is hyperphoria of one 
 eye, the other is usually cataphoric, and the one error is 
 about equal to the other. 
 
 A double hyperphoria and a double cataphoria cannot 
 so easily be shown, in the imbalance test, by the phorom- 
 eter. The proof test, which is by means of the Mad- 
 dox double prism, quickly shows either of these errors 
 when they exist. The base-line of these prisms (4) 
 should be held horizontally before first one eye and then 
 the other, having- each eye look at the distant test ob- 
 ject, first through the upper prism and then through 
 the lower, observing- that position which throws the 
 double objects closer tog-ether. If they are closer for 
 both eyes when the false object is seen through the 
 upper prism, there is double hyperphoria; but if the}" 
 are closer for both eyes when the false object is seen 
 through the lower prism, there is double cataphoria. 
 
 It can be readily understood that, if there is hyper- 
 phoria of one eye and cataphoria of the other, the two 
 objects will be closer together when the false one is 
 seen, by the hyperphoric eye, through the upper prism, 
 and by the cataphoric eye when seen through the lower 
 prism. Hence the reason for calling this use of the 
 double prism the proof test of hyperphoria and cata- 
 phoria. 
 
 The next step in the testing is to determine the ability
 
 194 HETEROPHORIA. 
 
 of the obliques to parallel the vertical axes of the eyes 
 with the median plane of the head. This can be done 
 rudely in any one of several ways : First, by means of 
 the Maddox double prism, the object looked at being- a 
 horizontal line on a blackboard, twenty feet distant, or 
 a horizontal line on a card held at the reading- distance; 
 preferably, both. The base-line of the double prism 
 (4) should be horizontal and so held before one eye as to 
 double the test-line. The two lines seen by this eye 
 must be parallel. The third line, seen by the other eye, 
 should be between the other two and parallel with them. 
 A dipping- of the true line toward the opposite side 
 would show a plus cyclophoria, while a dipping- toward 
 the corresponding side would show a minus cyclophoria. 
 The quantity of the error thus shown, however, cannot 
 be measured. 
 
 The same test may be made by means of a sing-le 
 prism of 4, base up or down, before the eye; but even 
 still more easily it may be made by the revolving- prism 
 in position for taking- the sub-ducting and superducting 
 power. The rotation, of course, must be carried beyond 
 the possibility of fusion. The false line is seen by the 
 eye before which the single prism is held or the rotary 
 prism has been placed, while the true line is seen by the 
 other eye. The refracting angle of the prism points in 
 the direction of the false line. When this line is seen
 
 HETEROPHORIA. 195 
 
 below, by the right eye, and the ends of the two toward 
 the right converge, there is plus cyclophoria; if they 
 diverge toward the right, then there is minus cyclopho- 
 ria. There is no method of measuring the error thus 
 found. In revolving the rotary prism or in turning the 
 single prism so as to make it possible for fusion to take 
 place, it is interesting for the patient to watch the man- 
 ner of fusing; if there is cyclophoria, the two lines will 
 come together at one end first and then quickly fuse 
 throughout. 
 
 The Stevens clinoscope will detect and measure any 
 existing cyclophoria; but the best instrument for detect- 
 ing cyclophoria and measuring the amount of the error 
 is the cyclo-phorometer. It is much cheaper than the 
 clinoscope, and, better still, it is simpler in construction 
 and much more easily manipulated. The 5 prism, base 
 up, behind one rod gives the second streak of light; the 
 thumbscrew makes it easy to place the one streak di- 
 rectly under the other ends even. If the axes of the 
 rods are at zero and the two streaks are not parallel, 
 cyclophoria is positively shown; if the lower streak is 
 seen by the left eye and the two streaks converge at the 
 left, there is plus cyclophoria; but if they diverge at the 
 left, there is minus cyclophoria. The extent of the 
 turning of the rod on the one side or the other, neces- 
 sary for paralleling the streaks, measures the quantity
 
 196 HETEROPHORIA. 
 
 of the cyclophoria. It is not necessary, with the cyclo- 
 phorometer, to keep in mind the fact that the lower 
 streak is seen by the eye that has the displacing- prism 
 before it, for the position of the axis of the rod at the 
 time the streaks are made parallel names the error as 
 well as measures its quantity: when the axes must be 
 moved into the nasal arc, there is plus cyclophoria; into 
 the temporal arc, there is minus cyclophoria. 
 
 The spirit level of the cyclo-phorometer enables one to 
 determine if the cyclophoria is monocular or binocular. 
 When the two streaks of light converge at one end or 
 the other, if the error is binocular, neither of the lines 
 will be horizontal. If one is horizontal while the other 
 is oblique, the error is monocular; if both lines are in- 
 clined in the same direction, it shows plus cyclophoria in 
 one eye and minus cyclophoria in the other. 
 
 Having- followed out the tests already described the 
 tests for imbalance one knows the kind of error or er- 
 rors in the individual case, but remains ignorant of the 
 character of these errors. The duction and version tests 
 alone can reveal the fact that an error is sthenic or as- 
 thenic, just as the study of the refractive errors alone re- 
 veals whether or not a given heterophoria is pseudo or 
 intrinsic. 
 
 The duction test is to determine the power the mus- 
 cles have for overcoming the displacing of images by
 
 HETEROPHORIA. 197 
 
 means of prisms. To this meaning- the word ditction, 
 with its several prefixes, should be restricted. The 
 method of determining duction power by means of the 
 monocular phorometer has already been set forth in 
 Chapter II. It can be accomplished by means of the 
 prisms in the refraction case, but not so quickly nor 
 so accurately. Duction is wholly an involuntary act, 
 and it is accomplished through the guiding sensation, in 
 obedience to the law of corresponding- retinal points; but 
 it has its limitations. Abduction is the power of an 
 externus to fuse with the image on the macula of the 
 fellow eye, an image that has been displaced to the 
 nasal side of the macula of its own eye. Less than 6 
 of such power is subnormal; more than 8 is supernor- 
 mal. Adduction is the power of an internus to move 
 the macula outward until it shall stand under the image 
 that has been displaced temporally, so that it may be 
 fused with the image on the macula in the fellow eye. 
 It is certainly subnormal if less than 18 to 25. The 
 adduction stimulus is much greater than any other, 
 and is much more variable. Its variableness makes it 
 less reliable than any other duction; but, neverthe- 
 less, it must be known in dealing intelligently with 
 esophoria. 
 
 Superduction is the power the superior rectus has for 
 fusing an image displaced below the macula, with the
 
 198 HETEROPHORIA. 
 
 image on the macula in the fellow eye. Less than 2 is 
 subnormal; more than 3 is supernormal. 
 
 Sub-duction is the power the inferior rectus has for 
 fusing- an image displaced above its macula, with the 
 image on the macula in the fellow eye. Less than 2 
 is subnormal; more than 3 is supernormal. 
 
 In all duction tests it is better that the image should 
 be slowly moved away from the point occupied by the 
 macula, when the eye is in the primary position, toward 
 the boundary line of the field of binocular fusion, which 
 should be considered as immovably fixed. So long as 
 this image is within this field there is binocular single 
 vision, for the macula moves with the moving image as 
 far as possible; but the moment it passes the border line 
 there results diplopia. The index of the rotary prism 
 marks the duction power of the muscle concerned. It 
 should be noted. The field of binocular fusion is larger 
 if the muscles are stronger, smaller if the muscles 
 are weaker. Its size can be changed both by exer- 
 cise and by operations. If it is too small, it may be in- 
 creased by exercise and by shortening and advancement 
 operations; if too large, it can be reduced only by tenoto- 
 mies, which should always be partial. 
 
 Cycloduction, which is involuntary, can be taken only 
 by the clinoscope or the cyclo-phorometer. With the for- 
 mer instrument the line as seen by one eye is turned by
 
 HETEROPHORIA. 199 
 
 means of the proper screw up to the point of doubling-. 
 The index marks the torsioning power of the oblique 
 involved. With the cyclo-phorometer the axis of one 
 rod is moved from zero toward the nose to test the 
 torsioning power of the inferior oblique, and toward 
 the temple for determining the power of the superior 
 oblique. An oblique should have a fusing power of from 
 7 to 10. The inferior oblique has a little greater fusing 
 power than the superior oblique. 
 
 In determining the several ductions the tests should 
 be monocular, except in cycloduction. 
 
 In any given heterophoric condition the duction test, 
 aided by the version test, determines whether the error 
 is sthenic or asthenic, and, therefore, the kind of opera- 
 tion, if any, that should be performed. No muscle whose 
 duction power is normal or subnormal should be weak- 
 ened by a partial tenotomy; but the imbalance should 
 be cured either by a shortening or an advancement of its 
 still weaker antagonist. 
 
 No examination of the recti muscles is complete with- 
 out the taking of the verting power of every one. As 
 shown in Chapter II., this can be rudely done by simply 
 watching the eyes while the patient looks as far as pos- 
 sible in the four cardinal directions. The objection to 
 this test is that there is no accuracy in it, and yet it is 
 better than no test. The reason for introducing the
 
 200 HETEROPHORIA. 
 
 terms adversion, abversion, superversion, and sub-ver~ 
 sion has been given already, and the extent of each, 
 considered as normal, has been shown in the same con- 
 nection. Of all instruments for making- the version 
 tests, the Stevens tropometer stands first, because of 
 simplicity, accuracy, and speed. The only part of the 
 instrument that should be dispensed with is the head 
 rest, and this for two reasons: First, it interferes with 
 the manipulation of the upper lid, when the sub-version 
 is being 1 taken, for now the lid must be held up or it 
 will entirely obscure the cornea; second, it obscures too 
 soon the small electric light or other test object which 
 the patient should fix as the superversion is being- taken. 
 The mouthpiece is necessary in order to insure that the 
 patient's head shall not turn while the verting power of 
 the eye is being taken. 
 
 A fairly good substitute for the tropometer is the per- 
 imeter, if properly used. There should be some means 
 for preventing the movement of the head, and nothing 
 could do this better than a mouthpiece, such as consti- 
 tutes a part of the tropometer. The eye under test 
 should be in the center of the perimeter curve. As with 
 the tropometer, the rotations should be taken in the 
 four cardinal directions only. With the arms of the 
 perimeter in the horizontal plane, abversion and adver- 
 sion can be easily taken; and if proper care is observed,
 
 HETEROPHORIA. 201 
 
 the result will be practically accurate. The small elec- 
 tric light, shaded toward the observer, should be placed 
 first directly in front of the eye while in the primary 
 position. From this position, the light, while being 
 kept in contact with the perimeter arm, should be moved 
 in the temporal arc the arc for abversion slowly, the 
 patient fixing the moving light, while the operator fixes 
 its image reflected from the center of the cornea, moving 
 his own head harmoniously with the moving light. The 
 patient should speak when he finds himself no longer 
 able to fix the light. At the same moment the observer 
 can see that the image is no longer reflected from the 
 center of the cornea. Thus the patient serves as a check 
 to the operator, while the operator also serves as a check 
 to the patient. When 5 beyond the point of fixation, 
 the small light becomes so blurred that the patient can 
 easily detect the change; hence, if the patient is closely 
 observant, there is small room for error. The operator 
 cannot so easily detect an error of 5, as shown by the 
 reflected image. For these reasons the subjective part 
 of the test is more reliable than the objective. The po- 
 sition of the light on the arc, when the patient can no 
 longer fix it, and when the reflected image begins to leave 
 the center of the cornea, indicates the degree of abversion. 
 With the light moving along the nasal arc, adversion 
 is taken in like manner, and its extent should be noted.
 
 202 HETEROPHORIA. 
 
 With the arms of the perimeter rotated into the ver- 
 tical plane, superversion and sub-version are taken 
 by moving* the light along the upper and lower arcs, 
 respectively, and their extent is noted. In taking- 
 sub-version, the reflected image cannot be so easily 
 watched, even when the upper lid is held out of the 
 way. Here the subjective part of the test must be re- 
 lied upon. 
 
 One eye having been thus tested, in the four cardinal 
 directions, the other eye should be properly placed and 
 the various duction powers should be determined and 
 noted. 
 
 Unlike the duction power, which is involuntary, ver- 
 sion power is a thing of volition. Neither one should be 
 depended on to the exclusion of the other. The result 
 of thess two tests (duction and version) should be com- 
 pounded, ir the surgeon would be safely guided in his 
 operative work, or even in the non-operative treatment 
 of heterophoria. 
 
 Cycloversion has no existence, since voluntary rota- 
 tion around the visual axis is impossible. 
 
 No muscle whose ducting or verting power is nor- 
 mal or subnormal should be weakened by a partial 
 tenotomy. No muscle should be increased in strength 
 by an advancement or by a shortening when the duction 
 and version are not subnormal.
 
 HETEROPHORIA. 203 
 
 SYMPTOMS OP HETEROPHORIA. 
 
 That there are cases of heterophoria without symp- 
 toms must be conceded, but such cases are not often 
 seen by the ophthalmic surgeon. It is a symptom, or 
 symptoms, of eye-strain that drives the patient to the 
 doctor. It may be that the symptoms, in a given case, 
 are dependent in part, if not wholly, on errors of refrac- 
 tion; but it is a serious mistake to suppose, as some do, 
 that eye-strain is always and only associated with the 
 ciliary muscle. The ciliary muscle is only one of eight 
 muscles connected with each eye; and each of the seven 
 other muscles, when called on to do abnormal work, is 
 just as capable of developing S3 r mptoms. People who 
 have no symptoms, and yet have heterophoria, are pos- 
 sessed of a stable nervous system and are physically 
 strong. The physically weak and the nervously unstable 
 must be sufferers from eye-strain, of whatever character. 
 The nervous centers of the one may be compared with 
 the steady leaves of the oak, which are shaken only by 
 a wind; while the nervous centers of the other may be 
 compared to the leaves of the aspen tree, which quiver 
 in the slightest zephyr. Or, again, the easily-disturbed 
 nerve centers may be compared to the leaves of the trail- 
 ing little vine seen in the old turned-out field, all the 
 leaves of which fold themselves up, if but one leaf be 
 touched by a human finger.
 
 204 HETEROPHORIA. 
 
 The strong, healthy person, with a stable nervous 
 system, may never have had a symptom resulting- from 
 muscle or focal errors that have always existed. Let 
 this individual have an attack of typhoid fever, measles, 
 or other depressing disease, or let her pass through a 
 pregnancy and confinement; now, on attempting too soon 
 the use of her eyes in near work, she begins to be a suf- 
 ferer. The suffering becomes a habit, and she gets no 
 permanent relief until the focal or muscle error has been 
 corrected. 
 
 A sudden shock to a nervous system that has been 
 strong, brings about a change that ever after makes the 
 patient feel the effects of errors whose existence before 
 made no impression. 
 
 Growing children, especially those that are delicate, 
 when too hard pressed in their school work, almost in- 
 variably present some one of the many symptoms of 
 strain. More women than men feel the effects of muscle 
 and refractive errors, mainly because of the fact that 
 the former are forced to spend a greater number of 
 hours every day in near work, than the latter. Book- 
 keepers, or men who are engaged in other continuous 
 near work, are often forced to seek aids to vision. 
 
 HEADACHE. The most common of all the symptoms 
 caused by heterophoria is headache. The aching may 
 be in the temple, brow, at the top of the head, over the
 
 HETEROPHORIA. 205 
 
 parietal region, or in the back of the head. In some 
 cases the suffering is in the back of the neck. The pain 
 may be on both sides of the head, but often it is unilat- 
 eral. It is periodic in character, and usually comes on as 
 the result of prolonged, hard near work. The headache 
 which one has on awaking in the morning or, more prop- 
 erly speaking, the headache which awakens the patient- 
 is usually due to disturbances in the sinuses, or cells, that 
 open into the nasal passages, brought about by mouth- 
 breathing, the mouth-breathing depending, of course, on 
 nasal stenosis. Rest in sleep usually relieves the head- 
 ache of heterophoria and of refractive errors. Head- 
 aches due to eye-strain, that come on unassociated with 
 near work, are usually heterophoric. and not refractive. 
 The headache that one has on bright days and when 
 amid bright surroundings, as the white buildings and 
 white walks of an exposition, is often due to overwork 
 of a weak sphincter of the iris, which is compelled to 
 keep the pupil small that the retina may be protected 
 from the glare. The headache of eye-strain is usually 
 of the nervous variety that is, unassociated with nausea 
 and vomiting. However, genuine sick headache pure 
 migraine is sometimes caused by both refractive and 
 muscle errors. The migraine which disappears as pres- 
 byopia comes on, proves itself clearly dependent on an 
 error of refraction; and the same may be said of other
 
 206 HETEROPHORIA. 
 
 headaches that disappear as one grows old. Indeed, 
 this coincidence should have attracted attention to focal 
 errors as causative of headache long- before any thing- 
 was known on this subject. 
 
 Not so with headaches that are dependent on hetero- 
 phoria, for strain of heterophoria once means strain of 
 heterophoria throughout life, unless relieved by treat- 
 ment, surg-ical or otherwise. 
 
 VERTIGO AND NAUSEA. The kind of muscle error 
 that is the most common cause of vertigo and nausea is 
 insufficiency of the obliques to prevent cyclophoria. The 
 correctness of this teaching is emphasized in cases of 
 paresis of an oblique or of a superior or an inferior 
 rectus, either one of which would be attended by a tor- 
 sioning of the eyes. The earliest and most marked 
 symptoms presented by these cases are vertigo and nau- 
 sea, which continue so long as the patient tries to use 
 both eyes. Excluding the vision of the affected eye, 
 the symptoms vanish. When cyclophoria is the cause, 
 these symptoms will be periodic, and will present them- 
 selves only when the weak obliques are no longer able 
 to maintain perfectly the parallelism between the verti- 
 cal axes of the eyes and the median plane of the head. 
 Overwork, worry, shock, ill health, sleeplessness all 
 tend to make these symptoms worse. 
 
 CONFUSION OF THOUGHT. Any one of the hetero-
 
 HETEROPHORIA. 207 
 
 phorias, whether associated with errors of refraction or 
 not, necessarily interferes with that clearness of com- 
 prehension one would have if his eyes were free from all 
 errors. Reading becomes a burden to heterophorics for 
 the reason that their thought centers work confusedly, 
 through sympathy with the motor centers that are over- 
 taxed in efforts at harmonizing the ocular muscles. How 
 far confusion of thought may be carried toward insan- 
 ity, because of continued existence of a muscle error, re- 
 mains to be shown. Cases of undoubted insanity have 
 been cured by operations on the ocular muscles. It has 
 been a matter of common observation that school chil- 
 dren who were counted as dull and incapable, not able 
 to comprehend clearly either books or teachers, have 
 been transformed into apt scholars by ocular treatment. 
 In the race for an education, a child who has any form 
 of heterophoria, or an error of refraction, is consider- 
 ably handicapped. 
 
 CHOREA. A spasmodic condition of the muscles of 
 the face a local chorea in children with unstable nerve 
 centers, is often caused by eye-strain, as is shown by 
 the quick relief that follows a correction of the condi- 
 tion causing the strain. The cause continuing to act, 
 the transformation of a local into a more general chorea 
 is often effected. It cannot be denied that chorea, some- 
 times in a very aggravated form, is caused by visual
 
 208 HETEROPHORIA. 
 
 errors; but it cannot be asserted that all choreas are 
 caused by ocular defects. It is safe and proper to say 
 that every child suffering- with chorea should be exam- 
 ined by an ophthalmic surgeon with the view of having 
 any existing- ocular error adjusted. It is generally con- 
 sidered that, whatever may be the cause, chorea is a re- 
 flex neurosis, and that finding- and removing the cause 
 brings a speedy cure. Medical treatment, without ref- 
 erence to cause, is at best slow. 
 
 EPILEPSY. There can be no longer any room for 
 doubt that, in many cases, epilepsy, whether in the se- 
 vere or in the light form, is often reflex in origin. If 
 wax impacted in the ear can be the cause of epilepsy, is 
 it unreasonable to suppose that hyperopia may cause 
 this motor-psychic disturbance? But it is no longer a 
 matter of supposition; for, beyond all question, man} 7 
 cases of epilepsy have been cured by the convex lenses 
 that corrected the focal error. If a phimosis can excite 
 epileptic seizures, is it any wonder that the excessive 
 tension of muscles, in cases of heterophoria, may now and 
 then be the cause of these attacks? In fact, scores of 
 epileptics have been cured by operations for the estab- 
 lishment of normal equilibrium between the ocular mus- 
 cles. Hundreds of other cases would have been cured, 
 before now, by partial tenotomies and advancements, if 
 the principles underlying heterophoria had been properly
 
 HETEROPHORIA. 209 
 
 understood. The proportion of cases of epilepsy caused 
 by heterophoria may not be large no one knows but 
 every case of epilepsy should be subjected to a most 
 careful examination of the visual apparatus, by a compe- 
 tent investigator; and all focal errors found should be 
 corrected and muscle imbalance should not be ig-nored. 
 
 o 
 
 That Stevens, Ranney, and others have spoken their 
 convictions, based on observation and practical experi- 
 ence, on this subject, the author believes. He himself 
 has had and has cured some cases, while failing on oth- 
 ers. In the light of no distant future, the statements 
 that have been made by Stevens and Ranney will not 
 appear to be so extravagant as some now judge them. 
 Of all the apparently extravagant statements, this one 
 is taken from "Ranney on Nervous Diseases," page 481: 
 "One of the most remarkable cases that ever came un- 
 der my observation was that of a combination of chorea, 
 epilepsy, and idiocy, in a girl about eleven years of age, 
 who completely recovered her health, strength, and men- 
 tal faculties, when a refractive error in her eyes was 
 corrected by glasses and a serious combination of muscu- 
 lar defects in the orbit was adjusted by tenotomy. This 
 case was one that I saw some three years ago, in con- 
 nection with the practice of Dr. Stevens. At the first 
 examinition, the child could not walk without being sup- 
 ported on both sides, drooled constantly, talked unintel-
 
 210 HETEROPHORIA. 
 
 ligibly, answered questions with apparently little con- 
 ception of their import, could hardly sit unsupported in 
 a chair on account of chorea, had epileptic seizures re- 
 peatedly during the day and night, and presented a piti- 
 able and apparently hopeless aspect. I saw her about a 
 year after the operations were performed, at the request 
 of Dr. Stevens. I found her free from chorea and epi- 
 lepsy, able to run and skip a rope unaided, rosy cheeked, 
 and in full possession of her mental faculties." Who 
 can wonder that Ranney, having observed this remarka- 
 ble case, has become a firm believer in the reflex charac- 
 ter of functional neurotic troubles? 
 
 It is not remarkable that the refractive error was de- 
 tected and measured in this case, but it must have been 
 exceedingly difficult to arrive at a correct understanding 
 of the complicating heterophoria. The phenomenal re- 
 sults that followed but emphasize the importance of the 
 early removal of the cause, before molecular changes in 
 both the motor and psychic areas of the brain shall have 
 become unalterably fixed. 
 
 That epilepsy should be caused by abnormal tension 
 of the delicate ocular muscles is certainly no more won- 
 derful than were the results of some experiments made 
 by Drs. Dercum and Parker, of the University of Penn- 
 sylvania, as published in the Journal of Nervous and 
 Mental Diseases, in 1884. Some of the subjects of ex-
 
 HETEROPHORIA. 21 1 
 
 perimentation were placed by a table, which they bare- 
 ly touched with the tips of the fingers of one or both 
 hands. "The fingers were not allowed to rest on the 
 table, but were maintained, by constant muscular effort, 
 barely in contact with it." Some of these subjects, in 
 from a few minutes to an hour, first became tremulous 
 and then violently convulsed, falling to the ground. 
 The oftener the experiments were repeated on the sus- 
 ceptible subjects, the more easily were the convulsions 
 induced. Abnormal muscular tension, in persons with 
 unstable nerve-centers, caused these convulsions, which 
 must have been very much like epileptic attacks. Those 
 experimented on who had stable nerve-centers did not 
 show violent symptoms, but, judging from that part of 
 the report published by Ranney, page 463, lighter symp- 
 toms must have shown themselves, even in these cases. 
 Other experiments showed that severe, long-continued 
 thought, fixed on one thing, excited direct trouble in the 
 psychic centers, and, sympathetically, disturbed the mo- 
 tor centers, resulting in convulsions. 
 
 If the result of the experiments made by Dercum and 
 Parker had been more generally known, there would be 
 fewer to doubt that severe functional neuroses may be 
 caused by abnormal muscle tension in cases of hetero- 
 phoria and errors of refraction. No other muscles of 
 the body have such a wonderful nervous endowment as
 
 212 HETEROPHORIA. 
 
 the muscles (extrinsic and intrinsic) of the eye. Each 
 of the twelve external muscles and each of the four mus- 
 cles inside the two eyes has its individual nerve-center, 
 and, besides these, there must be at least nine or ten con- 
 jugate nerve-centers. Only the eye muscles must work 
 with mathematical precision so as to have sharp images 
 and binocular single vision. Any necessity for overaction 
 abnormal tension on the part of any ocular muscle 
 should be counteracted, if the delicate nervous system 
 is to be freed from a prolific source of disturbance that 
 may be either psychic, motor, sensory, or visceral. 
 
 The emphasis given above is not intended to impress 
 the reader with the idea that the orbit is Pandora's box, 
 out of which come all functional ailments. Undue exci- 
 tation of the brain-center controlling any organ of the 
 body can reflexively disturb other centers near by and 
 remote centers psychic, centers motor, centers sensory, 
 centers controlling the viscera. It would be well for 
 humanity, if all other organs and parts of the body 
 could be so thoroughly and scientifically investigated as 
 can the eyes. 
 
 CATALEPSY. If clonic muscular contractions, asso- 
 ciated with unconsciousness, can be caused by errors of 
 refraction and heterophoria, the same errors may cause 
 tonic muscular contractions rigidity with mental ob- 
 livion. The cause should be sought and, when found,
 
 HETEROPHORIA. 213 
 
 removed. Occasionally excessive tension of the ocular 
 muscles is causative of catalepsy. 
 
 HYSTERIA. This disease is one of the terrible func- 
 tional neuroses, and, like the others already considered, 
 may depend on focal errors and imbalance of the ocular 
 muscles. The character of the hysteria in a given case 
 does not point to any definite cause. Whether the man- 
 ifestations are sensory, motor, psychic, visceral, or vaso- 
 motor, a cure can be effected, if the cause can be found; 
 hence the importance of a most thorough investigation 
 of these unfortunates. In these cases no investigation 
 is complete that leaves out the visual apparatus. Er- 
 rors of focus should be corrected, imbalanced muscles 
 sh'ould be adjusted, with the fair prospect that at least 
 some will be cured. 
 
 NEURASTHENIA. This condition of weakness of the 
 neuron elements is the very opposite of those just con- 
 sidered, and yet it may have the same cause. If errors 
 of refraction and heterophoric conditions do not cause 
 neurasthenia in certain cases, it must be conceded that 
 they can perpetuate it in all cases. The results of the 
 correction of errors of refraction, and the regulation of 
 the tension of the recti muscles by tenotomies and short- 
 enings or advancements, have been so marvelous as to 
 justify the declaration that every subject of neuras- 
 thenia should have the visual apparatus investigated.
 
 214 HETEROPHORIA. 
 
 The correction of any existing- errors, to say the least, 
 would tend to hasten a cure, whatever may have been 
 the chief cause. Many cases have been speedily cured by 
 these means alone, in which internal medication, electric- 
 ity, and rest had been tried in vain. In any case in which 
 but little nerve force is generated, the undue expendi- 
 ture of that little should be prevented, thus giving med- 
 icine, food, and rest a better chance to have full regen- 
 erating power restored to the weak brain cells. In no 
 case should the correction of visual errors be wholly re- 
 lied on, but other organs and parts of the body should 
 be investigated, and all local diseases found should be 
 treated such as those of the stomach, the rectum, the 
 bladder, the ovaries, and the womb; for these may have 
 been the chief cause of the prostration, the visual errors 
 having served only to aggravate and perpetuate the neu- 
 rasthenia. 
 
 Through the nervous system, errors of refraction 
 and heterophoria may cause functional derangement of 
 the thoracic, abdominal, and pelvic viscera. Indiges- 
 tion, torpidity of the liver, and constipation have dis- 
 appeared, in some cases, as a result of the correction 
 of visual errors. A case of stammering was unexpect- 
 edly cured by the wearing of prisms prescribed, by a 
 Denver oculist, for an exophoria. The Doctor was so 
 astonished at the result that he decided to remove the
 
 KETEROPHORIA. 21 5 
 
 prisms, so that he migLL determine whether the cure 
 was a coincidence or a consequence, impost hoc or a prop- 
 ter hoc. The stammering- retu. - A, and was again re- 
 lieved by the wearing- of the prisms. Disturbed respira- 
 tion and an irritable heart have been quieted by lenses 
 and by operations on the eye muscles. Dr. Hale, of Nash- 
 ville, once had a little patient suffering from a refractive 
 error, whose bladder was so irritable that micturition in 
 sleep was almost a nightly occurrence; but at the time 
 of the examination of the eyes nothing was told the Doc- 
 tor about the irritable bladder. Later the parents re- 
 ported that the glasses had done more than was contem- 
 plated, in that the irritability of the bladder had van- 
 ished. The Doctor's astonishment was great. He de- 
 cided to settle the question of relationship between the 
 wearing of the glasses and the disappearance of the 
 irritability of the bladder, by withholding the glasses. 
 Almost immediately the bladder trouble returned, to dis- 
 appear again, and permanently, when the spectacles were 
 restored to the child. 
 
 It has been a matter of common observation that dis- 
 menorrhoea in girls and young women has been wholly or 
 in part relieved by a correction of errors of the visual 
 apparatus. These things are marvelous and can be ex- 
 plained only by assuming that these remote organs have 
 sympathized with the eyes in their efforts to correct
 
 216 HETEROPHORIA. 
 
 errors of adjustment and errors of focus. To claim that 
 all cases like those referred to above have the exciting- 
 cause in the eyes would be absurd; but when the cause is 
 so simple, how easy and rapid the cure! So far the 
 symptoms considered have been in parts more or less re- 
 mote from the eyes. In many cases the only symptoms 
 of eye-strain are in the eyes themselves or in their ap- 
 pendages. 
 
 ASTHENOPIA. This is a weakness of the eyes that 
 may be shown in a sense of fatigue associated with more 
 or less pain in the eyes, tog-ether with an excessive secre- 
 tion of tears, whenever an attempt is made to do near 
 work. Letters, while being- looked at, may fade away 
 for a moment, because of relaxation of weak ciliary mus- 
 cles; the pag-e may become blurred or mixed from side to 
 side, because the imbalance of the lateral recti muscles 
 momentarily increases the angle of convergence, as in 
 esophoria, or by the temporary lessening- of this ang-le, 
 as in exophoria; or the blurring- may be from top to 
 bottom, caused by the sudden elevation of one visual axis 
 above the other, as in hyperphoria. 
 
 The conjunctival vessels often become cong-ested be- 
 cause of visual errors. Likewise the lid marg-ins become 
 eng-org-ed with blood, scales forming among the roots of 
 the lashes, and the nutrition of the lashes themselves 
 suffering. In high degrees of muscle imbalance, objects
 
 HETEROPHORIA. 217 
 
 in the distance sometimes become double momentarily. 
 Not only may the external structures of the eyes be- 
 come congested because of strain to overcome errors, 
 but the structures within the eyes also may become 
 congested. Functional disturbances without and with- 
 in the eye, if long continued and much aggravated, 
 may lead to organic changes and even result in the 
 development of some of those diseases that bring blind- 
 ness. 
 
 One of the most troublesome asthenopias presents 
 itself when a patient is exposed to bright light, either 
 natural or artificial, and is caused by a weak sphincter 
 of the iris, which must keep the pupil small so as to 
 protect the delicate retina. 
 
 TREATMENT OF HETEROPHORIA. 
 
 The treatment of heterophoria must be determined by 
 the kind and quantity of the error. Small 'errors of the 
 recti may be treated by prisms in positions of rest for the 
 too weak muscles. The base of the prism must always 
 point toward the muscle to be favored. In esophoria the 
 base would be out, and prisms of equal strength should 
 be placed before the two eyes.* If the error is small 
 and the interni are properly attached, or even if they are 
 attached in greater part above the horizontal plane, in 
 
 * Exceptions will be shown in the chapter on Esophoria
 
 218 HETEROPHORIA. 
 
 most cases they can be comfortably worn. If they do 
 not give comfort, it becomes evident that the interni are 
 attached too low, and that their forced action develops a 
 plus cyclophoria, which becomes a source of discomfort. 
 In exophoria the prisms should be of equal strength be- 
 fore the two eyes,* and their bases should be in. If the 
 error is small and the externi are correct!}" attached, the 
 rest prisms would certainly bring comfort, at least for a 
 time. If the externi are attached too low, the prisms, 
 as a rule, can be comfortably worn; but if they are at- 
 tached too high, the use of the prisms cannot bring com- 
 fort because of the plus cyclophoria developed. 
 
 In hyperphoria the correcting prism, in nearly all 
 cases, should be worn only in front of the hyperphoric 
 eye, the base being placed down, for the reason that the 
 action of the superior rectus for overcoming the prism 
 develops a minus cyclophoria, which, to a certain extent, 
 neutralizes the plus cyclophoria which nearly always ex- 
 ists. In the rare cases in which there is minus cyclopho- 
 ria, the rest prism should be placed, base up, before the 
 cataphoric eye, that a neutralizing plus cyclophoria may 
 be caused. Only when there is perfect balance of the 
 obliques would it be correct practice to divide the pris- 
 matic effect between the two eyes, base down before the 
 hyperphoric eye, base up before the cataphoric eye. The 
 
 * Exceptions will be shown in the chapter on Esophoria.
 
 HETEROPHORIA. 219 
 
 per cent of cases accepting- kindly the rest prism, base 
 down before the hyperphoric eye, is very large ; while 
 only a very small per cent of such cases would be im- 
 proved by placing- the rest prism, base up, before the 
 cataphoric eye. A full prismatic correction of a hyper- 
 phoria should be given only when there is a marked com- 
 plicating- cyclophoria. 
 
 In uncomplicated cyclophoria, the patient may be ben- 
 efited by wearing a weak pair of cylinders, axes in the 
 arcs of distortion for the stronger muscles, even when 
 there is no astigmatism ; or, if there is astigmatism, by 
 displacing the axes of the correcting cylinders in the 
 arcs of distortion for the stronger pair of obliques. As 
 will be shown in the chapter on cyclophoria, the arc of 
 distortion by plus cylinders for the superior oblique of the 
 right eye has its center always at 45, and for the left eye 
 it has it at 135; while the center of the arc of distortion 
 by plus cylinders for the inferior oblique of the right eye 
 is always at 135, and for the left eye it is at 45. The 
 reverse is true of minus cylinders. These arcs are equal 
 in extent only when the astigmatism is vertical or hori- 
 zontal, but their sum is always 180. The extent of the 
 displacement of the axes of the cylinders, requisite for 
 the relief sought, depends on the quantity of cyclo- 
 phoria and the strength of the astigmatic correction a 
 weak cylinder, more displacement; a strong cylinder,
 
 220 HETEROPHORIA. 
 
 less displacement. If there is no complicating hyper- 
 phoria, the displacing" effect of the cylinders should be 
 divided equally before the two eyes; but if there is a 
 hyperphoria complicating a plus cyclophoria, only the 
 cylinder before the cataphoric eye should be displaced; 
 while the reverse would be true when a hyperphoria 
 complicates a minus cyclophoria. It is clear that the 
 enforced action of an inferior oblique would elevate the 
 corresponding eye, to that extent neutralizing or correct- 
 ing the cataphoria; while the enforced action of a supe- 
 rior oblique would correspondingly depress the eye to 
 which it belongs, thus diminishing, if not correcting, 
 the hyperphoria. The displaced cylinders do for the 
 weak obliques what rest prisms do for the weak recti. 
 In both instances the law of direction is infringed, which, 
 in itself, is not good. For this reason it is better prac- 
 tice to relieve all forms of intrinsic heterophoria either 
 by exercise or by operations. An objection applies to 
 displaced cylinders that does not apply to prisms: by 
 the former vision is rendered less acute, while by the 
 latter there is no such interference. 
 
 GYMNASTIC EXERCISE. 
 
 In low degrees of heterophoria, of whatever kind, de- 
 velopment of the weaker muscles by exercise is the best 
 practice. The time necessary for curing these cases by
 
 HETEROPHORIA. 221 
 
 exercise and the trouble involved in carrying it out reg- 
 ularly and systematically, constitute the chief objections 
 to this method of treatment. 
 
 What the author wrote in 1893 so perfectly harmo- 
 nizes with his present views on the exercise of the ocu- 
 lar muscles that it is reproduced in the few following 
 pages: 
 
 The development of the ocular muscles, by means of 
 gymnastic exercise, has received but little attention from 
 modern authors. Noyes devotes about one page to the 
 subject; DeSchweinitz, less than one page; Schmidt- 
 Rimpler, three lines, as follows, "No improvement is to 
 be expected, as a general thing, from exercise of the in- 
 terni; overexertion, that is apt to occur, may result, on 
 the contrary, in a serious impairment of their power; " 
 Fuchs, not a line; Berry, not a line; Meyer, ten lines; 
 Landolt, not a line; Wells, one paragraph of ten lines; 
 Schweigger, not a line; Nettleship, not a line; Juler, 
 not one word; Carter, not a line. 
 
 Those of the twelve authors above named who teach 
 anything on the subject teach the same thing. This 
 teaching is illustrated by the following quotation from 
 DeSchweinitz: "Thus, to exercise the interni [in exo- 
 phoria] a prism of 10 is placed, base out, before one 
 eye, and as soon as the diplopia produced is overcome, 
 5 more are added, and so on until the limit of adductive
 
 222 HETEROPHORIA. 
 
 power is reached. . . . These exercises should be 
 repeated every day for ten or fifteen minutes at a time, 
 until the patient has acquired the power to overcome 
 readily a prism of 50." He recommends the same char- 
 acter of exercise for developing 1 the externi, beginning 
 with a 3 prism and increasing" to 8. 
 
 Noyes, following- Dyer, who wrote on this subject in 1865, 
 says: "He [the patient] takes a candle flame or door knob 
 at twenty feet for his object, and performs the efforts of 
 adduction and abduction by means of these prisms. He 
 begins, say, with adduction, and at first holds the prism 
 of 5, with base out, before one eye; then substitutes the 
 10; then before the other eye places 5, making- a total 
 of 15; then, if practicable, substitutes the other prism of 
 10 for the 5; and so climbs up the ladder of adduction 
 prisms by such steps as he can make. If the interval of 
 5 becomes too great, he may take that of 23." He 
 speaks of the exercise of the externi after the same plan, 
 using weaker prisms with their bases in. He directs 
 that the exercise be continued ten minutes at each sit- 
 ting, and that it be repeated not oftener than twice a 
 day, until, in case of the interni, a prism of 42^ can be 
 readily overcome, and, in the case of the externi, a prism 
 of 10. The prism of maximum strength having been 
 reached, its use should be continued, says this author, 
 once daily for a time. Noyes closes by saying: "A de-
 
 HETEROPHORIA. 223 
 
 cided gain in comfort and use of the eyes may be ob- 
 tained by this proceeding; and if this result is not ade- 
 quate, the true state of the muscular relations is brought 
 to view." 
 
 It is not necessary to make further quotations in order 
 to bring 1 clearly into view the character of the exercise. 
 It is the object of this paper to show that the plan is 
 unsound in principle, and must necessarily be unsuccess- 
 ful in practice. Continuous muscular contraction, aug- 
 mented at short intervals, for ten minutes, or for even five 
 minutes, may show what a muscle is capable of doing in 
 an emergency; but it is not calculated to build up or de- 
 velop the inherent power of the muscle. 
 
 In a modified form Dr. Charles E}. Michel, of St. Louis, 
 has persistently practiced the development of weak in- 
 ternal recti muscles by means of prisms, since 1877. 
 The prisms used by him have not been stronger than 4 
 nor weaker than 1. Beginning- with the weaker prism, 
 he directs the patient to exercise frequently (ten to fif- 
 teen times) during the day, each period of exercise to 
 last only four or five minutes for the first few days; 
 later they are to be worn only four or five times daily, 
 increasing the time of exercise by two to five minutes 
 daily, until they can be worn comfortably one hour. 
 When the patient, looking in the distance, becomes able 
 to wear the 4 prism one hour without discomfiture, he
 
 224 HETEROPHORIA. 
 
 is directed to commence reading. At first he must read 
 only from three to five minutes at a time; but later he 
 increases this time by two to five minutes daily, until he 
 can read comfortably one hour, four times a day. When- 
 ever this can be done, the patient is directed to continue 
 for several months the reading-exercise practice for from 
 a half to one hour, two or three times a day. To suit 
 individual cases, modifications as to strength of prism 
 and length of time and frequency of exercise must be 
 made. 
 
 Under Dr. Michel's treatment, fjilly 60 per cent of his 
 patients have full muscular power developed, and in this 
 way are enabled to use their eyes with comfort; 25 per 
 cent have greater or less gain in comfort; while 15 per 
 cent derive no benefit from the treatment. As a prelim- 
 inary step to the muscle treatment, the Doctor always 
 corrects any existing refractive errors, and has the pa- 
 tient wear these lenses behind the exercise prisms. 
 
 Dr. Michel's method of developing ocular muscles is 
 given for the reason that it differs essentially from that 
 set forth in the books, and for the additional reason 
 that a high percentage of cures results from his method. 
 The Doctor's success has been due to the fact that his 
 \veak prisms used made but little demand on the weak 
 muscles, thus making it possible for the continuous con- 
 traction to be borne and the muscle strengthened.
 
 HETEROPHORIA. 225 
 
 In contrast with Dr. Michel's practice, the method of 
 Dr. George T. Stevens, of New York, is here given in his 
 own words: "Adduction may be greatly improved by 
 gymnastic exercises of the interni, by means of prisms. 
 In these exercises the eyes are required to unite images 
 in overcoming gradually-increasing obstacles. A prism of 
 a few degrees, perhaps 10, is placed, base out, before one 
 of the eyes, \vhile gazing at a lighted candle at twenty 
 feet distance, when an effort is at once made to prevent 
 diplopia. As soon as the images are blended, another 
 prism, of perhaps less degree, is placed in the same man- 
 ner. The images being united, a stronger prism takes 
 the place of one of those already in place, or one is add- 
 ed to those already in position. Thus, little b} r little, 
 the eyes are required to overcome prisms until the im- 
 ages can no longer be united. Then all the glasses are 
 removed and the process is repeated; with each repeti- 
 tion something may be gained. The exercise should not 
 be continued, at a single sitting, more than five or six 
 minutes; and only a single sitting daily is desirable. By 
 this means the adducting power can, in most cases, be 
 raised, after a few exercises, to the desired point. 
 
 "The effect of such exercise upon the eyes is very of- 
 ten extremely salutary. With greater freedom of mus- 
 cular action comes a sense of relief from nervous strain, 
 which is often of a most gratifying character. Such an
 
 226 HETEROPHORIA. 
 
 exercise is in no way related to the practice sometimes 
 adopted, and which should be condemned, of requiring 
 the patient to gaze for a long time at a near object." 
 
 The virtue of Dr. Michel's method lies in the fact 
 that, though he taxes the muscles for a long while, 
 gradually reaching the maximum of time, he taxes them 
 but slightly, using only weak prisms; while the virtue 
 of Dr. Stevens' method lies in the fact that, though he 
 taxes the muscles severely, using the strongest prisms 
 possible, reaching the maximum strength by degrees, he 
 does not continue the exercise very long and does not re- 
 peat the sitting again the same day. And, too, he al- 
 most strikes the right principle in his method of inter- 
 mitting- the exercise. In contrast with both of these 
 methods, and with the methods laid down in the books, 
 the method of 
 
 RHYTHMIC EXERCISE 
 
 will now be given, the author feeling confident that it is 
 founded on sound principles and that it, therefore, can be 
 carried out successfully in practice. 
 
 Contraction and relaxation, alternating in short and 
 rhythmic order, and continued short of fatigue, is the 
 kind of exercise that develops a muscle in any part of the 
 body. It is the alternate contraction and relaxation that 
 develops the muscles of the arm of the blacksmith. If
 
 HETEROPHORIA. 227 
 
 the forearm should be flexed on the arm and held in that 
 position ten minutes, no one would suppose that the 
 muscles concerned could be developed thereby. There 
 would be greater reason for believing- that such action 
 would enfeeble the muscles. This is precisely the kind 
 of contraction effected by prisms in the old method of 
 exercising the recti muscles. There can be no wonder 
 that better results have not followed, and that the prac- 
 tice has been abandoned by almost all oculists. 
 
 It would be of little worth to condemn the old practice 
 as bad without setting forth a new line of practice, 
 based on sound principles, and one that must be success- 
 ful, in suitable cases. 
 
 While rhythmic contraction and relaxation, regulated 
 as to intensity and time, will develop any one of the recti 
 muscles, as is developed the biceps of the blacksmith's 
 arm, the writer would not be understood as believing that 
 one of these muscles can be developed out of a loiv state 
 of weakness into a high state of strength. There are 
 cases of exophoria that will remain exophoric still, in 
 spite of long-continued rhythmic and graduated exercise; 
 and these cases, to be cured at all, must be cured either 
 by partial tenotomies alone or by these supplemented 
 with rhythmic exercise. The same may be said of eso- 
 phoria and of hyperphoria. Only low degrees (not more 
 than 6) of lateral heterophoria can be converted, by
 
 228 HETEROPHORIA. 
 
 rhythmic exercise alone, into orthophoria; the higher 
 degrees can be corrected by partial tenotomies, shorten- 
 ing's, and exercise combined. While, in suitable cases, 
 the aim of partial tenotomies and shortenings should be 
 to approach orthophoria, yet the greatest care should 
 be exercised not to go beyond the "balance" line. The 
 safest thing is to leave, for correction by exercise, some 
 of the original condition. 
 
 Any one of the recti and either of the obliques weaker 
 than its opposing muscle, the difference in correspond- 
 ing strength not being too great, may be developed by 
 rhythmic exercise into a state that will enable it to work 
 harmoniously with its fellow. 
 
 EXERCISE FOR EXOPHORIA. 
 
 Exophoria may be taken first for study. The quanti- 
 ty should not be more than 6. The internal recti are 
 the muscles wanting in strength. There are two plans 
 of exercise, rhythmic in their nature, by either one of 
 which, or by both combined, these muscles can be per- 
 ceptibly strengthened: 
 
 (1) The wax taper method; 
 
 (2) The method by prisms, bases out. 
 
 The exercise with the taper (small wax candle) must 
 be conducted as follows: The patient is directed to light 
 the taper and hold it at arm's length from, and on a
 
 HETEROPHORIA. 229 
 
 plane with, the eyes, immediately in front of the face. 
 Fixing- his vision on the flame, he continues to look at it 
 while he brings it slowly to within seven inches of his 
 eyes, holding- it there about two seconds. He then closes 
 his eyes for a moment (at the same time moving- the 
 candle to one side) and, on opening them, fixes his vision 
 on some distant object. The same procedure is gone 
 through with a second time, and so on for five to fifteen 
 times at one sitting. The sittings may be repeated one 
 or more times daily for weeks or months. The best time 
 for this exercise is early in the morning, while the mus- 
 cles are fresh from sleep. In many cases the morning 
 sitting will be sufficient for the day. This is especially 
 so if the exophoria is low in degree. Reading or other 
 near work should not be done within the hour after the 
 exercise is taken. 
 
 In this taper exercise no one can doubt that the guid- 
 ing- sensation compels the internal recti to contract, in 
 obedience to the law of corresponding retinal points, as 
 the light advances, the maximum of contraction being 
 reached when the taper is seven inches from the eyes. 
 On closing the eyes partial relaxation of the interni oc- 
 curs (keeping the eyes closed long enough, the relaxa- 
 tion would become complete). The moment the eyes are 
 opened and the vision is fixed on a distant object, in 
 quick response to the guiding sensation, the relaxation
 
 230 HETEROPHORIA. 
 
 becomes complete. Thus is brought about contraction 
 and relaxation, which should be discontinued short of 
 fatigue. That this rhythmic exercise, properly regulat- 
 ed as to frequency and force, will develop the internal 
 recti, is susceptible of demonstration on the part of any 
 one who wishes to know the truth. 
 
 The second method for developing the interni is by 
 means of prisms, bases out. The prisms to be used may 
 be from 1 to 8, and one should be placed before each eye. 
 The treatment should be commenced with the weaker 
 prisms, and as development of the muscles advances, 
 the stronger should be brought into use. The object 
 looked at should be a candle, lamp, or gas jet, fifteen 
 to twenty feet distant. With the prisms before the eyes, 
 the image in each eye is displaced out, when the guiding- 
 sensation calls quickly into action the interni for fusing 
 them. After three seconds the interni must be allowed 
 to relax for the same length of time (three seconds), 
 which is readily effected by lifting the prisms up and al- 
 lowing the light to enter the eyes uninfluenced. The 
 guiding sensation at once causes the relaxation to take 
 place, so that the yellow spots may receive the images. 
 At the end of three seconds the prisms are again dropped 
 before the eyes, when the interni again contract. Then 
 a second time the relaxation is effected by lifting the 
 prisms; and so on throughout every sitting, which should
 
 HETEROPHORIA. 231 
 
 last from two to ten minutes, but should always be dis- 
 continued short of fatigue. The sittings should be re- 
 peated two or more times a day. While it will take 
 weeks, if not months, to establish orthophoria, neverthe- 
 less this end can be attained, in suitable cases, by this 
 method. It may be better in most cases to resort to the 
 two methods of development, the taper and the prisms, 
 each day, but not at the same sitting. 
 
 In resorting to the prism exercise, it would be more con- 
 venient to close the eyes, for the purpose of getting re- 
 laxation, than to lift the prisms; but when the eyes are 
 closed the relaxation is slow to take place, and is rarely 
 complete at the end of sixty seconds; whereas, when the 
 prisms are raised, the guiding sensation effects at once' 
 complete relaxation, which continues till the prisms are 
 again placed before the eyes. The rhythmic nature of 
 the exercise is more perfect in the latter than in the for- 
 mer, and results are better necessarily. 
 
 The method of exercise of the interni by means of 
 strong prisms, introduced by Dr. Deady, of New York, 
 and later reintroduced and earnestly advocated by Gould, 
 may have its merits, but certainly not in the line of mus- 
 cle building. The good resulting from this method must 
 come through excitation of the converging center, that 
 of the third conjugate innervation. An overdraft on a 
 nerve-center may be endured for a time, but should be
 
 232 HETEROPHORIA. 
 
 avoided, if possible. Ultimately exhaustion would be 
 expected to follow. At any rate, it would seem to be far 
 better to change the condition of the muscles so that the 
 normal nerve impulse would make them do their work 
 properly. That a muscle can be made stronger by light 
 rhythmic exercise, never carried to the point of fatigue, 
 does not admit of a doubt. The muscular Sandow, capa- 
 ble of lifting many hundred pounds, developed his mus- 
 cles by rhythmic exercise with three-pound dumb- 
 bells. 
 
 Without endorsing the use of strong prisms, in exo- 
 phoria, the method must here be given. The exer- 
 cise begins at a point twenty inches distant from a 
 lighted candle or gas jet, by placing before the eyes the 
 strongest prisms, bases out, that can possibly be over- 
 come. At once the light is carried from the patient, or 
 the patient recedes from the light, until a distance of 
 twenty feet intervenes. The prisms are then raised, 
 when, of course, relaxation occurs. When again within 
 twenty inches of the light, the prisms are lowered, and 
 recession follows as before. Thus the exercise is con- 
 tinued from three to five minutes, the powerful contrac- 
 ' tions and full relaxations following each other every 
 seven seconds. The periods of exercise are to be repeat- 
 ed several times a day. Very strong claims have been 
 made for this method, and there may be more in it than
 
 HETEROPHORIA. 233 
 
 would appear from reasoning- about it; but its most ar- 
 dent advocates confine its use to the treatment of ex- 
 ophoria. 
 
 ESOPHORIA. 
 
 In this condition the muscles to be built up are the ex- 
 ternal recti. There is but one method for doing this, 
 and that is by means of prisms. These should be from 
 2 to 3, certainly not more than 4, and their bases must 
 be placed in. Beginning with the weaker prisms, the 
 patient should look at the candle twenty feet distant for 
 three seconds, during which time the guiding sensation 
 has caused the externi to undergo contraction; and then 
 the prisms should be held up for three seconds to allow 
 relaxation to take place. These steps should be thus 
 regularly repeated throughout each sitting of two to ten 
 minutes, the sittings themselves being repeated two or 
 more times daily, as in the treatment of exophoria. In 
 suitable cases orthophoria can be brought about. 
 
 HYPERPHORIA. 
 
 Hyperphoria and cataphoria, like esophoria, are sus- 
 ceptible to exercise only by means of prisms. Given a 
 case of left hyperphoria (right cataphoria) of not more 
 than 1^, there is a possibility of developing vertical or- 
 thophoria by means of rhythmic exercise. The muscle 
 on the left side to be developed is the inferior rectus,
 
 234 HETEROPHORIA. 
 
 and that on the right side is the superior rectus. The 
 prisms used should vary from ^ to 2; most cases will 
 not require a stronger than a 1 prism. The base of the 
 left prism must be up; that of the right prism, down. 
 As in exophoria and esophoria, the patient should exer- 
 cise from two to ten minutes at a time, and two or more 
 times a day. The object looked at should be twenty 
 feet distant, and it should be seen through the prisms 
 three seconds, then without the prisms three seconds, 
 and so on throughout each sitting. Thus contraction 
 and relaxation of the weak left inferior rectus and weak 
 'right superior rectus are effected in rh} r thmic order. If 
 . the hyperphoria is on the right side (left cataphoria), 
 the base of the right prism must be up and that of the 
 left prism must be down, when exercising. In every 
 form of heterophoria the apex of the prism must point 
 in the direction of the muscle to be developed by it. 
 
 Occasionally cases present themselves in which there 
 is a general weakness of the recti muscles, and especial- 
 ly of the external and internal recti, unaccompanied by 
 general physical weakness. Such cases generally mani- 
 fest esophoria for distance and exophoria in the near, 
 neither muscle being able to overcome a prism of any- 
 thing like the usual strength. To operate on such a 
 case would be improper, since relief of the exophoria in 
 the near would be attended by a corresponding increase
 
 HETEROPHORIA. 235 
 
 of the esophoria for distance, and rice rcrsa. In such 
 cases the intern! should be brought under the influence 
 of the rhythmic exercise, as already set forth in the 
 study of exophoria, at one time of the day; and, at some 
 other time of the day, like attention should be paid to 
 the external recti, as in simple esophoria. In these 
 cases strychnia and electricity could be used with some 
 promise of aiding the exercise treatment. Such patients 
 should be allowed to undertake but little near work, un- 
 til the exercise treatment by means of prisms has be- 
 come well advanced. In these cases the wax-taper treat- 
 ment of the internal recti is not applicable until late in 
 the course. These cases are far more stubborn than 
 cases of simple exophoria or simple esophoria; and yet 
 great advantage can be derived from the rhythmic exer- 
 cise by means of weak prisms, aided by strychnia and 
 electricity. 
 
 For cases showing esophoria in the distant test and | 
 exophoria in the near, adduction and abduction both be- 
 ing low, wall-to-wall exercise, probably, can accomplish 
 more, in a shorter time, than the prism exercise referred 
 to above. To perform this task the patient must stand 
 against one wall of his room, equally distant from the 
 walls on the right and left; previously there must have 
 been pinned to the right and left walls two pieces of 
 white paper, each at an angle of 35 from the patient
 
 236 HETEROPHORIA. 
 
 when in position for exercising, and as high from the 
 floor as are his eyes. With his head in the primary po- 
 sition and his face directed toward the middle line of 
 the opposite wall, he must stiffen his neck while looking 
 first at one piece of paper and then at the other, chang- 
 ing from the one to the other with the regularity and in- 
 terval of the tick of an old-time clock. This should be 
 discontinued short of fatigue, and need not be prolonged 
 over five minutes. It may be done once or twice a day. 
 If exophoria in the near is 5 or more, the candle exercise 
 may be resorted to once a day and the wall-to-wall ex- 
 ercise once a day. Since this method of exercise costs 
 nothing, and the patient is more impressed with the fact 
 that he is doing something, in many cases it is better to 
 prescribe it than the prism method. 
 
 As in lateral, so in vertical, heterophoria, the imbal- 
 ance may be associated with subnormal superduction 
 and sub-duction. In such a case the prism exercise 
 should be resorted to once a day for curing the imbal- 
 ance, and the ceiling-to-floor exercise once a day, always 
 short of fatigue, but never longer than five minutes. 
 To do the ceiling-to-floor exercise, the patient must 
 place himself as for the wall-to-wall exercise. A piece 
 of paper, a spool of thread, or a pocketknife should be 
 placed on the floor as far in front of the patient as he is 
 tall. Fixing his head in the primary position, he is di-
 
 HETEROPHORIA. 237 
 
 rected to look first at the object on the floor, and then up 
 at the junction of ceiling and wall, changing- from the one 
 point of view to the other, as in the wall-to-wall exercise. 
 
 Occasionally there will be both a lateral and a vertical 
 imbalance with the duction power of every rectus below 
 normal. In such a case the candle exercise for exopho- 
 ria in the near, the prism exercise for the vertical im- 
 balance, and the conjoined wall-to-wall and ceiling-to- 
 floor exercise should be resorted to. In combining the 
 wall-to-wall and ceiling-to-floor exercise, it is best done 
 by looking, from four to six times, from wall to wall, and 
 then, from four to six times, from ceiling to floor, con- 
 tinuing thus to alternate for not longer than ten min- 
 utes, but always short of fatigue. 
 
 In cases in which the recti muscles are weak, because 
 of a low state of general health, no treatment should be 
 thought of except that intended for the well-being of 
 the whole system. Use of the eyes in near work should 
 be prohibited until recovery of the general health has 
 occurred. 
 
 CYCLOPHORIA. 
 
 The treatment of insufficiency of the oblique muscles* 
 is by means of cylindrical lenses (preferably convex), so 
 placed as to lead the guiding sensation to demand con- 
 
 See Ophthalmic Record, Vol. II., No. I.
 
 238 HETEROPHORIA. 
 
 traction on the part of the weak muscles. The +1.50 D. 
 cylinder is the most useful, but a weaker one may be 
 used at the beginning. One should be placed before 
 each eye; and if the weak muscles are the superior ob- 
 liques, their axes must be placed in the lower temporal 
 quadrant, at first 15 from the vertical, when, because of 
 slight retinal displacement of the object looked at, only 
 a slight demand is made on the muscles, which should 
 be kept up, in an intermitting way, for five minutes; 
 then the axes should be revolved to 30 from the verti- 
 cal, when, because of a greater displacement of the im- 
 ages, a greater demand for contraction is made on the 
 part of the weak obliques, which should be kept up 
 intermittingly for three minutes; now, lasth', the axes 
 of the cylinders are revolved to 45 from the vertical, 
 when the maximum displacement of the images occurs, 
 and hence the maximum demand is made on the muscles, 
 which should be continued intermittingly for two minutes 
 only. As in the exercise of the recti by means of prisms, 
 the best way to get contraction and relaxation alter- 
 nately and in rhythmic order, is to lower and raise the 
 frames containing the prisms every three seconds, so, 
 to get rhythmic contraction and relaxation of the ob- 
 liques under exercise, it is best to raise and lower the 
 frames containing the cylinders every three seconds 
 throughout the sitting. It is unfortunate for the con-
 
 HETEROPHORIA. 239 
 
 venience of the patient that the relaxation of ocular 
 muscles does not quickly follow the closing* of the eyes, 
 since it would be much easier to open and close the 
 eyes every three seconds than to lower and raise the 
 frames at the same interval. The oblique muscles re- 
 lax much more readily than the recti, on closing 1 the 
 eyes, but even these do not completely relax in the short 
 time of five seconds. 
 
 In most cases of insufficiency of the obliques, exercis- 
 ing" by means of cylinders once a day is sufficient; the 
 best time for this exercise is before breakfast. The ob- 
 ject looked at should be a horizontal black line on a white 
 background or a white line on a black background, at a 
 distance of ten feet. The cylinders should be properly 
 centered. 
 
 What prisms are to the recti, cylinders are to the ob- 
 liques. In either case the lenses correcting- refractive 
 errors should be worn during- the exercise, in order that 
 the best results may follow. The only exception to this 
 rule is the wax-taper exercise of the internal recti, when 
 no lenses should be worn. 
 
 OPERATIVE TREATMENT. 
 
 The heterophorias not curable by correction of errors 
 of refraction, by prisms in position of rest, or by rhyth- 
 mic exercise, should be subjected to operative procedure.
 
 240 HETEROPHORIA. 
 
 Such cases are not infrequent, and the relief from opera- 
 tions skillfully done is by no means uncertain. There is 
 no department of surgery that requires more care in the 
 making- of the diagnosis. The condition of every extrin- 
 sic ocular muscle must be determined before any one 
 muscle is to be operated upon. There are but two ob- 
 jects in view in muscle operations: the one is altering 
 the tension of a muscle, the other is chang-ing- its plane 
 of action. The tension of a muscle is to be altered either 
 by a central partial tenotomy, as when operating on the 
 too strong muscle; by shortening the muscle in the line 
 of its original plane, or by advancing it straight for- 
 ward, as when operating on the too weak muscle. In 
 making either one of these operations, the existence of a 
 cyclophoria must be first excluded. When there is a cy- 
 clophoria complicating any one of the other heteropho- 
 rias, the operation on a rectus muscle should alter the 
 tension of the muscle and, at the same time, change the 
 plane of its action. In such a case a partial tenotomy 
 should not be central only, but should include those pe- 
 ripheral fibers, a division of which would be corrective of 
 the cyclophoria. A shortening should be done in such a 
 way as either to raise or depress the plane of action of 
 the muscle as might be indicated by the complicating cy- 
 clophoria. In making- advancements, the new attach- 
 ment should be carried either higher or lower than the
 
 HETEROPHORIA. 241 
 
 original attachment, as the character of the cyclophoria 
 might determine. 
 
 The operation to simply alter the tension of a rectus 
 muscle with the view of lessening its power is a central 
 partial tenotomy. The operator should always be care- 
 ful to leave a sufficient number of peripheral fibers to 
 act as stay cords to prevent the cut muscle from re- 
 tracting- too much. The strength of the uncut fibers 
 in both directions should be equal, so that the plane of 
 the muscle may not be changed. Both judgment and 
 skill must be exercised, else too much or too little of 
 the tendon may be cut. It is better to aim at leaving 
 some of the old error uncorrected than to transform it 
 into the opposite condition. The conjunctiva may, but 
 the capsule of Tenon must, be divided coextensively with 
 the division of the tendon, to obtain the effect desired. 
 In no kind of heterophoria should a complete tenotomy 
 ever be done; but if by accident it should happen, the 
 tendon should be stitched to the sclera directly behind 
 the original insertion, and at that distance behind de- 
 termined by a correct understanding of the exact char- 
 acter of the error for which the operation has been un- 
 dertaken. 
 
 If a complicating cyclophoria is to be corrected by a 
 partial tenotomy of a rectus, not only must the tension 
 of the muscle be altered for the correction of the main
 
 242 HETEROPHORIA. 
 
 error, but its plane must be changed so as to correct the 
 complicating- cyclophoria. The kind of cyclophoria hav- 
 ing- been determined and it is nearly always a plus cy- 
 clophoria one is not left in doubt as to how the opera- 
 tion should be done. To cure a sthenic hyperphoria and 
 a plus cyclophoria, the nasal and central fibers of the su- 
 perior rectus of the hyperphoric eye should be divided, 
 while the temporal fibers should be left uncut and suffi- 
 ciently strong to prevent any over-correction of the hy- 
 perphoria; or the temporal and central fibers of the 
 inferior rectus of the cataphoric eye should be divided, 
 leaving the nasal fibers uncut and of sufficient strength 
 to prevent an over-correction of the error. 
 
 In a partial tenotomy for a sthenic esophoria compli- 
 cated with a plus cyclophoria, there being no hyperpho- 
 ria, the lower and some of the central fibers of both interni 
 should be divided, leaving the upper fibers uncut. In 
 this way the tension of the muscle is altered, curing, 
 wholly or in part, the esophoria, and the plane of each 
 muscle is elevated so as to correct the plus cyclophoria. 
 The plane of both interni having been equally elevated, 
 there is of necessity developed a slight double hyperpho- 
 ria which, however, will give no trouble, being easily 
 overcome by a pose of the head. 
 
 In operating on a case of sthenic esophoria compli- 
 cated by a right hyperphoria and a plus cyclophoria, the
 
 HETEROPHORIA. 243 
 
 first operation must be done on the internus of the cata- 
 phoric eye, and should consist of a complete division of 
 the lower and central fibers, leaving uncut the upper 
 fibers of the tendon. The threefold effect of this pro- 
 cedure is a correction, in part or wholly, of the esophoria; 
 a correction of thecataphoria; and a cure of the plus cy- 
 clophoria. Whatever part of the esophoria may remain 
 after this operation should be corrected by a partial cen- 
 tral tenotomy of the right internus. Should some of 
 the right hyperphoria remain, but no cyclophoria, a par- 
 tial central tenotomy of the right superior rectus should 
 be done; but if there should remain some uncorrected 
 plus cyclophoria as well as right hyperphoria, the inner 
 and enough of the central fibers of the right superior 
 rectus should be cut to cure these conditions. These 
 three operations sometimes even one or two of them 
 will cure a complicated case of this character. 
 
 If the esophoria is asthenic and uncomplicated, the 
 operation of shortening should be done on one or both 
 externi, and the plane of these muscles should be the 
 same after as before the operation, otherwise a hyper- 
 cyclophoria would be created. 
 
 If the asthenic esophoria is complicated with a right 
 hyperphoria only, the externi should be shortened as 
 though no complication existed, and later the hyperpho- 
 ria could be treated by exercise, by a prism in position
 
 244 HETEROPHORIA. 
 
 of rest for the hyperphoric eye, or by a central tenotomy 
 of the superior rectus of the hyperphoric eye. In such 
 a condition no muscle plane should ever be changed. 
 The plane of a muscle should never be changed unless 
 there is a cyclophoria to be corrected. 
 
 If the asthenic esophoria should be complicated with a 
 plus cyclophoria alone, not only should both externi be 
 shortened, but the plane of each should be depressed so 
 as to cure both the esophoria and plus cyclophoria. 
 
 If the asthenic esophoria is complicated by a right hy- 
 perphoria and a plus cyclophoria, the first operation 
 should be on the externus of the hyperphoric eye, and 
 should be a shortening so done as, at the same time, to 
 depress the plane of its action. The triple effect will 
 be to cure, more or less completely, the esophoria, the 
 right hyperphoria, and the plus cyclophoria. If the left 
 externus must be shortened for a remaining esophoria, 
 whether complicated or not by a cataphoria and plus cy- 
 clophoria, one or both, for obvious reasons the plane of 
 this muscle should not be altered. If the plane were 
 elevated, it would lessen the cataphoria, but would in- 
 crease the plus cyclophoria; if the plane were lowered, 
 it would decrease the plus cyclophoria, but would in- 
 crease the cataphoria. After the straight-forward short- 
 ening of the externus of the cataphoric eye, whatever 
 hyperphoria alone may exist should be treated, if suffi-
 
 HETEROPHORIA. 245 
 
 ciently great in quantity, by a central partial tenotomy 
 of the superior rectus of the hyperphoric eye; but if the 
 remaining- hyperphoria should be complicated with a re- 
 maining- plus cyclophoria, the inner, and as much as 
 necessary of the central, fibers of the superior rectus of 
 the hyperphoric eye should be cut. 
 
 The operation for sthenic exophoria, uncomplicated, is, 
 a central partial tenotomy of one or both externi, prefer- 
 ably both. The object in view being- only the alteration 
 of tension, care must be exercised that the plane of rota- 
 tion shall not be chang-ed. 
 
 When sthenic exophoria is complicated by a hyper- 
 phoria, the operation on the externi must not be done 
 with a view of affecting- the hyperphoria, hence central 
 partial tenotomies are indicated. Later the hyperpho- 
 ria must be relieved by a central partial tenotomy of the 
 superior rectus of the hyperphoric eye and, if necessary, 
 a central partial tenotomy of the inferior rectus of the 
 cataphoric eye. The tension of these muscles should be 
 altered without a chang-e of plane. 
 
 In sthenic exophoria, complicated by a right hyper- 
 phoria and a plus cyclophoria, the first operation should 
 be done on the externus of the hyperphoric eye, and it 
 should consist of a division of the upper and central 
 fibers, leaving- uncut the lower fibers. The threefold re- 
 sult of this operation will be: (1) relaxing- the tension of
 
 246 HETEROPHORIA. 
 
 the externus, lessening, if not curing, the exophoria; (2) 
 a turning- of the eye down, thus counteracting- the hy- 
 perphoria; (3) torting the eye in, curing the cyclophoria. 
 If some of the exophoria remain, whether still compli- 
 cated or not by a right hyperphoria and a plus cyclopho- 
 ria, the operation on the left externus must be a central 
 partial tenotomy. The reason is clear: a division of the 
 upper and central fibers would so change the muscle 
 plane as to increase the cataphoria, although diminish- 
 ing the cyclophoria; while a cutting of the lower and 
 central fibers would so change the plane as to lessen the 
 cataphoria, but increase the plus cyclophoria. The only 
 safe course between this Scylla and Charybdis is a cen- 
 tral partial tenotomy of the left externus. These two 
 operations having been done, any remaining right hyper- 
 phoria, without a plus cyclophoria, should be relieved by 
 a central partial tenotomy of the right superior rectus; 
 but if the remaining hyperphoria should be complicated 
 with plus cyclophoria, the nasal and central fibers 
 should be cut, with the double purpose of altering the 
 tension for the hyperphoria and changing the plane for 
 the cyclophoria. 
 
 When sthenic exophoria is complicated by a plus cyclo- 
 phoria only, the upper and central fibers of both externi 
 (not one alone) should be cut. The triple effect of 
 these operations is: (1) alteration of tension for the exo-
 
 HETEROPHORIA. 247 
 
 phoria; (2) lowering plane of both extern! for the plus 
 cyclophoria; (3) the development of a double cataphoria, 
 which, in itself, is not bad. 
 
 In asthenic exophoria, uncomplicated, the tension of 
 the interni must be increased by shortenings or advance- 
 ments so done as not to change the plane of rotation. 
 The same is true of asthenic exophoria complicated by a 
 hyperphoria alone. Later the hyperphoria may be re- 
 lieved by a central partial tenotomy of the superior rec- 
 tus of the hyperphoric eye. 
 
 When an asthenic exophoria is complicated with a 
 right hyperphoria and a plus cyclophoria, the internus 
 of the cataphoric eye should be so shortened or advanced 
 as to alter its tension, for the exophoria, and elevate its 
 plane, for counteracting the cataphoria and curing the 
 plus cyclophoria. If the internus of the once hyper- 
 phoric eye must be shortened or advanced to still fur- 
 ther correct the exophoria, not any longer complicated, 
 it must be so done as not to change its plane; and the 
 same is true if the only remaining complication is a hy- 
 perphoria, for in counteracting the hyperphoria, a plus 
 cyclophoria would be developed. It is also true that 
 only the tension of the internus should be altered by a 
 shortening or advancement when the remaining exopho- 
 ria is complicated by hyperphoria and plus cyclophoria, 
 for the reason that lowering the plane would increase
 
 248 HETEROPHORIA. 
 
 the cyclophoria, although lessening" the hyperphoria; 
 while elevating 1 the plane would increase the hyperpho- 
 ria, although diminishing the cyclophoria. Later the 
 hyperphoria or hyper-cyclophoria should be remedied by 
 the correct operation on the superior rectus. 
 
 An asthenic exophoria complicated by a plus cyclopho- 
 ria must be treated by such shortening or advancement 
 of both interni as to alter the tension for the exophoria 
 and elevate both planes for the plus cyclophoria. The 
 double hyperphoria resulting would be counteracted by 
 a pose of the head. 
 
 Cyclophoria may exist alone and may be so high in de- 
 gree as to demand relief by operation. This can be ac- 
 complished by operating on both superior or both infe- 
 rior recti. A plus cyclophoria, uncomplicated, can be 
 relieved by dividing a few of the nasal fibers or advan- 
 cing a few of the temporal fibers of both superior recti. 
 In doing the former a double cataphoria is developed, 
 while the cyclophoria is cured; in doing the latter the 
 cyclophoria is cured, but a double hyperphoria results. 
 Since a double cataphoria is preferable to a double hyper- 
 phoria, a division of the nasal fibers of the superior recti 
 should always be chosen. 
 
 The plus cyclophoria can be cured by a division of the 
 temporal fibers or an advancement of the nasal fibers of 
 both inferior recti. The former would give a double
 
 HETEROPHORIA. 
 
 249 
 
 hyperphoria, while the latter would give a double cata- 
 phoria; hence, of the two the latter should be chosen. 
 As to final results, a division of the nasal fibers of the 
 superior recti and an advancement of the nasal fibers of 
 the inferior recti are precisely alike; but the former 
 should be preferred, for it is more easily done and gives 
 the patient much less inconvenience. 
 
 OPERATIONS ON THE RECTI. 
 
 The strictest antiseptic precautions must be observed 
 in the preparation of the patient and the instruments; 
 and the operator and assistant must have clean, asep- 
 
 Fig. 36. THE STEVENS SCISSORS. 
 
 tic hands. Unless the patient is a child who cannot be 
 controlled, or a very nervous adult, general anesthesia 
 should not be produced. Under cocaine anesthesia, the 
 
 Fig- 37- THE STEVENS FORCEPS. 
 
 solution always being made fresh and sterile for each 
 case, muscle operations are practically painless. These
 
 250 HETEROPHORIA. 
 
 operations may be made almost bloodless by the use of 
 two or three drops of adrenaline chloride solution (1-1000) 
 dropped into the eye while cocainization is being- effected 
 in the usual way one drop of a 10 per cent solution at 
 
 Fig. 38. THE STEVENS FORCEPS. 
 
 intervals of two minutes, until three or four drops have 
 been instilled. In five minutes after the instillation of 
 the last drop of cocaine solution the operation should be 
 commenced. The stop-speculum, fixation forceps, Ste- 
 
 r iii ^~ 
 
 Fig- 39- THE STEVENS HOOK. 
 
 vens scissors, and Stevens hook constitute the array of 
 instruments necessary for doing partial tenotomies. If a 
 muscle is to be advanced, a needle holder, two small nee- 
 dles curved at the point, number five silk (either white 
 
 Fig. 40. THE STEVENS NEEDLE HOLDER. 
 
 or iron dyed), a large strabismus hook, and a silver su- 
 ture plate must be added to the instruments named; and 
 if a shortening operation is to be done, an additional 
 large strabismus hook, or, probably what would be bet-
 
 HETEROPHORIA. 25l 
 
 ter, the muscle forceps devised by Clark, of Columbus, 
 O. Most of these instruments are shown in accom- 
 panying 1 cuts. The time occupied in doing any of these 
 operations is short. The after treatment consists in 
 using- freely, several times a day, while the redness lasts, 
 an anodyne-antiseptic wash (Tinct. Opii, gtt. xxx,Acid 
 Boracic, gr. xx, Dist. water, oz. i). Both eyes should be 
 kept open, to favor easier binocular adjustment. A 
 muscle suture should be removed on the seventh day, unless 
 severe reaction should indicate an earlier removal. The 
 Price silver suture plate does its best work in facilitat- 
 ing- the removal of the suture, making- this step painless 
 as well as easy. It prevents the swollen tissue from 
 concealing- the knot. 
 
 PARTIAL TENOTOMY. 
 
 There are two kinds of partial tenotomy, central and 
 marginal. The indications for the one or the other may 
 always be well understood in any given case, as has been 
 set forth in another part of this chapter. The object of 
 the central tenotomy is only to lessen the tension of the 
 muscle; the object of the marginal tenotomy is both to 
 lessen the tension of the muscle and to change its plane 
 of action. 
 
 To do a central partial tenotomy, the lids must be 
 well separated by the speculum. The patient must look
 
 252 HETEROPHORIA. 
 
 as far as possible in the direction opposite the muscle to 
 be operated upon. The conjunctiva over the insertion 
 of the tendon must be lifted in a meridional fold with 
 the forceps, and this must be snipped with the scissors. 
 Through the cut in the conjunctiva the forceps should 
 be made to grasp the capsule of Tenon, which in turn 
 should be snipped. Through the openings in conjunctiva 
 and capsule, the central fibers of the tendon should be 
 grasped with the forceps and slightly raised from the 
 sclera, so that they may be cut with the scissors be- 
 tween the forceps and the attachment, as close to the 
 latter as possible. Thus the tendon is buttonholed. 
 If the operator is certain, from the resistance he feels 
 with the forceps, that he is not too near either margin 
 of the tendon, he may divide a few more fibers, in both 
 directions, while still holding the tendon with the forceps; 
 but in doing so he takes some risk of doing too much. 
 Now the forceps should be laid down for the small hook, 
 vhich should be passed through the buttonhole in the 
 tendon, first in one direction, then in the other, beneath 
 the uncut fibers, so as to determine the resistance. 
 Guided by the hook, the operator now divides fiber after 
 fiber with the scissors, until the lessened resistance warns 
 him that he has gone far enough in that direction. He 
 then repeats this step toward the other margin in the 
 same careful way. Some of the fibers in both directions
 
 HETEROPHORIA. 253 
 
 must be left uncut, so as to act as stay cords to prevent 
 a too far recession of the cut part of the tendon. The 
 strength of the uncut fibers at the margin should be left 
 as nearly equal as possible, so that the muscle plane may 
 be the same after as before the operation. Should' the 
 fibers be left stronger at the one margin than at the 
 other, the plane will be certainly shifted toward the 
 stronger fibers, and an undesired torsioning effect will 
 accompany the lessening of the tension. To get the full 
 effect of a partial tenotomy, the capsule of Tenon must 
 be cut coextensively with the division of the tendon. The 
 cut in the conjunctiva may or may not be of the same ex- 
 tent. There is no necessity for making either a very 
 small or a very large conjunctival incision; but for those 
 just beginning to operate, a large conjunctival incision 
 would make the tenotomy both easier and safer. 
 
 Dr. George H. Price, of Nashville, has just invented 
 an instrument that may prove to be most useful, in that 
 it can measure the amount of resistance of uncut fibers 
 when a partial tenotomy is being done. Up to the pres- 
 ent, operators have been guided only by an indefinable 
 sense of resistance when drawing on the hook. If that 
 resistance can be measured and the tendonometer gives 
 promise in that direction eventually a rule of practice 
 may be established which will be valuable to any opera- 
 tor, whether experienced or inexperienced. Fig. 41 will
 
 254 HETEROPHORIA. 
 
 give the reader a fair understanding" as to the construc- 
 tion of the instrument; however, a description by the in- 
 ventor follows : 
 
 THE TENDONOMETER. 
 
 " This instrument, as its name implies, is designed for 
 measuring- the resistance of the ocular muscles, either in 
 part or as a whole. It consists of a muscle hook (a), 
 with graduated shaft (s), which is suspended by a coil 
 spring (c) in a hollow metal handle (h), the construction 
 being upon the same general principle as an ordinary 
 spring balance. The hook proper is 5-16 of an inch long 
 and nearly straight, so that it can be passed under the 
 
 1 I I I I I I .' I II I I I II I ; I 
 
 I j 3 * j I 7 j t> 11 * H <t It 17 ) 
 
 Fig. 41. THE TENDONOMETER. 
 
 tendon when it is exposed, and its resistance tested; or it 
 can be passed into the buttonhole made in the tendon 
 when doing a partial tenotomy, and the remaining fibers 
 can be tested, both those above and below the opening 
 in the tendon. The shank of the hook is about 1 1-2 
 inches long, and round. The shaft of the hook (s) is 
 about 3 1-2 inches long, 1-16 of an inch thick, and 3-16 
 of an inch wide. The shaft is graduated on both sides, 
 as indicated in the diagram. At its upper end there is a
 
 HETEROPHORIA. 255 
 
 small eyelet into which the spring is caught, by which it 
 is suspended from the screw (x), which passes through 
 the cap (y), which fits into the upper end of the handle (h). 
 The spring is made of some material such as nickel plat- 
 ed steel, hardened gold, or bronze, to prevent rusting. 
 The handle is made of aluminium. It is rectangular in 
 cross section, being about 3-16 of an inch x 1-4 of an 
 inch, slightly roughened to prevent slipping in the fin- 
 gers of the operator. At (x) the body of the handle 
 is thickened, and its end is slotted with an opening just 
 large enough to admit the shaft of the hook, or it can be 
 provided with a cap which is slotted and slips into the 
 handle, the cap being made of harder metal. The cap (y) 
 at the upper end of the handle is made of hard metal, is 
 drilled and tapped, so that the screw (x) passes through 
 this and can be screwed in or out to adjust the tension 
 on the spring (c), so as to keep the zero mark of the 
 scale fixed. The screw (x) will be provided with a small 
 jam nut, not shown in the cut, so that when the spring 
 is set this nut can be jammed down against the cap (y) 
 and prevent displacement of the spring and shaft. The 
 graduations upon the shaft of the hook will measure the 
 units of resistance of a tendon or part of a tendon; and 
 the instrument is designed for the purpose of aiding in 
 the accurate performance of those operations which re- 
 quire a very delicate sense of touch on the part of the
 
 256 HETEROPHORIA. 
 
 operator, something very hard to acquire and not gov- 
 erned by any fixed standard." 
 
 A skilled operator can easily grasp conjunctiva, cap- 
 sule, and tendon at the same time, and go through them 
 all with one snip of the scissors. He then completes the 
 operation as already described. 
 
 If the indication is for a marginal tenotomy, the initial 
 cut of the conjunctiva, capsule, and tendon is made as for 
 a central tenotomy, care being exercised that the button- 
 hole in the tendon, if not in the center, shall be nearer 
 that margin which is to be completely severed later. 
 Still holding the tendon with the forceps, the scissors 
 may be passed in the direction in which complete divi- 
 sion is indicated, and be made to cut all the fibers at once. 
 The hook should now be used first, to determine that 
 all the tendon has been cut toward the one margin; and 
 next, to test the resistance of the uncut fibers at the other 
 margin. If this resistance is too great it would be un- 
 fortunate if it were too little other fibers may be di- 
 vided. But a sufficient number of fibers at this margin 
 should be left intact to prevent an over-effect. This op- 
 eration must not only lessen the tension of the muscle so 
 as to favor its direct antagonist, but it must also change 
 the plane of its action so as to cure a complicating cy- 
 clophoria. 
 
 There is no mathematical rule by which to be guided
 
 HETEROPHORIA. 257 
 
 in these operations. The beginner should always aim at 
 accomplishing- less than the effect desired, while the ex- 
 pert operator should be careful not to do loo much. In 
 these operations, as in all others, practice alone can give 
 the greatest skill and the highest degree of accuracy. 
 
 MUSCLE SHORTENING. 
 
 This operation,* rather than advancement, should be 
 done in nearly all cases of heterophoria, in which the in- 
 dication is to increase the tension of the muscle. Not 
 only can this operation alter the tension of the muscle, 
 but it can also be done so as, at the same time, to change 
 its plane of rotation. Its advantages over the advance- 
 ment operation are three: First, it is easier of accom- 
 plishment, though a little more painful; second, its plane 
 of rotation is less likely to be changed when there is no 
 indication for changing it; third, the stitch is not so 
 likely to cut its way out, and if it does so, or if the knot 
 should become untied, the case would be no worse than 
 before the operation; whereas, if either of these accidents 
 should happen to an advancement, before adhesion has 
 formed, the recession of the muscle might be farther 
 back than its original attachment. However, in some 
 cases of heterophoria, in which the indication is to in- 
 
 *See Ophthalmic Record, March, 1893, in which it was first described.
 
 258 HETEROPHORIA. 
 
 crease the tension, the muscle attachment is so far back, 
 or the muscle itself is so small, that an advancement 
 must be done. 
 
 The shortening operation for simply increasing" the 
 tension of the muscles is done as follows: Lids must be 
 widely separated with the speculum. The conjunctiva 
 must be seized with the forceps, so as to be thrown into 
 a fold parallel with the corneal margin, behind the tendon 
 insertion; and this conjunctival fold, if the muscle be an 
 externus or an internus, must be cut with the scissors a 
 little below the lower border of the muscle; but if it be 
 a superior or inferior rectus, the cut must be to the nasal 
 side of the muscle. Through this cut the capsule of 
 Tenon is grasped and cut in line (meridionally) with the 
 conjunctival cut. Through the opening thus made, one 
 of the large strabismus hooks is passed beneath the 
 muscle and drawn forward until stopped by the attach- 
 ment of the tendon; then, through the same opening, the 
 second large hook is passed beneath the belly of the 
 muscle and carried backward, at the same time lifting 
 the muscle from the sclera, so as to show the extent of 
 the possible shortening". If the opening in the conjunc- 
 tiva and capsule, by being too small, should stop the 
 second hook too soon, it should be enlarged toward the 
 equator by a cut or two of the scissors. Having already 
 armed the number five silk with two needles, the operator
 
 HETEROPHORIA. 259 
 
 places one of them in the needle holder, and, passing it 
 through the cut beneath the muscle, forces it through the 
 upper border of the tendon, close to the sclera (if an inter- 
 nus or an externus, but the outer border if a superior or 
 inferior rectus), and brings it out at once through the cap- 
 sule and conjunctiva. While doing this the tendon is 
 held up by the first hook and the needle is passed be- 
 tween this hook and the sclera. No other puncture will 
 have to be made with this needle, but it should remain 
 on the suture so as to facilitate the passing of that end 
 of the suture through one of the holes of the suture 
 plate later. The first hook remaining under the tendon 
 and still held by the operator, the assistant is directed 
 to pass the other hook as far back beneath the muscle as 
 possible, at the same time lifting the muscle well from 
 the sclera. The operator, with the second needle in the 
 holder, passes it through the opening beneath the belly 
 of the muscle as far back as he wishes, when he forces 
 it through the muscle, then through the capsule and con- 
 junctiva, so that a line connecting this and the first punc- 
 ture shall be parallel with the plane of rotation of this 
 muscle. The suture is now drawn on so as to make the 
 thread disappear beneath the muscle. The second needle 
 is again placed in the holder, and the operator passes it 
 through the conjunctiva, capsule, and the other border 
 of the muscle, bringing it out through the cut in the con-
 
 260 HETEROPHORIA. 
 
 junctiva and capsule. The third puncture is so made 
 that the loop of thread passing- from the point of the 
 second puncture to it, and lying 1 on the conjunctiva, shall 
 be parallel with the equator of the eye. Now the assist- 
 ant's hook may be removed. The surg-eon aguin places 
 the second needle in the holder and passes it through 
 the cut beneath the tendon, which he still lifts with his 
 own hook, and forces it through the other border of the 
 tendon close to its insertion, and bring-s it out through 
 capsule and con-junctiva, so that a line connecting- the 
 first puncture and this, the fourth, shall be parallel with 
 the corneal marg-in, and the line from the third to the 
 fourth puncture shall be parallel with the plane of rota- 
 tion. Drawing- on this end of the suture, that part of it 
 between the third and fourth punctures disappears be- 
 neath the muscle. The operator's hook is now removed, 
 and the two needles, after being- made to carry the two 
 ends of the suture througfh the holes in the silver plate, 
 are also removed. It only remains to tie a surg-eon's knot 
 over the plate, drawing- sufficiently hard to bring- forward 
 that portion of the muscle lying- beneath the loop which 
 rests on the conjunctiva, until it rests in contact with the 
 tendon at its insertion. The knuckle of muscle, capsule, 
 and conjunctiva thus made demands no attention, since, 
 in the course of a few weeks, it disappears by absorp- 
 tion atrophy. The patient will complain some at the
 
 HETEROPHORIA. 261 
 
 first two passages of the second needle, and also of the 
 drawing- brought about by tying- the knot. The after- 
 treatment is the same as that for partial tenotomies. 
 
 If a shortening- is to be done so as not only to alter the 
 tension of the muscle, but also to change its plane of 
 rotation, the operation differs from that already described 
 only in the making- of the four punctures while placing 
 the suture. Let the condition to be relieved be an asthen- 
 ic exophoria complicated by a plus cyclophoria, in short- 
 ening an internus it should be that one belonging to the 
 cataphoric eye, provided there is a vertical error, other- 
 wise both interni should be shortened. The first needle 
 should be passed as nearly as possible through the upper 
 border of the tendon; the second needle should make its 
 first puncture through the muscle below the plane bisect- 
 ing it, while its second puncture should be made as near 
 as possible to its lower border. The third puncture 
 with the second needle should be made between the first 
 puncture and the plane bisecting the attachment of the 
 tendon. Thus it will be seen that the first and fourth 
 punctures are above the natural plane of rotation, while 
 the second and third punctures are below this plane. In 
 tying the knot, the lower border of the muscle is carried 
 upward, and in this way the muscle is given a new and 
 higher attachment, and thereby the plane of rotation is 
 correspondingly elevated.
 
 262 HETEROPHORIA. 
 
 If the external rectus must be shortened to cure an 
 asthenic esophoria complicated by a plus cyclophoria, the 
 position of the punctures should be reversed; for in such 
 a case the plane of rotation must be depressed by the 
 creation of a lower attachment, and both externi must 
 be thus operated upon. If there is also a hyperphoria, 
 this operation should be done only on the externus be- 
 longing 1 to the hyperphoric eye. 
 
 If the superior rectus is to be shortened to cure an 
 asthenic cata-cyclophoria of the eye to which it belongs, 
 the first and fourth punctures must be to the outer side 
 of its old plane of rotation, while the second and third 
 punctures should be on the inner side of this plane. 
 Tying the knot will create a new attachment farther 
 toward the temple than the original one. Thus the 
 plane of rotation is shifted out. Just the reverse must 
 be true of the punctures if they are to be made on the 
 inferior rectus with the view of curing an asthenic hyper- 
 cyclophoria of the eye to which it belongs. This would 
 shift its point of attachment toward the nose, carrying 
 the plane of rotation with it. 
 
 Partial marginal shortenings may be done for the re- 
 lief of cyclophoria when there is no special indication for 
 altering the tension of the whole muscle. In such an 
 operation, all the needle punctures should be made on 
 the same side of the muscle plane. To illustrate: There
 
 HETEROPHORIA. 263 
 
 being- but little exophoria, the existing- plus cyclophoria 
 may be cured by changing the plane of both interni 
 without greatly increasing- the tension of these muscles. 
 For the accomplishment of this the conjunctival and 
 capsular cut must be at the upper border of the muscle; 
 the needles must be passed the four times entirely in the 
 upper half of the muscle and tendon; and the space be- 
 tw-een the insertion of the tendon and the loop of the suture 
 must not be anything- like so great as in a shortening- of 
 the whole muscle. Tying- the knot over the suture plate 
 folds only the upper part of the muscle, the power of 
 this part being- thereby increased. The same operation 
 should be done on the internus of the fellow eye. 
 
 If the partial marginal shortening, to cure a plus cyclo- 
 phoria, is to be done on the externi, the lower margin of 
 the muscle and tendon is the part to be folded, and the 
 effect should be divided between the two externi. If, for 
 the same condition, the operations are to be done on the 
 superior recti, the suture must be taken in the temporal 
 margin of each; if on the inferior recti, the inner margins 
 only must be folded. But better and easier than partial 
 marginal shortenings would be marginal advancements. 
 
 ADVANCEMENT OPERATION. 
 
 While the necessity for this operation exists only rarely 
 in cases of heterophoria, yet it must now and then be
 
 264 HE>TEROPHORIA. 
 
 done. If there is no complicating- cyclophoria, the ad- 
 vancement must be made directly forward, so that after 
 the operation the plane of rotation shall be the same 
 as before. The same careful preparation of patient, 
 instruments, and hands must be made as for shortening-; 
 and the same instruments are needed, except that only 
 one hook will be required. This operation, done under 
 cocaine, is less painful than a shortening 1 , and is about 
 as quickly done. The lids should be separated widely 
 with a speculum. The conjunctiva should be grasped 
 in line with the center of attachment of the tendon, half- 
 way between the attachment and the margin of the cor- 
 nea, and in such a way as to lift a meridional fold, which 
 should be cut with the scissors. This cut, after gaping, 
 should be about as large as the tendon insertion is wide. 
 The posterior flap should be drawn backward to a point 
 just behind the insertion. Now, by means of forceps 
 and scissors, a snip should be made through the capsule 
 at one border of the tendon, and through the opening 
 thus made a large hook should be passed beneath the 
 tendon. While the assistant holds the conjunctival flap 
 back, the operator raises the tendon with his hook, and 
 then passes one of the two needles with which the suture 
 is armed, twice through the capsule and tendon, so as to 
 include its center, and a little way behind its insertion. 
 This is done in the manner of taking a stitch in cloth.
 
 HETEROPHORIA. 265 
 
 The assistant now takes hold of the two ends of the 
 suture and draws the loop well up against the under 
 surface of the tendon, at the same time lifting- the ten- 
 don slightly away from the sclera. Aided by the hook, 
 the operator now completely divides the tendon, at its in- 
 sertion, with one or two snips of the scissors. The next 
 step is to make a pouch beneath the anterior conjunctival 
 flap, which is easily done with forceps to hold and scis- 
 sors to cut. This pouch should be made directly in front 
 of the old attachment, and neither higher nor lower, if 
 the muscle is an externus or an internus, nor farther out 
 or in, if the muscle is a superior or inferior rectus. In 
 either case, the pouch should extend up to the corneal 
 margin. The next step is to pass the two needles 
 through the posterior conjunctival flap a little way be- 
 hind its edge. Now the operator lifts the anterior con- 
 junctival flap with the forceps and carefully passes one 
 needle, held by the needle holder, into the pouch already 
 prepared, and makes it dip well into the sclera, but not 
 through it, a little above (if it be the upper needle) an 
 imaginary line bisecting the original attachment, and 
 only the slightest distance away from the cornea. In 
 passing out of the sclera the needle penetrates the con- 
 junctiva. This needle is now held out of the way by the 
 assistant, while the operator passes the second needle 
 in the same way, but a little below the line bisecting the
 
 266 HETEROPHORIA. 
 
 original insertion. The needles are now passed through 
 the holes in the silver plate, after which they are re- 
 moved. The assistant now grasps the conjunctiva, cap- 
 sule, and muscle just behind the loop and forcibly draws 
 these structures well forward, while the operator ties 
 the knot. The farther the loop of the suture is passed 
 through the tendon behind the insertion, the greater will 
 be the effect of the operation. The suture passed, as 
 described above, the tension of the muscle will be in- 
 creased, but its plane of rotation will not be changed. 
 
 Since a suture thus taken is not likely to cut its way 
 out, even to a small extent, too much over-effect should 
 not be attempted. If the needles were not made to dip 
 into the sclera, but simply passed through the conjunc- 
 tiva near the corneal margin, an over-effect would be 
 necessary, for the reason that the thread will partly cut 
 its way out before adhesion has formed, allowing some re- 
 cession of the advanced tendon. There is even danger 
 that the thread will cut its way entirely out if passed 
 only through the conjunctiva, when, of course, the re- 
 cession would be excessive. No advancement operation 
 is safe unless the suture is well anchored in the sclera. 
 
 An advancement intended not only to alter the tension, 
 but also to change its plane of rotation, differs from the 
 operation thus described only in selecting the place for 
 the sclero-conjunctival stitches. If the muscle to be
 
 HETEROPHORIA. 267 
 
 thus operated upon is an interims, and the exophoria is 
 complicated by a left hyper-cyclophoria, the one to be 
 advanced is the right internus, when one of the objects 
 in view is the elevation of its plane of rotation. The 
 tendon must be found, and a loop of the suture must be 
 passed through it, as for a straight-forward advancement. 
 After completely severing the tendon from the attach- 
 ment, the conjunctival pouch must be made higher than 
 the original attachment. The two needles must now be 
 passed into the pouch, and made to dip into the sclera, 
 then out through the conjunctiva, at chosen points, 
 higher up than the old attachment, and close to the cor- 
 neal margin. On tying the suture thus passed, the 
 muscle is carried higher up on the globe, as well as 
 farther forward. Thus its tension is altered so as to 
 cure the exophoria, and its plane is changed so as to 
 counteract the cataphoria and the plus cyclophoria. 
 
 In like manner the plane of either the externus or the 
 superior or inferior recti may be changed by an advance- 
 ment, the only difference being, in cases of plus cyclo- 
 phoria complicating other phorias, the direction in which 
 the plane is to be shifted. That of the externus must be 
 carried lower; that of the superior rectus, farther out; 
 that of the inferior rectus, farther in. 
 
 Marginal advancements may be done on both intern! 
 when there is only a slight asthenic exophoria complicated
 
 268 HETEROPHORIA. 
 
 by a plus cyclophoria. In doing- this, the stitch in the 
 tendon should be in its upper border; only the upper 
 fibers should be cut at the insertion, after which, by 
 means of scleral stitches, this part alone should be 
 brought straight forward, or only slightly higher, and 
 not very far in advance of the old insertion. 
 
 Similar operations on the externi, or on the superior 
 and inferior recti, may be done under proper indications, 
 the operator being certain that he has selected the proper 
 part of the tendon for the partial advancement. 
 
 In all advancement operations the suture should be 
 tied over the silver plate, and should be allowed to re- 
 main in place seven days, so as to give enough time for the 
 formation of adhesions. In removing the suture, care 
 should be exercised that the adhesions may not be torn 
 loose. 
 
 The after-treatment should be the same as for partial 
 tenotomies; that is, the free and frequent use of the 
 antiseptic-anodyne solution. 
 
 Other methods of making the advancement operation 
 might be given. The main objection to the high-and-low 
 stitch operations, devised and advocated by Beard, of 
 Chicago, and Black, of Denver, is that the advanced 
 tendon cannot be accurately placed, so that in one case 
 the plane of rotation may be changed, when it should 
 have remained as before; while in another case it might
 
 HETEROPHORIA. 269 
 
 remain as before, when it should have been changed. 
 Nor are these operations so simple or so free from trau- 
 matism as the very easy and safe method indorsed and 
 advised in this chapter. 
 
 Again, let it be said, advancements are rarely indicated 
 in the treatment of heterophorias, and, whenever pos- 
 sible, should be substituted by the operation of shorten- 
 ing", which is easier, safer, and better. But in Hetero- 
 tropias, as will be shown in Chapter IX., advancements 
 are indicated in a large proportion of cases. 
 
 The best of all advancement operations, therefore the 
 only one that should be done, is the " flat advancement " 
 without severing the tendon, devised by Lagleize. A 
 horseshoe incision, with the convexity toward the cor- 
 nea, should be made through the conjunctiva and capsule 
 of Tenon, from a point well in advance of the tendon at- 
 tachment, backward, over the muscle to be advanced, 
 sufficiently far to expose that part of the muscle through 
 which the loop of the suture must be passed. The as- 
 sistant must hold this flap out of the way by means of a 
 forceps. The operator then passes a large strabismus 
 hook beneath the tendon, and draws it well up against 
 the insertion of the tendon. Next he passes a second 
 large hook beneath the tendon and carries it backward 
 beneath the belly of the muscle to a point beyond where 
 he expects to pass the loop of suture. He now places
 
 270 HETEROPHORIA. 
 
 the second hook in the hand of the assistant, who gently 
 lifts the muscle away from the globe. With the first 
 hook the operator steadies the eye while passing" the 
 suture through the muscle, which he may do in one of 
 two ways: (1) He may take the muscle part of the stitch 
 with only one of the two needles with which the suture 
 is armed, by passing it through the muscle near one bor- 
 der and bringing it out at a point directly opposite, near 
 the other border. Drawing the suture after the needle 
 thus passed places the loop beneath the belly of the 
 muscle. Or (2) he may pass one needle beneath the mus- 
 cle and force it through near the far border, and then 
 pass the second needle through the near border, from 
 beneath, at a point directly opposite the puncture of the 
 other needle. Drawing the suture after the two needles 
 places the loop beneath the belly of the muscle, as if it 
 had been taken with one needle, as described in (1). 
 This loop must always be just as far behind the inser- 
 tion of the tendon as the later scleral stitches shall be in 
 front. The muscle part of the suture having been 
 passed, the two hooks should be removed. The next 
 step of the operation is the passing of both needles 
 through the anterior margin of the capsulo-conjunctival 
 flap. The operation must be completed without cutting- 
 the tendon. To enable him to pass easily the scleral 
 stitches, the operator fixes the eyeball by firmly grasp-
 
 HETEROPHORIA. 271 
 
 ing, with fixation forceps, the exposed tendon at its in- 
 sertion, and then passes first one needle and then the other 
 deep into, but not through, the sclera, at points just as 
 far in advance of the tendon insertion as the loop is be- 
 hind it. The scleral stitches are to be neither hig-her 
 nor lower than the two points of passing- of the muscle 
 part of the suture, if the rotation plane of the muscle is 
 not to be chang-ed. The needles should now be passed 
 throug-h the two holes of the Price suture plate, after 
 which they should be removed. In tying- the surg-eon's 
 knot on the silver plate, the muscle is carried over its 
 attachment until that part throug-h which the loop was 
 passed is at the line of the two scleral punctures, and it 
 is kept there by the completion of the knot- The cap- 
 sulo-conjunctival flap completel} T covers the operative 
 field by having- been included in the suturing-. The 
 stitches must be allowed to remain seven days. 
 
 If the rotation plane of the muscle must be chang-ed, 
 the scleral punctures must be made in the direction in- 
 dicated in any g-iven case. 
 
 There is no advancement operation that will compare 
 with the "flat advancement" operation of Lag-leize, in 
 the ease with which it is done, in simplicit}', and in safe- 
 ty; but even this operation should be done only when 
 more effect is needed than can be g-otten from the sim- 
 pler and safer operation of tucking-, or folding-, or short-
 
 272 HETEROPHORIA. 
 
 ening, devised by the author, but erroneously claimed by 
 sundry others. The shortening 1 operation is fully de- 
 scribed on pages 257 to 263. 
 
 In the treatment of heterophoric conditions by any 
 method outlined in this chapter, the aim is to relieve the 
 basal or fusion brain-centers from abnormal work, by 
 giving" equal tonicity to the two muscles of any pair 
 the establishment of orthophoria. 
 
 To withhold the treatment indicated in any given case 
 of heterophoria is unjust to the patient and will be hurt- 
 ful to the practitioner. The day has forever passed 
 when an oculist can securely boast of ignorance of heter- 
 ophorias, on his own part, and, in turn, speak dispara- 
 gingly of others who claim to know. Confession of ig- 
 norance on his own part disqualifies one for passing un- 
 favorable judgment on others who, by means of hard 
 study and close observation, have a right to claim that 
 they know.
 
 CHAPTER IV. 
 
 ESOPHORIA. 
 
 THERE is an esophoria which, because of its nature, may 
 be called "true," or "intrinsic;" while there is another 
 form that should be termed " pseudo." The one kind is 
 entirely distinct from the other, and yet the two often co- 
 exist, the one being- grafted on to the other. Whatever 
 may be the kind of esophoria, there is a tendency on the 
 part of the interni alone, or with the aid of their syner- 
 gists, to converge the visual axes at a point between the 
 observer and the object fixed; but this too near intersec- 
 tion of the visual axes is prevented by excessive nerve 
 impulses sent to the antagonizing muscles, increasing 
 their tension abnormally. In the interest of binocular 
 single vision the too great inherent tension of the interni 
 is counteracted by a corresponding nervous tension of 
 the externi. 
 
 INTRINSIC ESOPHORIA. In this condition the interni 
 have an advantage over the externi, which may be due 
 to any one of several conditions. It may be that the in- 
 terni are over-developed, or, what would result in the 
 same thing, the externi may be under-developed. In 
 
 (278)
 
 274 ESOPHORIA. 
 
 either case there would be an imbalance in favor of the 
 interni. That this is often true hardly admits of a doubt; 
 for every surgeon who has operated often will testify 
 that, in operating on the internus to lessen its tension, 
 he has frequently found it very large and strong, and 
 that, in operating on the externus to increase its tension, 
 he has found it small and weak. 
 
 The interni may not be over-developed, but abnor- 
 mally short; or the externi may be abnormally long, thus 
 giving an imbalance in favor of the interni. In oper- 
 ating on an internus to lessen its tension, it is sometimes 
 found to be tense, as if stretched; while in operating on 
 an externus to increase its tension, this muscle is found 
 loose and flabby. 
 
 The interni may not be over-developed nor the ex- 
 terni under-developed, nor may the interni be too tense 
 while the externi are too lax. The esophoria found in 
 such a case would be due to the interni having their at- 
 tachments too far forward, while the externi have their 
 attachments too far removed from the corneal margin. 
 
 If either of the conditions mentioned above should be 
 the cause of an esophoria, it can be understood readily 
 how the esophoria may be greater in the one eye than in 
 the other, and that it may exist only in one eye, the lat- 
 eral muscles of the other eye being perfectly balanced. 
 This can be determined quickly and accurately by means
 
 ESOPHORIA. 275 
 
 of the monocular phorometer, the binocular phorometer 
 being wholly unreliable for this purpose. 
 
 Whatever may be the cause, esophoria is usually about 
 equal in the two eyes. Regardless of the existence of 
 the one or the other of the four causes discussed, or that 
 two or more of them may coexist, the treatment, as will 
 be shown, must be directed either toward the interni 
 with the view of lessening their tension by partial tenoto- 
 mies, or toward the externi with the view of increasing 
 their power by means of exercise or by shortening or ad- 
 vancing one or both of them. In low degrees of the er- 
 ror, prisms in positions of rest for the weak externi may 
 be tried. 
 
 True, or intrinsic, esophoria may not depend on either 
 one of the four causes mentioned, but may be caused by 
 a naturally over-developed third conjugate innervation 
 center which, without being over-stimulated, continu- 
 ally, during waking hours, is sending excessive nerve 
 impulses to the otherwise normal interni, to counteract 
 which, over-stimulation of the centers controlling the ex- 
 terni is demanded; or there may be an under-develop- 
 ment of the centers controlling the externi, requiring 
 that these shall be over-stimulated in order that a nerve 
 impulse sufficiently strong shall be sent to the externi to 
 counteract the normal impulse sent to the interni. The 
 third conjugate innervation center is wholly undeveloped
 
 276 ESOPHORIA. 
 
 in some cases, there being- entire absence of power to 
 converge; in other cases it appears that this center is 
 not fully developed; hence it is reasonable to conclude 
 that now and then an over-development of this center 
 exists. If so, the esophoria is as true, or intrinsic, as if 
 the muscles themselves were at fault. There may be, 
 or there may not be, a conjugate innervation center for 
 the externi; but, if so, it is only intended that it shall 
 force the externi to counteract- the tendency on the part 
 of the interni to make the visual axes cross too soon. It 
 would not be in the interest of binocular single vision 
 for a conjugate divergence brain center to exist, hence 
 the supposition that there is no such center. 
 
 Unless one or more of the above-mentioned causes ex- 
 ists, there can be no such thing as an intrinsic esophoria. 
 The superior and inferior recti, when attached, in great- 
 er part, on the nasal side of the vertical meridian of the 
 eye, act as a secondary cause of true esophoria. 
 
 Malformation of the orbits cannot have much to do, 
 directly, with the causation of intrinsic or even pseudo- 
 esophoria. As has been shown in Chapter I., the an- 
 gle of convergence for eyes that are wide apart is but 
 little greater than the angle of convergence when the 
 eyes are close together, and yet that little may consti- 
 tute one of the factors in the production of an esophoria, 
 or, vice versa, of an exophoria. When the eyes are 3
 
 ESOPHORIA. 277 
 
 inches apart and the point of fixation is 16 inches, the 
 angle of convergence is 10.7, while the angle of con- 
 vergence for the same point, the eyes being 2 inches 
 apart, would be 7.16, a difference of 3.54. It is, there- 
 fore, reasonable to conclude that a muscle adjustment 
 that would give orthophoria when the eyes are 3 inches 
 apart would give esophoria if they were only 2 inches 
 apart. It is also reasonable to conclude that a muscle 
 adjustment that would give orthophoria, the base-line 
 being 2 inches, would give exophoria if the base-line 
 were 3 inches. Malformation of the orbit must play 
 only a very small part in the production of an esophoria 
 or an exophoria. 
 
 STHENIC ESOPHORIA. The quantity of the esophoria 
 does not determine its character with any certainty. If 
 the error is sthenic in character, it can be told only by 
 resorting to the duction and version tests. How to 
 make these tests has been fully set forth in Chapter II. 
 and Chapter III.; and so important are these tests, 
 from a therapeutic standpoint, they can never be safely 
 neglected. In sthenic esophoria adduction should be 
 more than 25, and adversion should be more than 50. 
 Abduction and abversion may be only little less than 
 normal, and rarely would these exceed the normal. 
 More dependence must be placed on abduction and ab- 
 version than on adduction and adversion in determining
 
 278 ESOPHORIA. 
 
 if an esophoria is sthenic. If, in a case of esophoria, ab- 
 duction and abversion are nearly normal, it is of the 
 sthenic type. 
 
 ASTHENIC ESOPHORIA. Here, again, it is not the 
 quantity of the error that determines its character. It is 
 only by the duction and version tests that the asthenic 
 may be distinguished from the sthenic. In such a 
 case the adduction power is less than 25, and the ad ver- 
 sion is less than 50. Abduction and abversion will be 
 correspondingly low. If in responding to these tests a 
 patient should show less duction and version power than 
 he really has, the error will be on the safe side. In as- 
 thenic esophoria the intern! should never be operated 
 upon. What to do for such cases will be fully set forth 
 under the head "Treatment." 
 
 PSEUDO-ESOPHORIA. As its name implies, it is an 
 esophoria that has neither of the above-mentioned 
 causes. It is wholly dependent on the relationship that 
 exists between the third conjugate innervation center 
 and the center controlling the ciliary muscles. It is never 
 found in a myope; it is never shown in the distant 
 test when the patient is an emmetrope. Even an emme- 
 trope may show a pseudo-esophoria in the near, but 
 only when the ciliary muscles are weak and must re- 
 ceive an abnormal impulse in order to focus near objects. 
 Pseudo-esophoria always exists in cases of hyperopia,
 
 ESOPHORIA. 279 
 
 manifesting- itself in one of three ways: first, lessening- 
 the quantity of an intrinsic exophoria; second, showing- 
 an esophoria when, in reality, there is no imbalance be- 
 tween the lateral recti; third, showing- a greater quan- 
 tity of esophoria than really exists. Thoug-h false in 
 character, it is nevertheless harmful, unless it compli- 
 cates an exophoria. Then, as will be shown in the 
 chapter on exophoria, it is helpful in the absence of any 
 treatment of the exophoria. 
 
 Bonders was rig-ht when he emphasized the influence 
 that accommodation has over converg-ence, thoug-h some 
 have doubted that there is any truth in his teaching- on 
 this subject. He may have attached too much impor- 
 tance to it; doubtless he did g-o be} T ond bounds when he 
 taug-ht that hyperopia was the chief cause of internal 
 strabismus. Some idea of the probable effect that ac- 
 commodation has over convergence may be obtained by 
 the study of eyes that are emmetropic and orthophoric. 
 Such eyes accommodate 3 D for a distance of 13 inches. 
 The distance between the centers of the eyes being- 2-1 
 inches, the angle of converg-ence for 13 inches will be 
 11. Each eye accommodates 3 D, and its visual axis is 
 turned toward the median plane of the head throug-h an 
 arc of 5.5, showing- nearly 2 of converg-ence for 1 D of 
 accommodation as the normal. This holds almost true 
 when the accommodation is 1 D, the point of fixation be-
 
 280 ESOPHORIA. 
 
 ing at a distance of 1 M. The base-line being 2i inches, 
 the angle of convergence will be 3:6, half of which 
 (1.8) will show the converging of each axis toward the 
 extended median plane of the head. To show how 
 nearly the proportion holds good, the following is given: 
 3 D: 5.5 : : 1 D: 1.8. Thus it would appear thai 
 1 D of hyperopia would give 1.8 of pseudo-esophoria, 
 the proportion practically holding good up to 6 D, there 
 being a variation of only .1. In 6 D of hyperopia the 
 pseudo-esophoria for each dioptre would be 1.9. 
 
 A pseudo-esophoria may be chargeable, in some unac- 
 countable way, to a complicating plus cyclophoria. This 
 surmise becomes stronger since it is well known that an 
 esotropia occasionally has for one of its causative factors 
 a plus cyclophoria, which must be corrected to make it 
 possible for the esotropia to be cured. There must be, 
 however, an intrinsic esophoria, which is only aggravated 
 by the cyclophoria. 
 
 In many cases of esophoria the distant test shows a 
 greater error than the test in the near, and in some cases 
 an esophoria is shown in the distant test and an exo- 
 phoria in the near. Occasionally the esophoria shown in 
 the near test is from 1 to 10 greater than that shown 
 in the far test. This variation will not show itself 
 when the esophoria is wholly intrinsic. If there is 
 emmetropia, the esophoria in the distant test is intrinsic.
 
 ESOPHORIA. 281 
 
 and the same quantity of the error will be shown in the 
 near test, if the ciliary muscles are ideal in structure 
 and size and ready to g-ive full response to the normal 
 stimulus sent to them from the brain-center that controls 
 their action, when accommodating- for the near point. If 
 the point to be fixed is 16 inches from the eyes, the 
 impulse sent from the brain to the ciliary muscles will 
 be a 2-50 D impulse and the muscles will respond so as 
 to increase the refraction of the lenses 2.50 D. The 
 associated impulse sent to the interni, the distance be- 
 tween the eyes being- 2 2 inches, would be enough to 
 make the two visual axes swing- toward each other 4.5, 
 so that the ang-le of convergence would be 9 (a small 
 fraction less). If the diplopia test in the distance 
 shows 6 of esophoria, the near test will show the 
 same, for nothing exists to break the evenness of the 
 error. In another case of emmetropia, suppose the 
 ciliary muscles to be subnormal in their development, so 
 that more than a 2.50 D impulse must be sent from the 
 brain-center in order to make them respond sufficiently 
 to increase the refraction of the lenses 2.50 D. For the 
 sake of arg-ument, let a nerve impulse of 5 D be neces- 
 sary to elicit a 2.50 D response on the part of the ciliary 
 muscles; the associated impulse sent to each internus 
 would be double that of the normal (4.5 X 2 = 9) in 
 the effort to accommodate at 16 inches. The distant
 
 282 ESOPHORIA. 
 
 test showing- 6 of esophoria, the near test would show 
 10.5 of esophoria (6 intrinsic esophoria + 4.5 pseudo- 
 esophoria = 10.5). 
 
 In another case of emmetropia, suppose the ciliary 
 muscles to be hyper-developed, so that only a 1.25 D 
 nerve impulse is necessary to elicit a 2.50 D response by 
 the ciliary muscles; the associated impulse sent to the 
 interni would be just half the normal (4.50 -4- 2 = 2.25) 
 when accommodating for a point at 16 inches. The 
 deficiency of associated impulse must be supplied by a 
 corresponding 1 amount of the inherent tension of the 
 interni, diminishing 1 the esophoria in the near test just 
 to that extent. To the convergence impulse (2.25) 
 must be added 2.25 of the esophoria in order to have 
 the visual axes form an angle of convergence of 9. 
 Then, the distance test showing 6 of esophoria, the near 
 test would show 3.75 of esophoria (6 -2. 25 = 3.75). 
 
 In still another case of emmetropia, there may be an 
 intrinsic esophoria of 2 in the distance. The ciliary 
 muscles may be such as to require only a 1 D impulse to 
 call forth 2.50 D of activity on the part of hyper-devel- 
 oped ciliary muscles, in accommodating for 16 inches. 
 The associated impulse sent to the interni would be only 
 1.8, when an impulse of 4.5 is required for convergence 
 at 16 inches. When the whole of the 2 of intrinsic ten- 
 sion of the interni is used in aiding convergence, the
 
 ESOPHORIA. 233 
 
 guiding- sensation must make a special call on the third 
 innervation center for .7 more of convergence on the 
 part of each internus in order that the proper angle of 
 convergence may be formed (associated impulse 1.8 -f 
 2 intrinsic esophoria -f .7 extra impulse from the third 
 conjugate center = 4.5). The diplopia test in the near 
 withdraws the extra impulse from the third conjugate 
 center and exophoria of .7 is shown. 
 
 It is not the response of the ciliary muscles in diop- 
 tre changes of the lenses that causes a definite asso- 
 ciated contraction of the interni, but it is the greater 
 or smaller impulse, measured in dioptres, generated 
 by the brain - center controlling the ciliary muscles, 
 that develops the associated action of the interni; for 
 every 1 D of ciliary impulse there is 1.8 of convergence 
 impulse. 
 
 Experiments and observation do not show that an 
 associated nerve impulse is sent to the ciliary muscles 
 from the center controlling them because of an over- 
 stimulation of the third conjugate innervation center. 
 This would be shown in spasm of accommodation 
 pseudo-myopia a condition never seen in cases of eso- 
 phoria, and rarely seen at all, even in a case of exo- 
 phoria. The condition so often spoken of as spasm of 
 accommodation is not such, but is the temporary con- 
 tinuance of the manifestation of an acquired tonicity of
 
 284 ESOPHORIA. 
 
 the ciliary muscles, when one begins the wearing 1 of con- 
 vex lenses for the correction of hyperopia. 
 
 Whatever may be true of other associated brain-cen- 
 ters, it appears that the center of the ciliary muscles 
 and the third conjugate innervation center can have the 
 associated impulse run in only one direction; that is, 
 from the former to the latter. 
 
 TESTS FOR ESOPHORIA. 
 
 No test for esophoria can be relied on when the eyes 
 are under the influence of a mydriatic. Within an hour, 
 and it may be for a much longer time, after the instilla- 
 tion of a mydriatic, the third conjugate innervation cen- 
 ter is excessively stimulated, either directly or indirectly, 
 more likely the latter, so that an esophoria will be 
 shown when there is none; existing esophoria will be 
 increased more or less; and an exophoria will be made to 
 appear less than it really is. All of these statements 
 are certainly true, in both the far and the near tests, if 
 the patient is a hyperope; they are true in the near, if 
 not in the far, if the patient is an emmetrope; they are 
 also true in the near, if not in the far, if the patient is a 
 myope of less than 2.50 or 3 D. 
 
 The explanation for this phenomenon, given by the 
 author in 1892, he still believes to be true. This ex- 
 planation is as follows:
 
 ESOPHORIA. 285 
 
 A very peculiar feature of the use of a mydriatic is 
 that at first probably from one to several, hours a 
 mydriatic, in hypermetropic eyes, will increase the eso- 
 phoria, will lessen an exophoria or convert it into ortho- 
 phoria, or even into an esophoria. Until now this has 
 been unexplained. The following- explanation must be 
 true: The mydriatic acts on either the ending's of the 
 accommodative nerve fibers or on the fibers of the 
 muscle of accommodation, certainly not on the accommo- 
 dative center, which, therefore, must remain in a state 
 susceptible of excitation by the demands from the guid- 
 ing- sensation. As the muscles of accommodation pass 
 into their forced rest, the retinal images become less 
 sharp in outline, the blurring increasing up to the point 
 of full suspension of accommodation. The guiding sen- 
 sation calls on the accommodative center for sharper 
 images, and the impulse is sent out, but finds the mus- 
 cles unresponsive; the call is repeated more eagerly, and 
 a stronger impulse is sent to the sleeping muscles, and 
 still no change is effected in the images; and thus the 
 calls and the responses are kept up for a longer or a 
 shorter time. For every degree of activity thus excited 
 in the accommodative center, there is a corresponding 
 tendency to activity generated in the converging center. 
 So long as the calls are made on, and responses are made 
 by, the accommodative center, the center of convergence
 
 286 ESOPHORIA. 
 
 stands ready to call into unusual action the interni, 
 which they do the moment the guiding- sensation is 
 robbed of its restraining 1 power by the test for hetero- 
 phoria, when an increased pseudo-esophoria is shown. 
 But finally the guiding sensation ceases its calls, or, 
 from exhaustion, the accommodative center ceases to re- 
 spond, and now the normal muscular condition is again 
 shown, and will remain manifest, although the mydriatic 
 may be continued. From this observation on the myd- 
 riatic as a disturber of the salutary relationship of the 
 centers of accommodation and convergence, we deduce 
 the following- conclusion: All tests for lateral hetero- 
 phoria are wholly unreliable within the first few hours 
 after eyes have been brought under the influence of a 
 mydriatic. 
 
 TESTS. 
 
 The exclusion test will always show an outward re- 
 setting- whenever the card is removed. The resetting 
 may be so slig-ht as not to be detected objectively; but 
 the patient will always be conscious of the apparent 
 movement of the test object toward the opposite side, 
 however slight may be the esophoria. 
 
 The red-glass test, by taking the eye slightly off its 
 guard because of the change in the color of the image, 
 will result in diplopia in many cases, the red light ap-
 
 ESOPHORIA. 287 
 
 pearing- on the side corresponding- to the eye before which 
 the red glass is held homonymous diplopia. It will 
 be distant from the true candle, more or less, depending 
 on the quantity of the error. The diplopia developed 
 by the red glass practically always indicates that an 
 operation should be done, but it does not determine the 
 muscle to be operated upon nor the kind of operation to 
 be done. This can be shown only by the duction and 
 version tests of both the interni and the externi. 
 
 The double prism, held with the 'line of union of the 
 bases horizontal, shows the middle, or true, object dis- 
 placed toward the corresponding side; or, if the true 
 object be fixed, the upper and lower false object will ap- 
 pear on the side corresponding to the position of the dou- 
 ble prism. A prism from the refraction case that places 
 the false and true objects in a vertical line, measures the 
 error, but does not indicate the method of procedure to 
 be adopted for effecting a cure. The duction and ver- 
 sion powers must be taken. 
 
 If the single prism be correctly held before the eye- 
 that is, the axis vertical and the base up the resulting 
 diplopia will be homonymous; and the extent of the devi- 
 ation can be measured by prisms, as when the Maddox 
 double prism is made the means of producing the diplo- 
 pia. The double prism has the advantage over the sin- 
 gle prism, whether they are placed in a trial frame or held
 
 288 ESOPHORIA. 
 
 in the hand, in that the examiner can always be certain, 
 with the double prism, that its axis is vertical, when the 
 two resulting- images are made to appear the one di- 
 rectly over the other. With the single prism there is no 
 such means of knowing the exact position of the axis, 
 hence the chance for the creeping in of an error that, on 
 the one hand, may show more esophoria, while, on the 
 other hand, it may show less, than really exists. The 
 ease with which this source of error might be eliminated 
 by the double prism was really the thought that led 
 Maddox to invent it. Of the two means for developing 
 diplopia by prisms, independent of the phorometer armed 
 with the spirit level, the double prism is by far the 
 better and more reliable. 
 
 The Maddox rod was invented because of a defect in 
 the double prism as first made, and as made even now 
 by some manufacturers. The grinding of both prisms 
 on one piece of glass left a somewhat rounded line of 
 union of the bases, so that not only would the candle 
 blaze be doubled when the base-line passed across the 
 pupil, but a streak of light, formed by the refraction of 
 the rays passing through the rounded line of union, ex- 
 tends more or less completely from the one false light to 
 the other. The streak served a good purpose, in that 
 it led to the invention of the indispensable rod; but 
 since it can no longer serve a good purpose, it should
 
 ESOPHORIA. 
 
 239 
 
 be eliminated by uniting- two separate prisms, base to 
 base. 
 
 While there is but one certain, therefore legitimate, 
 use for the Maddox rod viz., in testing 1 the oblique 
 muscles it is, nevertheless, frequently used in testing 
 the recti. 
 
 When the rod is horizontal before the rig-ht eye, the 
 vertical streak of light is seen to the rig-ht of the candle 
 
 UEFT 
 
 RIGHT 
 
 Fig. 42. RETINAL FUSION AREAS. 
 
 in every case of esophoria. The prism, base out, that 
 causes the streak to pass down through the light meas- 
 ures, but not accurately, the quantity of the esophoria. 
 The want of accuracy is due to the fact that the vertical 
 retinal meridian is not turned so far out, by contraction 
 of the internus, as to throw the streak entirely outside
 
 290 ESOPHORIA. 
 
 the retinal area in which resides the guiding- sensation; 
 therefore there would be some effort made at fusing 
 the part of the much-changed image with the true and 
 unchanged image in the other eye. Fig. 42 shows this 
 better than words can possibly portray. The figure 
 also shows how a displacing prism, with base up, would 
 throw the unchanged image of the candle blaze above 
 and entirely beyond the fusion area, so that no effort 
 would be made by the eye to disturb the position of 
 equilibrium into which it has turned. It will be seen 
 also that the rotary prism would carry the displaced 
 image to the vertical meridian without having it infringe 
 anywhere on the fusion area. The dotted line from e 
 represents the line of travel of the image while the 
 measurement of the error is being taken with the rotary 
 prism. At no time would a fusion impulse be excited. 
 Not so with the streak of light which crosses the fusion 
 area. The nearer this is carried by a rotary prism, or a 
 simple prism, base out, to the vertical retinal meridian, 
 the greater would be the demand made by the guiding 
 sensation on the center controlling the external rectus. 
 For this reason the rod test will give variable results 
 from time to time, and will always show less esophoria 
 than the patient really has. The same is true even to a 
 greater extent when the rod is used for testing for exo- 
 phoria and for hyperphoria and cataphoria. There is
 
 ESOPHORIA. 291 
 
 only one means for testing- for esophoria that is less reli- 
 able than the rod, and that is the strong- plus lens sug- 
 gested by Stevens. 
 
 From every standpoint the phorometer constitutes the 
 most desirable means for detecting- esophoria and meas- 
 uring- it. For reasons g-iven in Chapter II., the mo- 
 nocular phorometer is the best. The displacing- prism 
 should always be placed, base up, in the cell toward the 
 patient's eye; the thumbscrew for the rotary prism 
 should be in the horizontal; the index of the rotary 
 prism should stand at zero; and the spirit level should 
 be exactly reg-ulated. The upper, or true, object should 
 be fixed. The six-degree displacing- prism will throw 
 the false image above and entirely beyond the retinal 
 area of binocular fusion, taking the guiding sensation of 
 that eye entirely off its guard, so that the eye will at 
 once be turned in. The lower, or false, object will be 
 proportionately displaced from the vertical toward the 
 corresponding side- homonymous diplopia. Revolving 
 the rotary prism so that its index moves in the nasal arc, 
 the false object is brought farther and farther toward 
 the vertical line passing down from the true object, un- 
 til at last the patient observes that the false object is di- 
 rectly under the true object. The point at which the 
 index stops tells the degree of the error. The same re- 
 sult, practically, will be shown by any number of tests
 
 292 ESOPHORIA. 
 
 on the same day or on consecutive days, if the patient is 
 always careful to "fix" the true object. This point is 
 absolutely essential to the greatest accuracy; and if 
 strictly observed, there is no other factor to bring 1 in an 
 error. Certainly at no time will the false imag'e be 
 within the retinal area of binocular fusion. 
 
 The one eye tested, the instrument should be reversed 
 so as to test the other eye, for in this way only can it be 
 determined if there is more esophoria in the one eye than 
 in the other. 
 
 To know how to proceed in the treatment of any 
 grven case, this question must be answered: Is it 
 pseudo-esophoria? This is answered by a study of the 
 refraction under a mydriatic a little later. If there is 
 no hyperopia or hyperopic astigrnatism, the answer is: 
 "No." If there is hyperopia or hyperopic astig-matism, 
 the answer is, "Yes, at least in part," which part can 
 be easily calculated, for it would be 1.8, or nearly 2, 
 for every dioptre of the hyperopia and as much for every 
 2 D of hyperopic astigfmatism. The quantity of the 
 pseudo-esophoria thus determined, subtracted from the 
 full error, as shown by the phorometer, gfives the amount 
 of the true, or intrinsic, esophoria. 
 
 But before the mydriatic is used the duction and ver- 
 sion power of both interni and both externi should be 
 taken in order that the following* two questions may
 
 ESOPHORIA. 203 
 
 be answered: Is the intrinsic esophoria sthenic? Is it 
 asthenic ? 
 
 These three questions answered, the method of pro- 
 cedure becomes plain, as soon as complications have been 
 found or eliminated. 
 
 COMPLICATIONS OF ESOPHORIA. These are hypero- 
 pia and hyperopic astigmatism, hyperphoria and cata- 
 phoria, and plus and minus cyclophoria. The existence 
 or non-existence of one or more of these complications 
 must be known before it becomes possible to resort to 
 the correct treatment of esophoria. It has already been 
 shown how hyperopia and hyperopic astigmatism develop 
 a pseudo-esophoria, which can be cured by proper lenses. 
 A myopia and myopic astigmatism sometimes compli- 
 cate an esophoria, and when they do, their correction in- 
 creases the esophoria in the near, but not in the far. 
 
 A hyperphoria of one eye and a cataphoria of the 
 other will increase an esophoria, as will also a double 
 hyperphoria and a double cataphoria. How to deal with 
 these complications in the treatment of esophoria will be 
 shown under the head " Treatment." 
 
 As already stated, it is difficult to see how a plus or 
 a minus cyclophoria can add to an esophoria, since the 
 oblique muscles are abductors; but it can be seen readily 
 how an esophoria might be lessened by a cyclophoria. 
 It is possible, however, that a cyclophoria may excite
 
 294 ESOPHORIA. 
 
 the third conjugate innervation center in some way, so 
 as to develop a spasm of the interni, such as is excited in 
 cases of hyperopia; but there is not that definite rela- 
 tionship between the obliques and the interni that there 
 is between the ciliary muscles and the interni. Never- 
 theless, when cyclophoria complicates an esophoria, the 
 treatment of the esophoria must include the treatment of 
 the cyclophoria if the best and quickest results are to 
 follow; in fact, it is practically impossible to cure an 
 esophoria while the cyclophoria remains uncorrected. 
 
 For the methods of detecting- and measuring- hyper- 
 phoria and cataphoria, and plus and minus cyclophoria, 
 as complications of esophoria, the reader is referred to 
 Chapter VI. and Chapter VII. 
 
 SYMPTOMS OF ESOPHORIA. 
 
 These are any one or several of those mentioned as 
 resulting- from heterophoria, and the reader is referred 
 to that part of Chapter III. treating- of symptoms; 
 but not all the symptoms resulting- from abnormal 
 nervous tension of the ocular muscles are mentioned in 
 that chapter. It would be impossible to make a com- 
 plete list. There is not a single brain-center controll- 
 ing- any one organ or part of the body that may not be dis- 
 turbed, in sympathy with the centers that control the 
 ocular muscles; and,.wc<? versa, the centers controlling
 
 ESOPHORIA. 295 
 
 the ocular muscles may be sympathetically disturbed 
 because of excessive demands on the other centers. The 
 difference between other centers and those controlling 
 the ocular muscles is that the former have not so severe 
 a taskmaster as the guiding- sensation which compels 
 obedience, on the part of the ocular muscles, to the law 
 of corresponding retinal points in binocular vision. For 
 this reason no other centers are so likely to be over- 
 worked as are the eight fusional innervation-centers 
 whose duty is to control the recti muscles so that the 
 visual axes may always be in the same plane and may be 
 converged at the proper point, and the four conjugate 
 centers that force the obliques to parallel the vertical 
 axes with the median plane of the head. The only ex- 
 ception is the center that controls the action of the ciliary 
 muscles, which must also satisfy the guiding sensation 
 of the retina. 
 
 In monocular vision, as when one eye has been lost, 
 the possibility of the excitation of reflex nervous symp- 
 toms is greatly lessened. The centers not relieved of 
 the necessity of over-excitation when there is but one 
 eye are the center that sends impulses to the ciliary 
 muscle and the centers that must make the obliques 
 parallel the vertical axis with the median plane of the 
 head. Posing the head in monocular vision would re- 
 lieve the strain that may have been demanded of the
 
 296 ESOPHORIA. 
 
 recti in binocular vision. There is, therefore, truth in 
 the statement that has been made by people who have 
 lost one eye that ' ' the one eye is stronger than the two 
 ever were." 
 
 The symptoms of esophoria are not due directly to the 
 abnormally high inherent tension of the interni, but to 
 the abnormal nervous tension of the externi in their 
 effort to prevent the esophoria from being 1 transformed 
 into an esotropia, or to the nervous tension of other weak 
 muscles in their effort to counteract other errors that 
 may complicate the esophoria. 
 
 TREATMENT OF ESOPHORIA. 
 
 Errors of refraction that complicate an esophoria 
 should be measured under a mydriatic, and a full correc- 
 tion should be given. If the error is hyperopia, every 
 dioptre of correction will relieve 1.8, practically 2, of 
 the esophoria both in the far and in the near; if the error 
 is hyperopic astigmatism, every dioptre of correction will 
 relieve 0.9, practically 1, of the esophoria. The pseudo- 
 esophoria is thus cured. Any remaining esophoria is 
 intrinsic in character, unless it be caused by subnormally 
 developed ciliary muscles, which would be shown in the 
 near only. 
 
 If the refractive error is myopia, every dioptre of cor- 
 rection will add to the manifest esophoria in the near,
 
 ESOPHORIA. 297 
 
 but not in the far 1.8, that quantity of pseudo-exo- 
 phoria which, before correction, served to lessen the eso- 
 phoria; if the error be myopic astigmatism, every dioptre 
 of correction would add 0.9 to the formerly manifest 
 esophoria, but in the near only. With the correcting 
 lenses on, the esophoria shown by the phorometer is in- 
 trinsic in character. 
 
 Thus it is shown that the correction of hyperopia 
 and hyperopic astigmatism lessens the nervous tension 
 of the externi by relieving the associated nervous tension 
 of both the interni and the externi; while in intrinsic 
 esophoria the nervous tension is in the externi alone, the 
 tension of the interni being inherent. To obtain full 
 correction of the pseudo-esophoria, the hyperopia and 
 the hyperopic astigmatism should be fully corrected, 
 and the correction must be worn both for near and for 
 far seeing. If the esophoria is wholly pseudo, noth- 
 ing will be needed but the lenses for effecting a com- 
 plete cure; but if a part of the esophoria is intrinsic, 
 as may always be known without waiting, other treat- 
 ment will be necessary sooner or later. The double 
 nervous tension having been relieved by the lenses, all 
 symptoms may vanish for a time ; but ultimately the 
 nervous tension of the externi, necessary for correcting 
 the intrinsic esophoria, will cause symptoms to reappear. 
 This marked relief will follow only when the intrinsic
 
 298 ESOPHORIA. 
 
 esophoria is low in degree, while the pseudo-esophoria 
 is comparatively hig-h. 
 
 The wearing- of lenses correcting- myopia and myopic 
 astigmatism will cause no chang-e in the muscle imbal- 
 ance for distance ; but in the near, the wearing- of the 
 lenses will cause the whole of the esophoria to become 
 manifest, and the nervous tension of the externi will 
 be correspondingly augmented; the symptoms will be 
 aggravated, and the esophoria should receive immedi- 
 ate treatment. Until the esophoria has been cured it 
 will be better to let the patient take the lenses off when 
 engaging in near work, or, at most, wear only a partial 
 correction of the myopic error. Uncorrected myopia 
 lessens the nervous tension of the externi in esophoria 
 by diminishing the normal nervous impulse that would 
 be sent to the interni, if the ciliary muscles were in 
 action. 
 
 The effect of focal errors eliminated, the treatment of 
 the intrinsic esophoria depends on the quantity of the 
 error, in so far as non-operative efforts are concerned. 
 
 The non-operative treatment of esophoria of low 
 degree is of two kinds first, prisms in position of 
 action for the stronger muscles or of rest for the 
 weaker muscles; second, exercise of the weaker mus- 
 cles, which, in cases of esophoria, can be accomplished 
 only by prisms.
 
 ESOPHORIA. 299 
 
 PRISMS IN POSITIONS OF ACTION FOR THE 
 INTERNI. 
 
 Prisms to be worn constantly are always open to the 
 objection that they interfere with the law of direction, 
 but this is sometimes the less of two evils and should be 
 chosen. The visual axis under any and all circumstances 
 points to the apparent source of the light that throws 
 its image on the macula. In obedience to the law of cor- 
 responding- retinal points, an image that has been dis- 
 placed, by prismatic action, toward the temporal side 
 of the macula, makes the source of the light appear to be 
 on the opposite side and just as man} r degrees from its 
 real position as the image has been displaced from the 
 macula. When possible, fusion of the false object with 
 the true object is effected by the internus rotating the 
 eye until the macula is brought under the displaced im- 
 age. The visual axis points to where the object would 
 appear to be if no attempt at fusion had been made, and 
 of necessity passes through the center of retinal curva- 
 ture. The visual line that passes from the displaced im- 
 age to the fused object passes to the outer side of the 
 center of the retinal curve, and is a false line of direction. 
 
 Before placing a prism for constant wear by an eso- 
 phoric, the complicating muscle errors must be consid- 
 ered. The only indication for placing the axis of the 
 prism out of the horizontal is the coexistence of a cyclo-
 
 300 ESOPHORIA. 
 
 phoria, usually a plus cyclophoria, either with or with- 
 out a complicating hyperphoria of the one eye and a cata- 
 phoria of the other. If there is no vertical error, but 
 only a plus cyclophoria complicating- the esophoria, the 
 prismatic effect should be divided equally between the 
 two eyes, and the nasal end of each axis should be tilted 
 up through a sufficient arc for correcting the greater part 
 of the cyclophoria. This must be determined by test- 
 ing for the cyclophoria while the prisms are on. The 
 stronger the prisms, the smaller the arc of rotation of 
 the axes; and, vice versa, the weaker the prisms, the 
 larger the arc of rotation. To place the prisms, in such a 
 case, with the axes horizontal, would be to leave uncor- 
 rected the cyclophoria, a most important factor in the 
 causation of symptoms. To depress the nasal end of the 
 axes of the prisms, in a case of this kind, would be to 
 make the patient worse. 
 
 If there is a complicating hyperphoria of one eye and 
 cataphoria of the other eye, as well as a complicating 
 plus cyclophoria, the prismatic effect for the relief of 
 the esophoria should be applied wholly or in greater 
 part to the eye that is hyerphoric and the nasal end of 
 the axis should be elevated. As can be readily seen, a 
 prism thus placed would cause the eye to turn in and up, 
 the direction the strong muscles tend to take it, which 
 rotation w r ould tort the eye in, correcting the plus cyclo-
 
 ESOPHORIA. 301 
 
 phoria. If any of the prismatic effect is applied to the 
 cataphoric eye, the axis should be horizontal, for the rea- 
 son that, while depressing- the axis of the prism would 
 rest the weak superior rectus, it would increase the plus 
 cyclophoria; on the other hand, elevating the nasal end 
 of the axis \vould favor the weak superior oblique, but 
 would add to the abnormal nervous tension of the weak 
 superior rectus. 
 
 In a case of esophoria, complicated with a minus cy- 
 clophoria, the rule for tilting 1 the axes of the prisms 
 would be reversed all the way through. This compli- 
 cation is exceedingly rare. 
 
 If the esophoria is uncomplicated in a given case, the 
 prismatic effect should be equally divided between the 
 two eyes. These prisms can be worn with comfort, pro- 
 vided the two intern! are properly attached, and in many 
 cases they can be worn comfortably if the two interni 
 are attached, in greater part, above the horizontal plane 
 of the eyes. In many cases the superior obliques would 
 accept kindly the aid, in paralleling the vertical axes 
 with the median plane of the head, offered by the 
 interni that are attached too high. Constant prisms 
 for esophoria, when uncomfortable, point to attach- 
 ments of the interni that are, in greater part, below 
 the horizontal plane. In such a case the prisms 
 would have to be abandoned. The combined prismatic
 
 302 ESOPHORIA. 
 
 effect, as a rule, should not be more than half the eso- 
 phoria. 
 
 When focal errors require either convex or concave 
 lenses, these can be decentered so as to give the necessa- 
 ry prismatic effect. Por esophoria, convex lenses should 
 be decentered out and concave lenses should be decen- 
 tered in. The same rules for placing- prisms should 
 govern the decentering of lenses. It would seem 
 that authors ought to agree as to how much a given 
 lens should be decentered in order to obtain a definite 
 prismatic effect, but they do not. Maddox teaches that 
 a lens of 1 D must be decentered 1.75 cm. (17 5 mm.) to 
 obtain 1 of prismatic effect. He then gives the follow- 
 ing formula for determining the extent of decentration 
 of any lens for a required effect: C = P> ^> in which C is 
 the centimeters of decentering; P, the desired prismatic 
 effect; and D, the number of dioptres in the lens. Let 
 P = lij and D = 3, then the formula w^ould be: 
 C = 1H ^ 13 ^ = .875 cm., or 8.75 mm., which is about ^ of 
 an inch of decentering. 
 
 Jackson teaches that the following formula is practi- 
 cally correct : C = ^, in which C is the mm. of decen- 
 tering required; P, the prismatic effect desired; D, the 
 number of dioptres in the lens to be decentered; while 10 
 is the mm. of decentering of a 1 D lens for 1 (1 centrad) 
 of effect. Substituting figures for letters, as in the
 
 SSOPHORIA. 303 
 
 Maddox formula, we have : C = ULf == 5 mm>> or a b out 
 B of an inch of decentering, as compared with Maddox's 
 J- of an inch of decentering. 
 
 Thorington and May agree in taking 8.7 mm. for the 
 extent of decentering a 1 D lens in order to procure 1 
 of prismatic effect. For obtaining the amount of de- 
 centration of any lens, this would be their formula: 
 C = P$r?. Substituting figures for letters, as in the 
 other formulas, we have: C == l%->pl == 4.35 mm . ? or 
 about i of an inch of decentration, as compared with 
 Maddox's | of an inch and Jackson's of an inch ; or, 
 comparing in mm.: Maddox, 8.7; Jackson, 5; Thoring- 
 ton, 4.35; May, 4.35. By a little experimentation the 
 reader may satisfy himself that Jackson is practically 
 correct. The extent of decentration advised by Maddox 
 is entirely too much nearly double what it ought to be. 
 It may be that Maddox's estimate was for 1 of arc, and 
 not for 1 of prism, or 1 centrad. 
 
 One advantage that decentering a lens has over the 
 grinding of a lens on a prism is that the former is 
 cheaper ; another advantage is that the wearing of a 
 decentered lens is not attended by the reflected image of 
 any bright object, which is always toward the refract- 
 ing angle and in the line of the axis of the prism, unless 
 the prism is ground on both surfaces. Chromatic aber- 
 ration is no more, nor is it anv less, with a decentered
 
 304 ESOPHORIA. 
 
 lens than it is with a lens ground on a prism. The 
 great objection to decentered lenses is that the spherical 
 aberration must interfere to some extent \vith the sharp- 
 ness of retinal images; this, however, is but little when 
 the decentering is 6 mm. or less, and rarely is it more. 
 In very strong lenses, say 6 D, the decentering would 
 be only 5 mm. for 3 of effect. 
 
 The greatest objection to "relieving prisms" and to 
 decentered lenses is that they favor muscles in their 
 weakness. They lessen nervous tension, but not by 
 increasing the inherent power of weak muscles. It is 
 far better practice to increase the inherent power of 
 weak muscles, either by exercising them or by shorten- 
 ing or advancing them, or to increase the relative power 
 of the weaker muscles by lessening the tension of their 
 stronger antagonists by partial tenotomies. If patients 
 will not resort to exercise and decline to submit to 
 operations, they should be given the benefit which is to 
 be derived from prisms in positions of rest or from de- 
 centered lenses. 
 
 EXERCISE TREATMENT FOR ESOPHORIA. 
 
 Uncomplicated intrinsic esophoria of low degree may be 
 cured by proper exercise of the externi. The only means 
 applicable are prisms. The same gymnastic principles 
 apply to the externi as to the other muscles of the body.
 
 ESOPHORIA. 305 
 
 Light work, not continued too long, and rhythmic in 
 character, is exercise that increases muscular power. 
 Prisms of from 1 to 4, bases in, can be used for devel- 
 oping- the externi. Beginning- with the weaker prisms 
 and advancing to the next stronger at intervals of a 
 week or ten days, the strongest to be used are soon 
 reached. The exercise should be resorted to at the same 
 time every day, so as to easily form the habit of exer- 
 cising, and should be continued not longer than ten min- 
 utes at a time. One exercise daily or, at most, two ex- 
 ercises daily will be sufficient. I/enses correcting focal 
 errors should be worn at the time of exercising. The 
 exercise prisms in spectacle frames should be lowered 
 and raised alternately every three seconds throughout 
 the sitting. The object looked at may be anything that 
 can be seen distinctly, and it should be distant from the 
 observer not more than twenty feet nor less than ten 
 feet. Looking at the object through the prisms, the 
 externi are made to contract; raising the prisms, these 
 muscles at once relax. Thus contraction and relaxation, 
 rhythmic in character, are continued throughout the sit- 
 ting. Exercise that fatigues does not build, hence the 
 necessity of always stopping short of fatigue. A muscle 
 develops as the result of exercise in proportion to the 
 abundance of blood that can be brought into it. Abund- 
 ance of blood supply means quick results; scanty blood
 
 306 ESOPHORIA. 
 
 supply, because of smallness of the vessels supplying 
 the muscle, means slow results. These conditions can- 
 not be known beforehand; therefore it is better to tell 
 the patient that the treatment will have to be continued 
 for months. 
 
 Exercise of the externi that are attached, in greater 
 part, below the horizontal plane, will exercise, at the 
 same time, the inferior obliques, which would be good 
 in a case of minus cyclophoria, but bad in a case of plus 
 cyclophoria. If the externi have the ideal attachment 
 that is, half above and half below the transverse plane of 
 the eye exercise will always be well borne and will do 
 good. If attached too high, the exercise of the externi 
 will be associated with exercise of the superior obliques 
 and will usually be well borne and ought to do good. 
 These things can be known only as a result of exercise. 
 
 The object in view in exercising the externi is to so 
 increase their inherent power that, under a normal im- 
 pulse, they will be able to do a normal amount of work; 
 that their tension may be inherent, not nervous, and 
 sufficient to balance the inherent tension of the interni. 
 
 OPERATIONS. 
 
 No operation for pseudo-esophoria should ever be done. 
 The kind depending on hyperopia should be treated by a 
 full correction of the focal error; the kind due to subnor
 
 ESOPHORIA. 307 
 
 mal development of the ciliary muscles, making it neces- 
 sary that the center controlling them shall generate an 
 extraordinary nerve impulse, should be treated by gym- 
 nastic exercise of these muscles. 
 
 There can be drawn no unvarying line between opera- 
 tive and non-operative cases of intrinsic esophoria. If, 
 under the red-glass test, there is homonymous diplopia, 
 the case is almost certainly one to be operated upon; but 
 the kind of operation is not shown by this test. If the 
 esophoria at 16 inches is more than half the angle of con- 
 vergence (nearly 9) for that distance, the question of 
 operation should be considered; and if it is much in excess 
 of 5 in the near, there is no reason why an operation 
 should be delayed. Whatever the quantity of esophoria in 
 the distance, which is usually a little greater than that 
 in the near, it should not be relied on exclusively when de- 
 termining on an operation. Both the near and the far 
 tests should always be noted. The quantity of error be- 
 ing sufficiently great to indicate an operation, the next 
 thing to consider is the question as to whether the eso- 
 phoria is sthenic or asthenic. More than 25 of adduc- 
 tion and more than 50 of adversion would indicate a par- 
 tial tenotomy of one or both interni; there is nothing in 
 esophoria that can justify a complete tenotomy. If the 
 adduction is 25 or less and the adversion is 50 or less, 
 no operation should be done on the interni, but one or
 
 308 ESOPHORIA. 
 
 both extern! should be shortened. If in doubt as to 
 which of the two operations should be done, it would be 
 safer to choose the shortening- of an externus. Either 
 operation would cure wholly or in part the imbalance 
 the partial tenotomy, by lessening 1 the tension of the in- 
 ternus; the shortening-, by increasing the tension of the 
 externus. In properly selected cases either operation 
 would establish a sthenic orthophoria; in unfortunately 
 selected cases (those with normal or subnormal adduc- 
 tion) the tenotomy would establish an asthenic orthopho- 
 ria, a danger never attending the operation of shortening. 
 
 Abduction in an operable case of esophoria is a safe 
 guide in determining whether the operation should be 
 done to lessen the tension of an internus or to increase 
 the tension of an externus. If the abduction is above 5 
 or 6 and the abversion is but little below 50, the inter- 
 nus should be cut; if abduction is below 5 and abver- 
 sion is correspondingly low, the externus should be 
 shortened. 
 
 In uncomplicated cases of esophoria, the error about 
 equal in the two eyes, the operative effect should be di- 
 vided between them. In such cases the plane of rotation 
 must not be altered, hence the partial tenotomy must be 
 central and the shortening must be straight forward. 
 
 When esophoria is complicated with only hyperphoria 
 of one eye and cataphoria of the other, the operations on
 
 ESOPHORIA. 309 
 
 the lateral muscles should be done as if there were no 
 complications that is, the tension of the muscles should 
 be altered, but their planes should not be changed. 
 
 * o 
 
 Later the hyperphoria should be treated either by a per- 
 manent prism for the hyperphoric eye, by prismatic exer- 
 cise of the weaker muscle of each eye, or by a central 
 partial tenotomy of the superior rectus of the hyper- 
 phoric eye. 
 
 When esophoria is complicated by cyclophoria alone 
 or by cyclophoria and hyperphoria, the operation done 
 must not only alter the tension of the muscle, but must 
 also change its plane of rotation. If the complication is 
 plus cyclophoria alone and the operation is to lessen the 
 tension of the internus, it should be so done as to ele- 
 vate its plane of rotation. Th : s is accomplished by a 
 lower marginal tenotomy, leaving uncut the fibers at 
 the upper margin. A threefold effect attends this oper- 
 ation: (a) the tension is lessened, (b) the cyclophoria is 
 counteracted, (c) a hyperphoria is created. For the rea- 
 son that an operation on only one internus would give a 
 hyperphoria to the corresponding eye, the operative ef- 
 fect should be divided between the two eyes, the opera- 
 tion on the one internus being as nearly as possible like 
 the operation on the other. The two operations should 
 cure the esophoria and the plus cyclophoria; but at the 
 same time a double hyperphoria would be created, a con-
 
 310 ESOPHORIA. 
 
 dition far less objectionable than the two errors for the 
 cure of which the operations were done. 
 
 If the sthenic esophoria is complicated by plus cyclo- 
 phoria, with hyperphoria and cataphoria, the operative 
 effect should be confined, if possible, to the internus of 
 the cataphoric eye and should consist of a division of the 
 lower and central fibers, leaving 1 uncut enough of the 
 upper fibers to prevent an over-effect. The result of 
 this operation would be threefold: (a) lessening- or cur- 
 ing- the esophoria; (b) counteracting- the plus cyclophoria; 
 (c) converting- the cataphoria into a hyperphoria, thus 
 giving- the patient a double hyperphoria. If some of the 
 esophoria should remain, it should be relieved by a cen- 
 tral partial tenotomy of the internus of the other eye. A 
 marginal tenotomy of this muscle should not be done, even 
 if some of the plus cyclophoria and hyperphoria remained, 
 for the reason that dividing- its lower fibers would in- 
 crease the hyperphoria while curing the cyclophoria. 
 How to deal with any remaining- cyclophoria and hyper- 
 phoria will be shown in the discussion of those conditions. 
 
 If the esophoria is asthenic and uncomplicated, one of 
 the externi, if not both, should be shortened so as to in- 
 crease its tension without changing its plane of action. 
 If complicated by a hyperphoria of one eye and a cat- 
 aphoria of the other, there being- no cyclophoria, the 
 shortening of the externi should be done as if no compli-
 
 ESOPHORIA. 311 
 
 cation existed; that is, the tension should be increased, 
 but the plane should not be changed. If complicated by 
 a plus cyclophoria only, both externi should be shortened 
 to the same extent and the plane of each should be low- 
 ered sufficiently to effect a correction of the cyclophoria. 
 The alteration of the tension would cure the esophoria. 
 If the complications are plus cyclophoria and a hyper- 
 phoria of one eye and a cataphoria of the other, the oper- 
 ative effect, if possible, should be limited to the hyper- 
 phoric eye, and should be accomplished by a shortening 
 of the externus so as both to alter its tension and to de- 
 press its plane of action. The triple effect would be: 
 (a) increased tension for the esophoria; (b) lowered plane 
 for the plus cyclophoria; (c) lowered plane for the hyper- 
 phoria, converting it into a cataphoria, so that there 
 would be a double cataphoria. If any remaining esopho- 
 ria should require a shortening of the externus of the 
 other eye, the operation should be done so as to increase 
 its tension without changing its plane, even if there 
 should also remain, from the first operation, some of the 
 plus cyclophoria and some of the cataphoria; for a change 
 of the plane of action that would lessen one of these 
 complications would increase the other. 
 
 The complication of minus cyclophoria has only been 
 mentioned, for the reason that it is so rare. When it 
 does exist in connection with esophoria, every step for
 
 312 ESOPHORIA. 
 
 changing- the muscle plane, as set forth in the treatment 
 of a plus cyclophoria, must be reversed. 
 
 The operation of shortening- an externus, when enough 
 increase of tension can be had, should always be pre- 
 ferred to an advancement. While this can be done in 
 nearly all cases of asthenic esophoria, in which an in* 
 crease of tension of the externi is always indicated, 
 nevertheless, in some cases these muscles have their at- 
 tachment so far removed from the corneo-scleral junc- 
 tion that the advancement operation becomes clearly in- 
 dicated. The same rules as to alteration of tension and 
 chang-e of plane apply to advancements as have been set 
 forth in connection with shortening's. For the technic 
 of these operations, and the after-treatment, the reader 
 is referred to that part of Chapter III. in which these 
 operations are described. 
 
 While doing 1 these operations the judg-ment of the 
 operator must decide as to their extent. His judgment 
 cannot be g^ood unless he keeps in mind the exact nature 
 of the conditions for the relief of which he is operating". 
 The true essence of these conditions cannot be known 
 except as a result of the most skillful and careful use of 
 the phorometer, cyclo-phorometer, and tropometer or 
 perimeter. Before any operation is done, the refraction 
 of the eyes should be determined, under a mydriatic, by 
 means of the standard objective and subjective tests.
 
 ESOPHORIA. 313 
 
 The operator should always be careful not to do too 
 much; for it is far better to leave the patient with some 
 of his esophoria than it is to give him the smallest quan- 
 tity of the opposite error exophoria. The danger of re- 
 sorting to tests while operating is that it may lead to 
 the doing of too much. Tests while operating cannot 
 be reliable, and should, therefore, be avoided. When 
 more than one operation is needed, it is better to allow 
 from two to four weeks to intervene; but in errors of 
 high degree, two operations, a partial tenotomy of an in- 
 ternus and a shortening of the opposing externus, or a 
 partial tenotomy of both interni, or a shortening of both 
 externi, may be done at the same time. 
 
 The object of partial tenotomies of the interni, in 
 the treatment of esophoria, is to so reduce their tension 
 that the externi, under a normal impulse, may perfectly 
 balance them in action. The object of shortening the 
 externi is to so increase their inherent tension that, 
 under a normal impulse, they may perfectly balance the 
 interni. In either case the nervous tension of the ex- 
 terni would be relieved. 
 
 Whenever an intrinsic esophoria has been reduced by 
 operations so that the remainder can be cured by non- 
 operative means, these should be resorted to, but not 
 until the muscles operated upon have had time to com- 
 pletely recover from the operations.
 
 CHAPTER V. 
 
 EXOPHORIA. 
 
 As the word indicates, there is, in exophoria, a ten- 
 dency on the part of the external recti muscles and their 
 synergists to make the visual axes deviate from the point 
 of fixation. If this tendency were not counteracted by 
 antagonists of the externi, the visual axes would either 
 intersect beyond the point of fixation, or they would 
 become parallel or even divergent. Abnormal nervous 
 tension of the interni and their synergists counteracts 
 the inherent tension of the externi and their synergists, 
 so that the tendency is not allowed to become a turning. 
 The visual axes are thus forced to intersect at the point 
 of fixation; and binocular single vision is maintained, but 
 at the expenditure of an undue amount of nerve force. 
 Exophoria, like esophoria, is of two kinds, intrinsic and 
 pseudo. As to causation, the one kind is wholly different 
 from the other, but the two often coexist. As to the 
 results, the one is the same in kind as the other, but 
 the treatment of the one is not at all similar to the treat- 
 ment of the other. 
 
 (314)
 
 EXOPHORIA. 315 
 
 INTRINSIC EXOPHORIA. In this the extern! have the 
 advantage over the interni. This imbalance may be due 
 to the fact that the externi are hyper-developed or that 
 the interni are of subnormal development. It may be 
 that the error is not in the size of the muscles, but in the 
 nature of their attachment to the globe, the externi hav- 
 ing their attachment nearer the corneo-scleral junction 
 than normal, or that the interni are attached too far 
 back; it may be that the externi are short and tense or 
 that the interni are long and somewhat lax. When either 
 of these conditions causes exophoria, the error may be 
 greater in the one eye than in the other, though, as a 
 rule, the exophoria is about equal in the two eyes. When 
 there is a difference, the monocular phorometer quickly 
 shows it. 
 
 It must be conceded that the cause of intrinsic exopho- 
 ria may not reside in the muscles themselves, but may 
 be found in an unequal supply of nerve force, the centers 
 for the externi generating a quantity of nerve impulse 
 greater than normal, or the third conjugate brain-center, 
 of subnormal development, sending a weaker current to 
 the interni. 
 
 An intrinsic exophoria can exist without there being 
 a state of imbalance between the externi and the interni. 
 The oblique muscles are always more or less powerful as 
 abvertors. There is but little room for doubt that, in
 
 316 EXOPHORIA. 
 
 some cases, they may be too short and tense, or they may 
 be too large and powerful, or their attachments may be 
 nearer the posterior pole than normal, so that, in either 
 case, their abverting power would be increased. This 
 increase may be sufficiently great to cause an exophoria, 
 even when there is no cyclophoria. 
 
 Malformation of the orbits, only in the sense of their 
 being too far apart, can cause an exophoria; but when 
 this cause exists alone, the muscle imbalance cannot be 
 great. 
 
 The superior and inferior recti may have their attach- 
 ments so far toward the temples as to greatly lessen 
 their power to help the interni, and thus become a factor 
 in the production of exophoria. 
 
 Whether the one or the other of the several conditions 
 named is the cause of exophoria, or whether two or more 
 of them become factors in the production of this error, 
 the treatment, whether surgical or non-surgical, must be 
 directed toward the lateral muscles. As to surgical 
 means, either the tension of the externi must be lessened 
 or the tension of the interni must be increased. If brain- 
 centers are structurally over-developed or under-devel- 
 oped, they must remain so always; if the obliques, be- 
 cause of structure, attachment, or innervation, abvert 
 too powerfully, they cannot be changed; if the orbits 
 are too wide apart, surgery cannot bring them closer to-
 
 EXOPHORIA. 317 
 
 gether. If the superior and inferior recti, because of 
 faulty attachments, are feeble advertors, they must not 
 be subjected to operations on this account. For these 
 reasons it becomes apparent that any and every treat- 
 ment of intrinsic exophoria, whatever may be the cause, 
 must be directed toward the externi or toward the in- 
 terni. An exophoria that is wholly muscular, all inner- 
 vation centers being normal, will show the same num- 
 ber of degrees in the near as in the far. 
 
 Intrinsic exophoria is of two kinds, sthenic and asthen- 
 ic. The quantity of the error does not determine its char- 
 acter. Only the abduction and the abversion tests, in any 
 given case, can tell the operator that the error is sthenic 
 or that it is asthenic. Exophoria with abduction of less 
 than 8 and abversion of less than 50 is asthenic, and 
 clearly indicates that the externi should not have their 
 tension lessened, and just as clearly indicates that the 
 interni must have their tension increased. Exophoria 
 with abduction of more than 8 and abversion of more 
 than 50 is sthenic, and the case should be treated with 
 the view of lessening the tension of the externi. 
 
 Tests in myopic and emmetropic cases will always 
 show the full amount of intrinsic exophoria in the far. 
 In the near test of a myope, the intrinsic exophoria will 
 have the associated pseudo-exophoria added to it. If the 
 emmetrope does not show the same exophoria in the near
 
 318 EXOPHORIA. 
 
 as in the far, it is increased or diminished because of 
 an abnormal development of the ciliary muscles. If the 
 ciliary muscles are hyper-developed, there will be more 
 exophoria in the near than in the far, for the reason that 
 an impulse less powerful than normal is required of the 
 brain-center controlling 1 them, so that a correspondingly 
 slight associated impulse is sent to the interni. 'If the 
 ciliary muscles are subnormally developed, they will re- 
 quire an impulse more powerful than the normal, and a 
 correspondingly strong associated impulse must be sent 
 to the interni, causing a pseudo-esophoria, which, to a 
 certain extent, would neutralize the intrinsic exophoria. 
 
 The hyperope will always show less than the full 
 amount of intrinsic exophoria in both the far and the near 
 tests, for the reason that hyperopia always has a pseudo- 
 esophoria associated with it, which neutralizes in part an 
 existing intrinsic exophoria. 
 
 PSEUDO-EXOPHORIA. There can be but two causes 
 for this condition. One is myopia, or myopic astigma- 
 tism; the other is hyper-development of the ciliary mus- 
 cles, making it necessary for the centers controlling them 
 to generate a less powerful nerve current than would be 
 required by these muscles if normally developed. 
 
 When the cause is myopia, or myopic astigmatism, the 
 pseudo-exophoria shows itself only in the near, and is 
 due to the fact that the guiding sensation calls either for
 
 EXOPHORIA. 319 
 
 no nerve force to excite ciliary action or for a quantity 
 less than is required by an emmetrope, depending- on 
 the amount of the focal error; and a correspondingly 
 slight associated impulse is sent to the interni. If the 
 point of view is 16 inches distant, there should be 1.8 of 
 pseudo-exophoria for each dioptre of myopia up to 2.50 
 D, and .9 for each dioptre of myopic astigmatism up to 
 5 D. This kind of pseudo-exophoria does one of three 
 things: (a) it increases an intrinsic exophoria in the near, 
 (b) it shows an exophoria in the near when there is real 
 orthophoria, or (c) it lessens an intrinsic esophoria in the 
 near. 
 
 When the pseudo-exophoria is due to a hyper-develop- 
 ment of the ciliary muscles and the patient is an emme- 
 trope, the error will show itself only in the near test. 
 If a 1.50 D impulse is all that is necessary to effect a 3 
 D contraction of the ciliary muscles, the pseudo-exopho- 
 ria, with the test object at 13 inches, should be 2.7. 
 This may manifest itself in the same three ways as that 
 caused by myopia. Strictly speaking, a pseudo-exopho- 
 ria cannot exist in a hyperope; although, as shown in the 
 chapter on esophoria, the hyperope who has hyper-devel- 
 oped ciliary muscles will show a less amount of pseudo- 
 esophoria than would be shown if these muscles were of 
 normal development. The difference in amount is equiv- 
 alent to pseudo-exophoria.
 
 320 EXOPHORIA. 
 
 When the far test shows orthophoria and the near test 
 shows exophoria, the error is pseudo in character, and is 
 dependent on one or other of the two causes above men- 
 tioned; and the same is true when an exophoria is less in 
 the far than it is in the near. The same explanation 
 applies when there is esophoria in the far and exophoria 
 in the near. If in an emmetrope there is more exophoria 
 in the far than there is in the near, the ciliary muscles 
 are subnormally developed, and require an excessive im- 
 pulse to make them perform their work. The associated 
 impulse to the interni is correspondingly great. 
 
 There is a form of exophoria not yet referred to in this 
 chapter, and probably not fully set forth in any book. 
 The cause unquestionably resides in the third conju- 
 gate innervation center, and is structural in character; 
 in other words, the third conjugate innervation center is 
 subnormally developed, and, for this reason, sends a feeble 
 impulse to the interni. The most exaggerated manifes- 
 tation of this condition would lead one to judge that this 
 brain-center is entirely absent, for occasionally a case is 
 seen who has no power of convergence. Such a person 
 enjoys binocular vision in the distance, but has only mo- 
 nocular vision in the near. In such a case there is no ad- 
 duction power, for the one visual axis cannot be made to 
 approach the other. Abduction will be normal or even 
 above the normal. Adversion is unimpaired, showing
 
 EXOPHORIA. 321 
 
 that the fourth and fifth conjugate innervations have full 
 sway. The abversion of the right eye equals the adver- 
 sion of the left eye, and, vice versa, the abversion of the 
 left eye equals the adversion of the right eye. In these 
 movements the visual axes are kept parallel, as when 
 the eyes are looking straight ahead. That the condition 
 is congenital in most cases is shown by the fact that 
 there is no diplopia in the near. This must be due to an 
 acquired mental suppression of images that fall on the 
 temporal half of the retina, or, at least, a portion of it. 
 The power of mental suppression can be acquired only 
 in the earliest years of life. Hansell & Reber speak 
 of a patient in whom this loss of convergence power 
 was acquired, the result of some disease process in 
 the part of the brain in which is located the con- 
 vergence center. It is reasonable to suppose that this 
 center might be destroyed by disease. In such a case, 
 however, diplopia would exist everywhere except in the 
 distance. 
 
 If the third innervation center can be entirely absent 
 in one person and be present and fully developed in 
 another, it is reasonable to conclude that in still 
 another it may be present, but in a state of subnormal 
 development. There may be as many different grades 
 of development of this as there are individuals; but in 
 the majority of persons this center is able, doubtless,
 
 322 EXOPHORIA. 
 
 to generate 1 of impulse for every 1 of convergence, 
 in association with the center of the ciliary muscles. 
 
 Subnormal development of this center must manifest 
 itself in an exophoria in the near many degrees in excess 
 of the exophoria in the far (of itself it can never cause 
 exophoria in the far, but it may be associated with some 
 of those conditions that cause intrinsic exophoria); or, if 
 there is orthophoria or even slight esophoria in the far, 
 there will be considerable exophoria in the near. The 
 two ordinary causes of pseudo-exophoria that is, myo- 
 pia and hyper-developed ciliary muscles will not cause 
 more than 5 of the error. A greater degree of varia- 
 tion between the far and the near tests than this, in the 
 exophoric direction, must be attributed to a subnormally 
 developed third conjugate brain-center. A diagnostic 
 feature of this condition is the manifestation of very low 
 abduction power much lower than is found in intrinsic 
 exophoria of the same degree. 
 
 It is barely possible that a failure of connection be- 
 tween the ciliary center and the convergence center 
 accounts for the absence of convergence power in some 
 cases; and a slight connection may account for a feeble 
 
 convergence. 
 
 TESTS. 
 
 The cover test, allowing the eye to turn toward the 
 temple, will be attended by a resetting of the eye to-
 
 EXOPHORIA. 323 
 
 ward the nose when the cover is removed, and the false 
 object will move rapidly toward the corresponding- side 
 until fused with the true object. The examiner can 
 often see the resetting of the eye, but not so readily as 
 an intelligent patient can detect the apparent movement 
 of the test object. 
 
 The red glass, in the higher grades of exophoria, will 
 develop crossed diplopia. The distance between the red 
 light and the true light will give a fair idea of the quan- 
 tity of the error. This test, resulting in crossed diplo- 
 pia, practically always indicates operative treatment; 
 but since it does not show whether the case is sthenic or 
 asthenic, it cannot indicate the character of the opera- 
 tion to be done. 
 
 The double prism held before the right eye so that the 
 two lights seen through it shall be in the same vertical 
 line, the light seen by the left eye will be to the right, 
 if there is exophoria. The extent of the error is shown 
 by that prism, base toward the nose, that will place the 
 middle light in line with the other two. This test, so 
 far as it goes, is safe and accurate; but it cannot show 
 whether the exophoria is sthenic or asthenic, and cannot, 
 therefore, be relied upon in answering the question: 
 "What operation, if any, shall be done?" 
 
 The single six-degree prism, held base up before the 
 right eye, with the axis perfectly vertical, is as reliable
 
 324 EXOPHORIA. 
 
 as the double prism, though one can never be so certain 
 that the axis is vertical as he can be when using- the dou- 
 ble prism. The lower, or false, light will be on the op- 
 posite side crossed diplopia. The prism, base in, that 
 brings it directly under the true candle, measures the 
 amount of the exophoria. Like the double-prism test, 
 this one does not show whether the exophoria is sthenic 
 or asthenic. 
 
 The rod test is less reliable in exophoria than in eso- 
 phoria, for the reason that images displaced in the tem- 
 poral part of the retinal fusion area seem to excite a 
 greater demand for fusion than when displaced in the 
 nasal part. Nevertheless, if the exophoria is sufficiently 
 great, the rod held with its axis horizontal before the 
 right eye will cause the streak of light to appear to the 
 left of the candle. The prism, base in, that brings this 
 vertical streak into the candle, measures, but not with 
 accuracy, the exophoria. It always shows less exopho- 
 ria than really exists. Maddox thinks that a red rod 
 makes this test practically perfect, if, at the same time, 
 a plain green or blue glass be held before the other eye. 
 
 The safe, sure, speedy, and easy test for exophoria is 
 by means of the phorometer, and of all the phorometers 
 the monocular is the most reliable in its results. The 
 method of testing for exophoria is the same as that for 
 esophoria, the position of the false object always deter-
 
 EXOPHORIA. 325 
 
 mining' whether it is the one or the other error. It is 
 always on the opposite side in exophoria. The error is 
 measured by revolving- the rotary prism until the false 
 object is brought under the true object, when the index 
 will mark the quantity of the error. In the same way 
 the other eye should be tested. In the phorometer test, 
 as in all others, the exophoria at 16 inches should also 
 be determined. 
 
 The next step is the taking- of the abduction. This is 
 the chief means for determining whether the exophoria 
 is sthenic or asthenic. Unless the character of the error 
 is known, it is not possible to resort to rational treat- 
 ment. Whatever means may have been used in detect- 
 ing- the imbalance, the lifting- power of the externi ab- 
 duction must be taken. 
 
 This can be done, but not quickly nor accurately, by 
 holding- prism after prism, base in, before one eye, until 
 the patient can no longer fuse the imag-es. The chief 
 objection to this method is the uncertainty about the 
 axis of this prism being- perfectly horizontal. The 
 rotary prism of the phorometer, the instrument being- 
 perfectly leveled, is the quickest and best means for de- 
 termining- abduction or any other kind of duction. To 
 test abduction with the rotary prism, the handle must 
 be horizontal and the index must start from zero. Mov- 
 ing the index toward the temple it must be stopped the
 
 326 EXOPHORIA. 
 
 moment the patient says the test object becomes double. 
 The index stands opposite the number indicating the de- 
 gree of abduction. If this is less than 8, the exophoria 
 is asthenic; if more than 8, it is sthenic. If abduction 
 is just 8, since it would indicate that the tension of the 
 externus should not be lessened, the exophoria should be 
 classed as asthenic, from an operative standpoint. 
 
 Lastly, abversion should be taken either with the 
 perimeter or the tropometer. This will usually be found 
 less than 50 if abduction is low, and more than 50 if 
 abduction is high. 
 
 While abduction and abversion are to be relied on 
 most, adduction and adversion should always be taken. 
 In fact, the study of no one muscle error is complete 
 until all other errors have either been found or elimi- 
 nated; and the individual strength of every muscle must 
 be known. It is only in this way that the real nature 
 of an exophoria can be known, and without this knowl- 
 edge, rational treatment is impossible. 
 
 COMPLICATIONS OF EXOPHORIA. These are the 
 same as found in connection with the study of esophoria. 
 They need only be mentioned here, as, under the head 
 "Treatment,'-' it w r ill be shown how they modify the 
 management of the exophoria. They are: myopia and 
 myopic astigmatism, hyperopia and hyperopic astigma- 
 tism, and plus and minus cyclophoria. Thus it appears
 
 EXOPHORIA. 327 
 
 that not only the relationship of every pair of muscles, 
 and the condition of every individual muscle, must be 
 known, but the refraction must also be understood, if 
 one would deal successfully with exophoria. 
 
 SYMPTOMS. 
 
 The subjective symptoms or, more correctly speak- 
 ing-, the reflex nervous symptoms caused by exophoria 
 are those outlined in Chapter III. of this book, under 
 the head "Symptoms of Heterophoria. " The symp- 
 toms, whatever they may be, are not due to the inher- 
 ent tension of the externi and their synergists, but to 
 the nervous tension of the interni and their synergists, 
 necessary for maintaining binocular singular vision. 
 A symptom of which exophorics very commonly com- 
 plain is a blurring or running together of the letters of 
 the printed page, after more or less prolonged reading. 
 At such times the reader feels compelled to close the 
 eyes tightly before resuming his reading. Another 
 symptom, often present when near work is being done, 
 is a heavy, sleepy feeling of the upper lids, also a stiff 
 feeling of the upper lids, as if they were adherent to the 
 globes. Prolonged near work congests the margins of 
 the lids, even developing a marginal blepharitis, more 
 commonly in exophoria than in any other form of hetero- 
 phoria. A drawing sensation on the nasal side of the
 
 328 EXOPHORIA. 
 
 eyes is often complained of. There is no facial expres- 
 sion or pose of the head that is peculiar either to exopho- 
 ria or to esophoria. 
 
 TREATMENT. 
 
 NON- OPERATIVE. In pseudo-exophoria the cause 
 should always be removed, if practicable, by non-opera- 
 tive means. The pseudo-exophoria caused by myopia 
 and found only in the near, when it serves to neutralize 
 a part of an inherent esophoria, should be allowed to 
 continue until the esophoria has been cured by prisms 
 in positions of rest, by exercise of the externi, or by op- 
 erations. By the non-treatment of a pseudo-exophoria 
 of this character is meant that the myopic correction 
 should not be worn in near work. For distant seeing 
 the myopic correction should always be worn, for it 
 neither adds to nor diminishes any form of heterophoria. 
 If a myope is orthophoric for distance, the concave lenses 
 should be worn for all purposes. With the lenses on for 
 distant seeing" there will still be orthophoria; with them 
 on in near work the pseudo-exophoria is relieved and the 
 patient becomes orthophoric in the near as well. If the 
 myope is exophoric in the distance, the concave lenses 
 should be worn for all purposes. The distant test will 
 show the same exophoria with and without the lenses. 
 In the near test without the lenses, the exophoria shown 
 will be the intrinsic plus the pseudo; and with the
 
 EXOPHORIA. 329 
 
 lenses will be only the intrinsic, the pseudo-exophoria 
 having been cured by the establishment of the normal 
 relationship between the center of convergence and the 
 center of ciliary action. 
 
 The pseudo-exophoria caused by over-development of 
 the ciliary muscles, requiring less than a 1 D impulse to 
 effect a 1 D contraction of these muscles, is best treated 
 by the wearing of concave lenses, only in the near if the 
 patient is an emmetrope, but both in the far and in the 
 near if the patient is slightly hyperopic. By so doing a 
 pseudo-esophoria is developed which lessens the exopho- 
 ria. If the diagnosis is correct that is, if the exopho- 
 ria is wholly or in part pseudo the wearing of concave 
 lenses will be attended by a source of relief. "When 
 they cause discomfort, they should be discarded; for the 
 exophoria is due to some other cause than hyper-devel- 
 opment of the ciliary muscles. 
 
 It will be remembered by many that J. J. Chisolm, of 
 Baltimore, was in the habit, for many years, of pre- 
 scribing concave cylinders when his patients had hy- 
 peropic astigmatism. Although he did not so teach, 
 nevertheless his patients that were benefited had exo- 
 phoria. An esophoric patient would not have tolerated 
 such lenses. 
 
 Patients who are hyperopic and have either pseudo 
 or inherent exophoria should never be given the full
 
 330 EXOPHORIA. 
 
 correction of the hyperopia, for the imbalance would 
 be made worse. If the hyperopia is less than 2 diop- 
 tres and the exophoria in the near is more than 4, no 
 correction should be given; if more than 2 dioptres, only 
 the excess should be corrected. After an exophoria has 
 been cured by exercise or by operation, a full correction 
 of the hyperopia may be given, but in most cases 0.50 D 
 should go uncorrected. 
 
 What has been said of myopic and hyperopic correc- 
 tions, in cases of exophoria, applies proportionately to 
 astigmatic (myopic or hyperopic) corrections. How to 
 deal with these errors when there is a complicating eso- 
 phoria has been emphasized in Chapter IV. 
 
 Those unfortunate subjects who have no converging 
 power, probably because of absence of the third con- 
 jugate innervation center, cannot be relieved by either 
 lenses, prisms, exercise, or operations. 
 
 INHERENT EXOPHORIA. The treatment of the two 
 forms of inherent exophoria is the same, so far as con- 
 cerns non-operative means. The first of these is prisms 
 in positions of rest (bases in) for the weak interni. The 
 full correction of exophoria by prisms should not be at- 
 tempted; probably only a half correction of the error 
 should be given. Maddox suggests a correction of half 
 or a third of the distant and a quarter of the near exo- 
 phoria. When there is no complicating cyclophoria, the
 
 EXOPHORIA. 331 
 
 prismatic effect should be equally divided between the 
 two eyes, and the axes of the prisms should be perfectly 
 horizontal. The same rule holds good when there is a 
 hyperphoria of one eye and a cataphoria of the other. If 
 there is a complicating- plus cyclophoria without any 
 hyperphoria, the prismatic effect should be equally di- 
 vided between the two eyes; but the axis of each should 
 be tilted down at the temporal end, so as to make the 
 extern! tort the eyes in while turning- them out to fuse 
 the displaced images. The axes should be tilted in the 
 opposite direction if the complication is a minus cyclo- 
 phoria. When the complication is a plus cyclophoria 
 with a right hyperphoria and a left cataphoria, the exo- 
 phoric prism should be placed only before the hyper- 
 phoric eye and its axis should be tilted down at the 
 temporal end. The muscular action necessary for over- 
 coming the prism will turn the eye out and down and 
 tort it in. If discomfort results, it will be due to the work 
 that the inferior rectus has had to do to overcome the 
 prismatic displacement. If any prism is placed before 
 the left (cataphoric) eye, its axis should be perfectly hori- 
 zontal, for, if tilted down at the temporal end, it would 
 favor the cyclophoria, but increase the cataphoria; while, 
 if tilted up, it would force a correction of the cataphoria, 
 but would increase the plus cyclophoria. If there is doubt 
 as to whether the axes of the exophoric prisms should
 
 332 EXOPHORIA. 
 
 be tilted, it is better to place them exactly horizontal. 
 Weak exophoric prisms, with their axes perfectly hori- 
 zontal, should bring some relief to most patients. When 
 they do not relieve, it thus becomes evident that one 
 externus, if not both, is attached too high, and there is 
 developed a plus cyclophoria. 
 
 The objection raised against esophoric rest prisms, 
 that they interfere with the law of direction, applies 
 with equal force to prisms in positions of rest for exo- 
 phoria. 
 
 Decentration of lenses, in for convex and out for con- 
 cave, will accomplish the same results for exophoria as 
 will prisms with bases in. The rules for decentration 
 are given in Chapter IV. 
 
 EXERCISE TREATMENT. 
 
 There are two useful methods of exercising the weak 
 interni in cases of exophoria. The simplest, if not the 
 best, and certainly the cheapest, is the candle exercise. 
 The candle is mentioned for the reason that the images 
 of its blaze stimulate the two retinas so as to make it 
 more certain that the center of convergence will be ex- 
 cited sufficiently to converge the visual axes, as the candle 
 is brought from arm's length to a point six or seven inches 
 from the eyes. Images less bright, such as those of a pen- 
 cil, in some cases would not sufficiently stimulate. The
 
 EXOPHORIA. 333 
 
 method of conducting- the candle exercise is sufficiently 
 set forth in Chapter III., to which the reader is referred. 
 If properly conducted and continued sufficiently long, it 
 will do good in all cases except those in whom the interni 
 have attachments too high on the globes. Interni thus 
 attached, when exercised either with the candle or by 
 means of prisms, will call into simultaneous action the 
 inferior obliques, that they may prevent the convergence 
 of the vertical axes of the eyes. In the greater number 
 of cases this would either add to or develop a plus cyclo- 
 phoria while curing the exophoria. The patient would 
 not be benefited. But when the interni have the ideal 
 attachments, or even when they are attached too low, 
 the candle exercise, as well as prism exercise, will do 
 good. In cases of ideal attachment only the interni are 
 exercised; in cases with attachment too low every con- 
 traction of the interni is attended by a contraction of the 
 superior obliques, so that development of the interni is 
 attended by a corresponding development of the superior 
 obliques a thing to be desired in many cases. 
 
 The rapidity of a cure of exophoria by the candle ex- 
 ercise depends in part on the quantity of the exophoria 
 and in part on the character of the blood supply of the 
 interni; abundant blood supply means quicker results. 
 Gentle rhythmic exercise will increase the size and 
 power of a muscle, whether voluntary or involuntary.
 
 334 EXOPHORIA. 
 
 Permanent results follow such a method. No one can 
 doubt that a muscle can be developed; there is reasonable 
 doubt if a nerve center can be developed as a result of 
 either mild or severe stimulation. A nerve cell is very 
 different from a muscle fiber. 
 
 PRISM EXERCISE. 
 
 There are two methods of exercising- the interni by 
 means of prisms. The one is gentle rhythmic ex- 
 ercise by means of weak prisms witk their bases out; 
 the other method is that first suggested by Deady, 
 and later advocated by Gould loading the converg- 
 ence by means of the strongest prisms possible. The 
 former is intended for the strengthening of the mus- 
 cles themselves, while the latter is designed to stim- 
 ulate the convergence center to greater activity. The 
 advocates of the latter method claim that exophoria, in 
 most cases, is purely innervational and should be cured 
 by forced stimulation of the convergence brain-center, 
 the third conjugate innervation center. That this cen- 
 ter is susceptible to excessive stimulation cannot be de- 
 nied, but it is doubtful if this should be done. It is cer- 
 tainly more rational to develop the interni so as to make 
 them respond normally to the impulse that the brain - 
 center can easily generate in its real, though it may be 
 subnormal, state of development. If it were possible to
 
 EXOPHORIA. 335 
 
 enlarge the capacity of a brain-center, as it is possible to 
 increase the size and power of a muscle, the Deady method 
 would not be objectionable. The reader is ag-ain referred 
 to Chapter III., where the method is described. 
 
 In the rhythmic exercise of the interni by prisms, 
 the design is to produce slight contractions by means of 
 weak prisms (from 1 to 8) with their bases out, to be 
 followed by complete relaxation, each contraction and 
 relaxation to last about three seconds, throughout a sitting 
 of not more than ten minutes. The exercise should al- 
 ways stop short of fatigue, for exercise that tires does 
 not build. To get practically complete relaxation, the 
 object of fixation should be twenty feet distant. Per- 
 sistent exercise, after this method, in low degrees of in- 
 herent exophoria, will produce permanent results. This 
 method is fully set forth in Chapter III. 
 
 In high degrees of intrinsic exophoria, non-operative 
 measures will be productive of but little, and that little 
 will be slow of accomplishment. Exophoria in the 
 distance of 4 or more, and an exophoria in the near 
 equal to the angle of convergence at that point, give 
 little promise of yielding to non-operative means. An 
 exophoria that gives diplopia in the distance under 
 the red glass test, is practically always a case for 
 surgical treatment. All cases not showing good re- 
 sults, in a reasonable length of time, under non-oper-
 
 336 EXOPHORIA. 
 
 ative measures, should be given the advantage offered 
 by skilled surgery. 
 
 The object in view when exercising the interni in ex- 
 ophoria is to so develop them that they may respond 
 normally to a normal nerve impulse 1 of contraction 
 for every degree of impulse. 
 
 OPERATIVE TREATMENT. 
 
 Before any operation for exophoria is done, the pos- 
 sibility of a cure by non-operative means should be elim- 
 inated, and the condition of every extrinsic ocular muscle 
 should be known. Complicating muscle imbalances must 
 be taken into account, and, if possible, should be cor- 
 rected by the operations for the exophoria. In uncom- 
 plicated cases of exophoria, and in cases complicated 
 only by hyperphoria of one eye and cataphoria of the 
 other, the operations must either diminish the tension of 
 the extern! or increase the tension of the interni. When 
 the exophoria is complicated by a cyclophoria, not only 
 must the muscle tension be altered, but the muscle plane 
 must also be changed. 
 
 In sthenic exophoria the externi should be first sub- 
 jected to the operation of partial tenotomy, with the 
 view of reducing their tension. The case being uncom- 
 plicated, the tenotomy should be central. The operative 
 effect should be equally divided between the two externi,
 
 EXOPHORIA. 337 
 
 and should not be so extensive as to reduce abduction be- 
 low 8 or abversion below 50. In no case of exophoria 
 should a complete tenotomy of an externus ever be done, 
 for the reason that the risk of reducing both the duction 
 and version power below the normal would be too great. 
 After the two partial tenotomies, any remaining exo- 
 phoria that cannot be cured by non- operative meas- 
 ures should be still further relieved by a straight- 
 forward shortening of one or both interni, with the 
 view of increasing tension without changing the plane 
 of rotation. 
 
 When there is a complication of hyperphoria and cata- 
 phoria only, the operations, whether partial tenotomies or 
 shortenings, should be done as if no complication existed. 
 At some other time the vertical error must be given the 
 proper treatment. 
 
 A sthenic exophoria that is complicated by a plus cy- 
 clophoria only should be treated with the view of lessen- 
 ing the tension of both externi and lowering their planes 
 of action. This would be accomplished by cutting the 
 upper and central fibers of each externus as nearly alike 
 as possible, leaving the lower fibers intact. The three- 
 fold effect of these two operations would be: (a) lessen- 
 ing or curing the exophoria; (b) correction, wholly or in 
 part, of the plus cyclophoria; (c) the production of a dou- 
 ble cataphoria.
 
 338 EXOPHORIA. 
 
 A sthenic exophoria complicated by a plus cyclopho- 
 ria and a right hyperphoria and left cataphoria should 
 be subjected first to a partial marginal tenotomy of the 
 externus of the hyperphoric eye. The operation of cut- 
 ting the upper and central fibers of this externus would be 
 attended by these three results: (a) lessening of the ex- 
 ophoria; (b) a partial or complete correction of the plus 
 cyclophoria; (c) the production of a cataphoria equal to, 
 or a little less than, the cataphoria in the other eye. If 
 any remaining 1 exophoria should still be complicated with 
 plus cyclophoria and left cataphoria, the second opera- 
 tion should be a shortening of the left internus in such a 
 way as to both increase its tension and elevate its plane 
 of action. This would have three results: (a) still further 
 diminishing, if not curing, the exophoria; (b) a further 
 correction of the plus cyclophoria; (c) an elevation of the 
 cataphoric eye so as to bring it as nearly as possible 
 in the same horizontal plane with the eye that was pri- 
 marily hyperphoric. Should the first operation cure the 
 complicating plus cyclophoria, even if the hyperphoria 
 were not cured, the remaining exophoria should be re- 
 lieved by a central partial tenotomy of the externus of 
 the left eye, which would alter its tension without chang- 
 ing its plane of action. 
 
 Asthenic exophoria uncomplicated should be treated 
 by straight-forward shortening of both interni, the op-
 
 EXOPHORIA. 339 
 
 erative effect being as equally divided between them as 
 possible. In this way their tension would be increased, 
 but their planes of rotation would not be changed. The 
 same operations should be done when the exophoria is 
 complicated by hyperphoria and cataphoria. Operations 
 for a lateral error should attempt the simultaneous cor- 
 rection of a vertical error only when there is a complicat- 
 ing cyclophoria. 
 
 Asthenic exophoria, complicated by a plus cyclophoria 
 only, should have both conditions relieved by shortenings 
 of both interni in such a way as to increase their tension 
 and elevate their planes. The triple effect would be: 
 (a) correction of the exophoria; (b) cure of the plus 
 cyclophoria; (c) the production of a double hyperphoria. 
 When the complication is not only a plus cyclophoria, but 
 a right hyperphoria and left cataphoria as well, the first 
 operation should be a shortening of the left internus in 
 such a way as to both increase its tension and elevate its 
 plane. These would be the effects of this operation: (a) 
 correction, wholly or in part, of the exophoria; (b) a par- 
 tial or complete cure of the cyclophoria; (c) the produc- 
 tion of a double hyperphoria. If the internus of the 
 right eye must be operated upon, the shortening must 
 be straight-forward, even if the two complications still 
 existed; for an elevation of its plane would increase the 
 hyperphoria while lessening the plus cyclophoria, and
 
 340 EXOPHORIA. 
 
 lowering 1 its plane would increase the cyclophoria while 
 diminishing 1 the hyperphoria. 
 
 If a minus cyclophoria, which is rare, should alone 
 complicate an exophoria, the marginal tenotomies of the 
 externi would be below, and the shortenings of the in- 
 terni would have to be done so as to depress their plane 
 of rotation. If the minus cyclophoria \vith a hyperpho- 
 ria and cataphoria should complicate an exophoria, a 
 lower marginal tenotomy of an externus should be per- 
 formed only on the externus of the cataphoric eye; while 
 a shortening of an internus with depression of its plane 
 should be done only on the internus of the hyperphoric 
 eye, for reasons that are apparent. 
 
 The chief object in operating for exophoria, whether 
 the operation be partial tenotomies of the externi for 
 sthenic exophoria or shortenings of the interni for as- 
 thenic exophoria, is to so change the relative tension of 
 the interni as to enable them to respond normally to a 
 normal impulse from the third conjugate innervation 
 center 1 degree of convergence for every degree of im- 
 pulse and thus establish harmony between the externi 
 and the interni. 
 
 The change of the plane of action, though of vast im- 
 portance, depends solely on the existence of a compli- 
 cating cyclophoria.
 
 CHAPTER VI. 
 
 HYPERPHORIA AND CATAPHORIA. 
 
 THESE conditions can be studied intelligently only when 
 the head is in the primary position, with the test object 
 on the line of intersection of the extended median and 
 horizontal fixed planes of the head. The object should 
 be twenty feet distant from the eyes. If there is no imbal- 
 ance of the vertically-acting" muscles and the lateral 
 recti are properly attached and the eyes are contained 
 in orbits that have been normally developed, when the 
 test object is fixed, the two visual axes will lie in the ex- 
 tended horizontal plane, with no tendency for either axis 
 to rise above or dip below this plane. This will be 
 shown under any one or all of the tests for determining 
 the balance of the ocular muscles. Such a condition, as 
 already noted in Chapter II., is vertical orthophoria. 
 Hyperphoria is a tendency of one visual axis to rise above 
 this plane, the actual turning- easily occurring- as soon 
 as the eye is freed from the control of the guiding- sen- 
 sation, by any one of the tests to be given farther on. 
 Cataphoria is a tendency on the part of one visual axis 
 to fall below this plane, the tendency becoming a turning 
 
 (311)
 
 342 HYPERPHORIA AND CATAPHORIA. 
 
 so soon as the image has been changed in character or 
 position so that no effort at fusion will be made. Usu- 
 ally a hyperphoria of one eye is associated with a cata- 
 phoria of the other, and the two errors are practically 
 equal. Occasionally there will be found a case in which 
 there is a vertical orthophoria of one eye and a hyperpho- 
 ria or a cataphoria of the other. Less frequently there 
 will be double hyperphoria or double cataphoria. 
 
 Any one of these errors makes it a difficult matter for 
 the superior and inferior recti to obey the law governing 
 them to wit, they must keep the visual axes in the same 
 plane, in order to help relate, properly, corresponding 
 retinal points. 
 
 CAUSES. There are several conditions that may cause 
 a vertical imbalance. Since malformation of the orbits 
 has been emphasized, in recent years, as a cause of hy- 
 perphoria, this will be studied first. Only in the sense 
 of one orbit's being higher or lower than the other, can a 
 malformed orbit be the only cause either of a hyperpho- 
 ria or a cataphoria. Fig. 43 represents the median plane 
 of the head, A B; the horizontal plane of the head, C D; 
 and the two eyes. The right one is in a normal orbit, so 
 that its vertical axis g-h is parallel with the median plane 
 of the head and its transverse axis efis contained in the 
 horizontal plane of the head. The left eye is represented 
 as contained in a malformed orbit, in the sense that it is
 
 HYPERPHORIA AND CATAPHORIA. 
 
 343 
 
 lower than the fellow orbit; therefore the contained eye 
 is lower than its fellow, as is shown by its transverse 
 axis flying below the fixed horizontal plane of the head, 
 C D. It will be seen that the vertical axis g-h is parallel 
 with the median plane A B. The muscles of these two 
 eyes may be supposed to be perfectly balanced. Under 
 the phorometer test of the vertically-acting- muscles, the 
 
 B 
 
 Fig- 43- 
 
 rig-ht eye would show orthophoria, but the left eye would 
 show cataphoria. In binocular fixation of a point lying- 
 in the extended horizontal plane of the head, the visual 
 axis of the rig-lit eye, the muscles being- in a state of 
 equilibrium, would point to the object; while the visual 
 axis of the left eye would have to be raised by the supe- 
 rior rectus and inferior oblique, so as to intersect its fel- 
 low at the point of view. Thus elevated, its vertically-
 
 344 
 
 HYPERPHORIA AND CATAPHORIA. 
 
 acting muscles cannot be in a state of equilibrium. Un- 
 der test this eye would drop into a state of equilibrium 
 for all its muscles and would thus show cataphoria. No 
 posing- of the head would change the condition or lessen 
 the error. The right eye under test would continue in 
 its state of equilibrium, and would, therefore, show verti- 
 cal orthophoria. 
 
 B 
 
 Fig. 
 
 A figure could have been constructed showing the 
 right eye in a normal orbit, with its axes properly re- 
 lated to the median and horizontal planes of the head; 
 and the left eye in a malformed orbit, in the sense of its 
 being higher than the fellow orbit, with its transverse 
 axis ef above the fixed horizontal plane of the head, al- 
 though its vertical axis gh would be parallel with the 
 median plane. The right eye would show vertical ortho-
 
 HYPERPHORIA AND CATAPHORIA. 
 
 345 
 
 phoria, but the left eye would show hyperphoria. No 
 posing- of the head can change the relationship that these 
 two eyes bear to the two fixed planes of the head. 
 
 Fig-. 44 represents malformation of both orbits in the 
 sense that the right one is too high and the left one is 
 too low. The vertical axis of each eye is parallel with 
 the median plane of the head, but the transverse axis of 
 
 -J) 
 
 f 
 
 3 
 
 Fig- 45- 
 
 neither eye lies in the horizontal plane of the head; that of 
 the rig-lit eye is above, while that of the left eye is below 
 it, but both are necessarily parallel with it. The mal- 
 position of the rig-ht eye would g-ive to it hyperphoria, 
 while the malposition of the left eye would g-ive to it 
 cataphoria. A state of equilibrium of the vertically-act- 
 ing- muscles (granted to be normal) of the right eye would 
 place its axis above, but parallel with, the extended hor- 
 izontal plane of the head; while the same muscular state
 
 346 
 
 HYPERPHORIA AND CATAPHORIA. 
 
 of the left eye would place its visual axis below, but 
 parallel with this plane. No pose of the head can help 
 these eyes in the effort at binocular fixation. 
 
 Fig. 45 represents a pair of eyes that are set in mal- 
 formed orbits, in the sense that both are too low; hence 
 both of these eyes have their transverse axes below the 
 horizontal plane of the head, but parallel with it. This 
 
 B 
 
 Fig. 46. 
 
 kind of malformation gives a double cataphoria, which 
 can be detected with a fair degree of readiness by means 
 of the monocular phorometer, but is more certainly and 
 more easily shown by the proof test of hyperphoria a 
 double prism, the use of which, for this purpose, will be 
 described under the head "Tests." A pose of the head 
 cannot bring 1 the transverse axes of the eyes into the hor- 
 izontal plane of the head, but it can make vision easier.
 
 HYPERPHORIA AND CATAPHORIA. 347 
 
 The characteristic pose, in such cases, is an elevation of 
 the chin. Such people are high-headed. 
 
 Fig. 46 represents a pair of eyes set in malformed or- 
 bits, in the sense that they are both too hig-h. The ver- 
 tical axes are parallel with the median plane of the head, 
 but the transverse axes lie above the horizontal plane, 
 though parallel with it. With the head in the primary 
 position, a point in the extended horizontal plane and in 
 the line of its intersection by the extended median plane 
 cannot be fixed by these eyes without depression of the 
 visual axes by contraction of the inferior recti, aided by 
 the superior obliques. Under- test, either one of these 
 eyes not under control of the guiding sensation will turn 
 up into the position of muscle equilibrium, showing- a 
 double hyperphoria. 
 
 In the study of all these figures, all of the muscles are 
 supposed to be normal in development, correct in attach- 
 ment, and perfectly innervated. A hyperphoria, single 
 or double; a cataphoria, single or double; a h} r perphoria 
 of one eye and a cataphoria of the other, having mal- 
 formations of the orbits as the sole causative agent, 
 will not have a complicating cyclophoria; nor can any 
 kind of malformation of the orbits ever cause c\ r clo- 
 phoria. It has already been shown that orbits that are 
 too wide apart cause exophoria, while orbits that are too 
 close to each other will cause esophoria.
 
 348 HYPERPHORIA AXD CATAPHORIA. 
 
 It should be remembered that other causes of hyper- 
 phoria and cataphoria may exist when e} T es are set in 
 malformed orbits, and that the other causes may show 
 themselves in an increase of the error caused by the mal- 
 formation of the orbit, or ma} 7 neutralize it, or may even 
 reverse it. To illustrate: the right orbit may be nor- 
 mal, the contained eye having- its vertical and transverse 
 axes properly related to the median and horizontal fixed 
 planes of the head; while the left orbit may be too low, 
 so that the contained eye has its transverse axis below 
 the horizontal plane of the head (see Fig. 43). As a con- 
 sequence, the muscles being well balanced, there will be 
 a left cataphoria; but if the left superior rectus is too 
 strong for its opposing inferior rectus, the cataphoria of 
 orbital causation either will be neutralized or there will 
 be a left hyperphoria. 
 
 When malformation of the orbits is the only cause for 
 vertical imbalances, the resulting errors may be said to 
 be pseudo-h}-perphoria and pseudo-cataphoria. The 
 treatment of such errors should be by means of prisms 
 in positions of rest, of such strength as to fully correct 
 the errors. 
 
 There is no direct connection between the brain-center 
 for the ciliary muscles and those centers controlling the 
 muscles that elevate and depress the eyes; so that, 
 through these muscles, a focal error cannot cause a
 
 HYPERPHORIA AND CATAPHORIA. 349 
 
 hyperphoria or a cataphoria. It cannot be denied, how- 
 ever, that convex lenses given to correct hyperopia, 
 sometimes cure a hyperphoria or a cataphoria. Such 
 cases have always had a pseudo-esophoria which, like- 
 wise, was cured by the convex lenses. It is clear that 
 in such cases one internus is attached too high or the 
 other internus is attached too low, so that the one eye, 
 on being 1 turned in, is also turned up; while the other 
 eye, on being turned in, is also turned down. The same 
 agent (convex lenses) that relieved the in-turning (pseudo- 
 esophoria) relieved also the up-turning (pseudo-hyper- 
 phoria) and the down-turning (pseudo-cataphoria). Both 
 intern! attached too high would give, under the same 
 conditions, a double pseudo-hyperphoria; while both 
 interni attached too low would give a double pseudo- 
 cataphoria. There would also be a complicating cyclo- 
 phoria, which will be studied more fully in Chapter VII. 
 
 In the same way it could be shown how a pseudo-exo- 
 phoria, because of too high or too low attachment of one 
 or both externi, might cause a pseudo-hyperphoria or 
 cataphoria, one or both, or either in the double form, all 
 of which would be relieved by concave lenses. 
 
 Hyperphoria and cataphoria, in the great majority of 
 cases, are intrinsic, or inherent, in character. They are 
 never pseudo except when caused by pseudo-esophoria 
 and pseudo-exophoria, or malformed orbits.
 
 350 HYPERPHORIA AND CATAPHORIA. 
 
 The cause of an intrinsic vertical error may reside 
 wholly in the interni, but only when there is an intrin- 
 sic esophoria or an intrinsic exophoria. In such cases of 
 esophoria one or both interni are attached too high, or 
 one or both are attached too low, or one is attached too 
 high and the other is attached too low. In the one, the 
 esophoria would cause a double hyperphoria and a minus 
 cyclophoria; in the second case the esophoria would cause 
 double cataphoria and plus cyclophoria; and in the last 
 case the esophoria in one eye would cause a hyperphoria 
 and a minus cyclophoria, and in the other a cataphoria 
 and a plus cyclophoria. How to deal with such interni 
 has been pointed out in the chapter on esophoria. 
 
 Intrinsic exophoria, in which the externi are attached 
 too high, will cause double hyperphoria and plus cyclo- 
 phoria; if both interni are attached too low, the exophoria 
 will cause double cataphoria and minus cyclophoria. If 
 one internus is too high and the other is too low, the exo- 
 phoria of the former would cause hyperphoria and plus 
 cyclophoria; the exophoria of the latter would cause cat- 
 aphoria and minus cyclophoria. How to deal with the 
 externi in such cases has been set forth in the chapter 
 on exophoria. 
 
 Hyperphoria and cataphoria, in the greater number of 
 cases, are caused by imbalance of the vertically-acting 
 muscles the supervertors and subvertors, which are the
 
 HYPERPHORIA AND CATAPHORlA. 351 
 
 superior recti and inferior obliques and the inferior recti 
 and the superior obliques. When the cause is either in 
 the straight or oblique supervertors or in the straight 
 or oblique subvertors, the error is always inherent, and 
 never pseudo. 
 
 DOUBLE HYPERPHORIA. This condition may be 
 caused by the two superior recti being hyper-developed, 
 or by a subnormal development of the inferior recti; or 
 it may be caused by the superior recti having their at- 
 tachments too near the corneo-scleral junction, or by the 
 inferior recti having their attachments too far removed 
 from the corneo-scleral junction; or it may be that the 
 first conjugate innervation center is normally so endowed 
 as to send a more powerful impulse to the superior 
 recti than goes to the inferior recti from the second con- 
 jugate innervation center. If either of these conditions 
 is the cause of a double hyperphoria, there will also be a 
 minus cyclophoria, independent of any imbalance of the 
 obliques. 
 
 The superior and inferior recti may be well balanced, 
 and the externi and interni may have ideal attachments, 
 and yet there may be a double hyperphoria. The cause 
 would be found in imbalance of the obliques, the inferior 
 having the. advantage over the superior, either because 
 the former are more highly developed or because they 
 are attached nearer the posterior pole or because the
 
 352 HYPERPHORIA AND CATAPHORIA. 
 
 seventh conjugate innervation impulse is more intense 
 than that from the sixth conjugate innervation center. 
 In either case the double hyperphoria would be asso- 
 ciated with plus cyclophoria. 
 
 In double hyperphoria caused by the superior recti 
 being too strong, the nervous tension of the inferior 
 recti would counteract both the hyperphoria and the 
 minus cyclophoria, while nervous tension of the superior 
 obliques would help to counteract the hyperphoria, but 
 would augment the minus cyclophoria. It is reasonable, 
 therefore, to conclude that the counteracting nerve im- 
 pulse in such a case is sent only to the inferior recti. 
 Depressing the chin a downcast face would help re- 
 lieve the inferior recti of nervous tension. 
 
 In double hyperphoria caused by the inferior obliques 
 being too strong, nervous tension of the superior ob- 
 liques would counteract both the hyperphoria and the 
 plus cyclophoria, while nervous tension of the inferior 
 recti would help to counteract the hyperphoria, but 
 would increase the plus cyclophoria; hence the conclu- 
 sion that the counteracting impulse, in such a case, is 
 sent only to the superior obliques. 
 
 Such a patient would instinctively elevate the chin 
 carry a high head to relieve the nervous. tension of 
 the superior obliques. The most advantageous posi- 
 tion of the eyes for the in-torting action of the superior
 
 HYPERPHORIA AND CATAPHORIA. 353 
 
 obliques is a depression of the visual axes below the 
 fixed horizontal plane of the head; the greater this 
 depression of the visual axes (elevation of the head), 
 the more powerful the in-torting- action of the superior 
 obliques. 
 
 DOUBLE CATAPHORIA. This condition may be the 
 result of hyper-development of the inferior recti or sub- 
 normal development of the superior recti, or it may 
 result from the inferior recti having- their attachment 
 too far forward or from the superior recti being" at- 
 tached too far back; or it may be caused by a more pow- 
 ful impulse sent from the second con jug-ate innervation 
 center to the inferior recti than is generated by the first 
 conjug-ate center for the superior recti. In either case 
 the double cataphoria will be associated with plus cyclo- 
 phoria. Nervous tension of the superior recti will coun- 
 teract both the cataphoria and the plus cyclophoria; 
 while nervous tension of the inferior obliques would 
 counteract the cataphoria, but would increase the plus 
 cyclophoria. Hence, in cases like the above, the correct- 
 ive nerve impulse must be sent only to the superior 
 recti. The position of the eyes most favorable for ef- 
 fective action of the superior recti is a depression of the 
 visual axes below the horizontal plane of the head; hence 
 such patients will carry their heads hig"h, so as to lessen 
 the nervous tension of the superior recti.
 
 354 HYPERPHORIA AND CATAPHORIA. 
 
 Double cataphoria may be caused by imbalance of the 
 obliques, the superior being stronger than the inferior, 
 either because the former are hyper-developed or the lat- 
 ter are subnormally developed, or because the former are 
 attached nearer the posterior pole, or because the sixth 
 conjugate innervation is more powerful than the seventh. 
 In either case the double cataphoria would be associated 
 with minus cyclophoria. The corrective nerve impulse 
 would be sent to the inferior obliques, which would coun- 
 teract both the double cataphoria and the minus cyclo- 
 phoria. The position of the eyes most favorable for cor- 
 rective action of the inferior obliques is an elevation of 
 the visual axes above the extended horizontal plane of 
 the head; hence such patients would have their faces 
 downcast, for this pose of the head would help to relieve 
 the nervous tension of the inferior obliques. 
 
 Hyperphoria of one eye and cataphoria of the other, 
 independent of malformation of the orbits and faulty 
 attachments of the lateral recti muscles, are always in- 
 herent in the vertically-acting muscles, and never inner- 
 vational. For convenience of study the right eye will be 
 considered as hyperphoric and the left eye as cataphoric, 
 although the reverse is often found. The right hyper- 
 phoria is due to the fact that the superior rectus is too 
 strong for its direct antagonist, the inferior rectus, or 
 that the inferior oblique is too strong for the superior
 
 HYPERPHORIA AND CATAPHORIA. 355 
 
 oblique; or both of these conditions may unite in the de- 
 velopment of the hyperphoria. If the superior rectus 
 alone is the cause of the hyperphoria, it is because 
 this muscle is hyper -developed or that the inferior 
 rectus is of subnormal development, or that the supe- 
 rior rectus is attached too near the cornea or that the 
 attachment of the inferior rectus is too far removed from 
 the cornea. 
 
 The hyperphoria would be sthenic if the superior rectus 
 is hyper-developed or is attached too near the cornea; it 
 would be asthenic if the inferior rectus is subnormally 
 developed or is attached too far away from the cornea. 
 In either case the hyperphoria would manifest itself in 
 association with minus cyclophoria. 
 
 If the inferior oblique alone is the cause of the hyper- 
 phoria, it is because of hyper-development of this muscle 
 or a subnormal development of the superior oblique; or 
 because the inferior oblique is attached too far behind 
 the equator or the superior oblique is attached too near 
 the equator. The hyperphoria thus caused is sthenic in 
 cases in which the inferior oblique is hyper-developed or 
 is attached too far behind the equator; it is asthenic in 
 those cases in which the superior oblique is subnormally 
 developed or is attached too close to the equator. In 
 either condition the hyperphoria would show itself in 
 association with plus cyclophoria.
 
 356 HYPERPHORIA AND CATAPHORIA. 
 
 When the hyperphoria manifests itself unassociated 
 with either minus or plus cyclophoria, it becomes evident 
 that both the superior rectus and inferior oblique enter 
 into the causation. 
 
 The left eye under test will show cataphoria, usually 
 the same in quantity as the hyperphoria of the right 
 eye. The cataphoria is caused by either a too powerful 
 inferior rectus or a too powerful superior oblique; or 
 both of these muscles ma} T unite in the production of the 
 cataphoria. 
 
 In a case in which the inferior rectus alone is the 
 causative agent, it is either hyper-developed or has its at- 
 tachment too close to the cornea; or its direct antagonist, 
 the superior rectus, is subnormally developed or is at- 
 tached too far away from the cornea. The cataphoria 
 would be sthenic if the inferior rectus is either hyper- 
 developed or is attached too near the cornea; it would 
 be asthenic if the superior rectus is under-developed or 
 has its attachment too far removed from the cornea. In 
 either case the cataphoria would be associated with a 
 plus cyclophoria. 
 
 In a case in which the superior oblique is the sole 
 cause of the cataphoria, it is either because it is hyper- 
 developed or because it has its attachment too near the 
 posterior pole; or because its direct antagonist, the in- 
 ferior oblique, is subnormally developed or is attached
 
 HYPERPHORIA AND CATAPHORIA. 357 
 
 too near the equator. The resulting- cataphoria is sthenic 
 in those cases in which the superior oblique is either 
 hyper-developed or is attached too near the posterior 
 pole; it is asthenic when the inferior oblique is under- 
 developed or is attached too near the equator. In either 
 case the cataphoria would be associated with a minus 
 cyclophoria. Cataphoria will be unassociated with either 
 plus or minus cyclophoria only when both the inferior 
 rectus and superior oblique are united in the causation. 
 
 Nervous tension of the inferior rectus counteracts the 
 rig-ht hyperphoria, if caused by the superior rectus; 
 while nervous tension of the superior rectus will coun- 
 teract the left cataphoria, if caused by the inferior 
 rectus. Not only will the right hyperphoria and left 
 cataphoria be thus neutralized, but the minus cyclopho- 
 ria of the rig-ht and plus c} 7 clophoria of the left would 
 be suppressed by the nervous tension of the same 
 muscles. The corrective impulse would come not from 
 one conjugate center, as in double hyperphoria and 
 double cataphoria, but from two separate centers. 
 
 Nervous tension of the superior oblique counteracts 
 the rig-ht hyperphoria which is caused by the inferior 
 oblique, while nervous tension of the inferior oblique 
 will counteract the left cataphoria that is caused by the 
 superior oblique. The plus cyclophoria of the right eye 
 and the minus cyclophoria of the left eye will be sup-
 
 358 HYPERPHORIA AND CATAPHORIA. 
 
 pressed by the nervous tension of the same muscles that 
 counteract the hyperphoria and cataphoria. 
 
 TESTS. 
 
 The phorometer, with perfectly ad-justed prisms and 
 spirit level, alone can be depended on in testing for 
 hyperphoria and cataphoria. The slightest error in 
 testing will be followed by bad results in practice. In 
 attempting to test for these errors by means of a dis- 
 placing prism with its axis horizontal, held in the hand, 
 one would have to be very careful or the axis would be 
 slightly inclined in one direction or the other; so that, if 
 the eye under test is hyperphoric and the temporal end 
 of the prism inclines down, the error will be exagger- 
 ated, and if it inclines upward, the hyperphoria would 
 be neutralized more or less completely, or even a cata- 
 phoria might be shown. 
 
 For reasons already given the rod test is not to be 
 trusted implicitly, but it is much to be preferred over 
 the hand-prism test, or even the prism when set in the 
 trial frame of the refraction case. The test object being 
 a candle, a rod held with its axis vertical before one eye 
 will show the streak of light which, in orthophoria, 
 should pass directly through the blaze seen by the other 
 eye; in hyperphoria, the streak would pass below the 
 blaze, while in cataphoria it would pass above the blaze.
 
 HYPERPHORIA AND CATAPHORIA. 359 
 
 In the low degrees of vertical heterophoria, the streak 
 falling- on the area of binocular fusion will excite some 
 effort, however small, at fusion. In the higher errors, 
 the prism used for measuring the amount of the error, 
 by throwing the streak on the fusion area, would excite 
 some effort at fusion. When the rod is the means of 
 testing, the error is never shown in excess, and for this 
 reason is more safe than accurate. 
 
 The use of the plus 13 D lens before one eye, if not 
 worthy of trust in the examinations for esophoria and 
 exophoria, would certainly be less trustworthy in exami- 
 nations for hyperphoria and cataphoria. 
 
 In high degrees of a vertical error the plane red glass 
 held before one eye will cause diplopia, the red light 
 below in hyperphoria and above in cataphoria. When 
 the red image is entirely outside the area of binocular 
 fusion, the full error will be shown, but cannot be accu- 
 rately measured, for the reason that the rotary or other 
 prism that carries the red image into the fusion area, at 
 once excites some effort at fusion. Like the rod test, 
 the red-glass test will mislead only in that it will not 
 show, even on careful measurement, the full error. 
 
 The cover test will show the vertical errors, but no one 
 would think of basing the treatment of a case on this test. 
 
 Any of the standard phorometers may be used in test- 
 ing for vertical heterophoria, but in this the monocular
 
 360 HYPERPHORIA AND CATAPHORIA. 
 
 instrument is most useful and trustworthy. The 10 
 prism, base in, should be placed in the cell behind the 
 rotary prism; the controlling- screw should be vertical, 
 and the index should stand at zero. The instrument 
 should be perfectly level. The patient's head should be 
 in the primary position. The test object should be,a 
 white spot on a black background, and should be distant 
 twenty feet. With the instrument before the right eye 
 there will appear to be two spots, the true one to the 
 left and the false one to the right. If they are too 
 widely separated, as in cases that are esophoric, the 6 
 prism should be substituted for the 10 prism. The 
 patient should constantly fix the true spot, and by indirect 
 vision alone should locate and relate the false spot. If 
 the eye is hyperphoric, the false spot will be lower than the 
 true; and since its image is not on -the area of binocular 
 fusion, the full error will be shown. The index of the 
 rotary prism moved upward \vill accurately measure the 
 error; for in carrying the false object up to the level of 
 the true, the image of the former is not made to invade 
 the fusion area, provided the true object alone has been 
 fixed throughout the test. 
 
 The vertical imbalance of one eye having been taken, 
 the phorometer should be turned in front of the other. 
 Precisely the same steps should be taken in determining 
 the condition of its vertically-acting muscles. Hyper-
 
 HYPERPHORIA AND CATAPHORIA. 361 
 
 phoria having been found in the eye first tested, the fel- 
 low eye, as a rule, will be found cataphoric. The false 
 object will appear higher than the true. The index of 
 the rotary prism should be carried downward until the 
 false object reaches a level with the true object. The 
 quantity of the error, as indicated on the scale, should 
 be noted. In the greater number of cases the degree of 
 cataphoria will be the same as the hyperphoria of the 
 other eye. 
 
 One eye having shown hyperphoria, the other may 
 show vertical orthophoria or even hyperphoria. The 
 eye under test, seeing the false object by indirect vision, 
 does not receive any fusion stimulus; hence it always 
 turns into the position of equilibrium of all its muscles. 
 For this reason it is just as easy to determine the exist- 
 ence of a double hyperphoria, with the monocular pho- 
 rometer, as it is to ascertain the existence of any other 
 form of heterophoria. The patient must be impressed 
 with the absolute importance of always fixing- the true 
 object that is, must see it by direct vision. 
 
 Whether one or the other of the tests referred to 
 above should be adopted, the proof test for vertical im- 
 balance should not be neglected. Errors that may have 
 crept in because of carelessness of the operator or indif- 
 ference of the patient can be eliminated easily by the 
 proof test. The means of -proving- is the Maddox double
 
 362 HYPERPHORIA AND CATAPHORIA. 
 
 prism (4 to 6 each). This should be held in the hand 
 first before one eye and then the other, so that the line 
 of union of the prism bases shall be horizontal. The 
 fixing 1 eye should be the one not under test. The prism 
 should be moved up and down before the eye under test, 
 so that one moment the false object would be seen below 
 the true and the next moment above it, but always by 
 indirect vision. If the distance from the true to the 
 false object is the same when below as it is when above, 
 there is vertical orthophoria. If there is hyperphoria, 
 the false object, when seen through the upper prism, 
 will be closer to the true object, by twice the amount of 
 the error, than when seen through the lower; while the 
 reverse will be true if there is cataphoria. In double 
 hyperphoria the objects will be closer together for each 
 eye when the false object is seen through the upper 
 prism; while in double cataphoria the false object, when 
 seen through the lower prism by each eye, will be nearer 
 the true object than when seen through the upper 
 prism. If there is hyperphoria of one eye and catapho- 
 ria of the other, when the double-prism proof test is 
 applied to the hyperphoric eye, the false object seen 
 through the upper prism will be close to the true, and 
 will be farther removed from it when seen through the 
 lower prism. On shifting the test to the other eye, the 
 false object seen through the lower prism will be nearer
 
 HYPERPHORIA AND CATAPHORIA. 363 
 
 the true than when it is seen through the upper prism. 
 The double prisms should be of equal strength, and 
 each should be strong- enough to throw the image of the 
 test object entirely above or below the limits of the field 
 of fusion. 
 
 Dr. Doak, Assistant in Ophthalmology, Vanderbilt 
 University, has devised a test for vertical imbalances 
 that not only detects and measures the error, but is also 
 in itself a proof test. By this test the kind of error is 
 at once detected, but its quantity is not known until the 
 proof feature has been applied. The delicacy of the 
 test is shown by an apparent doubling of the quantity 
 of the error. This delicacy makes it dangerous only 
 when the operator forgets that the apparent error is 
 twice that of the real error. For making this test the 
 monocular phorometer must be placed before one eye, 
 and in the cell next to the eye must be placed either the 
 10 or 6 prism, base toward the nose. The controlling 
 screw must be vertical, and the index, at the beginning, 
 should stand at zero. The instrument must be level. 
 The patient must hold before the other eye a double 
 prism in such position as to make the test object (white 
 spot on a black background) double for that eye, the 
 one directly above the other, and the two should be 12 
 apart that is, each of the double prisms should be 6. 
 With the double prism thus adjusted, these two spots
 
 364 HYPERPHORIA AND CATAPHORIA. 
 
 must be seen by indirect vision, while the single spot seen 
 by the other eye should be observed by direct vision. 
 Because of the displacing prism behind the phorometer, 
 the single object will not be in line with the other two; 
 and when it is seen by direct vision, the other eye will 
 be so turned that the vertical imaginary line connecting 
 the two false objects will fall to the nasal side of the 
 fusion area, so that, as the test proceeds, there will be 
 made no effort at fusion. The eye behind the double 
 prism will be wholly off its guard. The moment the 
 single object is fixed, the patient can usually say whether 
 or not it would be halfway between the other two ob- 
 jects if it were in line with them. If the middle object 
 is seen nearer the lower, that eye is hyperphoric; if 
 nearer the upper, it is cataphoric. The proof feature of 
 the test results from the use of the rotary prism. When 
 the screw is turned so as to carry the index upward, the 
 patient is asked to speak the moment the single object is 
 in a horizontal line with the upper of the two false ob- 
 jects. The extent of the rotation is noted, after which 
 the rotary prism is again made neutral. The next step 
 is to carry the index of the rotary prism downward until 
 the patient says that the single object is in a horizontal 
 line with the lower of the two false objects. The extent 
 of downward rotation is now noted. If the two arcs 
 traversed by the index are equal, there is undoubtedly
 
 HYPERPHORIA AND CATAPHORIA. 365 
 
 vertical orthophoria of this eye. If the lower arc is 5 
 and the upper arc is 7, this eye is certainly hyperphoric 
 not to the extent of the difference between these two 
 arcs, which would be 2, but only half this amount viz., 
 1. If the upper arc is 5 and the lower arc is 7, there is 
 cataphoria not of 2, but of 1. The reason for saying 
 that the real vertical error is only one-half of the appar- 
 ent error is clear. Since each of the double prisms is 
 6, the double objects seen through them, \vhen the base- 
 line is in the extended horizontal plane of the head, are 
 12 apart. The extended horizontal plane of the head 
 cuts the imaginary line connecting the two false objects 
 at the midway point 6 from each. If the displaced ob- 
 ject seen by direct vision with the other eye is in this 
 plane, it would have to be carried up or down by the 
 rotary prism just 6 to be placed in a horizontal line 
 with the one or the other of the false objects, hence the 
 eye would be orthophoric vertically. If the true object 
 is 1 below the extended horizontal plane of the head, it 
 will have to be carried downward by the rotary prism 
 only 5 to be placed in a horizontal line with the lower 
 object, while it would have to be carried upward 7 to 
 stand in a horizontal line with the upper object. Thus 
 it is clear that the hyperphoria shown by this test is 
 one-half the difference between the arcs traversed by the 
 index of the phorometer in placing the true object in a
 
 366 HYPERPHORIA AND CATAPHORIA. 
 
 horizontal line first with the one false object and then 
 with the other, the index each time starting from zero. 
 Throughout the entire test the single object must be 
 fixed. Although this test is in a sense binocular, it is 
 probably better than any other test for two reasons: (a) 
 It doubles the real error, so that a small error will be less 
 likely to be overlooked; (b) this test proves itself. 
 
 The eye under the Doak test is the one behind the 
 rotary prism. Both eyes" should be subjected to the same 
 test. 
 
 The duction and version power of the superior and in- 
 ferior recti of both eyes must be taken in order to deter- 
 mine whether the hyperphoria and cataphoria are sthenic 
 or asthenic, for on this knowlege must depend the treat- 
 ment of the case. 
 
 If the superduction is less than 3 and the superver- 
 sion is 33 or less, the hyperphoria is asthenic; if sub- 
 duction is less than 3 and sub-version is below 50, the 
 cataphoria is asthenic. If superduction is more than 3 
 and superversion is greater than 33, the hyperphoria is 
 sthenic; if sub-duction is more than 3 and sub-version is 
 greater than 50, the cataphoria is sthenic. 
 
 COMPLICATIONS. Focal errors do not complicate ver- 
 tical heterophorias, except in cases in which there is 
 pseudo-esophoria or pseudo-exophoria with too high or 
 too low attachments of the lateral recti muscles. A
 
 HYPERPHORIA AND CATAPHORIA. 367 
 
 vertical error thus caused is pseudo in character and is 
 cured, as is also the lateral pseudo-error, by correction 
 of the focal errors. 
 
 The only complication that must always be thought of 
 in the study of hyperphoria and cataphoria is cyclopho- 
 ria; for by this complication is determined the treatment, 
 surgical or otherwise, of these errors. How to find and 
 measure this all-important complication will be set forth 
 ; .n the next chapter. If a hyperphoria is only complicated 
 by esophoria or exophoria or by any focal error, all these 
 troubles must be treated as if they existed alone. 
 
 SYMPTOMS. 
 
 Any and all of the symptoms mentioned in the chapter 
 on heterophoria may be caused by vertical imbalance. 
 There is no facial expression that can be dignified as 
 diagnostic of hyperphoria and cataphoria. There are 
 poses of the head peculiar to both double hyperphoria 
 and double cataphoria. High-headedness is a symptom 
 of double hyperphoria when the inferior obliques cause 
 the error, and is just as certainly a sign of double cata- 
 phoria when the inferior recti are the cause of the error. 
 The most favorable position of the eyes for effective ac- 
 tion of weak superior obliques and weak superior recti 
 under a corrective nerve impulse is a depression of the 
 visual axes below the extended horizontal plane of the
 
 368 HYPERPHORIA AND CATAPHORIA. 
 
 head, or (what is the same thing") elevation of the ex- 
 tended horizontal plane of the head. 
 
 The downcast look is a sign of double hyperphoria 
 when the error is caused by the superior recti, and of 
 double cataphoria when the error is caused by the supe- 
 rior obliques. 
 
 The most favorable position of the eyes for effective 
 action of weak inferior obliques and weak inferior recti, 
 under a corrective nervous impulse, is an elevation of the 
 visual axes above the extended horizontal plane of the 
 head, or (what is equal to it) a depression of the hori- 
 zontal plane of the head. 
 
 A tilting- of the head toward one shoulder or the other 
 occurs only in cases in which there is a hyperphoria of 
 one eye and a cataphoria of the other, complicated by 
 either plus or minus cyclophoria of both eyes, and never 
 in simple cases of hyperphoria. The hyperphoria and 
 cataphoria are not the cause of the tilting- of the head; 
 the cause is the complicating- cyclophoria. If the com- 
 plication is plus cyclophoria, the head will be tilted 
 toward the cataphoric side. In a case of this kind, tilt- 
 ing the head elevates the hyperphoric eye and depresses 
 the cataphoric eye; so that to fix an object that would 
 be in the extended horizontal plane of the head, if the 
 head were erect, makes it necessary that the visual axis 
 of the eye that is higher shall be depressed and that the
 
 HYPERPHORIA AND CATAPHORIA. 369 
 
 visual axis of the eye that is lower shall be elevated, so 
 as to make them intersect at the object. Depression of 
 the visual axis of the hyperphoric eye places the eye in 
 such a position (elevated posterior pole) as to g-ive to the 
 superior oblique, under the whole of the stimulus of the 
 sixth fusional innervation, its greatest torsioning- power, 
 which would enable it easily to parallel the vertical axis 
 of the eye with the now-inclined median plane of the 
 head. The hyperphoria in such a case is due largely 
 to the inferior oblique, and the plus cyclophoria is 
 wholly caused by it. The elevated posterior pole of 
 the eye, made necessary by the tilting 1 of the head, 
 places the inferior oblique at a disadvantage to the 
 weak superior oblique; hence, the greater ease with 
 which both the hyperphoria and the plus cyclophoria 
 are counteracted. 
 
 The cataphoria of the other eye must be caused by the 
 inferior rectus, and the same muscle most probably causes 
 the whole of the plus cyclophoria of this eve. The cor- 
 rective stimulus most likely conies from the first fu- 
 sional innervation center and is wholl} r expended on 
 the superior rectus of the cataphoric eye (none of it is 
 needed for the superior rectus of the hyperphoric eye), 
 enabling- it to counteract both the cataphoria and the 
 plus cyclophoria. Its action is not favored by posi- 
 tion. A corrective stimulus sent to the superior oblique
 
 370 HYPERPHORIA AND CATAPHORIA. 
 
 would lessen the cyclophoria, but increase the cata- 
 phoria; therefore it is reasonable to conclude that none 
 is sent to it. 
 
 In a case of hyperphoria of one eye and cataphoria of 
 the other, complicated by a minus cyclophoria, the head 
 is tilted toward the hyperphoric side. The cataphoric 
 eye is elevated, the hyperphoric eye is depressed, by this 
 position of the head; so that the visual axis of the higher 
 eye must be depressed and that of the lower eye must be 
 elevated, so as to intersect at a point that would be in 
 the extended horizontal plane of the head, if it were 
 erect. In this case the hyperphoria and minus cyclopho- 
 ria must be due to the superior rectus of that eye, while 
 the cataphoria and the minus cyclophoria of the other 
 eye must be due to its superior oblique. The corrective 
 impulse of the hyperphoria must be sent to the inferior 
 rectus which is favored in its action by the necessary 
 elevated position of its visual axis. It must also receive 
 nearly the whole of the impulse that comes from the 
 second fusional innervation center; for the inferior 
 rectus of the other eye needs but little, if any, of it. 
 Thus are counteracted both the hyperphoria and the 
 minus cyclophoria. 
 
 The cataphoria and the minus cyclophoria of the other 
 eye are counteracted by a corrective nervous impulse that 
 is sent to its inferior oblique whose action is not favored
 
 HYPERPHORIA AND CATAPHORIA. 371 
 
 by the position that this eye must assume an elevated 
 posterior pole. 
 
 From what has been said above it will be observed 
 that the tilting- of the head toward the cataphoric side 
 when there is plus cyclophoria, and toward the hyper- 
 phoric side when there is minus cyclophoria, is favorable 
 only to the muscle that must correct the double error of 
 the hyperphoric eye, thus showing- that the depressor 
 muscles are in greater need of the help that comes from 
 posing. The tilting- is really unfavorable to the muscle 
 that must correct the double error of the cataphoric eye. 
 It may be that a nervous impulse gets a readier response, 
 in unfavorable positions of the head, from the muscles 
 that elevate the eyes than from those that depress them. 
 It is well known that when the eyes are closed in sleep, 
 or even in meditation, they turn slightly up; and the 
 same is true under anesthesia that is not profound. 
 This peculiar endowment of the supervertors seems to 
 be necessary in order that the cornea may be carried 
 instantly, for protection, into the position of greatest 
 security. 
 
 It is doubtful if there is a symptom or sign, other than 
 the posing of the head, that is peculiar to vertical im- 
 balance. Excessive secretion of tears may be associated, 
 in some unaccountable way, with hyperphoria and cata- 
 phoria.
 
 372 HYPERPHORIA AND CATAPHORIA. 
 
 TREATMENT. 
 
 Vertical imbalance associated with pseudo-esophoria 
 or pseudo-exophoria may be dependent on it; and if so, 
 it should be relieved by the same lenses that cure the 
 lateral pseudo error. 
 
 Since a double hyperphoria may be caused by abnormal 
 action of the inferior obliques, excited by oblique astig- 
 matism with the meridians of greatest curvature con- 
 verging above, and since double cataphoria may be caused 
 by abnormal action of the superior obliques, excited by 
 oblique astigmatism with the meridians of greatest curv- 
 ature diverging above, these errors may be relieved, in 
 such cases, by the correcting plus or minus cylinders. 
 
 Inherent vertical imbalance is made neither better nor 
 worse by the lenses that correct focal errors. These 
 must be treated by exercise, by prisms in positions of 
 rest, or by operations. 
 
 EXERCISE. 
 
 Double hyperphoria may be treated by exercise of the 
 inferior recti, which is best done by looking straight 
 ahead and then down to an object on the floor five 
 or six feet distant, then again straight ahead and 
 then down again, repeating this at regular intervals 
 of three, seconds. This straight-forward-to-floor exer- 
 cise should be stopped short of fatigue, and should not be
 
 HYPERPHORIA AND CATAPHORIA. 
 
 373 
 
 continued longer than ten minutes. One exercise a day 
 is sufficient. 
 
 The exercise for double cataphoria is straight-forward- 
 to-ceiling exercise, and should be carried out in the same 
 manner as the straight-forward-to-floor exercise. 
 
 Prism exercise alone is applicable when there is hyper- 
 phoria of one eye and cataphoria of the other. The 
 
 Fig- 47. 
 
 prisms with which to begin the exercise should be weak, 
 and gradually stronger ones should be used, but they 
 should never be stronger than 2. Except for the cost, 
 the prisms should be in pairs of equal strength. The 
 hyperphoric set shown in the accompanying cut (Fig. 47) 
 consists of five prisms, as follows: ?, 5, 1, l^ * and 2.
 
 374 HYPERPHORIA AND CATAPHORIA. 
 
 The apex of the prism must point toward the muscle to 
 be exercised that is, it must be down for the hyper- 
 phoric eye and up for the cataphoric eye. When the 
 prisms are of unequal strength, after three or four days' 
 use they should be transferred and the exercise continued 
 for three or four days longer. Now the weaker prism 
 (j) may be removed and the 1 prism put in its place. 
 At the proper time the prism and the 1 prism should 
 be transferred, and the exercise should be continued with 
 them for three days, when the 2 prism should be re- 
 moved and the l^ prism put in its place. The substitu- 
 tions should thus continue until the 1^ and 2 prisms 
 are in the frames. The exercise should be continued 
 indefinitely with these prisms, transferring- them from 
 side to side at regular intervals, always placing apex 
 down for the hyperphoric eye and apex up for the cata- 
 phoric eye. The muscles should be exercised rhythmic- 
 ally by lowering and raising the frames containing the 
 prisms, at intervals of three seconds. The exercise should 
 be stopped short of fatigue and need not be continued 
 longer than ten minutes. Once a day is sufficiently often 
 to exercise. The object of fixation while exercising 
 should be twenty feet distant, and should be sufficiently 
 sharp in outline and bright to excite ready response of 
 the muscles for the purpose of fusing the two displaced 
 images.
 
 HYPERPHORIA AND CATAPHORIA. 375 
 
 Relieving- prisms for vertical imbalance are often of 
 great use. Hyperphoria and cataphoria, uncompli- 
 cated, of less than 1|, should be relieved, if possible, 
 either by exercise or by rest prisms. Cases in which 
 these errors are as great as 2 or greater, whether 
 complicated or not, may obtain some relief from non- 
 surg-ical means, but cannot be cured short of operations. 
 If the vertical errors are as low as 1 and there is a 
 complicating" cyclophoria, surgery is the thing 1 indi- 
 cated. 
 
 The sub-ducting- muscles stand in greater need of rest 
 prisms than do the superducting- muscles, for the reason 
 g-iven in the study of the posing 1 of the head, in that part 
 of this chapter devoted to symptoms. If there were no 
 other reason, it would be g-ood practice in many cases, 
 not complicated with minus cyclophoria, to apply the 
 whole prismatic correction to the hyperphoric eye; and 
 certainly this should be the practice if there is a com- 
 plicating- plus cyclophoria, however small in quantity. 
 The superior rectus raising- the eye to overcome the 
 effect of the prism, in the interest of binocular single 
 vision, torts it in, thus aiding- the superior oblique to 
 parallel the vertical axis of the eye with the median 
 plane of the head. 
 
 In the few cases of hyperphoria and cataphoria that 
 are complicated by minus cyclophoria, the whole of the
 
 376 HYPERPHORIA AND CATAPHORIA. 
 
 prismatic effect should be applied to the cataphoric eye. 
 The prism, with its base up before this eye, calls into 
 action the inferior rectus in the interest of fusion; and 
 thus aid is given the inferior oblique in its efforts to 
 parallel the vertical axis of the eye with the median 
 plane of the head. 
 
 Those cases of hyperphoria and cataphoria that are 
 not complicated by cyclophoria will be given more com- 
 fort if the greater part (two-thirds) of prismatic effect 
 is applied to the hyperphoric eye, than would be given 
 if this rule were reversed, or even if the effect were 
 equally divided between the two eyes. 
 
 If the rules given above are observed, many cases will 
 take even a full correction of the hyperphoria, and not 
 less than half the full correction should ever be given. 
 The purpose may be attained either by prisms or lenses 
 rendered prismatic by decentration. 
 
 Double cataphoria that causes the patient to hold his 
 head too high should be given prisms or prismatic lenses, 
 bases up, so as to let them assume a more nearly normal 
 position of the head, provided there is no complicating 
 plus cyclophoria. The effect should be equally divided 
 between the two eyes. 
 
 Patients suffering from double hyperphoria should be 
 given prisms or prismatic lenses, bases down, except 
 when there is a complicating minus cyclophoria. These
 
 HYPERPHORIA AXD CATAPHoRIA. 377 
 
 would enable the patient to carry his head comfortably 
 in a more nearly erect position. 
 
 Hyperphoria, single or double; cataphoria, single or 
 double; and hyperphoria of one eye and cataphoria of 
 the other, caused bv malformation of the orbits, should 
 always be given full prismatic correction of the error 
 found in each eye. 
 
 OPERATIVE TREATMENT. 
 
 A double hyperphoria that cannot be relieved by prisms 
 or by straight-forward-to-floor exercise, to the extent of 
 enabling the patient to carry his head erect, instead of 
 downcast, should be subjected to a partial tenotomy of 
 both superior recti. If there is no complicating minus 
 cyclophoria, the tenotomies should be central; but should 
 this complication exist as it would if the superior recti 
 are wholly at fault the tenotomies should be peripheral, 
 including only the temporal fibers. Should there be a 
 complicating plus cyclophoria as there would be if the 
 inferior obliques were wholly to blame for the double 
 hyperphoria peripheral tenotomies of the superior recti 
 should be done, including only the nasal fibers. In 
 either case, the operative effect should be equally divided 
 between the two muscles. 
 
 A double cataphoria does not so urgently demand 
 operations, for high-headedness is not so objectionable as
 
 378 HYPERPHORIA AND CATAPHORIA. 
 
 the downcast look. The position of the head in double 
 cataphoria is more favorable to the respiratory act than 
 is the position caused by double hyperphoria another 
 reason why operative interference is less urgent in double 
 cataphoria. The lid pressure pressure of the upper 
 lids against the globe is much less in double cataphoria 
 than in double hyperphoria. Since great lid pressure is 
 probably more favorable to the retention and develop- 
 ment of germs, especially the trachoma germ, as sug- 
 gested by Stevens, there is an additional reason for 
 operating more frequently for double hyperphoria than 
 for double cataphoria. 
 
 Straight-forward-to-ceiling exercise, or prisms with 
 their bases up, should always be tried in cases of double 
 cataphoria; but should these fail to enable the patient to 
 carry his head in the natural, erect position, a partial 
 tenotomy of both inferior recti should be done, and these 
 operations should be central, unless there is a complicat- 
 ing cyclophoria. In cases in which there is a complicat- 
 ing plus cyclophoria as there would be if the double 
 cataphoria is caused by the inferior recti peripheral 
 tenotomies should be done, including only the temporal 
 fibers. In those cases complicated by a minus cyclopho- 
 ria, the superior obliques are the cause; but since these 
 muscles cannot be, or ought not to be, operated upon, 
 peripheral tenotomies of the inferior recti, including only
 
 HYPERPHORIA AND CATAPHORIA. 379 
 
 the nasal fibers, should be done. The operative effect 
 should be equally divided between the two inferior recti. 
 Great care should be exercised, in operating- for double 
 cataphoria, not to convert it into a double hyperphoria. 
 Operations on the inferior recti are as easily done as on 
 the superior recti. 
 
 Since double cataphoria is preferable to double hyper- 
 phoria, there is g-ood reason for always operating- first on 
 the superior rectus of the hyperphoric eye in cases in 
 which there is hyperphoria of one eye and cataphoria of 
 the other. While the tenotomy should never be com- 
 plete, it should be more extensive when done with the 
 view of lowering- the hyperphoric e} r e than when done 
 for elevating the cataphoric eye; hence, th<, reason for 
 doing- the first operation as set forth in the beg-inning- of 
 this paragraph. After the first operation, the remaining- 
 imbalance must be corrected by a partial tenotomy of 
 the inferior rectus of the cataphoric eye. As in the 
 lateral heterophorias, so in the vertical errors, tenotomies 
 are indicated only in the sthenic forms. A superduction 
 of 3 or less should never be diminished by lessening- the 
 tension of a superior rectus; and a sub-duction of 3 or 
 less likewise contraindicates a tenotomy. An asthenic 
 hyperphoria and cataphoria demands, first of all, a short- 
 ening- of the inferior rectus of the hyperphoric eye, by 
 means of which the greater part of the effect should be
 
 380 HYPERPHORIA AND CATAPHORIA. 
 
 accomplished, the remaining 1 part of the imbalance to be 
 corrected later by a shortening 1 of the superior rectus of 
 the cataphoric eye. 
 
 In all cases of hyperphoria and cataphoria, uncompli- 
 cated by cyclophoria, the operations, if partial tenoto- 
 mies, should be central; and if shortenings, should be 
 straight-forward, so as not to change the plane of rota- 
 tion. The complication of plus cyclophoria calls for a 
 peripheral tenotomy of the superior rectus of the hyper- 
 phoric eye, including* only the nasal fibers, and a periph- 
 eral tenotomy of the inferior rectus of the cataphoric 
 eye, including only the temporal fibers. These two 
 operations should be as nearly coextensive as possible, 
 because of the desire to correct the cyclophoria. Should 
 a case of this character be asthenic, the inferior rectus 
 of the hyperphoric eye should be shortened in such a way 
 as to carry its plane of rotation farther in, and the supe- 
 rior rectus of the cataphoric eye should be so shortened 
 as to carry its plane of rotation farther toward the tem- 
 ple. The operative effect should be equally divided be- 
 tween the two muscles. 
 
 The complication of minus cyclophoria, which is rare, 
 indicates a peripheral tenotomy of the superior rectus of 
 the hyperphoric eye, including only its temporal fibers, 
 so as to carry its plane of rotation farther toward the 
 nose, and a like operation on the nasal fibers of the in-
 
 HYPERPHORIA AND CATAPHORIA. 381 
 
 ferior rectus of the cataphoric eye, so as to carry its 
 plane of rotation farther toward the temple. An equal 
 effect should be attained by these two operations. If a 
 case of this character should be asthenic, the inferior 
 rectus of the hyperphoric eye shonld be so shortened as 
 to carry its plane of rotation farther toward the temple, 
 while the superior rectus of the cataphoric eye should be 
 so shortened as to carry its plane of rotation farther 
 toward the nose. 
 
 The methods of doing- these operations are set forth in 
 the chapter on heterophoria, and the after-treatment is 
 also described in that chapter.
 
 CHAPTER VII. 
 
 CYCLOPHORIA. 
 
 CYCLOPHORIA is the tendency of the vertical axes of 
 the eyes to lose parallelism with the median plane of the 
 head. In the interest of binocular single vision this 
 parallelism must be maintained by the oblique muscles, 
 except in cases of oblique astigmatism. For this pur- 
 pose there are four conjugate innervation brain-centers: 
 (1) The sixth conjugate center sends an impulse to the 
 two superior obliques to prevent divergence of the verti- 
 cal axes when the point of view is in the extended median 
 plane of the head, but below the extended horizontal 
 plane; (2) the seventh conjugate center sends an impulse 
 to the two inferior obliques to prevent convergence of 
 the vertical axes when there is to be cardinal fixation 
 above the horizontal plane; (3) the eighth conjugate cen- 
 ter sends an impulse to the superior oblique of the right 
 e} T e and inferior oblique of the left eye to prevent torsion 
 when the point of fixation is obliquely up and to the 
 right, or down and to the left; and (4) the ninth conju- 
 gate center sends an impulse to the superior oblique of 
 the left eye and inferior oblique of the right eye to pre- 
 
 (382)
 
 CYCLOPHORIA. 383 
 
 vent torsion when the point of fixation is up and to the 
 left, or down and to the right. Under the influence of 
 one or another of these conjugate centers, parallelism of 
 the vertical axes of the eyes with the median plane of the 
 head is maintained, regardless of the direction of the point 
 of fixation. In a normal condition of all the extrinsic ocu- 
 lar muscles, the obliques accomplish this purpose with 
 ease. Whenever conditions are such as to make it dif- 
 ficult for the obliques to maintain this parallelism, ex- 
 cept when under an excessive nervous tension, there is 
 cyclophoria. 
 
 When this condition was first described in the Archives 
 of Ophthalmology, in its issue of January, 1891, the name 
 given it was "insufficiency of the obliques," which was 
 not inapt; for whatever may be the chief cause or causes 
 of this error, the obliques are insufficient for the work of 
 easily keeping the vertical axes of the eyes parallel with 
 the median plane of the head. In 1893, in conformity 
 with the terminology introduced by Stevens, the term 
 "cyclophoria" was coined by Price. Plus cyclophoria 
 means that the vertical axes of the eyes have a tendency 
 from the median plane of the head; minus cyclophoria 
 is "a tendency of these axes toward the median plane. 
 For the same conditions Maddox uses the terms "plus 
 torsion " and "minus torsion; " and Stevens, " plus decli- 
 nation " and " minus declination." Either of these term?
 
 384 CYCLOPHORIA. 
 
 would be as good as those coined by Price, except for 
 the desirableness of uniformity in terminology. 
 
 While cyclophoria is most important as it pertains to 
 the two eyes in their efforts to maintain binocular single 
 vision, it is, nevertheless, a factor for disturbance in 
 monocular vision. In order that the law of direction 
 may not be interfered with, in vision with one eye, its 
 vertical axis must always be parallel with the median 
 plane of the head; and, necessarily, its transverse axis 
 must always lie in the plane of the primary isogonal 
 circle. 
 
 There are two kinds of cyclophoria viz., symmetrical 
 and non-symmetrical. Symmetrical cyclophoria is either 
 plus or minus for both eyes; non-symmetrical cyclophoria 
 is plus for one eye and minus for the other. Rarely 
 there may be a plus or minus cyclophoria for one eye, 
 while the obliques of the other perform their work 
 easily. Plus cyclophoria is by far more common than 
 minus cyclophoria. 
 
 CAUSES OF CYCLOPHORIA. The cause may be wholly 
 in the obliques. The nearer the attachment of an oblique 
 muscle is to the equator, the greater is its torsioning 
 power; while attachment of an oblique nearer the poste- 
 rior pole of the eye gives it less torsioning power. At- 
 tachment of both inferior obliques nearer the equator 
 than that of the superior obliques, would give a plus
 
 CYCLOPHORIA. 385 
 
 cyclophoria, the muscles themselves being normal in de- 
 velopment. When the superior obliques are attached 
 nearer the equator than are the inferior obliques, a minus 
 cyclophoria would result. Granting- that the attach- 
 ments are correct, hyper-development of the inferior ob- 
 liques or subnormal development of the superior obliques 
 would give a plus cyclophoria; while hyper-development 
 of the superior obliques or subnormal development of the 
 inferior obliques would cause a minus cyclophoria. This 
 presupposes that the innervations are normal. 
 
 Hyper-development of the seventh conjugate innerva- 
 tion center, or subnormal development of the sixth, would 
 cause a plus cyclophoria; while hyper-development of the 
 sixth or subnormal development of the seventh conjugate 
 center, would cause a minus cyclophoria. This presup- 
 poses that the muscles themselves are normal in both 
 structure and attachment. In either case the plus cy- 
 clophoria would be complicated by a double hyperphoria, 
 and the minus cyclophoria would be complicated by a 
 double cataphoria. 
 
 A too high attachment of the interni or a too low at- 
 tachment of the extern! would cause a minus cyclopho- 
 ria, while a too low attachment of the interni or a too 
 high attachment of the extern! would cause a plus cyclo- 
 phoria. When there is a normal attachment of the in- 
 terni, there can result from their action no cyclophoria.
 
 386 CYCLOPHORIA. 
 
 The superior and inferior recti constitute the only 
 remaining* source of symmetrical cyclophoria. When 
 these muscles are normal in structure and attachment, 
 there can be no cyclophoria resulting from their ac- 
 tion. A double hyperphoria due to hyper-development 
 of the superior recti or subnormal development of the 
 inferior recti, gives a minus cyclophoria; while hyper- 
 developed inferior recti or subnormally developed supe- 
 rior recti, in causing double cataphoria, also cause plus 
 cyclophoria. 
 
 Non -symmetrical cyclophoria is a tendency to parallel 
 deviation of the vertical axes of the eyes, being plus for 
 one eye and minus for the other. This tendency may be 
 to the right or to the left. If this kind of tendency 
 should become a turning, diplopia would not result, but 
 there would be interference with the law of direction. 
 Because of this interference the weaker obliques (supe- 
 rior of one eye and inferior of the other) are kept in a 
 state of nervous tension, that they may keep the vertical 
 axes of the eyes parallel with the median plane of the 
 head. The corrective impulse comes from the eighth con- 
 jugate center when the tendency of the vertical axes is 
 toward the right, and from the ninth center when the 
 tendency is toward the left. When the tendency is 
 toward the right, rotation of the eyes obliquely up 
 and to the right, or down and to the left, is more dif-
 
 CYCLOPHORIA. 387 
 
 ficult than rotation up and to the left, or down and to 
 the right; and vice versa, when the tendency is toward 
 the left. 
 
 The obliques may cause this condition. To do so the 
 superior oblique of one eye must be too strong for its in- 
 ferior oblique, or the former must be attached nearer the 
 equator than the latter; while the inferior oblique of the 
 other eye is either stronger than its superior oblique or 
 is attached nearer the equator. In such a case there 
 would be not only parallel cyclophoria, but there would 
 be also a cataphoria of the one eye and a hyperphoria of 
 the other. Parallel cyclophoria can be caused by the 
 interni when one is attached in greater part above the 
 transverse plane of its eye, while the other is attached in 
 greater part below this plane. There would also result 
 a hyperphoria of the one eye and a cataphoria of the 
 other. Faulty attachment of the externi, the one too 
 high and the other too low, would cause parallel cyclo- 
 phoria. In such a case there would also be a hyperpho- 
 ria of one eye and a cataphoria of the other. When hy- 
 perphoria of one eye is caused by a too strong superior 
 rectus and cataphoria of the other is caused by a too 
 powerful inferior rectus, parallel cyclophoria will also 
 result, the tendency being- to the right when there is left 
 hyperphoria and to the left when there is right hyper- 
 phoria.
 
 388 CYCLOPHORIA. 
 
 TESTS. 
 
 Cyclophoria was first discovered in 1890 by means of 
 a Maddox double prism which was being used for deter- 
 mining- an imbalance of the lateral recti. The patient 
 was asked if the middle candle was in a vertical line with 
 the upper and lower candles. She stated that the lower 
 candle was not directly under the upper one, although 
 the axis of the double prism was vertical, or so judged 
 by the eye of the operator. The axis of the prism had 
 to be tilted 5 or more toward the temple before the 
 patient claimed that the upper and lower candles were 
 in a vertical line. This showed clearly that the vertical 
 retinal meridian was inclined toward the temple and to 
 a greater extent than Helmholtz had taught as normal. 
 At once a line was drawn across a card and held before 
 the patient. She saw two lines with the eye before 
 which the double prism was held, and these lines were 
 parallel. The other eye was then uncovered, when she 
 saw a third line between the other two lines, but not 
 parallel with them. The middle line was seen by the left 
 eye, and it was seen inclined down to the right. Other 
 cases were investigated, about twenty-five per cent of 
 them showing the same error found in the first patient, 
 which was plus cyclophoria. The first publication was 
 made in the Archives of Ophthalmology, Vol. XX., No. 1, 
 page 105. This paper was gloomy in that it presented no
 
 CYCLOPHORIA. 389 
 
 prospect of either prevention or cure. From the time of 
 the discovery of cyclophoria, in 1890, up to May, 1892, many 
 cases had been found, but none of them had been treated; 
 nor was it thought possible, up to this time, that any 
 curative measure would ever be devised. On May 17, 
 1892, the thought of developing weak oblique muscles by 
 exercising them with cylinders first presented itself. 
 This thought was put into practice at once, and the re- 
 sults were gratifying. This led to the presentation of 
 a second paper which was read before the Section of 
 Ophthalmology of the American Medical Association at 
 the Detroit meeting, in June, 1892. 
 
 The double prism will always show cyclophoria when 
 the test- object is a horizontal line. The kind of cyclo- 
 phoria whether plus or minus is easily ascertained in 
 this way, but its quantity cannot be measured. Substi- 
 tuting a dot for the line, the error may be measured by 
 revolving the double prism until the two dots seen 
 through the prism are in a vertical line. The extent of 
 inclination of the axis of the prism would be equal to the 
 amount of the cyclophoria. In using the double prism 
 for this measurement test of cyclophoria, the operator 
 must be careful to have the axis of the prism vertical in 
 the beginning and note its inclination at the end of the 
 test. He need not be so careful to have the patient's 
 head erect, for the result will be the same whether the
 
 390 CYCLOPHORIA. 
 
 head is erect or inclined. However, since tests of some 
 of the eye muscles require that the head shall be erect, 
 it is better to have it thus in all tests. 
 
 The cut used to illustrate the first paper is reproduced 
 here, together with the descriptive text: 
 
 " Place a double prism, axis vertical, before one eye, the 
 other for the moment being- covered, and ask the patient 
 to look at a horizontal line on a card held sixteen inches 
 away. The effect of the double prism (each 6) is to 
 make the line appear to be two, each parallel with the 
 other. The other eye is now uncovered, and a third line 
 is seen between the other two, with which it should be 
 perfectly parallel. 
 
 "While a change of the position of the axis, of the 
 double prism, from the vertical toward the horizontal, 
 will alter the distance between the lines, their direction 
 will be unchanged hence, no loss of parallelism. This 
 fact admits of a little carelessness in the placing of the 
 prism in the trial frames, though the axis should be 
 vertical, so as to give the maximum distance between 
 the two extreme lines. 
 
 "If there is a want of harmony on the part of the 
 oblique muscles, this test will show it at once in a want 
 of parallelism of the middle line with the two other 
 lines, the right end of the middle line pointing toward 
 the bottom line and the left end toward the top line, or
 
 CYCLOPHORIA. 
 
 391 
 
 vice versa, depending- on the nature of the individual 
 case. 
 
 " Consider the eye before which no prism is held as 
 the one under test. With the double prism before the 
 right eye, the patient is asked about the position and 
 
 Fig. 48. 
 
 Fig- 49- 
 
 Fig. 50. 
 
 Fig- 
 
 Fig- 52. 
 
 the direction of the middle line. It may be nearer the 
 bottom line, thus showing left hyperphoria; or, again, 
 it may extend farther to the right than the other two, 
 and not so far to the left, thus showing exophoria; or 
 vice versa, showing esophoria.
 
 392 CYCLOPHORIA. 
 
 "If the right ends of the middle and bottom lines con- 
 verge while the left ends diverge, the superior oblique 
 of the left eye is at once shown to be in a state of under- 
 action. Fig. 48 represents such a test of the left eye; 
 Fig. 49 shows a test of the left eye when the inferior 
 oblique is the too weak muscle; Fig. 50 represents a 
 test of the right eye, the loss of the parallelism between 
 the lines being due to under-action of its superior oblique; 
 Fig. 51, the same condition of the inferior oblique 
 of the right eye; Fig. 52 represents a test of both 
 eyes when there is perfect equilibrium of the oblique 
 muscles." 
 
 The single prism of 6, with its base up or down be- 
 fore one eye, the test object being a horizontal line on a 
 blackboard at twenty feet distance, or on a card at the 
 reading distance, w r ill double the line. If the two are 
 not parallel, there is cyclophoria. The false line inclined 
 toward the opposite side shows plus cyclophoria; the same 
 line inclined toward the corresponding side shows minus 
 cyclophoria. The quantity of the cyclophoria cannot be 
 measured with the single prism by substituting a dot for 
 the line, as in the use of the double prism. 
 
 The rotary prism of either the Wilson or the monocu- 
 lar phorometer can easily show the existence of cyclo- 
 phoria, or its absence. As with other prisms, the test 
 object is a line. The rotary prism is adjusted for taking
 
 CYCLOPHORIA. 393 
 
 sub-duction and superduction. When it is rotated up or 
 down beyond the point of possible fusion, the line be- 
 comes double. If they converge at one end or the other, 
 there is cyclophoria plus if the false line is inclined to- 
 ward the opposite side, minus if it is inclined toward the 
 same side. Rotating the prism slowly so as to carry the 
 index toward zero, the two lines fuse, first at one end and 
 then quickly fuse throughout. The rotary prism cannot 
 possibly measure the amount of cyclophoria. 
 
 The Stevens clinoscope both detects and measures any 
 form of cyclophoria. The opaque discs with a single pin, 
 with the head in the center, drawn on each, should be 
 placed so that the point may be up for one eye and down 
 for the other. E}ach pin should be vertical, and the in- 
 strument should be so adjusted as to allow easy fusion 
 of the heads of the pins. When the two discs appear 
 as one, the two pins should be the vertical diameter of 
 the fused disc. If the one pin is a radius pointing ob- 
 liquely in one direction and the other is a radius pointing 
 obliquely in the other direction (one toward the right 
 and the other toward the left, making an oblique diam- 
 eter), there is plus cyclophoria of one eye and minus cy- 
 clophoria of the other. If the upper pin is seen by the 
 left eye and the lower pin is seen by the right eye, the 
 two pins pointing to the right would show plus cyclo- 
 phoria; while minus cyclophoria would be shown by the
 
 394 CYCLOPHORIA. 
 
 two pins pointing 1 to the left. If the top pin is vertical 
 and the bottom one points to the right, there is plus cy- 
 clophoria of the right eye alone; or, if the bottom pin 
 points to the left, while the top one is vertical, there is 
 minus cyclophoria of the right eye alone. When both 
 pins are oblique, the tubes to which the discs are fastened 
 should be revolved until the two pins are vertical, forming 
 apparently the vertical diameter of the fused disc. The 
 index connected with each tube will point to the mark on 
 the scale indicating the quantity of the error for each eye. 
 The errors of the obliques could be detected with equal 
 ease and measured with as much exactness, if the discs 
 were placed so that the pins would be horizontal, the one 
 seen by the left eye pointing to the left and the one seen 
 by the right eye pointing to the right, their heads being 
 fused. To eyes whose oblique muscles are perfectly 
 balanced the pins would appear as the horizontal diame- 
 ter of the fused disc. If the two pins appear to point 
 downward, there is minus cyclophoria; if they appear 
 to point upward, there is plus cyclophoria. If the left 
 pin points downward, while the right pin points upward, 
 there is minus cyclophoria of the left eye and plus cyclo- 
 phoria of the right eye (parallel cyclophoria). In either 
 case, rotation of the two tubes until the pins appear to 
 be horizontal, constituting the apparent horizontal diam- 
 eter of the fused disc, measures the error.
 
 CYCLOPHORIA. 395 
 
 The cyclo-phorometer will also detect and measure both 
 symmetrical and non-symmetrical cyclophoria. The in- 
 strument must be perfectly level, and the index of each 
 triple rod must stand at zero. The 5 prism, base up, 
 must be placed in the slot behind one rod, while a red 
 glass may be put in the slot behind the other rod. The 
 test object must be a candle, gas jet, or small electric 
 light. The red streak above and the yellow streak be- 
 low must be made even by the regulating screw. To 
 perfectly balanced eyes these streaks would appear par- 
 allel. If the red streak is seen by the right e} T e and 
 the two converge at the left, there is plus cyclophoria; 
 if they converge at the right, there is minus cyclophoria. 
 If they appear parallel, but inclined, there is plus cyclo- 
 phoria of one eye and minus cyclophoria of the other. 
 If one is horizontal and the other is inclined, there is cy- 
 clophoria of one eye alone. The disc containing the rods 
 should be turned until both streaks are perfectly hori- 
 zontal and, therefore, parallel. If the index of each stands 
 in the nasal arc when the streaks are made to appear 
 horizontal, there is plus cyclophoria; and if they stand in 
 the temporal arcs, there is minus cyclophoria. The 
 quantity of the error in each eye is measured by the arc 
 traversed by the index and is shown on the scale. If 
 only one rod is turned until the two streaks become par- 
 allel, but not horizontal, the quantity marked by the in-
 
 396 CYCLOPHORIA. 
 
 dex is the sum of the cyclophoria of the two eyes. If 
 there is parallel cyclophoria, the quantity is shown by 
 revolving- the two rods until the two streaks are hori- 
 zontal. 
 
 Cyclo-duction can be taken either with the clinoscope 
 or the cyclo-phorometer. If the clinoscope is used, the 
 discs, with a diameter drawn across each, should be at- 
 tached. They can be set with the diameters either ver- 
 tical or horizontal. When vertical, revolving the tubes 
 so that the lines shall deviate from each other above 
 will put into action the inferior obliques. If only one tube 
 is revolved, only one inferior oblique is called into action, 
 while revolving both tubes will call into action both in- 
 ferior obliques. The normal duction power of the ob- 
 liques is not so well known as that of the recti. It is 
 somewhere between 7 and 14 for one, and 22 or less, for 
 both inferior obliques. 
 
 Revolving the tubes so that the lines converge above 
 puts the superior obliques to the strength test. If only 
 one tube is revolved, only one superior oblique is called 
 on for a fusion effort; but if both are revolved, both eyes 
 must be cyclo-ducted by the two superior obliques. The 
 fusion power of the superior obliques is less than that of 
 the inferior obliques, but how much less normally is not 
 known. In plus cyclophoria, minus cyclo-duction is di- 
 minished and plus cyclo-duction is increased; while in
 
 CYCLOPHORIA. 397 
 
 minus cyclophoria, plus cyclo-duction is less and minus 
 cyclo-duction is greater. In taking- either minus or plus 
 cyclo-duction the revolution of the cylinders must be 
 stopped the moment the lines begin to be seen separate- 
 ly. The index will point to the number indicating the 
 extent of the fusion rotation. 
 
 Placing the discs so that the two diameters shall be 
 horizontal, both plus and minus cyclo-duction can be 
 taken as easily and accurately as, if not more accurate- 
 ly than, when these lines are vertical. Rotating the tubes 
 so that these lines are made to point downward at their 
 outer ends will call into fusion activity the two inferior 
 obliques, while rotating them so that they shall point 
 upward will excite into fusion activity the superior ob- 
 liques. 
 
 When the cyclo-phorometer is used for measuring the 
 fusion power of the obliques, the instrument should be 
 adjusted as for testing for cyclophoria. As soon as the 
 rods are so rotated that the one streak of light is di- 
 rectly under the other, both the displacing prism and 
 the red glass should be removed. At once the two lines 
 would be fused into one horizontal line. Revolving one 
 rod so that the index shall move in the nasal arc puts to 
 the test the inferior oblique of that eye; revolving both 
 rods so that each index shall be in the nasal arc puts 
 both inferior obliques to the test. When the two streaks
 
 398 CYCLOPHORIA. 
 
 of light are well defined and exactly alike as to width 
 and color, the plus cyclo-duction should be as great with 
 this instrument as with the clinoscope. 
 
 Revolving- the rods so that the index of each shall 
 move in the temporal arc, excites into fusion activit}- both 
 superior obliques. If one alone is to be tested, only the 
 one rod should be revolved, the other being- allowed to 
 stand at zero. Thus plus and minus cyclo-duction should 
 be taken in all cases of cyclophoria; and even when there 
 is no cyclophoria, these should be taken and noted, so 
 that a standard may be attained. 
 
 The first instrument for taking- cyclo-duction was in- 
 vented by Dr. C. H. Perry, of Oneida, N. Y., and for 
 this purpose is but little, if at all, inferior to the clino- 
 scope or the cyclo-phorometer. A description of this in- 
 strument and its use was published by the Ophthalmic 
 Record, in its issue of November, 1895, in the inventor's 
 own lang-uag-e. It reads as follows: 
 
 "Fig 1 . 53 represents a stereoscopic card, to which are 
 centrally pivoted two thin discs, each three inches in 
 diameter, their centers being- three inches apart in a hor- 
 izontal line. 
 
 "These discs are mashed tog-ether at their point of 
 contact by a single interlocking slot in each. 
 
 " The left disc is moved by a lever passing under the 
 right, and is provided with an index, which shows, on a
 
 CYCLOPHORIA. 
 
 399 
 
 graduated scale at the right-hand of the card, the num- 
 ber of degrees that each disc is rotated. Having equal 
 diameters, and being geared together, the}- move syn- 
 chronously equal distances, but in opposite directions. 
 
 . 53- 
 
 Horizontally over the center of each disc is printed a 
 word, and vertically through each of said centers is 
 drawn a line. 
 
 "When this apparatus is seen in a stereoscope and the 
 discs are rotated by moving the lever, the two words 
 will remain blended while each disc moves through an 
 arc of about 5 (and much more in some subjects); and if 
 attention is given to the perpendicular lines, they will 
 appear as a single line during the rotation of about the 
 same arc. If used with due care, this instrument gives 
 a practically accurate measurement not only of the rela-
 
 400 CYCLOPHORIA. 
 
 tive, but of the absolute, power of rotation in each direc- 
 tion." 
 
 Cyclo-version is impossible, since voluntary rotation of 
 the eyes around the visual axes cannot be accomplished. 
 
 In the study of the causes of cyclophoria, all of the 
 complications have been considered. Under the head 
 "Treatment" they will be referred to ag-ain, since the 
 treatment, whether surg-ical or otherwise, is largely de- 
 termined by these complications. 
 
 SYMPTOMS. 
 
 Any one or several of the symptoms mentioned in the 
 chapter on heterophoria may result from cyclophoria. 
 Vertigo and nausea are more commonly found associated 
 with cyclophoria than with any other form of heteropho- 
 ria. As already shown in the study of hyperphoria and 
 cataphoria, it is plus cyclophoria that causes the tilting- 
 of the head toward the cataphoric side, and minus cyclo- 
 phoria that causes the tilting" of the head toward the 
 hyperphoric side. 
 
 Symmetrical plus cyclophoria associated with double 
 hyperphoria causes hig'h-headedness, for the reason that 
 the superior obliques can more easily counteract a plus 
 cyclophoria when the visual axes are depressed below 
 the extended horizontal plane of the head. Symmetrical 
 minus cyclophoria with double cataphoria causes the pa-
 
 CYCLOPHORIA. 401 
 
 tient to carry his head thrown forward, giving- a down- 
 cast appearance, because, in this position, the inferior 
 oblique can counteract more easily the minus cyclophoria. 
 
 TREATMENT. 
 
 Rest cylinders, exercise cylinders, and operations on 
 the recti constitute the means for curing- cyclophoria. 
 When cyclophoria was discovered, in 1890, a cure was 
 thought to be impossible. In 1892 the first case was 
 treated with exercise cylinders. In 1888 the late Dr. 
 H. Culbertson, in a paper read by him before the Section 
 of Ophthalmology of the American Medical Association, 
 embodied the idea of the usefulness of cylinders not only 
 for the correction of astigmatism, but also for giving rest 
 to weak oblique muscles. The title of that paper was 
 "Binocular Astigmatism," and in it he advocated rotat- 
 ing cylinders out of the positions indicated in the monoc- 
 ular test, so that distortions of objects might be over- 
 come. He claimed, and correctly so, that many of his 
 patients obtained comfort from this procedure. He 
 claimed no basis for this practice other than empiri- 
 cism, whereas there is a scientific basis for it, which 
 will be given farther on. 
 
 The germ of the idea of operating on the recti so as to 
 help weak obliques is embodied in language found in the 
 Ophthalmic Record, in its issue of March, 1893. These
 
 402 CYCLOPHORIA. 
 
 are the words: "/ doing- advancement operations on the 
 recti muscles, one of the chief dangers is turning' the eye- 
 ball on its antero-posterior diameter so as to throw un- 
 bearable strain on either the superior or inferior oblique 
 muscles." At once it should have occurred to the author 
 of the quotation just made that, naturally, the recti might 
 be so attached as to do the very same thing 1 that is, de- 
 velop a cyclophoria. 
 
 While in attendance on the first Pan-American Medi- 
 cal Congress, Dr. Swan M. Burnett suggested to the 
 author that the superior and inferior recti might have 
 such a scleral attachment as to throw an undue amount 
 of strain on the obliques. On hearing- this statement 
 the author made this suggestion: " If you are correct, 
 some cases of insufficiency of the obliques can be cured 
 by dividing the offending- fibers of the inferior (or supe- 
 rior} recti." This was published in the first edition 
 of "New Truths in Ophthalmology" (1893), page 41. 
 
 REST CYLINDERS. These can be given for either plus 
 or minus cyclophoria even when there is no astigmatism 
 to be corrected. The objection to this practice is that, 
 while they give rest to the weak obliques, they, at the 
 same time, make images on the retinas less distinct. It 
 is the distorting, or it would probably be better to say 
 " the displacing, " of images that gives rest to the weaker 
 obliques. It is no longer denied that, in astigmatism,
 
 CYCLOPHORIA. 403 
 
 all lines not parallel with one or the other of the two 
 principal meridians have their images displaced toward 
 the meridian of greatest curvature. To fuse such dis- 
 placed images (displaced in opposite directions) there 
 must be cyclotropia, just as there must be esotropia in 
 order to fuse images that are thrown to the temporal 
 side of the maculas by prisms with their bases out. 
 The law of corresponding retinal points, which is su- 
 preme, compels the cyclotropia of oblique astigmatism, 
 notwithstanding it must interfere with the law of direc- 
 tion, in that the vertical axes of the eyes are made either 
 to converge or diverge above. Artificial oblique astig- 
 matism produces the same changes in images of vertical 
 and horizontal lines as does natural oblique astigmatism. 
 When there is plus cyclophoria, natural oblique astig- 
 matism of 1 or 2 D, with the meridians of greatest 
 curvature converging above, is often attended by more 
 comfort, because of the rest it gives to the superior ob- 
 liques, than the correcting cylinders would give; for 
 when the correction is given, the image of every line in 
 space is in a plane with the line itself, and to fuse these 
 images the weak superior obliques must parallel the 
 vertical axes of the eyes with the median plane of the 
 head. To do this their normal tension must be sup- 
 plemented by a nervous tension which they poorly bear. 
 What natural astigmatism will do, artificial astigmatism
 
 404 CYCLOPHORIA. 
 
 will accomplish. Only weak cylinders should be used 
 for non-astigmatics, with the view of resting- weak 
 oblique muscles. More than 1 D, whether the axis be 
 made to incline little or much, would blur objects un- 
 necessarily. Cylinders of .50 D are usually strong- 
 enough, especially when their axes are made to incline 
 far toward maximum points, in the proper arcs. For 
 plus cyclophoria the arc of distortion for plus cylinders 
 is the lower nasal arc; for minus cylinders, the lower 
 temporal arc. The maximum distortion by the cylin- 
 der is accomplished when its axis stands at 45 from 
 the vertical. For minus cyclophoria the arc of distor- 
 tion for plus cylinders is the lower temporal arc; for 
 minus cylinders, the lower nasal arc. For non-astig- 
 matics each arc of distortion is 90, the distortion or dis- 
 placement gradually increasing as the axis of the cylin- 
 der is carried up to the midway point (45) of the arc, and 
 then gradually grows less as the axis is carried on toward 
 the horizontal, at which point there can be no distortion. 
 The most useful cylinder is a plus .50 D when there is 
 esophoria as well as cyclophoria, or a minus .50 D when 
 there are exophoria and cyclophoria. The quantity of the 
 cyclophoria determines the location of the axes of the cylin- 
 ders, but in no case need they be placed farther from the 
 vertical than 45, for this is the point where they accom- 
 plish the maximum distortion, thereby securing, for the
 
 CYCLOPHORIA. 405 
 
 weak obliques, the greatest amount of rest. Given a 
 case of plus cyclophoria that is also esophoric, but non- 
 astigmatic, to obtain rest for the weak superior obliques 
 a plus .50 D cylinder should be given for each eye, placing 
 the axis of the right cylinder at some point between 90 
 and 135 or at the latter, while placing the axis of the 
 left cylinder at some point between 90 and 45 or at the 
 latter. These cylinders will give additional comfort to 
 nearly all cases of this kind. 
 
 It is better, however, to cure these cases either by ex- 
 ercising the weak superior obliques or by operating on 
 the interni. 
 
 If there is a hyperphoria of one eye and a cataphoria 
 of the other, as well as plus cyclophoria, the rest cylinder 
 should be applied only to the cataphoric eye. The infe- 
 rior oblique, in torting this eye out for fusing images with 
 the fellow eye, would also elevate the eye, counteracting 
 the cataphoria. For a like reason, the rest cylinder should 
 be applied only to the hyperphoric eye for the relief of 
 minus cyclophoria. But it would be better practice to 
 cure the plus cyclophoria by a marginal tenotomy (on 
 nasal side) of the superior rectus of the hyperphoric eye, 
 or by exercising both superior obliques. 
 
 Cylinders given for the correction of astigmatism, ob- 
 lique or non-oblique, may be so placed as to give rest to 
 weak superior obliques when there is plus cyclophoria,
 
 406 CYCLOPHORIA. 
 
 or to weak inferior obliques when there is minus cyclo- 
 phoria. If the astigmatism is vertical and hyperopic, 
 the arc of distortion by the plus cylinder for the superior 
 oblique is 90, and that for the inferior oblique is also 
 90, their sum being 180; if the astigmatism is oblique, 
 the meridian of greatest curvature of the right eye being 
 at 60 and that of the left eye at 120, the arc of distor- 
 tion by the correcting cylinders for the superior obliques 
 will be 30, and that of the inferior obliques will be 150, 
 their sum being 180. If the meridian of greatest curva- 
 ture of the right eye is at 45, and of the left eye at 135, 
 there is no arc of distortion for the superior obliques, 
 but the arc of distortion for the inferior obliques is 180. 
 The center of the arc of distortion by plus cylinders for 
 the superior obliques is at 45 in the lower temporal arcs, 
 and for the inferior obliques is at 45 in the lower nasal 
 arcs. This is reversed in the use of minus cylinders. 
 This will be elucidated further in the chapter on cy- 
 clotropia. 
 
 Prom what has just been said, it will be understood 
 that, when plus cylinders are used for correcting astig- 
 matic errors,, their axes must be turned from the point 
 indicated by the astigmatism toward the center of the 
 lower nasal arc for the relief of weak superior obliques 
 in plus cyclophoria, and toward the center of the lower 
 temporal arc for the relief of weak inferior obliques in
 
 CYCTvOPHOKIA. 407 
 
 minus cyclophoria. The extent of the displacement of 
 the axes depends both on the strength of the cylinders 
 and the quantity of the cyclophoria. Rarely should this 
 displacement be more than 5 if the cylinders are plus 1 
 D, or stronger; but weaker cylinders may be revolved 
 much farther. 
 
 Culbertson displaced the axes of his cylinders with the 
 view of correcting- the appearance of slanting floors, 
 leaning walls, and distorted figures, without any refer- 
 ence at all to the oblique muscles; but, after all, the 
 benefit derived was from giving rest to the weak ob- 
 liques. In vertical astigmatism, the cylinders do not 
 cause the floor to slant or the wall to lean; and yet it is 
 just as essential to displace the axes of the correcting 
 cylinders in the proper arcs, when there is cyclophoria, as 
 it is to displace the axes of cylinders correcting oblique 
 astigmatism. 
 
 In 1894, Nettleship, and probably others on the staff 
 of the Royal Ophthalmic Hospital, London, was in the 
 habit of directing that the axes of cylinders should be 
 placed at 90 or 180, when accurate measurements 
 showed that the two principal meridians were removed 
 only a few degrees from these points. When asked why 
 he did this, he said that some patients derived more com- 
 fort from the displaced cylinders. There was then pres- 
 ent a female patient who could not wear her cylinders
 
 408 CYCLOPHORIA. 
 
 thus displaced. Inquiry elicited the fact that she had 
 been given plus cylinders axes, 90 for each eye, when 
 the record showed that the meridian of greatest curvature 
 of the right eye was at 100, and of the left eye at 80. 
 These cylinders were displaced in the arcs of distortion 
 for the superior obliques, which were evidently too weak 
 to bear the consequent over-action. In that case, it would 
 have been better to have displaced these axes farther from 
 the vertical instead of to it. 
 
 Better than displacing the axes of correcting cylinders, 
 so that they may give rest to the weak oblique muscles, 
 is to make these muscles strong by exercise, or else cor- 
 rect the cyclophoria by operating on one or more of the 
 
 recti. 
 
 EXERCISE OF THE OBLIQUES. 
 
 This can be accomplished by the Perry cards (see Fig. 
 53) used in the stereoscope. This would require the time 
 of the surgeon or his assistant, throughout each exercise, 
 for revolving the cards. Depressing the handle would 
 make the printed word incline toward the opposite side; 
 and to keep the two words fused, the superior obliques 
 would be called into action. Again, raising the handle, 
 so that the pointer shall stand at zero, will bring the two 
 words into a horizontal line, and thus cause the superior 
 obliques to relax. Repeating these steps, alternate con- 
 traction and relaxation of the superior obliques can be
 
 CYCLOPHORIA. 409 
 
 accomplished. This exercise stopped short of fatigue 
 would tend to strengthen these muscles, and thus cure 
 the plus cyclophoria. 
 
 In minus cyclophoria the discs would have to be so ro- 
 tated as to make the words incline toward the corre- 
 sponding- side, in order to call into action the inferior ob- 
 liques. 
 
 The Stevens clinoscope also can be used for exercising* 
 the obliques; but this, too, would require the time of the 
 surgeon or his assistant. The discs used should be those 
 marked with the diameter, and not with the radius, un- 
 less the two radii should be made both to point in the 
 same direction. The former would be better. The 
 discs could be placed with the diameters either vertical 
 or horizontal. Revolving 1 the two tubes, so that the 
 indicators would point toward each other, would call 
 into action the superior oblique muscles; but when made 
 to diverge from each other, the inferior obliques would be 
 called into action. Reversing- the revolution, in either 
 case, so that each indicator would stand at zero, would 
 bring- the obliques into the state of rest. In this way 
 rhythmic exercise of the obliques may be accomplished, 
 and a plus or minus cyclophoria cured. 
 
 The cyclo-phorometer likewise can be used for exer- 
 cising- the obliques; but this, too, would require the time 
 of the surgeon or his assistant. It should be adjusted
 
 410 CYCLOPHORIA. 
 
 for easy fusion of the two streaks of light, as if for the 
 purpose of taking- the cyclo-duction. Revolving 1 the two 
 rods, so that the indicators would move in the temporal 
 arcs, would call into action the superior obliques; and 
 revolving- them so that the indicators would move in the 
 nasal arcs would call into action the inferior obliques. In 
 either case, reversing- the motion, so that the indicators 
 may be made to stand at zero, would cause relaxation of 
 these muscles. The revolutions could be repeated so as to 
 cause rhythmic exercise of the obliques, and thus cure 
 cyclophoria. The displacement should not be more than 
 half that for cyclo-duction in either of these methods. 
 
 Whether the one or the other of these means should 
 be used, the exercise should not cause fatigue, and in no 
 case should it be continued longer than ten minutes. It 
 need not be repeated oftener than once a day. 
 
 The only means for exercising the oblique muscles, 
 which a patient can use without assistance, consists of a 
 pair of cylinders set in circular rims, so that they may 
 be turned in the proper directions for displacing a hori- 
 zontal line so as to call into action the proper muscles in 
 the treatment of cyclophoria. The frames for this pur- 
 pose are made of German silver, with circular rims. 
 These rims are deeply grooved to allow a free rotation 
 of the lenses. The rims are marked at points fifteen 
 degrees apart, from 90 to 45, in either the lower tern-
 
 CYCLOPHORIA. 
 
 411 
 
 poral or lower nasal quadrant, depending- on the pair of 
 muscles affected. The cylinders used are usually plus 
 1.50 D., and the axis of each is plainly marked, as shown 
 in the cuts. The frames are not marked, nor are the 
 cylinders cut, except by the oculist's order. 
 
 Fig-. 54 represents a pair of exercise cylinders ordered 
 for a patient's own use, whose superior obliques are in- 
 sufficient. The rims, as shown, are marked in the lower 
 
 Fig- 54- 
 
 temporal quadrant, at four points fifteen degrees apart- 
 three of which are numbered 1, 2, and 3. The cylinders, 
 whose axes are distinctly marked, can be readily revolved- 
 The patient is directed to place the mark on each lens at 
 the notch marked No. 1. Placing- them now before her 
 eyes, she is instructed to look at a horizontal line eigfht or 
 ten feet distant for five seconds, then without them for five 
 seconds, then ag-ain with them for five seconds, and so on
 
 412 CYCLOPHORIA. 
 
 for five minutes. Now the two lenses are to be revolved so 
 that their marks point to the No. 2 notch on the rim. 
 The line is now looked at, as above, for three minutes. 
 Now the last change in position of the lenses is made 
 by revolving- their marks to notch No. 3, the point of 
 maximum action. The patient again looks at the line, as 
 above, for two minutes, which ends the exercise for that 
 day ten minutes in all. 
 
 The marking of the rims must be in the lower nasal 
 quadrant when the patient has insufficiency of the inferior 
 obliques, the exercise lenses to be plus cylinders. The 
 revolution is made in the direction of the notching- in both 
 classes of cases. The points at which to stop and the 
 time to look at the line are the same for both plus and 
 minus cyclophoria. The exercise is accomplished by rais- 
 ing- and lowering- the frames at intervals of three seconds. 
 This exercise should not be carried to the point of fa- 
 tig-ue, nor should it be continued long-er than ten minutes. 
 
 Once a day is sufficiently often to resort to the exer- 
 cise. The lig-htest work is done when the axes of the 
 cylinders stand at the first notch, and it is continued 
 long-est; while the heaviest work is demanded when the 
 axes stand at the hig-hest notch, and for this reason it is 
 continued the shortest time. 
 
 It is clear that these cylinders are intended for the 
 production of artificial oblique astig-matism, which must
 
 CYCLOPHORIA. 413 
 
 effect the same changes in images as are found in natural 
 oblique astigmatism. Plus cylinders revolved as shown 
 in Fig. 54 make the meridians of greatest refraction 
 diverge from each other above; for the axes of the cylin- 
 ders, representing the meridians of least curvature, con- 
 verge above. These cylinders make horizontal lines dip 
 toward the opposite side. To keep the images fused, the 
 superior obliques must tort the eyes in. Raising the 
 frames, the images of the horizontal line are no longer 
 oblique, hence the muscles that torted the eyes in must 
 now relax. 
 
 If minus cylinders are used, their axes should be placed 
 in the nasal arcs of the frames for exercising the superior 
 obliques, and in the temporal arcs for exercising the in- 
 ferior obliques. The axis of the minus cylinder repre- 
 sents the meridian of most refraction, hence the need 
 for rotating it in a direction different from that for the 
 plus cylinder. 
 
 The cylinders, whether plus or minus, may be of any 
 strength from .50 D to 1.50 D. Rarely should the 
 cylinder be stronger than 1.50 D. 
 
 These cylinders were first used for exercising the ob- 
 liques on May 17, 1892. The first case was cured of a 
 plus cyclophoria after a reasonably short time of faith- 
 ful exercise, and remains cured to this day September 
 26, 1901.
 
 414 CYCLOPHORIA. 
 
 OPERATIVE TREATMENT. 
 
 A plus cyclophoria uncomplicated by any other form 
 of imbalance, if high in degree and unrelievable by non- 
 surgical means, should be treated by operating on both 
 superior recti, dividing only their nasal fibers; or by 
 operating on both inferior recti, shortening or advancing 
 their nasal fibers. In either case, the cyclophoria would 
 be cured and double cataphoria would be developed. 
 
 A plus cyclophoria complicated by a double hyperpho- 
 ria should be relieved by cutting the nasal fibers of both 
 superior recti, which should result in a cure of both con- 
 ditions. 
 
 A plus cyclophoria complicated by double cataphoria 
 should be treated by dividing the temporal fibers of both 
 inferior recti. 
 
 A plus cyclophoria complicated by right hyperphoria 
 and left cataphoria calls for a division of the nasal fibers 
 of the right superior rectus and the temporal fibers of 
 the left inferior rectus. These operations should cure 
 both conditions. 
 
 A plus cyclophoria complicated by sthenic esophoria 
 should be treated by dividing the lower fibers of both in- 
 terni; but when the esophoria is asthenic, the operation 
 should be a shortening or advancement of the lower fibers 
 of both externi. 
 
 A plus cyclophoria complicated by sthenic exophoria
 
 CYCLOPHORiA. 415 
 
 calls for a division of the upper fibers of both externi; 
 but when the exophoria is asthenic, the upper fibers of 
 both interni either should be shortened or advanced. 
 
 A plus cyclophoria complicated by sthenic esophoria, 
 right hyperphoria, and left cataphoria, demands that the 
 lower fiber, of the left internus should be divided, so as 
 both to elevate the cataphoric eye and tort it in. If there 
 remains some of both the plus cyclophoria and right hy- 
 perphoria, the nasal fibers of the right superior rectus 
 should be cut. 
 
 A plus cyclophoria complicated by sthenic exophoria, 
 right hyperphoria, and left cataphoria, calls for a division 
 of the upper fibers of the right externus, so as both to 
 depress the hyperphoric eye and tort it in. Should there 
 remain some of the plus cyclophoria and left cataphoria, 
 the temporal fibers of the left inferior rectus should be 
 severed. 
 
 Very rarely there is minus cyclophoria, either compli- 
 cated or uncomplicated, that calls for surgical treatment. 
 It only must be remembered that the part of a muscle 
 cut, shortened, or advanced for plus cyclophoria must 
 remain intact when the condition is minus cyclopho- 
 ria; and that the margins left intact in the treatment of 
 plus cyclophoria must be either divided, shortened, or 
 advanced for minus cyclophoria. 
 
 Plus cyclophoria ol the right eye and minus cyclopho- 
 
 21.
 
 416 CYCLOPHORIA. 
 
 riaof the left eye (parallel cyclophoria), if uncomplicated, 
 calls for a division of the nasal fibers of the right superior 
 rectus and the temporal fibers of the left superior rectus. 
 While these operations would parallel the vertical axes 
 of the eyes with the median plane of the head, they 
 would develop a double cataphoria. A case of this kind, 
 complicated by right hyperphoria and left cataphoria, 
 calls for a division of the nasal fibers of the right su- 
 perior rectus and the nasal fibers of the left inferior 
 rectus. 
 
 The obliques themselves should never be subjected to 
 an operation for cyclophoria; but, as will be shown in 
 the next chapter, the inferior oblique may be divided 
 when there is plus cyclotropia.
 
 CHAPTER VIII. 
 
 COMPENSATING CYCLOTROPIA. 
 
 THE law governing- the oblique muscles is that they 
 must keep the vertical axes of the two eyes parallel 
 with the median plane of the head. They do this in 
 obedience to the unalterable law of corresponding- retinal 
 points, and must do it in all states of refraction not 
 causing- a displacement, in opposite directions, of the two 
 retinal imag-es as related to the one object. They must 
 also maintain this parallelism of the vertical axes in 
 those eyes whose refractive condition displaces both im- 
 ag-es, but in the same direction and to the same extent. 
 In emmetropia, hyperopia, and myopia there is no dis- 
 placement of imag-es; hence the law of corresponding- 
 retinal points is satisfied when the obliques obey the 
 subordinate law governing- them that is, when they 
 parallel the vertical axes with the median plane of the 
 head. In vertical and horizontal astig-matism there is 
 no displacement of imag-es of vertical and horizontal 
 lines lines that are parallel with the two principal me- 
 ridians while imag-es of oblique lines are displaced, but 
 
 (417)
 
 418 COMPENSATING CYCLOTROPIA. 
 
 in the same direction and to the same extent in the two 
 eyes; hence the law of corresponding- retinal points can 
 be satisfied only when the subordinate law governing 1 the 
 obliques is obeyed. 
 
 In oblique astigmatism, with the meridians of great- 
 est curvature either diverging 1 or converging- above, the 
 imag-es of vertical and horizontal lines are displaced so 
 that they no long-er bear a proper relationship to the 
 lines themselves; hence the imag-es must fall on non- 
 corresponding- retinal points more properly, lines. In 
 such eyes, no line in space can have both imag-es prop- 
 erly related to it, for a line that would be parallel with 
 the meridian of greatest curvature of one eye would not 
 be parallel with the meridian of greatest curvature of 
 the other; therefore, while in the former the line and 
 its image would be properly related, in the latter this 
 could not be, for the imag-e would be displaced. The 
 two imag-es of no line can fall on corresponding- retinal 
 parts when, in oblique astig-matism, the meridians of 
 greatest curvature are not parallel. To harmonize these 
 images, and satisfy as best possible, but never perfectly, 
 the law of corresponding retinal points, the individual law 
 governing the obliques must be suspended, and the ver- 
 tical axes of the eyes must be made to either converge or 
 diverge above the former if the meridians of greatest 
 curvature diverge above, the latter if these meridians
 
 COMPENSATING CYCLOTROPIA. 419 
 
 converg-e above. The same is true when the principal 
 meridians of one eye are vertical and horizontal, while 
 those of the other are oblique. 
 
 While there seems to be no one who now doubts that, 
 in astigmatism, there is displacement of the images of 
 all lines not parallel with the one or the other of the 
 two principal meridians, it will not be out of place here 
 to present some incontrovertible demonstrations, show- 
 ing- that these displacements are always toward the me- 
 ridian of greatest curvature. 
 
 The accompanying illustrations are simple, are easily 
 understood, and are at the same time correct. These, at a 
 glance, make clear what has been taught since 1891 con- 
 cerning the obliquity of retinal images in oblique astig- 
 matism. Criticism of this teaching would not have been 
 made if the author had thought to use these illustrations 
 in his first publication.* 
 
 In justice to Dr. P. C. Hotz, of Chicago, it must be 
 stated here that he gracefully retracted his criticism, 
 which was most severe, and showed before the Chicago 
 Ophthalmological Society how it was that he was led 
 into the error that formed the basis of his criticism. It 
 was before this society that he thought t he had demon- 
 strated that oblique astigmatism did not cause any dis- 
 placement of the retinal image of a vertical or horizontal 
 
 *See Ophthalmic Record, Vol. I., No. 1, 1891.
 
 420 COMPENSATING CYCLOTROPIA. 
 
 line. He used for this purpose a camera, the lens of 
 which he had rendered astigmatic by adding a cylinder 
 with its axis at 45. On the ground glass of his camera 
 he focused the image of a horizontal line. This image 
 he believed to be horizontal, as did all who saw his dem- 
 onstration, but it was not. With the same camera, he 
 later focused the images of two lines crossing each other 
 at right angles the one line, vertical; the other, horizon- 
 tal. These images were readily seen displaced, in oppo- 
 site directions, so that the angles formed at their point of 
 crossing were not right angles. These two lines enabled 
 the camera to magnify the truth so as to enable Hotz 
 and his fellow-members of the Ophthalmological Society 
 to see the error into which he had led them at a pre- 
 vious meeting. Hotz was kind enough to invite the 
 author, whom he had formerly criticised, to be present 
 at his last demonstration and speak on oblique astig- 
 matism. 
 
 Dr. Harold Wilson (of Detroit), another critic, was 
 later forced to yield to the argument of his camera ren- 
 dered astigmatic, which he had focused on a church spire. 
 He thought that the spire in the photograph was vertical, 
 and so published. Later he studied both the axis of the 
 spire and the base-line, and found that the photograph 
 did not show them to be at right angles; that these 
 were both inclined in opposite directions. His error in
 
 COMPENSATING CYCLOTROPIA. 
 
 421 
 
 observing only one line was very similar to the one into 
 which Hotz had fallen. 
 
 But to a study of the illustrations: 
 
 Fig. 55 is complex, showing a square as seen by a non- 
 astigmatic eye, as seen by an eye astigmatic according 
 
 a" O f d' 
 
 Fig- 55- 
 
 to the rule, and as seen by the latter after the astigma- 
 tism has been corrected by a plus cylinder. The rec- 
 tangie a-b-c-d is the square seen by the non-astigmatic 
 eye, and a-c and d-b show the diagonals of this square. 
 The rectangle a'-b'-c'-d' is the figure seen by the astig- 
 matic eye with the meridian of greatest curvature verti-
 
 422 COMPENSATING CYCLOTROPIA. 
 
 cal. The axial rays from the ends of the lines a-b and d-c 
 enter the eye through parts of the cornea parallel with 
 the meridian of greatest curvature and so near to it that 
 their refractive power is practically the same. The re- 
 fraction of these axial rays from a and b, by the cornea, 
 is such as to make them cross each other, on their way 
 back to the retina, sooner than they would have done if 
 there had been no astigmatism; hence their points of 
 impingement on the retina are more widely separated, 
 and the line itself must be proportionately increased. 
 The same is true of the axial rays from the ends of the 
 line d-c. Hence it is clear that the line a-b must become 
 the line a'-b' and the line d-c must become the line d'-c 1 . 
 Because of the increase of the length of the line a-b and 
 d-c the lines a-d and b-c are more widely separated, be- 
 coming lines a'-d' and b'-c', and we have not a square, 
 but the rectangular parallelogram a'-b'-c'-d'. The di- 
 agonal a-c has been rotated toward the vertical and be- 
 comes a'-c' ; and the diagonal d-b has been rotated in the 
 opposite direction, but also toward the vertical, and be- 
 comes d'-b' . They have both been rotated, by the refrac- 
 tion of the astigmatic cornea, toward the meridian of 
 greatest curvature. The image changes effected by the 
 astigmatic cornea are, as shown in the figure: an in- 
 crease in the length of the lines parallel with the merid- 
 ian of greatest curvature, an increase in the distance
 
 COMPENSATING CYCLOTROPIA. 423 
 
 between the lines parallel with the meridian of least 
 curvature, and a corresponding rotation of the diago- 
 nals toward the meridian of greatest curvature. The 
 proper plus cylinder placed before this eye gives such 
 aid to the least curved meridian of the cornea as to 
 make its refractive power exactly equal to the unaided 
 refractive power of the meridian of greatest curvature. 
 The result will be a lengthening of the horizontal lines 
 a'-d' and d'-c' into the lines a"-d" and b"-c" and a dis- 
 placement of the lines a'-b' and d'-c' until they become 
 a"-b" and d"-c". Since two of the sides (a-b and d-c} 
 of the square have been lengthened by the astigmatism 
 and the remaining two sides (a-d and b-c) have been 
 lengthened to exactly the same extent by the correct 
 plus cylinder, the figure a"-b"-c"-d" , seen by the cor- 
 rected astigmatic eye, is a square. The cylinder, in 
 changing the rectangular parallelogram a'-b' -d-d' to the 
 square a"-b"-c"-d", has also rotated the diagonals a'-c' 
 and d'-b' back to their original positions; for the diagonal 
 a' '-c' ' coincides with the diagonal a-c, and the diagonal 
 d"-b" coincides with d-b. 
 
 If the astigmatism had been corrected by a minus 
 cylinder, the lines a'-b' and d'-c' would have been short- 
 ened into the lines a-b and d-c; the lines a'-d' and b'-c 1 
 would have been brought closer together, a'-d' becoming 
 a-d and b'-c! becoming b-c; and the diagonals a'-c? and
 
 424 COMPENSATING CYCLOTROPIA. 
 
 d'-b' would have been rotated back into the diagonals a-c 
 and d-b, respectively, so that the figure thus seen would 
 be the square a-b-c-d. Thus it is shown that an astig- 
 matic eye, corrected with a minus cylinder, sees the 
 square with the same measurements as that seen by the 
 non-astigmatic eye; while the square seen by the astig- 
 matic eye, corrected with a plus cylinder, is magnified. 
 
 Turning the right side of Fig. 55 up, it shows the im- 
 age changes when the meridian of greatest curvature is 
 horizontal. In either case the lines parallel with the 
 meridian of greatest curvature are made longer by the 
 astigmatism, with a corresponding increase of distance 
 between the lines parallel with the meridian of least 
 curvature, and the diagonals are rotated toward the 
 meridian of greatest curvature. 
 
 If there is astigmatism of one eye with the meridian 
 of greatest curvature vertical and astigmatism of the 
 same kind in the other with the meridian of greatest 
 curvature horizontal, the former would see a square 
 changed into a rectangular parallelogram, with the longer 
 sides vertical; while the latter would see the square 
 similarly changed, but with the longer sides horizontal. 
 The images in such eyes would be dissimilar and could 
 not be perfectly fused; correcting cylinders would make 
 the images alike and thus make complete fusion possible. 
 
 What is true of squares is true of rectangular paral-
 
 COMPENSATING CYCLOTROPIA. 
 
 425 
 
 lelograms, as shown by Fig. 56 in .which there is the 
 same proportionate lengthening- of two of the sides by 
 the astigmatism, and of the other two sides by the astig- 
 matic correction with plus cylinders, also the same char- 
 
 Fig. 56. 
 
 acter of rotations of the diagonals, the principal merid- 
 ians being" vertical and horizontal. 
 
 Fig. 57 shows the image changes when the astigma- 
 tism is oblique, the meridian of greatest curvature be- 
 ing at 135. That part of the complex figure shown by 
 a-b-c-d is a square as seen by a non-astigmatic eye. 
 L/ooked at by the oblique astigmatic eye already men- 
 tioned, the diagonal a-c, being at an angle of 135, is in a 
 plane with the meridian of greatest curvature, while the 
 diagonal d-b is in a plane with the meridian of least 
 curvature. For reasons already given in discussing
 
 426 
 
 COMPENSATING CYCLOTROPIA. 
 
 Fig. 55, the diagonal a-c is increased in length by the 
 astigmatism into a'-c' , while the diagonal d-b is neither 
 altered in length nor in direction. The sides of the square, 
 not being parallel with the principal meridians, must be 
 rotated toward the meridian of greatest curvature, a-b 
 
 Fig- 57- 
 
 becoming a'-b, a-d becoming a'-d^ b-c becoming b-c', and 
 d-c becoming d-d '. The figure a'-b-d-d is a non-rectan- 
 gular parallelogram leaning down and to the right. A 
 plus cylinder correcting - the astigmatism will increase 
 the length of diagonal d-b into d'-b' to exactly the length 
 of the diagonal a'-J and at the same time will rotate the
 
 COMPENSATING CYCLOTROPIA. 427 
 
 lines a'-b to a'-b', a'-d to a'-d', c'-b to c'-b', and c'-d to 
 c'-d ', thus converting the non-rectangular parallelogram 
 a'-b-d-d into the magnified square a'-b' -c'-d'. 
 
 Turning the right side of Fig. 57 up, the image changes 
 are shown when the meridian of greatest curvature is at 
 45. It is clear that, if the astigmatism is equal and of 
 
 Fig. 58- 
 
 the same kind in the two eyes, the meridians of greatest 
 curvature being parallel, though oblique, the two images 
 of a square held vertically will be distorted alike, and 
 hence will fuse readily and completely. If the meridian 
 of greatest curvature in the right eye is at 135, and in 
 the left eye at 45, the image in each eye will be a non-
 
 428 COMPENSATING CYCLOTROPIA. 
 
 rectangular parallelogram leaning in the opposite direc- 
 tion from the image in the other eye; and the two cannot 
 be perfectly fused, though an attempt at fusion will be 
 made, in an effort on the part of the eyes to obey the 
 supreme law of binocular single vision, the law of cor- 
 responding retinal points. 
 
 Fig. 58 shows how the fusion of the images would 
 make the square appear. This fusion is effected by the 
 superior obliques converging the vertical axes of the eyes. 
 
 Soon after Hotz and Wilson had tried the camera and 
 had published their conclusions unfavorable to the dis- 
 tortion of retinal images by oblique astigmatism, Dr. 
 Perry, of Oneida, N. Y., betook himself to the camera, 
 with the result shown in the accompanying half-tone 
 cut, Fig. 59: 
 
 Dr. Perry's own words, descriptive of this cut, are as 
 follows : 
 
 "Fig. 59 was produced by taking a photograph of the 
 graduated circle with printed words as shown; and then, 
 without moving camera or object, placing a .50 D cylin- 
 drical lens in front of the objective and exposing a sec- 
 ond negative, and, when the photographs were finished, 
 cutting away the outer circle from the astigmatic print 
 and pasting it over the other in such a way as to make 
 the horizontal and vertical lines, respectively, coincide on 
 the two prints. If the cut is held so that the line of the
 
 Fig. 59-
 
 430 COMPENSATING CYCLOTROPIA. 
 
 print reading- 'Astigmatism Oblique, 135,' is horizontal, 
 it will be observed that the distortion of the field is such 
 that this particular line is moved along the scale nearly 
 two degrees, while the line which is perpendicular to it 
 is moved an equal distance, but in a contrary direction. 
 This shows what must happen to a retinal image in ob- 
 lique astigmatism." 
 
 Dr. Lowry, at the time a private student of the au- 
 thor, was incited by the published criticisms of Hotz 
 and Wilson to use his camera. Half-tone cuts were made 
 from his photographs, and, notwithstanding these speak 
 for themselves, his descriptive text is here reproduced: 
 
 "It has often been noted that the camera obscura is 
 very strikingly similar, in its mechanism, to the human 
 eye. In this simple optical instrument we have a me- 
 chanical eye, so far as refraction is concerned. If we 
 compare to the eye the component parts of the photo- 
 graphic camera, which is merely a camera obscura with 
 a device for receiving the image on a sensitized plate, we 
 find the refractive media of the former correspond to the 
 photographic lens; the iris, to the stop; the accommo- 
 dation, to the focusing apparatus; and the retina, to the 
 ground glass. Focus the camera properly, and we have 
 the emmetropic eye. By placing a concave cylindrical 
 lens, axis at 90, in apposition to the photographic lens, 
 we have simple hypermetropic astigmatism according to
 
 COMPENSATING CYCJUOTKOPIA. 
 
 431 
 
 the rule; if we place the axis at 180, we have simple hy- 
 permetropic astigmatism against the rule; if we place 
 the axis anywhere between the \ertical and horizontal, 
 
 Fig. 60. 
 
 we get oblique astigmatism. Whether or not the image 
 will be oblique on the ground glass will be seen later. 
 
 "To illustrate these points, I have made the accompa- 
 nying- photographs with a rapid rectilinear lens, used in 
 the Rochester Optical Company's 5x7 midget camera. 
 The camera was not moved or changed in any way foi
 
 432 
 
 COMPENSATING CYCLOTROPIA. 
 
 the first five photographs. Fig 1 . 65 was made at another 
 time. The rectangle was made mathematically accurate 
 on a piece of cardboard 24 x 30. The lines, one inch wide, 
 
 Fig. 61. 
 
 are prolonged beyond the rectangle to show more clearly 
 the obliquity of imagfes that may be produced by the 
 cylinders obliquely placed. The watch is used as a 
 plumb, and is seen in the same position in all. The 
 photographs are not inverted as the images \vould be on 
 the ground glass or the retina.
 
 COMPENSATING CYCLOTROPIA. 
 
 433 
 
 "In Fig. 60, no cylindrical lens is used, and we get 
 a perfect rectangle, sharp and distinct in its outline, as 
 would be seen by an emmetropic eye. 
 
 Fig. 62. 
 
 "In making Fig. 61 a minus 3 D. cylindrical lens is 
 placed just in front of, and in apposition to, the photo- 
 graphic lens, with its axis at 45. * A plus 1.50 D spher- 
 ical lens is used with the cylinder in order to give the 
 
 * These prints are all the reverse o 
 it would be seen. AUTHOR. 
 
 f the images, therefore the reverse of the object as
 
 434 
 
 COMPENSATING CYCLOTROPIA. 
 
 middle of the focal interval without changing- the camera. 
 In this the vertical and horizontal lines are equally indis- 
 tinct. The vertical lines deviate to the left at the top, 
 
 ""/ 
 
 Fig. 63. 
 
 and to the right at the bottom, while the horizontal lines 
 are depressed at the right and elevated at the left. T^ne 
 plumb shows that the card is in just the same position 
 as in Fig. 60, and the camera has not been moved from 
 its original position. This picture is clearly a non-rec- 
 tangular parallelogram.
 
 COMPENSATING CYCLOTROPIA. 
 
 435 
 
 " If the axis of the cylinder be changed to 90, we get 
 Fig. 62, which represents simple vertical hypermetropic 
 astigmatism. This is made without the plus 1.50 D sphere 
 and without the camera's being changed in the least from 
 
 Fig. 64. 
 
 its position in Fig. 60 and Fig. 61. The meridian of great- 
 est curvature here is at 90, with the least at 180. It is 
 a perfect rectangle, with its horizontal lines sharply cut 
 and the vertical very indistinct. 
 
 "Now if we place the axis of the cylinder at 135, 
 again adding the plus 1.50 D sphere, a non-rectangular
 
 436 COMPENSATING CYCLOTROPIA. 
 
 parallelogram is formed with its sides deviating- in the 
 opposite direction to those in Fig-. 61. This is shown in 
 Fig-. 63. Every part is equally indistinct, and nowhere 
 are the lines at right angles as in the original. 
 
 Fig. 65. 
 
 " By placing the axis of the cylinder at 180, without 
 the plus 1.50 D sphere, we produce simple hypermetropic 
 horizontal astigmatism, the effect of which is illustrated 
 in Fig. 64. Here we have the meridian of greatest curva- 
 ture at 180, and the least at 90. We obtain a perfect
 
 COMPENSATING CYCLOTROPIA. 437 
 
 rectangle, with its vertical lines clear and its horizontal 
 very indistinct, in contradistinction to Fig. 62. 
 
 "Fig 1 . 65 is the same as Fig 1 . 61 without the plus 1.50 D 
 sphere to give the focal interval, nor is the camera re- 
 focused to give it. This photograph was made at a dif- 
 ferent time, and the camera was not in exactly the same 
 position as for the other five. An eye with the meridian 
 of greatest curvature at 45 and 3 D of simple hyper- 
 metropic astigmatism would see the object as shown 
 in this figure, if, under the influence of a mydriatic or 
 in old age, it were relieved of all ciliary action. The 
 rhomboidal figures are seen very clearly here at the 
 angles and on the watch. 
 
 " Suppose one of the meridians of greatest curvature 
 to be at 45, and the other at 135, one image would be 
 seen as in Fig 1 . 61, and the other as in Fig-. 63; in obedi- 
 ence to the law of corresponding- retinal points, we would 
 have these two fig-ures superimposed, forming- a trape- 
 zoid. If the meridians diverged above, we would have 
 the long- side above, and the short side below. In this 
 form of astigmatism we would not only have a ciliary 
 strain, but the superior obliques would make an attempt 
 to bring the harmonizing parts of the two retinas under 
 the dissimilar -images in order to have a single object. If 
 the meridians converged above, the short side of the trape- 
 Zoid would be above, and the long side below. This fu-
 
 438 COMPENSATING CYCLOTROPIA. 
 
 sion of dissimilar parallelograms into a trapezoid, long- 
 side below, would be effected by the inferior obliques. 
 
 "But the bone of contention has been principally the 
 question of the deviation or the non-deviation of the image 
 on the retina in oblique astigmatism. Others have proved 
 it by the laws of optics, by clinical experience, and by 
 logical reasoning; and it seems to me that my pho- 
 tographic demonstrations have added very conclusive 
 evidence to the theory that, in oblique astigmatism, the 
 retinal images of vertical and horizontal objects deviate 
 from their normal direction." 
 
 Since 1887, it has been taught that, in oblique as- 
 tigmatism, abnormal work is required of the obliques. 
 However, it was not until 1891 that the cause of this ab- 
 normal action on the part of the obliques was discovered 
 to be a want of parallelism of the meridians of greatest 
 curvature of the corneas and a consequent dissimilar dis- 
 tortion of retinal images. It was then announced that, 
 in oblique astigmatism, be the obliquity much or little, 
 it is a physical impossibility for a horizontal line and its 
 retinal image to lie in the same plane.* The same is 
 true of all lines not parallel with one or the other of the 
 two principal meridians. 
 
 The obliquity of retinal images was first demonstrated, 
 in the latter part of 1890, by the production of artificial 
 
 *See Ophthalmic Record, Vol. I., No. 1.
 
 COMPENSATING CYCLOTROPIA. 
 
 439 
 
 oblique astigmatism, at which time the following law 
 was formulated: " The retinal image is displaced toward 
 the meridian of greatest curvature" This being true 
 and there is no exception to this rule the image of a ver- 
 tical or horizontal line is displaced toward the meridian 
 of best curvature in oblique hyperopic astigmatism, from 
 the best meridian in oblique myopic astigmatism, and to- 
 ward the myopic meridian in oblique mixed astigmatism. 
 
 RIGHT LEFT 
 
 Fig. 66. 
 
 As a result of the experiments with artificially pro- 
 duced astigmatism, the next eight figures were con- 
 structed, some of them showing the character of the 
 images of a horizontal arrow, formed on the two retinas; 
 while other of these figures show clearly the compensat- 
 ing cyclotropia made necessary that the images might be 
 fused. This cyclotropia corresponds with the compen- 
 sating esotropia which occurs when both images are dis-
 
 440 COMPENSATING CYCLOTROPIA. 
 
 placed by prisms with their bases out; with the compen- 
 sating' exotropia, when images are displaced by prisms 
 with their bases in; with the compensating- hypertropia 
 of one eye and catatropia of the other, when a prism is 
 base down before one eye and base up before the other. 
 In either case, the turning 1 must occur in obedience to the 
 supreme law of binocular single vision, the law of cor- 
 responding- retinal points. 
 
 Fig-. 66 represents a pair of eyes in which the two 
 principal meridians are vertical and horizontal (they can 
 also represent eyes that are non-astigrnatic). If an 
 arrow, or the picture of an arrow, be held horizontally 
 before these eyes, the arrow-head toward the patient's 
 left eye, it will throw a reversed imag'e on each retina, 
 and the two images will be in the same plane with the 
 object. These two imag-es fall on parts of the two 
 retinas that act tog-ether; hence, but one object is seen. 
 
 Fig". 67 represents a pair of eyes in which there is hy- 
 peropic astig-matism, either simple or compound. The 
 left eye has its best meridian vertical. In this eye the 
 arrow, held as before, throws its image on the horizontal 
 meridian of the retina, hence in the same plane with it. 
 In the rig-ht eye the best meridian is at 135, as shown 
 by the dotted line. In obedience to the well-known law 
 of refraction by curved surfaces, the imag-e of the same 
 arrow must be oblique in this eye, and, hence, not in the
 
 COMPENSATING CYCLOTROPIA. 
 
 441 
 
 same plane with the object. The obliquity of the image 
 will be greater or less, depending- on the quantity of the 
 astigmatism. It is represented as falling 1 on meridian 
 170 of the retina. The horizontal image in the left eye 
 
 RIGHT 
 
 Fig. 67. 
 
 LEFT 
 
 and the oblique image in the right eye do not fall on 
 parts of the two retinas that harmonize. The direction 
 of either image in relation to the other cannot be changed 
 except by artificial means a proper cylindrical lens. 
 
 Fig. 68. 
 
 This being- true, the pair of unaided astigmatic eyes, 
 represented by Fig. 67, must see the arrow double, as 
 shown in Fig. 68, unless something is done by the eyes 
 themselves for the purpose of harmonizing the images.
 
 442 COMPENSATING CYCLOTROPIA. 
 
 In all cases of oblique astigmatism, unless the obliquity 
 is in the same direction in the two eyes, and the astig- 
 matism the same in kind and quantity, something 1 must 
 be done in order to prevent double vision, as represented 
 in Fig 1 . 68. There are but two ways of accounting- for 
 the absence of this peculiar kind of double vision in such 
 forms of astigmatism as that represented in Fig". 67. 
 Sectional ciliary contraction would account for it. If it 
 were possible for the ciliary muscle thus to act, one can 
 readily understand how the curvature of the lens could 
 be so changed as to result in lenticular astigmatism 
 equal, but at right angles, to the corneal astigmatism. 
 If such ciliary action were to take place in the right eye 
 of Fig. 67, the retinal image would not only be made as 
 sharp as if in an emmetropic eye, but it would also be 
 made to lose its obliquity, and thus double vision would 
 be prevented. As beautifully as this sectional ciliary 
 action would account for the absence of double vision 
 in cases of oblique astigmatism, it is certainly a false 
 theory, since, when all ciliary power has been suspended 
 by atropine or age, the eyes are still able to do something 
 by means of which the double vision represented by Fig. 
 68 is prevented. 
 
 There must be double vision, unless the oblique image 
 in the right eye and the horizontal image in the left eye 
 can be made to occupy corresponding parts of the two
 
 COMPENSATING CYCLOTROPIA. 
 
 443 
 
 retinas. This could be effected easily by the harmonious 
 symmetrical action of the superior oblique muscles. 
 
 Fig. 69 shows how the eyes represented by Fig. 67 act 
 in order to have the images fall on corresponding parts of 
 the retinas. The superior oblique muscle of the right 
 eye has so revolved it as to bring meridian 175 of the 
 retina in position to receive the impress of the oblique 
 image; while, at the same moment, the superior oblique 
 
 RIGHT 
 
 Fig. 69. 
 
 LEFT 
 
 muscle of the left eye has so revolved it as to bring me- 
 ridian 175 to the horizontal, hence in position to receive 
 the horizontal image. The oblique and horizontal im- 
 ages being now on harmonizing portions of the retinas, 
 there is no double vision. 
 
 Fig. 70 represents a pair of hyperopic astigmatic eyes, 
 the left one having its best meridian vertical and the 
 right one having its best meridian at 45. In these eyes
 
 444 
 
 COMPENSATING CYCLOTROPIA. 
 
 there are a left horizontal image (image and arrow in same 
 plane) and a right oblique image, this time on retinal 
 meridian 10. Nothing but artificial means will change 
 the relative direction of these images; and there must be 
 double vision, unless the oblique image can be made to 
 fall on a portion of the retina that will harmonize with 
 that portion of the other retina on which the horizontal 
 image may fall. 
 
 RIGHT 
 
 LEFT 
 
 Fig. 70. 
 
 The double vision that would exist in astigmatic eyes 
 represented in Fig. 70 is prevented by the harmonious 
 action of the inferior oblique muscles, as shown by Fig. 
 71, the inferior oblique of the right eye bringing meridian 
 5 under the oblique image, while the inferior oblique of 
 the left eye causes meridian 5 to come under the hori- 
 zontal image. Thus the two images are made to fall on 
 corresponding parts of the two retinas.
 
 COMPENSATING CYCLOTROPIA. 
 
 445 
 
 RlSHT 
 
 Fig. 71. 
 
 LETT 
 
 Fig. 72 represents a pair of hypermetropic astigmatic 
 eyes, with half the quantity of astigmatism found in the 
 eyes represented by Fig. 67 and Fig. 70; but in both eyes 
 the best meridian is oblique in the left eye at 45, and in 
 the right eye at 135. An arrow held in the horizontal 
 position before these eyes will throw an oblique image on 
 each retina, the one in the left eye on meridian 5, and the 
 
 RI6H 
 
 Fig. 72. 
 
 LEFT
 
 446 
 
 COMPENSATING CYCLOTROP1A. 
 
 one in the right eye on meridian 175. Without some 
 change double vision, as shown in Fig. 68, will be inevit- 
 able. 
 
 In the oblique astigmatism of the two eyes represented 
 by Fig. 72, the two oblique images are made to fall on 
 corresponding parts of the two retinas by the harmonious 
 action of the two superior oblique muscles, as shown in 
 Fig. 73. 
 
 RIGHT 
 
 . 73- 
 
 The obliquity of the image and the consequent strain 
 on the oblique muscles fully account for the greater 
 trouble attending oblique astigmatism than is found 
 connected with astigmatism in the vertical or horizontal. 
 As is well known, non-oblique myopic astigmatism is un- 
 attended by any sort of ciliary strain in distant vision. 
 
 In oblique myopic astigmatism, there is strain on either 
 the two superior or the two inferior oblique muscles in
 
 COMPENSATING CYCLOTROPIA. 447 
 
 both distant and near seeing". In all other forms of non- 
 parallel oblique astigmatism, there is likewise strain on 
 the oblique muscles. 
 
 In all kinds of non-oblique astigmatism, also in simple 
 hyperopia, the time comes when all nervous phenomena 
 caused by their existence pass away. Their disappear- 
 ance, being gradual, but finally complete, coincides with 
 the failure and final loss of ciliary power brought about 
 by advancing age. The symptoms caused by oblique 
 astigmatism may be modified by old age putting at rest 
 the ciliary muscles; but they cannot be made to vanish, 
 for the oblique muscles are forced to continue to act in 
 age as in youth, so as to harmonize the images on the 
 two retinas. 
 
 The plates made to illustrate the paper read by the 
 author at the meeting of the Eighth International Con- 
 gress of Ophthalmology (Edinburgh, 1894), are both in- 
 teresting and instructive. They are reproduced here, 
 together with the descriptive text. 
 
 Plate I. represents a pair of eyes that are non-astig- 
 matic; or, if astigmatism exists, the principal meridians 
 are vertical and horizontal. These eyes are represented 
 as looking at a rectangle. The line ep across the right 
 eye is the horizontal meridian, and the line g~h is the 
 vertical meridian, while their point of intersection (5) 
 is the macula. Similarly the line ep in the left eye rep-
 
 COMPENSATING CYCLOTROPIA. 449 
 
 resents the horizontal meridian, and gh represents the 
 vertical meridian, their point of intersection (5) being- the 
 macula. The vertical meridian of the right eye and that 
 of the left eye are parallel. Point 5 in the rectangle is 
 the point of fixation. The line 5-5 from the macula of 
 the right e} r e is the visual axis of that eye, and likewise 
 the line 5-5 is the visual axis of the left eye. These 
 intersect at point 5 of the rectangle. 
 
 According to the well-known law of refraction by 
 curved surfaces, such as are now under consideration, 
 the rectangular object will throw a rectangular image 
 on each retina, the size of which will bear a definite pro- 
 portion to the size of the object. The center of retinal 
 curvature of the right eye is x, through which all lines 
 of direction from this eye must pass. The lower inner 
 corner of this image is thus connected with the upper 
 right-hand corner of the object by the line 1-1; in the 
 same way the upper inner corner of the image is con- 
 nected with the lower right-hand corner of the object 
 by the visual line 2-2; and so on for the other corners 
 of image and object. In like manner the corners of the 
 rectangular image in the left eye may be connected with 
 corresponding corners of the object by lines passing 
 through the center of retinal curvature (x) of that eye. 
 If the left eye should be excluded, the right eye would 
 see the rectangle 1-2-3-4; if the right eye should be
 
 450 COMPENSATING CYCLOTROPlA. 
 
 screened, the left eye would see the same rectangular fig- 
 ure. Both eyes together, in obedience to both the law of 
 corresponding retinal points and the law of projection, 
 would see the one common rectangle 1-2-3-4. The supe- 
 rior and inferior recti in these eyes have kept the visual 
 axes in the same plane, the external and internal recti 
 have regulated their tension so that they have converged 
 these axes to the point 5, and the superior and inferior 
 obliques have kept the naturally vertical axes parallel 
 with the median plane of the head. 
 
 The obliques have to perform only the simple function 
 in oblique astigmatism, the meridians of greatest curva- 
 ture being parallel, and the degree of astigmatism the 
 same in the two eyes; but it would not be possible for 
 such eyes to see the rectangle held in the position shown 
 in Plate I. as a rectangle. L/et the meridians of greatest 
 curvature be at 45 in the right eye and also at 45 in the 
 left eye. As a result of the refraction of the astigmatic 
 cornea of the right eye, the rectangular figure would 
 throw a parallelogram image on the retina, the image 
 inclining down and out. A parallelogram image would 
 be thrown on the left retina also, and it would incline 
 down and in. Looked at with either eye alone, the rec- 
 tangle would be seen as a parallelogram inclined down 
 and to the right; looked at with both eyes, it would be 
 a parallelogram of the same shape and inclination as
 
 COMPENSATING CYCLOTROPIA. 451 
 
 seen by each eye separately. The extrinsic muscles of 
 these eyes have performed the same function as the mus- 
 cles of the eyes shown in Plate I. and with the same re- 
 sult viz., binocular single vision. The law of corre- 
 sponding- retinal points and the law of projection having 
 full sway in both pairs of eyes, the one pair sees the 
 figure as it is a rectangle while the other pair sees 
 the same figure, when held in the same position, as a 
 parallelogram leaning down and to the right. With the 
 visual axes properly directed by the recti and the verti- 
 cal meridians kept parallel by the obliques, the two 
 eyes are kept so related that the two images of the 
 object looked at fall on harmonizing parts of the 
 two retinas, and the object is necessarily seen as one, 
 and of the same shape as when seen with each eye sep- 
 arately. 
 
 In any state of refraction the relationship between 
 corresponding points of the two retinas is unalterable. 
 It is well known that, taken as a whole, the nasal half 
 of one retina harmonizes with the temporal half of the 
 other, and that all points of either retina bear a fixed 
 and unalterable relationship to the macula and to the 
 vertical and horizontal meridians. A retinal point in 
 the nasal half of the right retina, bearing a definite re- 
 lationship to the macula and the vertical and horizontal 
 meridians, must harmonize with a point in the temporal
 
 452 COMPENSATING CYCLOTROPIA. 
 
 half of the left retina similarly located; and it can har- 
 monize with no other retinal point under any conditions. 
 
 The complicated function of the obliques is necessary 
 in oblique astigmatism when the meridians of greatest 
 curvature diverge or converge above. This is necessary 
 that they may bring harmonizing parts of the two retinas 
 under dissimilar images, and thus insure binocular single 
 vision; but, as will be shown, the object, though seen as 
 one, will be distorted. 
 
 Plate II. may be taken for stud} T . Both eyes have 
 oblique astigmatism of the same kind and quantity. In 
 the right eye the meridian of greatest curvature is at 
 135 and in the left eye at 45. If the rectangular figure 
 represented in Plate I. be held in the same position be- 
 fore the eyes represented in Plate II., it would not be 
 seen with one eye alone or with both together as a rectan- 
 gle. The rectangle shown in Plate I., when held before 
 the right eye in Plate II., instead of throwing a rec- 
 tangular, would throw a non-rectangular, parallelogram 
 image on the right retina; the same rectangle would 
 also throw a non-rectangular parallelogram image on 
 the left retina. The state of refraction of the right eye 
 would make the distorted image lean down and toward 
 the left side, while the distorted image in the left eye 
 would lean down and toward the right side. Cutting 
 off the view of the left eye, the law of direction would
 
 (453)
 
 454 COMPENSATING CYCLOTROPIA. 
 
 have full sway, while the law of corresponding- points 
 would be suspended. Since in one eye alone the law of 
 direction is unalterable, all lines of direction must cross 
 in the center of retinal curvature; and the right eye, 
 with the parallelogram image leaning down and to the 
 left, must see the figure casting the image, not as a 
 rectangle, but as a parallelogram leaning down and to 
 the left. Screening the right eye while the left eye 
 looks on the rectangle, it is seen, not as a rectangle, 
 but as a parallelogram leaning down and to the right, 
 the law of direction determining the shape of the figure 
 seen by the left eye, just as it fixed the shape of the 
 figure seen by the right eye. Fig. 1-2-3-4 is what is 
 seen with the right eye alone; Fig. l'-2'-3'-4' is what is 
 seen by the left eye alone. The moment these two eyes 
 are allowed to look at the rectangular figure, the law of 
 corresponding retinal points is brought into conflict with 
 the law of direction, and the latter is modified by the 
 former. There is no necessity for changing the visual 
 axes when looking at the rectangle with these two eyes; 
 but, unless some change is effected in some way, each 
 eye would see its own parallelogram leaning down and 
 toward the opposite side. Instantly a change does take 
 place in both eyes, so that the two together see, not a 
 rectangle nor a parallelogram, but a trapezoid, with the 
 longer side above. A clear understanding of what this
 
 COMPENSATING CYCLOTROPIA. 455 
 
 change is and how it is effected may be had by a further 
 study of Plate II. In the right eye is shown a dotted 
 parallelogram a-b-c-d, of precisely the same form as the 
 parallelogram image 1-2-3-4; but in the former the upper 
 and lower lines are parallel with the horizontal meridian. 
 In the left eye also is shown a dotted parallelogram 
 a'-b'-c'-d', of the same form as the parallelogram l'-2'- 
 3'-4', with its upper and lower lines parallel with the 
 horizontal meridian of this eye. The line c-b in the right 
 eye bears throughout the same relation to the macula, 
 the horizontal and vertical meridians of this eye, that the 
 line c'-b' does to the same parts of the left eye, and they, 
 therefore, correspond. The greater part of the line d-a 
 in the right eye also corresponds with the greater part 
 of the line d'-a' in the left eye, the parts of these lines 
 not corresponding being their extremities. But the line 
 c-d in the right eye nowhere corresponds with the line 
 c'-d f in the left eye, except at the points of beginning 
 above; and the same is true of lines b-a and d'-a', in their 
 respective eyes. If the dotted parallelograms could be 
 made to coincide with the parallelogram images, the re- 
 sult would be that the two eyes together would see the 
 figure a-b-c-d', a trapezoid, with the longer side above. 
 How this is effected is shown in Plate III., where each 
 eye has been revolved on its visual axis by its superior 
 oblique muscle, so that the horizontal meridian is made
 
 456 COMPENSATING CYCLOTROPIA. 
 
 parallel with the upper and lower borders of the parallel- 
 ogram image; and thus, as far as possible, correspond- 
 ing 1 parts of the two retinas are brought under the two 
 dissimilar images, and the figure seen binocularl} 7 " is 
 a-b-c-d'. The part of this trapezoid seen in common by 
 the two eyes is a'-b-c-d, the part seen by the right eye 
 alone is a-b-a', and that seen by the left eye alone is 
 d-c-d' '. As will be seen, the law of corresponding- points 
 has so modified the law of projection that the visual lines 
 no longer have a common crossing" point. This is anarchy, 
 so far as projection is concerned, in these eyes. 
 
 When the law of direction is interfered with, as a re- 
 sult of the conflict between it and the more imperious 
 law of corresponding- retinal points, the object seen is 
 always in the position that it would have been in, had 
 the images primarily fallen on the parts of the two ret- 
 inas that have been rotated under them, in obedience to 
 the supreme law of binocular single vision the law of 
 corresponding retinal points. The displaced images, as a 
 result of either natural or artificial means, cover areas of 
 the two retinas that do not correspond. In order to have 
 binocular single vision, retinal areas that more nearly 
 correspond, and are of the same shape and size as the im- 
 ages, must be brought under them. The object will be 
 seen as though no rotation had taken place, as if the im- 
 ages had primarily fallen on these parts, in perfect obe-
 
 (457)
 
 458 COMPENSATING CYCLOTROPIA. 
 
 dience to the law of projection, although the lines of di- 
 rection drawn from the images to the single object will 
 not cross at the center of retinal curvature. In cases of 
 decentration of the maculas, and in displaced images by 
 means of prisms, all lines of direction will cross at one 
 point, but that point will be above, below, to the outer 
 or inner side of the true point; while in oblique astigma- 
 tism, and when the axes of correcting cylinders are dis- 
 placed, no three lines of direction cross at the same point. 
 
 In like manner a plate could be made showing how 
 astigmatic eyes, with meridians of greatest curvature 
 converging above, would see a rectangle distorted into 
 a trapezoid, the longer side below. In each eye there 
 would be a parallelogram image inclining down and out. 
 To fuse these into a trapezoid, the inferior oblique mus- 
 cles would be brought into action, in order, as far as 
 possible, to bring corresponding retinal parts under dis- 
 similar images, which is done the moment the obliques 
 displace the horizontal meridians so that they become 
 parallel with the upper and lower borders of the dis- 
 torted images. 
 
 Imperfect as is binocular single vision in uncorrected 
 oblique astigmatism, the meridians of greatest curvature 
 either diverging or converging above, it could be effected 
 in no other way than by a revolution of the eyes by the 
 symmetric harmonious action of the oblique muscles. It
 
 COMPENSATING CYCLOTROPIA. 459 
 
 is true that Nature has one other method of preventing 
 diplopia namely, mental suppression of one of the dis- 
 placed images. It may be that amblyopia resulting- from 
 oblique astigmatism high in degree, and from insufficiency 
 of the obliques, is more common than one would at first 
 think. Certainly, if the obliques cannot do their proper 
 work in effecting binocular single vision, in the first 
 years of life, nothing is more reasonable than to suppose 
 that amblyopia ex anopsia would develop. Who has 
 not seen cases of amblyopia without being able to ac- 
 count for it ? 
 
 The phenomena outlined can be demonstrated experi- 
 mentally by any one who desires to prove all things; for 
 he can produce in his own case, at pleasure, any form of as- 
 tigmatism. But some may be ready to say that artificial 
 astigmatism is one thing and natural astigmatism is an- 
 other thing. This is true, but only in name. That 3 D 
 of artificial hyperopic astigmatism is the same error of 
 refraction as 3 D of natural hyperopic astigmatism is 
 abundantly proved by the fact that each is thoroughly 
 corrected by a plus 3 cylinder, axis properly placed. 
 Either plus or minus cylinders may be used in the ex- 
 periments, for the one is as capable of producing arti- 
 ficial astigmatism as the other. If the plus cylinders 
 (3 D) be used, the astigmatism produced has its meridian 
 of greatest curvature at right angles to the axis of the
 
 460 COMPENSATING CYCLOTROPIA. 
 
 cylinder, while the meridian of greatest curvature would 
 correspond with the axis of the minus cylinder (3 D) if 
 it were used. 
 
 By either means it can be easily proved that in astig- 
 matism of any kind (myopic, hyperopic, or mixed), whose 
 meridians of greatest curvature diverge above, there is a 
 necessity for action on the part of the superior oblique 
 muscles in order to prevent diplopia. This action, hav- 
 ing its beginning in the earliest days of infancy and con- 
 tinuing during waking hours until the cause is corrected 
 or one eye is lost, converges the naturally vertical axes 
 above. If the meridians of greatest curvature converge 
 above, the images of all objects are so displaced in the 
 two eyes as to throw into activity the inferior obliques, 
 so that diplopia may be prevented. 
 
 In astigmatism with the principal meridians vertical 
 and horizontal, the only eye muscles brought into ac- 
 tion to remedy, in any way, the condition, are the ciliary 
 muscles. In oblique astigmatism with the meridians of 
 greatest curvature diverging above, there is the same 
 state of ciliary strain to sharpen as much as possible the 
 images, and there is also a necessary activity of the su- 
 perior obliques so as to bring corresponding parts of the 
 two retinas under the oblique images, that there may be 
 binocular single vision. Again, in oblique astigmatism 
 with the meridians of greatest curvature converging
 
 COMPENSATING CYCLOTROPIA 461 
 
 above, there is the ciliary strain for sharpening the 
 images, and there is also a consequent activity of the 
 inferior obliques so as to bring similar parts of the 
 retinas under the dissimilar images, resulting in binoc- 
 ular single vision. 
 
 When there is equality of strength of the obliques of 
 the two eyes, vertical and horizontal astigmatism will 
 give less trouble than when the astigmatism is oblique 
 in either direction, and astigmatism with the meridians 
 of greatest curvature diverging above need give no more 
 annoyance to the patient than if these meridians con- 
 verged above; for, in the former case, the superior ob- 
 liques would be as able to bear the strain as would the 
 inferior obliques in the latter condition. 
 
 But the obliques are not always harmonious : the 
 superior obliques are insufficient in at least twenty-five 
 per cent of all cases, while the inferior obliques are in- 
 sufficient in less than one per cent of all cases. In 
 cases of insufficiency of the superior obliques, the ver- 
 tical form of astigmatism would be worse on the patient 
 than if he had oblique astigmatism with the meridians 
 of greatest curvature converging above; and the worst 
 form of astigmatism would be that in which the merid- 
 ians of greatest curvature diverge above. The reverse 
 would be true if the inferior, obliques were insufficient 
 a rare condition.
 
 462 COMPENSATING CYCLOTROPIA. 
 
 The complicated function of the oblique muscles exists 
 only in cases of oblique astigmatism with the meridians 
 of greatest curvature converging or diverging- above, and 
 in unequal degrees of oblique astigmatism when the 
 meridians of greatest curvature are parallel. The ne- 
 cessity for this function is entirely destroyed when the 
 astigmatism is properly corrected; but the action of the 
 obliques does not always cease at once in binocular single 
 vision through the correcting cylinders. The old habit 
 of rotation often continues for hours, and sometimes for 
 days (although there is no longer a need for it), and the 
 result is metamorphopsia. Inherent weakness of the 
 superior oblique muscles, in a large per cent of the 
 cases, leads to a more speedy disappearance of the met- 
 amorphopsia when the meridians of greatest curvature 
 diverge above than when they converge. The reverse 
 would be true in a case of insufficiency of the inferior 
 obliques. The habit of action is more quickly suspended 
 in a weak muscle than in a strong one. In all cases, 
 however, it ceases, and the metamorphopsia vanishes, 
 under the continuous wearing of the correcting cylinders. 
 
 A careful study of what precedes in this chapter will 
 show that, while the superior obliques must fuse the 
 displaced images of a horizontal line, in cases of astig- 
 matism with the meridians of greatest curvature diverg- 
 ing above, the inferior obliques must fuse the displaced
 
 COMPENSATING CYCLOTROPIA. 463 
 
 images of a vertical line, in the same kind of cases. 
 When the meridians of greatest curvature converge 
 above, the displaced images of a horizontal line must 
 be fused by the inferior obliques, while the displaced 
 images of a vertical line would be fused by action of the 
 superior obliques. In most cases of oblique astigmatism 
 the inferior obliques can fuse images more easily than 
 the superior obliques, for the reason that the former are 
 usually stronger than the latter; but when a figure con- 
 sists of both vertical and horizontal lines, such as a 
 rectangle, the upper and lower borders, respectively, of 
 the images must be fused, whether by the inferior obliques 
 or the superior obliques. The lateral borders the verti- 
 cal ends of the rectangle become divergent above if the 
 fusion has been effected by the superior obliques, while 
 they become divergent below if the fusion has been ef- 
 fected by the inferior obliques. There is no known rea- 
 son for the fusion of the upper and lower borders of 
 images to the detriment of the lateral borders, and it 
 may remain always an unexplainable fact. 
 
 The extent of displacement of images of horizontal 
 lines by oblique astigmatism can be measured only b} 
 the cyclo-phorometer, but this measurement cannot be 
 accurately made if there is a complicating cyclophoria. 
 If the meridians of greatest curvature diverge above and 
 there is a complicating plus cyclophoria, the measure-
 
 464 COMPENSATING CYCIXXTROPIA. 
 
 ment will show greater displacement than really exists; 
 while the measurement will show less than the real dis- 
 placement when the meridians of greatest curvature con- 
 verge above and there is a complicating plus cyclophoria. 
 In measuring the displacement of the image by oblique 
 astigmatism, the single Maddox rod must be used, in the 
 cyclophrometer, and the vertical displacing prism must 
 be behind one rod so as to make one streak of lisrht be- 
 
 O 
 
 low the other. The axis of each rod should be vertical. 
 Both eyes having oblique astigmatism, the meridians of 
 greatest curvature diverging above, each streak of light 
 will dip toward the opposite side. Revolving one rod 
 until the two streaks are parallel, though not horizontal, 
 shows the sum of the displacement of the two images; 
 while revolving each rod until the two streaks are hori- 
 zontal, therefore parallel, the extent of displacement of 
 the image in each eye is easily read on the scale. This 
 shows, also, the amount of minus cyclotropia necessary 
 for the fusion of the two images of a horizontal line. 
 The degree of displacement of the image of a horizontal 
 line depends on both the quantity of the astigmatism 
 and the extent of the obliquity of the meridian of great- 
 est curvature up to 45 from the vertical, at which point 
 there is the maximum of displacement. The compensat- 
 ing cyclotropia of the two eyes always equals the sum of 
 the displacements of the two images.
 
 COMPENSATING CYCLOTROPIA. 465 
 
 The apparent dipping of the streak of light due to 
 cyclophoria may be differentiated from that caused by 
 oblique astigmatism by substituting the triple rod for 
 the simple rod. With the triple rod the dipping line of 
 cyclophoria will be unbroken, while the dipping line of 
 oblique astigmatism will be broken into as many parts 
 as there are rods, the one part slightly over-riding the 
 other in the direction of the obliquity of the most- 
 curved meridian. 
 
 This obliquity of the image varies from a few minutes 
 to a few degrees, but is always enough, even in slight 
 cases of oblique astigmatism, to force the obliques to 
 disturb the parallelism of the vertical axes with the 
 median plane of the head. Persons with oblique astig- 
 matism, with the meridians of greatest curvature con- 
 verging or diverging above, cannot have correct ideas of 
 direction, except in line of the visual axes, nor can they 
 judge correctly of verticality, horizontality, and goni- 
 ometry. 
 
 The abnormal work required of the obliques because 
 of oblique astigmatism (non-parallel) develops symptoms 
 not unlike those caused by cyclophoria. 
 
 TREATMENT. 
 
 The treatment of compensating cyclotropia is always 
 non-surgical. The careful correction of the astigmatism
 
 466 COMPENSATING CYCLOTROPIA. 
 
 will counteract the distortion of the retinal images and 
 relieve the cyclotropia, but not at once; the lifetime 
 habit of the obliques cannot be broken at once; but 
 sooner or later these muscles will learn that, under the 
 new condition (the wearing of the correcting cylinders), 
 they must parallel the vertical axes of the eyes with the 
 median plane of the head, in order to satisfy the law of 
 corresponding retinal points. 
 
 In all cases of astigmatism, one eye looking through 
 its correcting cylinder will see at once a rectangle as 
 a rectangle; and if the meridians of greatest curvature 
 are parallel whether vertical, horizontal, or oblique' the 
 two eyes looking through the cylinders will show no dis- 
 tortion of a rectangular figure. The reason for this is 
 that, in such cases, the obliques have never done other 
 work than the keeping of the vertical axes of the eyes 
 parallel with the median plane of the head; therefore 
 they have no habit to break when cylinders are given. 
 In such cases the glasses are worn with gladness from 
 the beginning. 
 
 There is always metamorphopsia to annoy a patient 
 whose astigmatism was such that the meridians of 
 greatest curvature diverged above, when she begins the 
 wearing of correcting cylinders, whether they be plus 
 or minus. This distortion is easily noticed, for it is the 
 opposite of that to which she has always been accustomed
 
 COMPENSATING CYCLOTROPIA. 467 
 
 and which she may never have noticed. Seen through 
 the correcting 1 cylinders, a rectangle will appear as a 
 a trapezoid, with the longer side below; a level surface 
 will slant toward her; and a vertical object will lean 
 toward her. The metamorphopsia is due to the fact 
 that the superior obliques, always in the habit of con- 
 verging the vertical axes of the eyes in binocular vision, 
 continue to thus converge them for a time, so that the 
 axis of the plus cylinder and the meridian of greatest 
 curvature do not remain in the same plane. The supe- 
 rior obliques, possibly because they are usually weaker 
 than the inferior obliques, readily break from tljeir old 
 habit, and the metamorphopsia vanishes. In such cases 
 it is a question of only a few hours or, at most, a few 
 days until the correcting cylinders can be worn without 
 annoyance of any kind. The old habit broken, the me- 
 ridian of greatest curvature (least if a minus cylinder is 
 used) and the axis of the cylinder lie in the same plane 
 in binocular as well as in monocular vision. 
 
 When the meridians of greatest curvature converge 
 above, the wearing of the cylinders will be attended by 
 metamorphopsia for a much longer time, possibly be- 
 cause the inferior obliques, being stronger than the su- 
 perior obliques, are less inclined to give up the old habit 
 of diverging the vertical axes of the eyes, in the act 
 of binocular vision. With either eye alone, a rectangle,
 
 468 COMPENSATING CYCLOTROPIA. 
 
 seen through the correcting- cylinder, will be a rectangle; 
 the floor will appear level, and a vertical object will not 
 be inclined. In binocular vision througfh the cylinders a 
 rectangle will appear as a trapezoid, with its longer side 
 above; a level surface will slant from the patient; and a 
 vertical object will lean from her. These appearances, 
 being" new, will be easily noticed, and will often prove 
 very annoying* to the patient, unless previously told 
 about them. Finally, the old habit of rotation will 
 cease, and the metamorphopsia will disappear, but 
 only after days or weeks of constant wearing of the 
 cylinders. 
 
 After the disappearance of the metamorphopsia, caused 
 by plus cylinders, whose axes diverge above, on raising 
 the lenses a rectangle will appear as a trapezoid, with 
 the longer side above; but if the axes of the cylinders 
 converge above, on raising the lenses a rectangle will 
 appear as a trapezoid, with the longer side below. The 
 same changes in the rectangle existed before the cyl- 
 inders were ever prescribed, but they were unnoticed. 
 Now that the cylinders have corrected the misshaped 
 images, giving perfect vision, on raising the lenses the 
 misshaped images at once make the patient conscious of 
 the distortion of the object. 
 
 There are two methods of dealing with cases of non- 
 parallel oblique astigmatism so as to shorten the annoy-
 
 COMPENSATING CYCLOTROPIA. 469 
 
 ing- period of habit-breaking on the part of the oblique 
 muscles. One method was suggested by Lippincott, 
 of Pittsburg, Pa. He advises that the full error be 
 determined under a mydriatic, and that the exact lo- 
 cation of the principal meridians be found, which can 
 be easily done, if the compensating cyclotropia is not 
 complicated by a cyclophoria, by excluding one eye whil 
 testing the other; for then the one eye assumes that po- 
 sition which makes its vertical axis parallel with the 
 median plane of the head. The findings, both as to 
 strength of cylinders and positions of axes, are to be 
 recorded. At first the cylinders given should be one- 
 third the full strength required, but their axes must be 
 placed according to the record. When the little meta- 
 morphopsia caused by the partial correction has disap- 
 peared, new cylinders of two-thirds the required strength 
 are given. The little metamorphopsia caused by these, 
 having vanished, the full correction is given. These 
 cause but slight metamorphopsia, and that for only a 
 short while. 
 
 This method is more necessary and more helpful when 
 the meridians of greatest curvature converge above, and 
 consequently when the inferior obliques are the muscles 
 involved. A full correction of the astigmatism at once 
 corrects the shape of the images, so as to make them 
 correspond with the object. These images would now
 
 470 COMPENSATING CYCLOTROPIA. 
 
 fall on corresponding 1 retinal points if the vertical axes 
 of the eyes were made parallel with the median plane of 
 the head. To thus relate the vertical axes, the inferior 
 obliques must cease their efforts to diverge them, and the 
 superior obliques must assume the labor of paralleling 
 them. Work must be transferred from the inferior ob- 
 liques (usually stronger) to the superior obliques (usu- 
 ally weaker). The whole load cannot be shifted at once; 
 and as long as the inferior obliques continue to diverge 
 the vertical axes, so long will the metamorphopsia re- 
 main. Righting the images one-third transfers one-third 
 of the work from the inferior obliques to the superior ob- 
 liques. This small load is kindly and quickly accepted 
 by the superior obliques. The next step rights the 
 images two-thirds, and transfers another one-third of 
 the work from the inferior obliques to the superior ob- 
 liques. Having become accustomed to the first trans- 
 ference, the superior obliques kindly take on the newly 
 added load. The next step fully corrects the misshaped 
 images, and transfers the balance of the abnormal work 
 from the inferior obliques, in the shape of normal work 
 to the superior obliques. Having already become accus- 
 tomed to doing two-thirds of the work necessary for 
 paralleling the vertical axes of the eyes, the superior ob- 
 liques readily assume the remaining one-third of the load 
 that they must now carry. For this class of astigmatics
 
 COMPENSATING CYCLOTROPIA. 471 
 
 the Lippincott plan is a good one. The only objection 
 to the method is the cost of changing" the lenses. 
 
 There is nothing 1 to contraindicate the giving of the 
 full correction, at once, of astigmatism in which the 
 meridians of greatest curvature are parallel, whether 
 vertical, horizontal, or oblique; for, in these cases, the 
 oblique muscles have done the same work without the 
 correcting cylinders that they must do when these are 
 given. 
 
 In only high degrees of oblique astigmatism, with the 
 meridians of greatest curvature diverging above, will it 
 be necessary to adopt the Lippincott plan; for, as a 
 rule, the weak superior obliques are ready enough to 
 cease doing the work of converging the vertical axes 
 of the eyes, \vhile the inferior obliques just as readily 
 assume the new duty of paralleling these axes. In all 
 cases, as soon as the obliques learn to parallel the verti- 
 cal axes of the eyes with the median plane of the head, 
 just that quickly does metamorphopsia vanish. 
 
 The other method of correcting oblique astigmatism so 
 that there shall be but little annoyance from metamor- 
 phopsia is to give at once the cylinders that fully correct 
 the errors, and to have each lens cut so that, placed 
 straight in the frame, its axis shall be in a plane with 
 the meridian of greatest curvature (least curvature if 
 the lens is a minus cylinder) when the vertical axis of
 
 472 COMPENSATING CYCLOTROPIA. 
 
 the eye is parallel with the median plane of the head. 
 However, these lenses must not be placed in their final 
 positions in the rims at first, but each must have its axis 
 rotated into the arc of distortion for the obliques that 
 have been accustomed to doing abnormal work. The 
 rule formulated by Dr. N. C. Steele, of Chattanooga, 
 Tenn., for the placing of the axes of cylinders in oblique 
 astigmatism, is a good one to follow temporarily under 
 certain conditions. His rule, as applied to plus cylinders, 
 is as follows: 
 
 " In those cases in which the axes of the proper con- 
 vex cylinders for the two eyes diverge, place the cylin- 
 ders in those positions which will give the axes the great- 
 est divergence permitted by the tests; and in those cases 
 in which the axes converge, place them at the points 
 which will give them the greatest convergence permitted 
 by the tests." 
 
 The Steele rule for placing the axes of plus cylinders 
 is applicable only when these axes are \vithin 45 of the 
 vertical. Above the 45 point the shifting of these axes 
 should be from the vertical; below the 45 point the 
 shifting should be from the horizontal. In every case 
 of oblique astigmatism with the meridians of greatest 
 curvature diverging or converging above, the axes of 
 plus cylinders should be displaced toward the center of 
 the quadrants in which they are found, and the axes of
 
 COMPENSATING CYCLOTROPIA. 473 
 
 minus cylinders should be shifted from the center of the 
 quadrants in which they are found. 
 
 The shifting should be only enough to counteract the 
 metamorphopsia, and should be the same for the two 
 cylinders. Every two or three days these axes should 
 be turned a degree or two toward the location determined 
 in the monocular test. With each turning the meta- 
 morphopsia will be so little as hardly to be noticed; and 
 finally, when the cylinders are properly located, there is no 
 metamorphopsia. As the result of each backward turn- 
 ing of the axes of the cylinders, the obliques more nearly 
 parallel the vertical axes of the eyes; and when the last 
 turn has been made, the vertical axes of the eyes stand 
 parallel with the median plane of the head. 
 
 As the Lippincott method is specially applicable to 
 those cases of astigmatism in which the meridians of 
 greatest curvature converge above, so is it with the ro- 
 tation method. When the meridians of greatest curva- 
 ture diverge above whether the astigmatism be hyper- 
 opic, myopic, or mixed, unless high in degree the full 
 correction should be given at once, and the axes should 
 be placed in the positions determined by the monocular 
 tests. 
 
 If the Lippincott method be resorted to, full acuity of 
 vision is not obtained until the full correction of the 
 astigmatism has been given; in the method of rotating
 
 474 COMPENSATING CYCLOTROPIA. 
 
 the full-strength cylinders, vision is more or less blurred 
 until the axes are placed at last in their final positions. 
 As to acuteness of vision, the one method has no advan- 
 tage over the other, and there is just as little annoying 
 metamorphopsia in the one method as in the other. 
 
 It is almost universally true that astigmatics whose 
 meridians of greatest curvature diverge above, become 
 speedily accustomed to the correcting cylinders, for the 
 reason that insufficiency of the inferior obliques is so 
 rare probably not found in more than one case in two 
 hundred. There are some astigmatics whose meridians 
 of greatest curvature converge above, who can never 
 wear comfortably the correcting cylinders because of 
 insufficiency of the superior obliques, which exists in 
 about twenty-five per cent of all cases. 
 
 There are three reasons why the arcs of distortion, by 
 cylinders, for the oblique muscles, should be studied: (1) 
 That the operator may know how to place cylinders that 
 they may give rest to the weaker obliques in cyclopho- 
 ria; (2) that he may know how to shift the cylinders for 
 oblique astigmatics so as to lessen the annoyance from 
 metamorphopsia; (3) that he may appreciate the impor- 
 tance of having the frames, containing the cylinders that 
 correct any kind of astigmatism, so shaped as to set 
 perfectly straight before the eyes. 
 
 Several curious facts may be brought forward here,
 
 RIGHT 
 
 UFT 
 
 V Fij. * 
 
 PLATE IV 
 
 (475)
 
 476 COMPENSATING CYCLOTROPIA. 
 
 and reasons have been given why advantage should be 
 temporarily taken of these facts in certain cases. Fig 1 . 
 1, in Plate IV., represents a pair of hyperopic astig- 
 matic eyes, the meridians of greatest curvature being 
 vertical in each eye. The plus cylinders axes, 90 (a) 
 insure against strain of either the superior obliques or the 
 inferior obliques; but let the glasses be turned in their 
 rims so that the axis of the right shall stand at 80 () 
 and the axis of the left at 100 (&), images will be dis- 
 torted, as shown in Plate II., which would necessitate 
 strain on the part of the superior oblique muscles. The 
 distortion of the images would increase, and the strain 
 on the superior obliques would be greater, as the axes 
 are revolved farther away from the vertical, the maxi- 
 mum being reached at 45 (c) for the right eye and 135 
 (c) for the left eye. Passing these points, the distor- 
 tion grows less, until at 180 (d~) for each eye. it disap- 
 pears. 
 
 Fig. 2 represents the same pair of eyes. If now the 
 axis of the right cylinder should be revolved from 90 (a) 
 to 100 () and that of the left cylinder from 90 () to 80 
 (), the distortion of images \vould be such as to call into 
 activity the inferior obliques, so that there might be 
 binocular single vision. This distortion would reach its 
 maximum when the axis of the right cylinder stands at 
 135 (c) and that of the left cylinder at 45 (c), again les-
 
 COMPENSATING CYCLOTROPIA. 477 
 
 sening as the axes are made to approach the horizontal, 
 where the distortion ceases. 
 
 Fig 1 . 3, Plate IV., represents a pair of hypermetropic 
 astigmatic eyes with the meridian of greatest curvature 
 of the right at 70 (a) and that of the left at 110 (a). 
 (In all the figures of Plate IV., Plate V., and Plate VI., 
 the mark within the circle shows the location of the 
 meridian of greatest curvature.) These meridians, con- 
 verging above, would cause strain of the inferior ob- 
 liques, which -would be relieved by the correcting cylin- 
 ders, axis of the right at 70 (a) and of the left at 110 
 (). A revolution of the axis of the right cylinder to 45 
 (&) and that of the left cylinder to 135 (&) would so dis- 
 place the images as to call into action the superior ob- 
 liques, the displacement increasing as the axes are moved 
 until these points (b for each eye) are reached. Continu- 
 ing the revolution of the cylinders in the same directions, 
 the displacement lessens, and disappears entirely when 
 the axis of the right reaches 20 (c) and that of the left 
 reaches 160 (c), when the necessity for over-action of the 
 obliques no longer exists. If the axes of the cylinders are 
 moved from their correct positions (70 for the right eye 
 and 110 for the left eye) tp 90 (/) for each eye, images 
 will be so displaced as to call into compensating activity 
 the inferior obliques. The maximum of displacement 
 would be effected when the axis reaches 135 (e) in the right
 
 478 COMPENSATING CYCLOTROPIA. 
 
 eye and 45 (e] in the left eye. Continuing' the revolution 
 in the same directions, the displacement would grow less, 
 and finally disappear when the axis of the right eye stands 
 at d, and that of the left eye at d, each 20 above the hori- 
 zontal. As will be seen, the arc of distortion, so as to 
 throw strain on the superior obliques, is 50 (from 70 to 
 20 in the right eye and from 110 to 160 in the left eye), 
 while the arc of distortion that would throw strain on the 
 inferior obliques is 130 (from a to d}. 
 
 Fig 1 . 4, Plate IV., shows the meridians of greatest 
 curvature of these hypermetropic astigmatic eyes at 
 110 () for the right and 70 () for the left. These me- 
 ridians, diverging above, would call into compensating 
 activity the superior oblique muscles. Correctly chosen 
 and properly placed cylinders, by correcting the distor- 
 tion of the images, would remove the necessity for the 
 performance of the complicated function of the superior 
 obliques. Displacing the axes of these cylinders, the 
 right to 135 (&) and the left to 45 (&), would cause a 
 maximum of distortion of the images, of the kind to call 
 into action the inferior obliques. Continuing the revo- 
 lution of the cylinders, the distortion would disappear 
 when the axis of the right reaches 160 (c) and that of 
 the left reaches 20 (c). Should the axes of the cylinders 
 be revolved from their proper places at 110 (a) in the 
 right and 70 (a) in the left to 90 (/) for each eye, the
 
 COMPENSATING CYCLOTROPlA. 479 
 
 images would be so changed as to call into harmonious 
 activity the superior obliques. The maximum distortion 
 would occur when the axis of the right is at 45 (<?) and 
 that of the left at 135 (e). Continuing the revolution, 
 the distortion would disappear when the axes reach the 
 points d above the horizontal meridians. In this case 
 the arc of distortion causing activity of the inferior ob- 
 liques is 50 (from a to c), while the arc of distortion that 
 would throw strain on the superior obliques is 130 (from 
 a to d). If in this pair of eyes the meridians of greatest 
 curvature had been at 130 for the right and 50 for the 
 left, the arc of distortion that would call the inferior ob- 
 liques into action would be only 10, while the one that 
 would cause activity of the superior obliques would be 
 170 (180 less 10). 
 
 Fig. 1, Plate V., represents hypermetropic astigmatic 
 eyes, the meridians of greatest curvature being at 180 
 (a) in each eye a condition that, in itself, would not call 
 either the superior obliques or the inferior obliques into 
 activity. The correct plus cylinders axes, 180 would 
 sharpen the blurred, but not distorted, images. Displa- 
 cing these axes in the lower temporal quadrants would so 
 distort the images as to throw into action the superior 
 obliques; and the maximum of distortion would be effected 
 when the axes reached 45 (c) in the right e} r e and 135 (c) 
 in the left eye. With the axes turned to 90 (</), there
 
 (ISO) 
 
 FIJ + 
 
 PLATE V.
 
 COMPENSATING CYCLOTROPIA. 483 
 
 would be no distortion of images, though there would be 
 blurring-, as in all cases of displaced cylinders. 
 
 Fig. 2, Plate V., represents the same pair of eyes 
 shown in Fig. 1. Revolving the axes of the correcting 
 cylinders in the lower nasal quadrant, would so distort 
 images as to call into action the inferior oblique muscles, 
 the maximum being effected when the axes stand at 135 
 (c) for the right eye and 45 (c) for the left eye, the distor- 
 tion lessening as the axes approach, and disappearing 
 altogether when they reach, 90 (d'). 
 
 A comparative study of Fig. 1 and Fig. 2 of Plate IV., 
 with Fig. 1 and Fig. 2 of Plate V., will show that, in 
 hypermetropic astigmatism with the meridians of great- 
 est curvature either vertical or horizontal, a revolution 
 of the axes of the cylinders in the lower temporal quad- 
 rant will distort images (as of a rectangle) down and in, 
 and will thus call into harmonious action the superior 
 obliques; and it will also show that a revolution of the 
 cylinders in the lower nasal quadrants will so displace 
 the images as to call into harmonious action the inferior 
 obliques. 
 
 Fig. 3, Plate V., represents a pair of hypermetropic 
 astigmatic eyes with the meridian of greatest curvature 
 for the right eye at 20 (a) and that of the left eye at 160 
 (a). Since these meridians converge above, the uncor- 
 rected condition would cause harmonious action of the
 
 482 COMPENSATING CYCLOTROPIA. 
 
 inferior obliques. Properly chosen and correctly placed 
 cylinders, axes at 20 (a) for the right eye and 160 () for 
 the left eye, would relieve the distortion of the images 
 and do away with the necessity for the compensating ac- 
 tion of the obliques. Revolving the axis of the right cyl- 
 inder from 20 () to 45 () and that of the left cylinder 
 from 160 (a) to 135 () would cause a maximum displace- 
 ment of images in such a way as to call into action the 
 superior oblique muscles, the distortion disappearing 
 when these axes reach 70 (e) for the right eye and 110 
 (c) for the left eye. Passing 70 (c) in the right eye and 
 110 (c) in the left eye, the distortion becomes reversed, 
 so that the strain will be thrown on the inferior obliques, 
 the maximum being attained when the axis of the right 
 stands at 135 (<?) and that of the left at 45 (*). The 
 distortion decreases as the axes are still farther turned 
 in the same directions, and disappears at the end of the 
 arc of 130 (from c to/") when they coincide with the 
 meridians of greatest curvature. Thus the arc of dis- 
 tortion involving the superior obliques is 50 ( from a to 
 c\ while that involving the inferior obliques is 130 
 (from ctof). 
 
 The eyes ( hypermetropic astigmatic) represented by 
 Fig. 4, Plate V., have their meridians of greatest cur- 
 vature at 160 () in the" right and 20 () in the left. 
 These meridians diverging above would result, in the
 
 COMPENSATING CYCLOTROPIA. 483 
 
 uncorrected case, in calling- into harmonious action the 
 superior obliques. Proper cylinders with the axis of the 
 right at 160 (a) and that of the left at 20 (a) would cor- 
 rect the distortion of the images and relieve the strain 
 on the superior obliques. A turning of these C}'linders 
 in the arcs a-c would distort the retinal images so as to 
 bring 1 into action the inferior oblique muscles, the maxi- 
 mum distortion existing- when the axes are at b. Con- 
 tinuing- the revolution from c, the distortion becomes re- 
 versed, and, as a consequence, the superior obliques are 
 brought into activity, the maximum being- attained when 
 the axes reach e. As the axes are revolved farther, the 
 distortion lessens, and finally disappears when they stand 
 at f, again coinciding- with -the meridians of greatest 
 curvature. In this pair of eyes the arc of distortion in- 
 volving- the inferior obliques is 50 (from a to c}, while 
 that involving the superior obliques is 130, the maximum 
 of distortion in both instances being attained when the 
 halfway point of the arc is reached by the axis of the 
 cylinder. 
 
 A comparative study of any two, or all, of the figures 
 in Plate IV. and Plate V., will show that the arc of dis- 
 tortion, by corrective plus cylinders, involving the supe- 
 rior obliques, is always in the lower temporal quadrant, 
 wholly or in greater part; and if entirely within this 
 quadrant, its length is always t\vice the distance from
 
 484 COMPENSATING CYCLOTROPIA. 
 
 the meridian of greatest curvature to the 45 point of the 
 quadrant, the other half being 1 on the opposite side of 
 the latter. In like manner it will be seen that the arc 
 of distortion involving' the inferior obliques, by a revo- 
 lution of plus cylinders, is always in the lower nasal 
 quadrant, wholly or in greater part; and if entirely 
 within the quadrant, its length is twice the distance 
 from the meridian of greatest curvature to the 45 point 
 of the quadrant, the other half being 1 on the opposite 
 side of the latter. When the arc of distortion involving 
 the superior obliques is 90, that involving* the inferior 
 obliques is 90, and vice versa; when the arc of distor- 
 tion involving* the superior obliques is less than 90, the 
 arc involving* the inferior obliques is always the differ- 
 ence between the former and 180, and vice versa. The 
 maximum of distortion is always attained when the axis 
 of the cylinder is at the halfway point of the arc. 
 
 Fig*. 1, Plate VI., represents a pair of hypermetropic 
 astig*matic eyes, the meridian of greatest curvature of 
 the right eye at 45 (a] and that of the left eye at 135 (a). 
 These meridians converging above would cause such dis- 
 tortion of images as to throw into harmonious action the 
 inferior oblique muscles. The proper cylinders, correct- 
 ly placed the axis of the right at 45 (a) and the axis 
 of the left at 135 (a) would counteract the distortion 
 and relieve the inferior obliques of the necessity of over-
 
 COMPENSATING CYCLOTROPIA. 
 
 485 
 
 acting. Revolving- the axes of the correcting 1 cylinders 
 in either direction would so distort images as to call into 
 harmonious action the inferior oblique muscles. Since 
 the arc of distortion for the superior obliques in this 
 case is nothing-, the arc of distortion for the inferior 
 
 R/GHT 
 
 obliques is 180, from a to d in either direction, the 
 maximum of distortion being- attained, respectively, at e 
 above and at c below. 
 
 Fig-. 2, Plate VI., represents a pair of the same kind of 
 eyes, but with the meridian of greatest curvature at 135 
 (a) for the right eye and 45 (a) for the left eye. These
 
 486 COMPENSATING CYCLOTROPIA. 
 
 meridians diverging- above, the refraction is such as to 
 distort images so as to call into harmonious action the 
 superior obliques. As in the other case, the correct cyl- 
 inders, properly placed, counteract the distortion and re- 
 lieve the superior obliques from action. Rotating the 
 axes of these cylinders in either direction from a would 
 so distort images as to call into activity the superior ob- 
 liques. In this case the arc of distortion for the inferior 
 obliques is nothing, and, therefore, the arc of distortion 
 for the superior obliques is 180, from a to d in either 
 direction, the maximum being attained at c above and at 
 e below. 
 
 In the adjustment of cylinders for the correction of 
 astigmatism whether it be vertical, horizontal, or ob- 
 lique a knowledge of the arcs of distortion by displaced 
 cylinders is of great importance. Patients should be 
 impressed with the absolute necessity of keeping the 
 rims containing the glasses in such relationship to each 
 other that a straight edge would pass through the fol- 
 lowing four points : the two points where the temple 
 pieces join the rims and the two points of attachment of 
 the nose bridge to the rims. If the frames should be so 
 bent that the long axis of each lens would lean down and 
 out, and the astigmatism is according to the rule, the 
 cylinders would be displaced in the arc of distortion for 
 the inferior obliques, which, usually, would be borne
 
 COMPENSATING CYCLOTROPIA. 487 
 
 fairly well; but when the astigmatism is against the 
 rule, this displacement would be in the arc of distortion 
 for the superior obliques, and would cause much annoy- 
 ance. This would be true, whether the astigmatism 
 were hyperopic, myopic, or mixed. 
 
 If the frames should be so bent that the long axes of 
 the lenses pointed down and in, the astigmatism being 
 according to the rule, the axes of the cylinders would be 
 displaced in the arcs of distortion for the superior ob- 
 liques, and would cause trouble; but if the astigmatism 
 were against the rule, the displaced axes \vould be in the 
 arcs of distortion for the inferior obliques, and but little 
 trouble would result unless the displacement should be 
 considerable. 
 
 If the frames are so shaped that the long axis of each 
 lens lies in the same plane with the long axis of the 
 other, the leaning of the common plane down and to the 
 right, resulting from a bend upward of the temple piece 
 on the corresponding side, or a bend downward of the 
 temple piece on the opposite side, the cylinders being 
 of equal strength, no strain of the obliques will be 
 excited, for the reason that the distortion in the one 
 eye would be similar to the distortion in the other. 
 Vision would be blurred and all objects would appear 
 out of their proper places. The ciliary muscles might 
 make an attempt to sharpen the images, but there would
 
 488 COMPENSATING CYCLOTROPIA. 
 
 be no necessity for the obliques to make an effort either 
 to diverge or converge the vertical axes of the eyes in 
 order that there might be fusion of the displaced images. 
 The same would be true if the straight frames were 
 made to incline down and to the left. Bent frames are 
 capable of doing more or less harm through abnormal 
 excitation of the brain-centers controlling the oblique 
 muscles. 
 
 Spectacle frames should be given astigmatics, for the 
 reason that they can be much better adapted to the face 
 than the most perfect-fitting nose-glass frames that have 
 ever been invented. 
 
 A knowledge of the character of distortion of retinal 
 images, by oblique corneal astigmatism, enables the op- 
 erator to tell the patient beforehand just the kind of 
 metamorphopsia that will result from the wearing of 
 the correcting cylinders, and whether it will soon van- 
 ish or be a long time in disappearing. 
 
 When one eye is set lower in its orbit than the other, 
 there must be a compensating cyclotropia in the direction 
 of the lower eye, effected by either the 8th conjugate 
 center (left eye, the lower) or the 9th conjugate center 
 (right eye, the lower). For this there is no relief. If 
 such a patient should be astigmatic, the correcting 
 cylinders, whether plus or minus, should both be rotated 
 in the direction of the lower eye, through a small arc.
 
 CHAPTER IX. 
 
 COMPENSATING LATERAL AND VERTICAL 
 HETEROTROPIA. 
 
 THE recti muscles may be perfectly developed, their 
 attachments may be ideal, and their innervation centers 
 may be faultless; nevertheless, if there is any form of 
 anisometropia, there must be some form of heterotropia 
 whenever the visual lines are made to sweep from the 
 primary point to some other point of view. If the right 
 eye is emmetropic and the left eye is hyperopic, the im- 
 age of a square will be larger in the former than in the 
 latter. When the point of fixation is the center of the 
 square, the recti will have the visual axes in the same 
 plane and will cause them to intersect at the point of 
 view. If the point of view is to be changed from the 
 center of the square upward, so as to fuse the upper 
 border, it becomes evident that the visual axis of the 
 right eye must rise higher than the visual axis of the 
 left eye. Without this compensating hypertropia these 
 borders could not be fused. Again, if the point of view 
 is to be changed from the center of the square down- 
 
 U89)
 
 490 COMPENSATING LATERAL AND 
 
 ward, so as to fuse the lower border, the visual axis of 
 the emmetropic eye must travel farther than that of the 
 hyperopic eye in order to fuse the lower borders. The 
 cause of the fusion is a compensating- catatropia of the 
 emmetropic e} r e. If the point of view is to be changed 
 from the center of the square to its right border, the 
 visual axis of the right eye must sweep farther to the 
 right than that of the left eye, or the borders cannot be 
 fused. This is accomplished by a compensating exotro- 
 pia of the right eye. Likewise there must be a compen- 
 sating esotropia of the right eye, if the point of view 
 must be changed from the center of the square to its left 
 border. All of this is illustrated by Fig. 74, taken from 
 Chapter VIII., in which a-b-c-d represents the square 
 as seen by the hyperopic eye, and a"-b"-c"-d" repre- 
 sents the square as seen by the emmetropic eye. The 
 distance from e to the line a"-d" is greater than to the 
 line a-d. 
 
 The same figure shows that if one eye were emme- 
 tropic and the other eye were myopic, the larger square 
 a"-b"-c"-d" would be seen by the myopic eye, while 
 the smaller square (a-b-c-d} would be seen by the emme- 
 tropic eye. In such a pair of eyes the compensating 
 heterotropia would be confined to the myopic eye. 
 
 Again referring to the same figure, if one eye had 
 myopic astigmatism, the meridian of greatest curvature
 
 VERTICAL, HETEROTROPIA. 
 
 491 
 
 vertical, it would see the square as a'-b'-c'-d', while the 
 other eye, being" emmetropic, would see the square as it 
 really is a-b-c-d. In such eyes there would be no com- 
 pensating' lateral heterotropia, for a-b coincides with 
 a'-b' and d-c coincides with d'-c' ; but there will be ver- 
 
 Fig- 74- 
 
 tical compensating 1 heterotropia, for the reason that e is 
 nearer a-d and b-c than it is to a'-d' and b'-c' . 
 
 In the same way all forms of anisometropia may be 
 studied, showing 1 the necessity for compensating hetero- 
 tropia on the part of the eye having- the greater refract- 
 ive power, or the eye that is long-er.
 
 492 COMPENSATING LATERAL AND 
 
 As compensating cyclotropia is always cured by the 
 application of obliquely-placed cylinders, so compensat- 
 ing lateral and vertical heterotropias are cured by the 
 lenses needed for the correction of the focal errors. It 
 is more necessary to correct unequal refraction, though 
 the errors be not great, than it is to correct greater er- 
 rors that are equal in the two eyes. 
 
 Prisms and lenses rendered prismatic by decentration 
 cause compensating heterotropia in the direction of the 
 apex of the prism; therefore, prisms given for con- 
 stant wearing to an exophoric, cause compensating exo- 
 tropia; prisms given to an esophoric develop a compen- 
 sating esotropia; and a prism placed base down for the 
 relief of a hyperphoria generates a compensating hyper- 
 tropia of that eye. 
 
 In spherical anisometropia the law of direction is in- 
 terfered with, so far as the eye of greatest refraction is 
 concerned, except when the two eyes are in the primary 
 position. When there is astigmatism of one eye and 
 emmetropia, hyperopia, or myopia of the other, there can 
 be no heterotropia in the direction of that principal me- 
 ridian of the astigmatic eye which has the same radius of 
 curvature as the non-astigmatic cornea of the other eye; 
 but in the direction of the other meridian there will be 
 compensating heterotropia. In the compensating hetero- 
 tropia caused by prisms and decentered lenses there is
 
 VERTICAL HETEROTROPIA. 493 
 
 interference with the law of direction in all parts of the 
 field of view. 
 
 DECENTERED CORNEAS AND MISPLACED MACULAS. 
 There are two other causes for compensating- vertical 
 and lateral heterotropia. The one is a decentration of 
 the cornea; the other is displacement of the macula. It 
 would probably be more nearly correct to say that there 
 is but one other cause that is, decentration of the cornea. 
 The antero-posterior axis of the eye, that axis controlled 
 by the recti muscles, which must always be at right 
 angles to the equator of the eye, can be none other than 
 the visual axis. Commencing always at the fovea cen- 
 tralis, it passes always through the center of retinal 
 curvature and thence through the center of an ideally 
 placed cornea; but if the cornea is not properly centered, 
 the visual axis passes through some other part than the 
 center. The posterior pole of the eye, whether near to 
 or far away from the optic disc, or above or below it, is 
 the center of the macula; the anterior pole may or may 
 not be the center of the cornea. In ideal eyes eyes that 
 see best or can be made to see best the anterior pole is 
 the center of the cornea. The antero-posterior axis of 
 the eye, as given by anatomists and adopted by writers of 
 books on the eye, has its beginning at the center of the 
 cornea, passes backward through the center of rotation, 
 and strikes the retina, maybe at the macula, but is just as
 
 494 COMPENSATING LATERAL AND 
 
 likely to strike it elsewhere. The error is in giving the 
 anterior pole a fixed location the center of the cornea. 
 Such an axis can be at right angles to the equator of the 
 eye in which lie the vertical and transverse axes of the 
 eye, only when it coincides with the visual axis. It can 
 be of value only in determining the extent of the decen- 
 tration of the cornea, or how much the cornea lacks of 
 occupying the ideal position. 
 
 In true compensating heterotropia, retinal images on 
 the maculas are either sharp or can be made so; but 
 when there is decentration of the corneas, the rays of 
 light that strike the maculas are never perfectly focused, 
 nor can they be made to focus perfectly by any artificial 
 means. In true compensating heterotropia, that caused 
 by anisometropia, or by prisms, there is interference 
 with the law of direction. This is not true of decentra- 
 tion of the cornea; for the visual axis points directly to 
 the source of the light, although the eye appears to be 
 pointing in some other direction as indicated by the posi- 
 tion of the center of the cornea. The heterotropia, then, 
 is apparent, and not real; therefore it cannot be prop- 
 erly called a "compensating heterotropia." The angle 
 gamma measures the apparent deviation of the eye and 
 the real displacement of the cornea. 
 
 When an eye whose cornea is ideally situated is ex- 
 amined with the Javal ophthalmometer, the reflected
 
 VERTICAL, HETEROTROPIA. 495 
 
 disc will have its center coincide with the center of the 
 cornea; but if the cornea is displaced out, the reflection 
 will be more from the nasal side; if displaced in, the re- 
 flection will be in greater part from the temporal side; 
 if displaced down, the greater part of the reflection will 
 be from the upper part of the cornea; and if displaced 
 up, the reflected image will be more below than above. 
 Oblique displacement of the cornea will show an oblique 
 displacement of tie reflected image of the ophthalmom- 
 eter disc. These examinations, to be accurate, must be 
 made while the patient is looking* directly into the center 
 of the telescopic tube, and the reflected image must be 
 looked at through the center of the leveling slit above 
 the telescope. A considerable proportion of corneas thus 
 examined will show slight displacements, but rarely 
 more than 5. When the angle gamma is much in ex- 
 cess of 5, it means that the acuteness of vision can- 
 not be made equal to 20-20. 
 
 The various forms of heterophoria, and anyone of the 
 true heterotropias, may be found in e}^es whose corneas 
 are not properly centered. The former should be dealt 
 with in the manner prescribed in the chapters preceding 
 this one; and the true heterotropias should be treated 
 after the methods to be set forth in the next chapter. 
 For apparent heterotropia nothing can be done; so, there- 
 fore, nothing should be attempted. In operating for the
 
 496 COMPENSATING HETEROTROPIA. 
 
 relief of true heterotropia, it should be known whether 
 or not there is a false heterotropia as well, else the treat- 
 ment might result disastrously. 
 
 The new-formed physiologic macula that some think 
 they have found in a squinting eye, is the old macula of 
 an eye whose cornea is not correctly placed. There is 
 no part of one eye, save the macula, that can harmonize 
 with the macula of the other. Because of opacities in 
 the refractive media, or because of disease of the cho- 
 roid behind the macula, a peripheral part of the retina 
 of that eye must be used, but it can never be made 
 a macula; it can never be made to harmonize with the 
 macula of the healthy fellow eye.
 
 CHAPTER X. 
 
 HETEROTROPIA. 
 
 THE appearance of eyes whose muscles fail to co- 
 ordinate them, rendering" binocular single vision impos- 
 sible, has been designated by the terms "squint," 
 "strabismus," and "cross-eyes," by both ancient and 
 modern writers. It may be long before these terms can 
 be entirely eliminated, although there is now no good 
 reason for retaining them. " Heterotropia, " a term in- 
 troduced by Stevens, carries its own meaning with it, 
 the plain English of \vhich is a "wrong turning." This 
 term should be preferred, not only because of its sim- 
 plicity, but also because it is in conformity with the now 
 universally accepted term, "heterophoria," as applied to 
 the muscles whose relationship to each other is such as 
 to render it difficult for them to so relate the eyes as to 
 make binocular vision possible. "Heterotropia" is a 
 generic term, and includes all forms of deviation of the 
 visual axes and the vertical axes of the eyes; ' ' esotropia " 
 means that there is a deviation of the visual axes in- 
 ward, so that they cross each other between the observer
 
 498 HETEROTROPIA. 
 
 and the point of observation; "exotropia" means that 
 there is an outward deviation of the visual axes, so that 
 they either cross beyond the point of view or become par- 
 allel, or even become divergent; " hypertropia " means 
 that one visual axis is raised above the other, while 
 "catatropia" means that one visual axis is turned be- 
 low the other; " cyclotropia " means that the vertical 
 axes of the eyes are not kept parallel with the median 
 plane of the head, either diverging* from it above (plus 
 cyclotropia) or converging toward it above (minus cyclo- 
 tropia). One form of heterotropia may be complicated 
 by one or more of the other forms. 
 
 As taught in Chapter I. of this book, binocular sin- 
 gle vision is possible only when the superior and infe- 
 rior recti muscles keep the two visual axes in the same 
 plane; when the internal and external recti so control 
 these axes, in that plane, as to make them intersect at 
 the point of view; and when the superior and inferior 
 obliques parallel the vertical axes of the eyes with the 
 median plane of the head. These muscles accomplish 
 this work in obedience to the unalterable law of corre- 
 sponding retinal points. Disobedience on the part of 
 these muscles develops diplopia, for the reason that the 
 two images of the one object cannot fall on correspond- 
 ing retinal points. That objects are not always seen 
 double by persons who have any form of heterotropia
 
 HETEROTROPIA. 499 
 
 can be due to nothing- else than mental suppression of 
 one image. 
 
 Before entering- minutely into the study of heterotro- 
 pia, it will be interesting- to review, briefly, its history. 
 That the condition has existed in every g-eneration from 
 the beginning- of the human family, can hardly be doubted. 
 What it was interpreted to mean in ancient times cannot 
 now be known. Hippocrates wrote of the deformity as 
 a thing of inheritance, but sometimes resulting from dis- 
 ease. From the time of his writing, on down through 
 the centuries, there is no evidence of any careful or scien- 
 tific study of heterotropia until in the second quarter of 
 the nineteenth century. About this time Stromeyer an- 
 nounced that strabismus was due to abnormal contrac- 
 tions of the eye muscles, and that it might be cured by 
 tenotomies. He performed experimental tenotomies on 
 the dead subject to his satisfaction. One year later, in 
 1839, Dieffenbach operated on his first case of internal 
 squint, dividing the tendon of the internal rectus close to 
 its attachment to the sclera. He thus continued to op- 
 erate throiigh a lengthy series of cases. Other German 
 surgeons, and surgeons in France and England, began 
 at once to accept the teaching of Stromeyer and to adopt 
 the practice of Dieffenbach. After the French Academy 
 of Sciences had awarded its prize of six thousand francs 
 half to Stromeyer for conceiving the operation and
 
 500 HETEROTROPIA. 
 
 demonstrating' it on the dead subject, and half to Dieffen- 
 bach for having first operated on the living subject by 
 cutting the tendon of the muscle close to its attachment 
 to the sclera Dieffenbach himself led in the bad prac- 
 tice of cutting the tendon farther back. He reasoned 
 that the farther from the insertion the cut was made, 
 the greater would be the effect, and by this reasoning he 
 was induced, in severe cases, to make the cut through 
 the muscle structure itself. So disastrous were these 
 myotomies, or tenotomies far behind the insertions of the 
 tendons, that the operation for strabismus began to fall 
 into disrepute. It required the master mind of Graefe 
 to check the tide of professional feeling against tenot- 
 omies of the recti muscles. His voice called operators 
 back to the original operation of Dieffenbach, after which 
 external squints were less frequently found as a result 
 of operations for internal squint, and once more the op- 
 eration came into favor. Graefe even went farther in 
 the direction of safety than a simple return to the Dief- 
 fenbach original tenotomy, in that he advised partial 
 tenotomies in the slighter cases. He even made mar- 
 ginal tenotomies, but apparently these were done em- 
 pirically; at any rate, he did not give any reason for 
 doing these marginal operations, other than that the un- 
 cut fibers would prevent the muscle from retracting too 
 far. If done empirically, while some of them may have
 
 HETEROTROPIA. 501 
 
 been helpful, others must have been hurtful, because of 
 the wrong- kind of torsioning- resulting-. It appears that 
 Graefe abandoned marg-inal tenotomies, possibly because 
 of the unfortunate torsional results that followed in many 
 of his cases. That there is a scientific and, therefore, 
 sound basis for marginal tenotomies has already been 
 shown in previous chapters, and will be set forth ag-ain, 
 in the proper place, in this chapter. It would also appear 
 that Graefe ceased to do even central partial tenotomies; 
 for, in conversation with Knapp, who was telling- him of 
 these operations which, thus earl}" in his professional 
 career, he was doing, he said, "You will not do that 
 long-,"* thus indicating- that he himself had already 
 abandoned the practice of partial tenotomies. Yet it 
 will be shown in this chapter that partial, and not com- 
 plete, tenotomies only should be done, even in the hig-her 
 degrees of heterotropia. 
 
 As was natural, soon after Dieffenbach's tenotomy 
 operation on the contracted muscle was introduced, ad- 
 vancement of the relaxed muscle was sug-g-ested and 
 practiced by Querin. The author has been unable to 
 learn the exact method he employed, but it must have 
 been very crude and unsatisfactory. A. von Graefe's 
 improvement of Querin 's operation is worthy of mention 
 only as a curiosity. The only connection that the ad- 
 
 *See Norris and Oliver, Vol. III., page 877.
 
 502 HETEROTROPIA. 
 
 vancing thread had with the eye was the loop which he 
 passed through the end of the severed tendon; for the 
 two ends of the thread were carried across the cornea 
 and anchored by adhesive plaster to the nose, if the 
 muscle were the externus, and to the temple, if it were 
 the internus, to be advanced. The threads in contact 
 with the cornea occasionally excited suppuration of that 
 structure, and for this reason the operation was aban- 
 doned. 
 
 The elder Critchett, in 1862, at the Heidelberg Con- 
 gress, made public his "method of advancement by 
 stitching- the tendon forward." This operation as de- 
 scribed by Knapp* is attended by unnecessary trauma- 
 tism, and is not comparable, in simplicity and ease of 
 execution, with the advancement operation described in 
 Chapter III. of this book. The Critchett operation was 
 adopted at once by Graefe, who was glad to substitute 
 it for his own method. It seems not to have been in- 
 tended by Critchett that this operation should supplant 
 the operation of tenotomy for the cure of heterotropia, 
 but that it should act only as an aid to the tenotomy. 
 
 Since 1878 L/andolt has been an earnest advocate of 
 advancement of the relaxed muscle, as against tenotomy 
 of the contracted muscle, in all cases of heterotropia, 
 and as the years have gone by his advocacy of advance- 
 
 *See Norris and Oliver, Vol. III., pages 871-72.
 
 HETEROTROPIA. 503 
 
 ment has grown stronger. Except for the greater ease 
 with which a tenotomy is done, as contrasted with the 
 advancement of a muscle, Landolt's voice would have 
 been heard, and to a greater extent would have been 
 heeded. But, strange to say, while Landolt has been 
 opposing with all his might the cutting of the tendons 
 of the ocular muscles, the tenotomists have found, or 
 think they have found, the check ligaments of the recti 
 muscles; and some of them, not content with completely 
 severing the tendon, have dared to reach back with the 
 scissors and cut these checks. That there are connect- 
 ive tissue fibers that extend from these muscles to the 
 walls of the orbit cannot be denied, but they must be 
 concerned more in firmly fixing the bed of fat through 
 which the muscles pass, than with the action of the 
 muscles, by either hindering or helping them. The dis- 
 section accomplished in cutting these ligaments can but 
 allow a greater retraction of the divided tendon, which 
 often proved to be too much even before the ligaments 
 were known to exist. 
 
 The only important suggestion in connection with 
 complete tenotomies, since Graefe called operators back 
 to the insertion of the tendon, has come from Panas; but 
 even this suggestion does not redeem the operation of 
 complete tenotomy from the condemnation laid upon it 
 by Landolt. Panas stretches the muscle before sever-
 
 504 HETEROTROPIA. 
 
 ing" its tendon. The stretching of the muscle necessa- 
 rily results in a state of paresis for the time being, and 
 it is probable that it takes days for the recovery to be 
 effected. A paretic muscle when cut is not in a condi- 
 tion to retract far, hence adhesive inflammation has the 
 opportunity to reattach the cut end of the tendon to the 
 sclera only a little way behind the line of its original at- 
 tachment. Panas' operation is the only safe complete 
 tenotomy that can be done, but it is doubtful if it should 
 ever be done. Words cannot be made strong enough 
 to condemn a complete tenotomy associated with a cut- 
 ting of the check ligaments. After any complete tenot- 
 omy, except the one suggested by Panas, the operator is 
 exceedingly fortunate if, in a few months, he does not 
 find a condition opposite that for which he operated. 
 Even in Panas' operation the risk of limiting the verting 
 power of the muscle is too great; and occasionally, in 
 spite of the paresis caused by the stretching, the muscle 
 will retract too far and an external squint will replace 
 the former internal squint, or vice versa. 
 
 One of the strange things connected with the study of 
 the ocular muscles, soon after Dieffenbach did his first 
 operation, was the conclusion that the inferior oblique 
 was an advertor of the eye. Certainly its origin, course, 
 and insertion gave no foundation for such a conclusion. 
 Lucas, in his little book on " The Cure of Strabismus,"
 
 HETEROTROPIA. 505 
 
 published in 1840, says on page 8: "The action of the 
 inferior oblique is to direct the eye upward and in- 
 ward." That the above reference to the inferior oblique 
 could not have been a typographical error is abundantly 
 shown in other parts of the book. On page 15 the fol- 
 lowing sentence occurs: " When either eye is drawn out- 
 ward by the action of the external rectus muscle, the 
 other is directed inward by the action of the inner rectus 
 and inferior oblique muscles." 
 
 That the inferior obliques, without being advertors, 
 may cause a condition that becomes an important com- 
 plication of esotropia, will be shown later in this chap- 
 ter. 
 
 It is not uninteresting to study the work of a quack, 
 John Taylor, who flourished in the first half of the 
 eighteenth century, at least one hundred years before 
 Stromeyer and Dieffenbach. He evidently found the 
 secret of some cases of squint, and it is just as evident 
 that his secret was kept by him and died with him. He 
 wrote a pamphlet, entitled "De Vera Causa Strabismi," 
 which was published in 1738, in which, it is said, he 
 exploited his cures without exposing his method of oper- 
 ating. In traveling from city to city on the continent 
 of Europe, distributing his pamphlet as a means of ad- 
 vertising, he styled himself as "Oculist to George II., of 
 England," whom he probably had never seen; and when
 
 506 HETEROTROPIA. 
 
 it suited him better, he claimed to be oculist to the 
 Pope. 
 
 Taylor was a man of some penetration; but he must 
 have been a man too full of self-interest to give to 
 science and progress the benefit of his insight. He lost 
 his opportunity to build for himself a monument that 
 would have been to his enduring- credit, by burying 
 within himself the knowledge on which he based his 
 practice of straightening cross-eyes. He seems not only 
 to have been an oculist, but a general surgeon as well, 
 for he carried about with him a dazzling display of in- 
 struments. His methods of secrecy and his disposition 
 toward self-display must have disgusted surgeons of 
 that time, so that they avoided him, just as honorable 
 medical men of to-day feel disgraced when found in 
 company with a quack. It appears, however, that L/e- 
 Cat either witnessed an operation or that he had an op- 
 portunity to question Taylor, for he says: *"I availed 
 myself of the freedom which he accorded me to inquire 
 the motive for an operation which appeared to me to be 
 absolutely useless, not to say dangerous. He replied 
 that an eye only squinted because the equilibrium be- 
 tween its muscles was destroyed, and that to reestablish 
 this equilibrium it was only necessary to weaken the 
 
 *See Stevens' address before the Ophthalmological Association, as published in "An- 
 nals of Ophthalmology," Vol. VIII., No. 2.
 
 HETEROTROPIA. 507 
 
 muscle which dominated the others, and this is what he 
 did in cutting- one of the nerve filaments which was dis- 
 tributed to this too powerful muscle." 
 
 Heuerman, in 1756, wrote: " Taylor has also proposed 
 to cure squinting by the division of the tendon of the 
 superior oblique muscle of the eye." Another writer 
 says that Taylor passed a silk thread through a fold of 
 conjunctiva at the lower-inner part of the g-lobe, and, 
 drawing 1 this fold forward by means of his loop of thread, 
 cut it with a pair of scissors. The location of this con- 
 junctival cut makes it appear possible that, through it, 
 he passed his scissors with the point of one blade in con- 
 tact with the orbital floor, and sufficiently far backward 
 to include the inferior oblique muscle, which he may have 
 divided by closing- the blades of the scissors; or through 
 the opening he may have passed, in a skillful way, one 
 blade of the scissors between the sclera and the tendon 
 of the internus while keeping- the other blade between 
 the conjunctiva and the tendon, and thus effected the di- 
 vision of this tendon. 
 
 Taylor must have had some cures, whatever may have 
 been the nature of his operation. Simply sealing with 
 plaster the eye not operated upon, for a few days, could 
 not have effected a cure, unaided. There is no evidence 
 of the existence of a nerve fiber far forward giving to 
 the internus a part of its power; hence it is reasonable
 
 508 HETEROTROPIA. 
 
 to conclude that he purposely made a misstatement when 
 he told L/eCat that his operation was a division of such 
 a fiber. It is very unlikely that any case of internal 
 squint ever had, as an etiolog-ical factor, a too strong 
 superior oblique; hence it is not probable that Taylor 
 ever divided this muscle. That a too strong- inferior 
 oblique may be an indirect factor in the production of a 
 small per cent of cases of internal squint will be shown 
 farther on; hence it is not unreasonable to suppose that 
 he may have divided this muscle in some of his opera- 
 tions. To have done so when this muscle elevated the 
 eye and torted it outward, while the internus turned it 
 in, would have been helpful, if not entirely corrective. 
 A simple esotropia could not have been thus corrected; 
 so it appears possible that in simple cases he had learned 
 to divide only the internus. Since Taylor left nothing- 
 descriptive of the cause (termed by him " Vera Causa ") 
 of esotropia, and failed to print, either in pamphlet or lay 
 press, anything- as to the method of his operation, one 
 can only surmise what he really thoug-ht and did. It is 
 certain that a whole century intervened between him and 
 Stromeyer, during- which time no advance was made in 
 the practical study of the errors of the ocular muscles. 
 
 The author almost feels that he should apolog-ize for 
 making- any reference to Taylor, the quack, who deserved 
 contempt while living- and oblivion after death.
 
 HETEROTROPIA. 509 
 
 A more pleasant task presents itself in a brief study 
 of the work of the immortal Bonders, who gave so much 
 thought to the etiology of heterotropia. His investiga- 
 tion into the relationship between accommodation and 
 convergence proved conclusively that hyperopia is one of 
 the factors of esotropia. This doctrine is almost uni- 
 versally accepted, and there seems to be absolutely no 
 room for doubting its truthfulness. It must be granted, 
 however, that Bonders placed too much emphasis on this 
 potent factor. If hyperopia were even the chief cause 
 of internal squint, the cases demanding operative inter- 
 ference would be few and far between. Hyperopia must 
 occupy a secondary place as a causative factor of esotro- 
 pia; nevertheless, it is an important place, for a removal 
 of this cause, by the wearing of convex lenses, early in 
 childhood, often will make the other cause or causes in- 
 operative. The world is indebted to Bonders for this 
 knowledge, and for acquiring and imparting it he de- 
 serves a monument. 
 
 Finally, before taking up systematically the study of 
 heterotropia, it may be stated that it has always been a 
 matter of observation that some cases of internal squint 
 became cured without artificial aid. This spontaneous 
 cure came as the patients grew older, and doubtless de- 
 pended on the fact that the brain-centers controlling the 
 ciliary muscles no longer generated so great an impulse
 
 510 HETEROTROPIA. 
 
 for these muscles, as, because of association, would have 
 continued to over-excite the centers controlling the in- 
 terni. The diminished nerve impulse coming- to the in- 
 terni gave the externi a chance to swing- the visual axes 
 into positions of harmony. It is not explainable how 
 other forms of heterotropia could ever recover spontane- 
 ously, and it is doubtful if they ever have thus recovered. 
 As early as the seventh century of the Christian era 
 an appliance was devised for straightening cross-eyes. 
 It consisted of a mask with a hole in it for each eye, 
 which the patient was compelled to wear. There may 
 have been some cures, but the annoj^ance to the wearer 
 must have been great. The practice may have been 
 abandoned, but, if so, it was revived again by Pare in 
 the sixteenth century. 
 
 CLASSES OF HETEROTROPIA. 
 
 There are two classes of heterotropia the one occur- 
 ring at any period of life, and always due to paralysis 
 or paresis of one or more of the ocular muscles, and 
 practically always curable by medication; the other oc- 
 curring in infancy or early childhood, and never caused 
 by either paralysis or paresis. The former will be stud- 
 ied in Chapter XI., where the means of making a differ- 
 ential diagnosis will be set forth. It will be studied as 
 paralytic heterotropia.
 
 HETEROTROPIA. 511 
 
 COMITANT HETEROTROPIA. Of this condition there 
 are the several varieties that have already been men- 
 tioned, each of which will be studied separately from 
 the standpoint of both etiology and treatment. In lat- 
 eral heterotropia, although the visual axes are not prop- 
 erly related either crossing- within the point of view, 
 as in esotropia, or crossing- beyond the point of view, 
 often being- parallel, or even divergent, as in exotropia 
 the two eyes, nevertheless, are made to move equally 
 far directly to the rig-lit or left, or in any oblique direc- 
 tion that is, the one visual axis accompanies the other 
 in every movement, in any direction, the degree of varia- 
 tion from the normal always remaining- the same. In ver- 
 tical heterotropia one visual axis rises above the other, as 
 in hypertropia, or one visual axis falls below the other, 
 as in catatropia; but when the two eyes are rotated di- 
 rectly up or down, or in any oblique direction, the ang-le 
 of deviation always remains the same. In comitant cy- 
 clotropia, it is reasonable to suppose that the vertical 
 axes diverg-e or converg-e the same in all movements of 
 the visual axes. No better word, therefore, could be 
 chosen for defining- these conditions than " comitant." 
 The old term, "concomitant," is probably neither better 
 nor worse than the shorter term adopted by Maddox, 
 Jackson, and other authors. 
 
 The term ' ' comitant " would not be needed except that
 
 512 HETEROTROPIA. 
 
 it makes it easy to distinguish true heterotropia from 
 paralytic heterotropia. In the discussion of the latter in 
 the next chapter, it will be shown that, in some one part 
 of the field of rotation, the visual axes will be properly 
 related, giving binocular single vision, whatever muscle 
 maybe paralyzed; while rotation in the opposite part of 
 the field will be attended by a lagging behind of the 
 visual axis of the eye to which the affected muscle be- 
 longs, which will always be shown by diplopia, and often 
 may be detected by the observer. Diplopia, under ordi- 
 nary conditions, does not manifest itself in comitant 
 heterotropia, for the reason that the occurrence of the 
 error early in life made it possible for the mind to sup- 
 press the images in the wrongly-directed eye that other- 
 wise would have interfered with objects seen by the 
 properly-directed eye. Equal deviation in all positions 
 of the eyes and no diplopia means comitant heterotropia; 
 unequal deviations none at all in one direction, but 
 greater or less in the opposite direction, with single vi- 
 sion, in one part of the field and diplopia in the opposite 
 part mean paralytic heterotropia. In the former there 
 is no disturbance of locomotion, while in the latter the 
 patient becomes more or less dizzy. In the former, the 
 secondary deviation is equal to the primary deviation; in 
 the latter, the secondary deviation is always greater than 
 the primary.
 
 ESOTROPIA. 513 
 
 The etiology of comitant heterotropia can be studied 
 to better advantage in the discussion of the individual 
 varieties. 
 
 COMITANT ESOTROPIA. This condition known also 
 as internal strabismus, internal squint, and cross-eyes 
 is the most common form of heterotropia. It always 
 occurs in early life, usually at the age of two or three 
 years. The conditions causing 1 the error exist from 
 birth, and only one of the several natural causes un- 
 dergoes any change at any time after birth. In the 
 greater number of cases it is the character of the nerve 
 impulse to the ciliary muscles that causes over-stimula- 
 tion of the third conjugate innervation center, which 
 over-stimulation causes an actual deviation, when pre- 
 viously there was only a tendency toward deviation a 
 conversion of an esophoria into an esotropia. Why this 
 change should not occur earlier than the second or third 
 year is variously explained. Usually authors are agreed 
 that children look at near objects but little until two 
 years old, at which time they begin to take interest in 
 toys and pictures, looking intentl} r at them, at close 
 range. Children who become esotropic are nearly al- 
 ways hyperopic, hence are forced to use their ciliary 
 muscles in far vision, which means that, in near vision, 
 an excessive nerve impulse must be generated and sent 
 to these muscles. A correspondingly increased impulse
 
 514 ESOTROPIA. 
 
 is sent to the intern!, which are naturally too strong- for 
 the externi, and the eyes cross. 
 
 Maddox teaches in his work, * ' The Ocular Muscles, ' ' 
 that the lenses increase in density even in infancy, and 
 by the time the child is two or three years old a greater 
 impulse is needed by the ciliary muscles to effect the 
 necessary change in the convexity of the lenses. This 
 increase of ciliary impulse is attended by a corresponding- 
 increase of the converg-ence impulse, which develops the 
 esotropia. This would occur whether the child were 
 hyperopic or emmetropic. An acceptance of either ex- 
 planation throws the immediate blame for the crossing- 
 of the eyes on the ciliary muscles. 
 
 Whatever may be the reason for the short delay in 
 the manifestation of esotropia, there must be a cause or 
 causes that finally develop the condition. The follow- 
 ing- factors will be discussed in the order of their im- 
 portance: Esophoria, hyperopia, hyperphoria of one eye 
 and cataphoria of the other; a lower state of visual 
 acuity in one eye than in the other, either from some 
 cong-enital abnormality in the perceptive, transmitting-, 
 or receptive part of the apparatus, or some opacity or 
 irreg-ularity of the refractive media, either cong-enital or 
 the result of disease, or because there is a greater error 
 of refraction in one eye than in the other. Finally, 
 the whole of the macula in one eye may be connected
 
 ESOTROPIA. 515 
 
 with one side of the brain, while the whole of the macula 
 in the other eye may be connected with the other side of 
 the brain. A sixth complication, if not a cause, is a plus 
 or minus cyclophoria. 
 
 ESOPHORIA AS A CAUSE. It is safe to say that with- 
 out esophoria there can be no esotropia; but ordinarily 
 esophoria must be aided by one or more of the other 
 causes in the production of esotropia. Esophoria, when 
 high in degree, may eventuate in esotropia, and at the 
 usual age or earlier, when there is no hyperopia, even 
 when the refractive error is myopic. When esophoria 
 alone is the cause of esotropia, the actual turning occurs 
 when the externi, always too weak as compared with the 
 interni, give up the task of so antagonizing the interni 
 as to make binocular vision possible. At this time the 
 mind selects one eye for use, and the other is allowed to 
 turn into the position predetermined by the excessive 
 power of its internus. If its plane of action coincides 
 with the horizontal plane of the eye, the position as- 
 sumed will be directly in toward the nose; if the plane 
 of its action is elevated, its attachment being too high, 
 the eye will turn up as well as in and will be torted in; 
 but if its plane of rotation is depressed, its attachment 
 being too low, the eye will be turned down as well as in, 
 and will be torted out. At the time of the beginning of 
 the in-turning, the mind, in the interest of single vision,
 
 516 ESOTROPIA. 
 
 begins the work of suppressing the images on the retina 
 of the in-turned eye. If the esotropia is not periodic or 
 alternating, the work of mental suppression is soon 
 accomplished, the patient becoming mind-blind in the 
 crossed eye. When an esophoria alone is the cause of 
 esotropia, the error probably shows itself earlier than 
 usual. Spontaneous recovery, in such a case, will never 
 occur. For a study of esophoria, the reader is referred 
 to Chapter IV. of this book. 
 
 HYPEROPIA AS A CAUSE. When hyperopia, or hy- 
 peropic astigmatism, is one of the causes of esotropia, 
 it is not the quantity of the error, but the character of 
 the required impulse for its correction, that enters as a 
 factor. A greatly excessive impulse may be needed for 
 the correction of a small error, while an impulse not so 
 great gets a more ready response on the part of the cil- 
 iary muscles for the correction of a greater error. The 
 excessive activity of the center for the ciliary muscles 
 causes over-excitation of the third conjugate center, thus 
 developing a pseudo-esophoria. This grafted on an in- 
 trinsic esophoria may readily convert it into an esotropia. 
 The foundation for every permanent esotropia is intrinsic 
 esophoria. An esotropia caused by hyperopia alone will 
 be periodic, and never permanent. In such cases, sup- 
 pression of images is impossible. In cases of esotropia, 
 in which spontaneous recovery takes place, hyperopia has
 
 ESOTROPIA. 517 
 
 been the chief cause. If the esotropia spontaneously 
 cured has lasted very long, mental suppression has ac- 
 complished its work, and the eye once crossed remains 
 low in visual acuity. 
 
 The position assumed by an esotropic eye when the 
 two factors, esophoria and hyperopia, have acted to- 
 gether, is always determined by the character of attach- 
 ment the internal rectus may have. The eye may be 
 turned straight in, or in and up with inward torsion ing, 
 or in and down with outward torsioning. 
 
 The esophoria unassociated with hyperopia, in many 
 cases, would not have caused esotropia; hence it ap- 
 pears reasonable to conclude that a correction of the 
 hyperopia would result in a reconversion of the esotro- 
 pia back into esophoria. This is just what is accom- 
 plished in a large per cent of the cases of esotropia that 
 are brought early to the oculist. Thus cross-e} T es are 
 straightened without operation; but this does not mean 
 that an operation may not be required later for the cure 
 of the esophoria, for the relief of reflex troubles. 
 
 HYPERPHORIA AND CATAPHORIA AS CAUSES. The 
 plane of action of the superior and inferior recti is such 
 that they not only turn the eyes, respectively, up and 
 down, but they also turn them in. Imbalance of the 
 superior and inferior recti, whether that imbalance is 
 shown in a hyperphoria of one eye and a cataphoria of
 
 518 ESOTROPIA. 
 
 
 
 the other, or in a double hyperphoria or in a double 
 cataphoria, will become a factor in the production of eso- 
 tropia only when there is an esophoria. When these 
 two causes act together, the crossing" will occur at the 
 usual age (in the second or third year); but the esotro- 
 pia will be complicated by a hypertropia or catatropia. 
 If there is an eso-hypertropia and the superior rectus 
 is the cause of the hypertropia, there will be a minus 
 cyclotropia of that eye. If the fellow eye becomes eso- 
 catatropic under cover and the catatropia is caused by 
 the inferior rectus, there will be a plus cyclotropia of 
 this eye. In double eso-hypertropia, the hypertropia 
 being caused by the superior recti, there will be also a 
 minus cyclotropia of each eye; and in double eso-cata- 
 tropia, the catatropia being caused by the inferior recti, 
 there will be also a plus cyclotropia. When, in eso- 
 hypertropia, the hypertropia is effected by both the su- 
 perior rectus and the inferior oblique, there will be no 
 cyclotropia; when, in eso-catatropia, the catatropia is 
 caused by both the inferior rectus and the superior ob- 
 lique, there will be no cyclotropia. 
 
 There are cases of double eso-hypertropia, in which 
 there is marked plus cyclotropia, easily observed without 
 instrumental aid. The cause of the hypertropia in these 
 cases is to be found in the inferior obliques, which mus- 
 cles also cause the plus cyclotropia. In these cases the
 
 ESOTROPIA. 519 
 
 esotropia is wholly due to the interni. That the turn- 
 ing- up is not helped by the interni is shown by the ex- 
 istence of the plus cyclotropia; for, while a too high in- 
 ternus will turn the eye up, it will not tort it out. Thus 
 it appears that a hyperphoria, caused by the inferior ob- 
 liques, cannot be a direct factor in the causation of eso- 
 tropia. If not a cause, it must be considered as a most 
 important complication. The possible factors of esotro- 
 pia and its complications can be found only by means of 
 a most painstaking- examination with the phorometer, 
 cyclo-phorometer, and tropometer, or perimeter. 
 
 Low STATE OF VISUAL ACUITY AS A CAUSE. This 
 condition, whatever may be its cause, can be only a 
 secondary factor in the production of esotropia; for in 
 these cases, as in all others, esophoria is the chief factor. 
 If the low visual acuity is due to some congenital condi- 
 tion, or is caused by disease or injury in early infancy, 
 the esophoria will be transformed into esotropia in early 
 life. If both eyes have been g-ood for any number of 
 years, when disease or injury renders the vision of one 
 eye bad, or even destroys vision altogether, this eye will 
 become esotropic, if esophoria has previously existed; if 
 there is no esophoria, there can be no esotropia, however 
 low may become the vision of one eye. An eye that be- 
 comes blind will continue to move in harmony with its 
 fellow, if previously there has been no form of hetero-
 
 520 ESOTROPIA. 
 
 phoria. If there is known to be a certain kind of imbal- 
 ance of the muscles when the vision in both eyes is good, 
 should the vision of one eye be much reduced, or even 
 lost, a positive prediction can be made as to the kind of 
 heterotropia that will result: the turning will always be 
 in the direction of the tendency. If there is perfect bal- 
 ance of all the ocular muscles, diminution, or loss, of 
 vision of one eye will not interfere with the harmonious 
 movements of the two eyes; a blind e} T e, under perfect 
 muscle adjustment, will always appear to fix the object 
 seen with the good eye. 
 
 FAULTY CONNECTION OF THE MACULAS WITH THE 
 BRAIN AS A CAUSE. There are cases of esotropia in 
 which it is impossible to fuse the two images of an ob- 
 ject. Such cases were observed by Graefe, who defined 
 the condition as "antipathy to binocular single vision." 
 The cause of this antipathy, in all probabilit} T , is that 
 the macula of one eye is connected with one side of the 
 brain, while the macula of the fellow eye is connected 
 with the other side of the brain. To fuse images on the 
 two maculas their impressions must be carried to the 
 same side of the brain, which cannot be accomplished un- 
 less the nerve fibers passing from the two maculas find 
 their way into the same optic tract and thence go to the 
 same cuneus. If the maculas fail to have a common con- 
 nection with the brain, other retinal points that ought to
 
 ESOTROPIA. 521 
 
 correspond cannot do so, and there must be diplopia in 
 all parts of the field. The condition, if it exists, is con- 
 genital, and the only reason why there is not annoying 
 diplopia must be due to the habit of mental suppression 
 acquired in infancy. Esotropia due to such a cause 
 must occur earlier in life than is usual, possibly within 
 the first few \veeks after birth. 
 
 Pathology points to the possibility of such a cause for 
 esotropia. A disease involving the center of sight in 
 one cuneus, or a disease involving all the nerve fibers 
 as they pass from one cuneus in their course to the optic 
 chiasm, whether in the tract or farther back, must cause 
 hemianopsia, involving corresponding halves of the two 
 retinas, the temporal half of one retina anc the nasal 
 half of the other. Many such cases have been observed. 
 In some cases the line dividing the blind part from the 
 seeing part of each retina has been vertical, passing 
 down through the macula; in other cases, while these 
 lines were vertical, they missed the maculas, passing a 
 few degrees either to the right or to the left of both, the 
 two maculas falling either in the blind or in the seeing 
 parts, in either case showing that both were connected 
 with the same side of the brain; in other cases the divid- 
 ing lines have not been vertical, the obliquity being some- 
 times as much as ten degrees, but the same in the two 
 eyes. The oblique lines have passed, in the reported
 
 522 ESOTROPIA. 
 
 cases, either through the maculas or have fallen on cor- 
 responding- sides. No case, so far as the author knows, 
 has ever been reported showing that the blindness in 
 the temporal half of one retina included the macula, 
 while the blindness in the nasal half of the other retina 
 did not include the macula, else no further argument 
 would be necessary. That pathology has shown no 
 cases of faulty connection of the maculas with the 
 brain is probably due to the rarity of the condition- 
 certainly as rare as is "antipathy to binocular single 
 vision," for the one must be a synonym of the other. If 
 the lines dividing the retinas into two halves pass, in 
 some cases, down through the maculas, while in other 
 cases both these lines pass either to the right or to the 
 left of the maculas, it must be conceded as a possibility 
 that the dividing line in one retina may pass to the right 
 of the macula, while the dividing line in the other retina 
 may pass to the left of the macula. In this case disease 
 of one cuneus or of one tract would destroy the per- 
 ceptive power of one macula, while the other macula 
 would be uninvolved. There being no disease in such 
 a case, the impress of an image on one macula would be 
 conveyed to one side of the brain, while the impress 
 of the image on the other macula would be sent to 
 the other side of the brain, and there could be no 
 fusion of the two. So far as the author can see, nothing
 
 ESOTROPIA. 523 
 
 else can account for "antipathy to binocular single 
 vision." 
 
 Every surgeon of much experience with esotropia has 
 had cases that he could not cure, however skilled as an 
 operator. Each attempt to correct the error in such a 
 case makes the patient worse, for the reason that, under 
 the old condition, the power of suppression of images in 
 one eye had been acquired, while under the new condi- 
 tion, the images fall on new parts of the retina of the 
 eye operated upon, and diplopia is at once made manifest. 
 The more nearly the readjustment of the muscles brings 
 the eyes straight to exactly straighten them is impos- 
 sible the more annoying becomes the diplopia. If the 
 patient is mature at the time the operation is done, his 
 diplopia will always be annoying, for he can never re- 
 acquire the power of mental suppression. To have let 
 such a patient alone would have been a mercy. 
 
 Fortunately, esotropia due to the cause under discus- 
 sion is rare. That the mistake of operating on such 
 cases may not be made, the operator should give most 
 careful study to every case. When there is great am- 
 blyopia of the esotropic eye, one may feel fairly sure 
 that the case is not of this character; for usually a case 
 of this kind has fairly good vision in either eye when the 
 other is excluded, for the esotropia is alternating. But 
 all cases of alternating esotropia, with fairly good vi-
 
 524 ESOTROPIA. 
 
 sion in each eye, do not belong to this hopeless class. In 
 any case of esotropia the fusion test should be applied; 
 but in alternating* esotropia this test becomes absolutely 
 essential. When the images can be fused, the case can 
 be cured; if the images cannot be fused, a cure is im- 
 possible, and should never be attempted. The method 
 of making the fusion test will be given farther on, and 
 the peculiar play of images that cannot be fused will be 
 shown. 
 
 The varieties of comitant esotropia have already been 
 mentioned incidentally. They may be grouped here as 
 follows: Periodic, alternating, and permanent. The 
 same case, at different times, may present these different 
 conditions. Periodic esotropia is always curable; while 
 alternating esotropia may be curable, it is always open 
 to the suspicion that there is ' ' antipathy to binocular 
 single vision." Permanent esotropia is usually attended 
 by pronounced amblyopia in the deviating eye, and prac- 
 tically always depends on causes that can be relieved. 
 Occasionally a case of permanent esotropia may belong 
 to the incurable class, in which there is "antipathy to 
 binocular single vision." 
 
 Comitant esotropia must be differentiated from appar- 
 ent esotropia and from paretic esotropia. The cover 
 test at once settles the question as to apparent esotropia, 
 for, on covering and uncovering the eyes alternately,
 
 ESOTROPIA. 525 
 
 there will be no resetting- of either eye, both visual axes 
 always pointing toward the test object. The cover test, 
 in comitant esotropia, always shows a resetting 1 of both 
 eyes when covered and uncovered alternately. Under 
 this test there are always present the primary and the 
 secondary deviations the one equal to the other. In pa- 
 retic esotropia the secondary deviation is always greater 
 than the primary deviation, for the reason that if the 
 paretic muscle is the right externus, the fourth con ju- 
 g-ate innervation center sends an excessive impulse to 
 the right externus, because it is paretic, and to the left 
 internus, causing 1 the latter to manifest excessive power. 
 On covering- the paretic eye and uncovering the good 
 eye, the fifth conjugate innervation center sends only 
 an ordinary impulse to the left externus and the right 
 internus, hence the slighter deviation of the eye to which 
 belongs the paretic muscle. 
 
 The complications of esotropia are: hypertropia of one 
 eye and catatropia of the other, double hypertropia, 
 double catatropia, and cyclotropia. Hyperopia and hy- 
 peropic astigmatism may also be considered as compli- 
 cations. In the treatment of esotropia, it is essential 
 that all these complications shall be either found or 
 excluded. 
 
 THE FUSION TEST. There is no test, in the investi- 
 gation of a case of comitant esotropia, so important as
 
 526 ESOTROPIA. 
 
 the fusion test. The ability to fuse images should be 
 determined, regardless of the time it may take. If a pa- 
 tient could be made conscious of double vision at once, the 
 ability to fuse could be quickly found. The test object 
 should be a candle or a gas jet. Placing a red glass be- 
 fore the good eye, the natural light is often easily found 
 by the deviating eye, and on the corresponding side. If 
 the red glass before the good eye does not bring out the 
 consciousness of the double candle, then a green or a 
 blue glass ma} r be held before the deviating eye, thus 
 discoloring both images. As soon as the two discolored 
 lights are seen, the glass before the deviating eye may 
 be removed, when, with comparative ease, the natural 
 light is seen by this eye, while the red light is seen by 
 the fellow e} T e. If the two are not level, they should be 
 made so by means of the proper prism, placed vertically. 
 Now, by means of the rotary prism before the deviating 
 eye, the yellow blaze should be made to approach the 
 red one. If they are more than ten degrees apart, a 
 supernumerary prism should be placed, with its base 
 out, behind the rotary prism, when, starting again at 
 zero, the index is again carried into the nasal quadrant; 
 and as it revolves, the lights are brought nearer and 
 nearer, until finally they merge into one. In the whole 
 test, the fixing eye is the good eye, and the fixed object 
 is the red light. The fusion is effected the moment the
 
 ESOTROPIA. 527 
 
 yellow image is thrown, by prismatic action, on the mac- 
 ula. Once fused, there should be no diplopia so long as 
 the fusing prisms remain unchanged. Whenever fusion 
 is found possible, the case is curable. 
 
 If there is antipathy to binocular single vision, the 
 false (yellow) light can be made to approach the true 
 (red) light, but cannot be made to fuse with it. The 
 two will "kiss" and then recede, or the one will rise 
 above or fall below the other and pass to the opposite 
 side. Any number of repetitions of the effort to fuse, by 
 means of the most careful use of the rotary prism, will 
 result in failure. Such a case is incurable by any and 
 every means; and, therefore, no attempt should be made. 
 Operations certainly make these cases \vorse. 
 
 Comitant esotropia is a monocular trouble only in ap- 
 pearance. In reality it is binocular a fact that should 
 always be remembered when operations are about to be 
 done for its relief. The binocular character of esotropia 
 is shown by the cover test; for the moment the deviating 
 eye is made to fix, because the good eye is covered, the 
 latter turns in. After operations have been done on the 
 deviating eye, it sometimes becomes easier to use this eye, 
 at which time the fellow eye turns in, but not so much as 
 the original eye had turned. This use of the eye that 
 before deviated, favors the cure of the amblyopia, with- 
 out detriment to the other eye.
 
 528 ESOTROPIA. 
 
 MEASUREMENTS OF ESOTROPIA. 
 
 There are several methods, some more accurate than 
 others, but all of them of some value. The phorometer 
 test is the only one that is perfectly correct; and, unfor- 
 tunately, it is the hardest one to accomplish, for the rea- 
 son that it is so difficult to develop consciousness of di- 
 plopia. If diplopia could always be made manifest, the 
 other methods of measurement would soon be discarded. 
 The angle gamma does not interfere with the phorometer 
 test, but it does militate against all other tests. This an- 
 gle is formed at the crossing of the visual axis and the 
 line commonly called the "optic axis," at the center of 
 the retinal curve, which is the center of rotation of the 
 eye. For a better understanding of the angle gamma 
 the lines whose intersection forms it should be studied. 
 The visual axis begins always at the fovea centralis, 
 and must always pass through the center of motion, 
 which is the center of retinal curvature, and thence it 
 must pass through the cornea, but at no definite point; 
 it may be its center, but more often the point through 
 which the visual axis passes is away from the corneal 
 center. The visual axis is the antero-posterior axis of 
 rotation. It is strange how the line of fixation should 
 ever have been conceived as other than the visual axis; 
 and yet the cut in Swanzy's book, edition of 1900, page 
 25, shows the visual axis passing from the supposed
 
 ESOTROPIA. 529 
 
 macula through the nodal point out to an object in space. 
 The same cut shows the line of fixation extended from 
 the object in space to the center of rotation, stopping 
 there. Had he extended it back to the retina, he would 
 have missed the supposed macula, as shown in his cut; 
 but it would have passed to the real macula, for the line 
 of fixation can be none other than the straight line that, 
 passing through the center of rotation, connects the ob- 
 ject and its image on the macula. The so-called "op- 
 tic axis " is the line that must begin at the center of the 
 cornea and must pass through the center of rotation and 
 may reach the macula, but more often misses it. This 
 line, unless it coincides with the line of fixation, cannot 
 be an axis of rotation, for the reason that it cannot pass 
 through the equatorial plane at right angles; for the equa- 
 torial plane must be at right angles to the line of fixation 
 the visual axis. The point always common to these tsvo 
 axes, or lines, is the center of rotation of the eye, and the 
 angle formed by their intersection is the angle gamma. 
 The average size of this angle is about five degrees, 
 though in an ideal eye it is nothing. When this angle is 
 to the nasal side of the visual axis, the eye that is straight 
 would appear to be esotropic; if to the temporal side, 
 the eye would appear to be exotropic. The angle is 
 more often temporal than nasal; hence an esotropia 
 would appear less than it really is, while an exotropia
 
 530 ESOTROPIA. 
 
 would be exaggerated by it. This angle can always 
 be measured by the perimeter, and, when known, can be 
 taken from or added to, as the case may be, the esotro- 
 pia that has been previously measured in any other way 
 than by the phorometer. 
 
 MEASUREMENT BY THE PHOROMETER. A red glass 
 should be placed before the good eye. Before the deviat- 
 ing eye should be placed the rotary prism in the position 
 for testing- for lateral heterophoria, with the displacing 
 prism of six degrees, base up, in the cell toward the eye. 
 The red and the yellow blazes of the candle or gas jet 
 having been found, the latter will appear more or less 
 removed from the vertical line passing down through the 
 red light and in the direction corresponding to the de- 
 viating eye. The fifteen-degree supernumerary prism 
 should be placed, base out, in the front cell, which will 
 carry the yellow light just that far toward the vertical 
 line passing through the red light. Revolving the rotary 
 prism in the nasal arc, the yellow light is carried still 
 nearer the vertical line, which it may be made to reach at 
 some point between zero and ten degrees; but if this falls 
 short, the rotary prism should be revolved back to zero, 
 and a stronger supernumerary prism (twenty degrees, 
 twenty-five degrees, or thirty degrees) should be placed 
 in the anterior cell. Now the rotary prism should be 
 turned again in the nasal arc and then stopped at that
 
 ESOTROPIA. 531 
 
 point where the patient declares the yellow light direct- 
 ly under the red one. If the twenty-five-degree prism 
 is in the front cell and the rotary prism stands at seven 
 degrees, the prism-degree measurement of the esotropia 
 is thirty-two degrees, one-half of which would give the 
 degrees of arc viz., sixteen degrees. As already stated, 
 the angle gamma does not have to be considered in con- 
 nection with the phorometer measurement. It would be 
 very difficult to take the measurement of esotropia with 
 the prisms of the refraction case held by the hands of 
 the operator. Though this would be tiresome and tedi- 
 ous, it, nevertheless, would be accurate. 
 
 MEASUREMENT BY THE PERIMETER. Have the head 
 placed as if the purpose were to take the field of the 
 non-deviating eye, which should be made to fix the point 
 in the center of the semicircle. A candle or small elec- 
 tric light should be moved along that arc toward which 
 the deviating eye points, and it should be stopped the 
 moment that the image reflected from the center of the 
 cornea, the light, and the eye of the observer are in line. 
 The number on the perimeter arm, at the point where 
 the light was stopped, gives the measurement of the 
 deviation in arc degrees. If the esotropia thus meas- 
 ured should appear to be twenty-five degrees, it will be 
 more if the angle gamma is temporal, or less if this 
 angle is nasal. The next step is to determine the pres-
 
 532 ESOTROPIA. 
 
 ence or absence of the angle g-amma, and, if present, its 
 size. To do this, the good eye must be covered while 
 the patient fixes, with the esotropic e} r e, the point in the 
 center of the perimeter arc. When the candle is held 
 immediately behind this point, if the image is reflected 
 from the center of the cornea so that the image, the 
 light, and the eye of the observer are in line, there is no 
 angle g-amma, and, therefore, nothing is to be taken 
 from nor added to the measurement of the esotropia; 
 but if the light must be moved in the temporal arc for 
 the image, the light, and the eye of the observer to be 
 in line, there is an angle gramma, the size of which is 
 shown by the number at the point on the perimeter arm 
 at which the light was stopped when the image appeared 
 reflected from the center of the corneal surface. The 
 angle thus formed being temporal, it should be added to 
 the measurement of the apparent esotropia, in order to 
 show the quantity of the real deviation; but if, in find- 
 ing the angle g~amma, the light has been moved into the 
 nasal arc, the angle would be nasal, and should be sub- 
 tracted from the measurement of the apparent esotropia, 
 in order to show the quantity of the actual deviation. 
 If the perimeter is carefully used in the manner set 
 forth, the results must be correct. It is applicable to 
 all cases of esotropia in which the deviating eye can be 
 made to fix when the good eye is covered; while the
 
 ESOTROPIA. 533 
 
 phorometer method can be used only in those cases in 
 which, by means of a red glass before the good eye, con- 
 sciousness of diplopia can be awakened. 
 
 When the squinting 1 eye cannot see, therefore cannot 
 fix, the angle g-amma cannot be measured, and for this 
 reason it cannot be taken from nor added to the perimeter 
 measurement of the esotropia. 
 
 THE TAPE MEASUREMENT. Priestly Smith's method 
 of measuring esotropia is easy and fairly accurate. By 
 this method the angle g-amma is not considered. To 
 make this test, one must have an ophthalmoscope; two 
 tape lines, each one meter long-; and a candle, a lamp, or 
 a gas jet. The tape lines, at one end, should be fas- 
 tened to a ring large enough to allow the handle of the 
 ophthalmoscope to pass through it, while the other two 
 ends should be free, and on one tape should be a scale 
 indicating arc degrees. With the light above and be- 
 hind the patient, the operator seats himself one meter in 
 front of him. He gives to the patient the free end of 
 the unmarked meter tape, and tells him to place it im- 
 mediately beneath his good eye; and then, with the oph- 
 thalmoscope in front of his own eye which corresponds 
 with the patient's non-deviating eye that is, his right 
 eye, if it is the patient's left eye that turns in he with- 
 draws from the patient as far as the tape will allow 
 whose ring end is fastened to the ophthalmoscope, or to
 
 534 ESOTROPIA. 
 
 the thumb of the hand holding- the ophthalmoscope. He 
 directs the patient to fix the hole in the mirror while he 
 reflects the light into the fixing- eye. If there is no 
 angle gamma, the operator sees the image of the blaze 
 reflected from the center of this cornea; but on reflect- 
 ing the light into the deviating eye, while the good eye 
 still fixes the hole in the mirror, the image of the blaze 
 will be seen toward the temporal margin of this cornea, 
 the distance from the center corresponding to the amount 
 of the esotropia. The operator now takes the marked 
 meter tape in his free hand (he holds the mirror before 
 his right eye with his left hand, and vice versa) close to 
 its attachment to the ring, and, slowly extending it at 
 right angles to the other tape, he directs the patient to 
 look at his moving thumb with his good eye. Through- 
 out this step in the test, the light from the mirror is 
 kept on the cornea of the deviating eye, and the operator 
 watches the reflected image as it approaches the center 
 of the cornea. The moment the image is seen at the 
 center of the cornea the operator stops the movement of 
 his hand, and immediately reads on the scale the number 
 of degrees the good eye had to move toward the nose 
 in order that the deviating eye might become straight. 
 Since the two eyes moved comitantly, the reading on the 
 scale is the measurement of the esotropia. This method 
 is not as accurate as either the phorometer or the perim-
 
 ESOTROPIA. 535 
 
 euer methods, for the reason that one cannot be certain 
 that the marked tape is at right angles to the unmarked 
 tape. 
 
 LINEAR MEASUREMENT 1/awrence 's strabismome- 
 ter, which is the best means for taking the linear meas- 
 urement of squint, is rapid, but not accurate, in its work. 
 The lid piece is concave on one side so as to rest evenly 
 against the lower lid; on the convex side it is graduated 
 in millimeters in both directions from the central point, 
 which is marked zero. In making the test, the operator 
 covers the good eye, thus forcing the patient to fix some 
 distant object, immediately in front, with the deviating 
 eye. The instrument is now placed in contact with the 
 lower lid of the now-fixing eye, so that the point marked 
 zero may be directly in line with the center of the pupil. 
 On uncovering the good eye, it at once fixes the test ob- 
 ject, while the deviating eye turns toward the nose. The 
 extent of the turning in millimeters is shown by that 
 mark on the scale that falls immediately beneath the 
 center of the pupil. 
 
 HIRSCHBERG'S METHOD. By this method accuracy 
 cannot be attained. The test object is a candle held 
 twelve inches from the patient, and immediately before 
 him on a level with his eyes. With both eyes uncovered 
 he is directed to look at the candle. The image of the 
 candle is reflected from the corneal center of the fixing
 
 536 ESOTROPIA. 
 
 eye, but from the temporal side of the cornea of the 
 esotropic eye Hirschberg estimates that the deviation 
 is ten degrees or less, if the reflected image is nearer the 
 center than the margin of the pupillary area; from twelve 
 degrees to fifteen degrees, if the image is at the margin 
 of the pupil; twenty-five degrees, if the image is halfway 
 between the center of the cornea and its margin; from for- 
 ty-five degrees to fifty degrees, if the image is at the cor- 
 neal margin. Esotropic cases were divided by Hirsch- 
 berg' into these several groups that he might determine 
 the kind of operations to be done in any individual case. 
 Since complete tenotomies ought never to be performed 
 on esotropes, the Hirschberg method of testing* is of no 
 
 use. 
 
 SYMPTOMS OP COMITANT ESOTROPIA. 
 
 There is no nervous tension of the externus of the eso- 
 tropic eye, for the position assumed by this eye is that of 
 equilibrium of all the recti and the oblique muscles. 
 The tension of the externus of the fixing eye may be 
 lessened, if not relieved, by a turning of the face toward 
 the corresponding side, so as to let the visual axis cross 
 the extended median plane of the head between the eye 
 and the object of fixation. Headache or other symp- 
 toms, in these cases, usually attributed to eye-strain, 
 depend largely on the abnormal tension of the externus 
 of the fixing eye, though this is sometimes relieved by
 
 ESOTROPIA. 537 
 
 an acquired side-pose of the head. But in some of these 
 cases it may depend on the nervous tension of the ciliary 
 muscle in its effort to correct the hyperopia or hyperopic 
 astigmatism of the fixing eye, together with the asso- 
 ciated tension of the ciliary muscle of the non-fixing eye; 
 or it may result from the effort of the obliques to par- 
 allel the vertical axis of the fixing eye with the median 
 plane of the head. 
 
 AMBL,YOPIA. The one subjective symptom common 
 to most cases of permanent esotropia, and that may ex- 
 ist unnoticed for many years, is amblyopia of the non- 
 fixing eye. While in some cases this may be congenital, 
 in most cases it is acquired. The blindness is in the 
 mind, and not in the eye. Nature has provided only two 
 methods by either one of which a person may be freed 
 from the annoyance of seeing everything double: First, 
 the proper regulation of the visual axes by the recti 
 muscles, so that they may always be in the same plane 
 and converged at the point of view, and the paralleling 
 of the vertical axes of the eyes with the median plane 
 of the head, thus making binocular single vision possible; 
 second, in the absence of any one or all three of the con- 
 ditions essential to binocular single vision, then mental 
 suppression of the images in one eye. The habit of 
 mental suppression cannot be established, except in in- 
 fancy and early childhood. Once this habit is estab-
 
 538 ESOTROPIA. 
 
 lished, it is hard to break at any period of life; but the 
 task can be more easily accomplished early in life than 
 in later years. In all cases it is probable that the am- 
 blyopic eye would become useful, if accident or disease 
 should destroy the fellow eye. W. B. Johnson, of Pat- 
 erson, N. J., has observed and reported two such cases. 
 His report has done much to prove that amblyopia ex 
 anopsia is not a myth. Faithful exercise of the little 
 visual power of the amblyopic eye, by covering- the good 
 eye, will greatly improve its vision, especially in young- 
 persons. Without this special exercise it has often been 
 noticed that vision improved in the formerly non-fixing 
 eye after the muscles had been readjusted so as to 
 properly regulate the visual axes and the vertical axes. 
 There is now but little room for doubting that the am- 
 blyopia of esotropia is mental, and not ocular. 
 
 The chief objective symptom is disfigurement. How- 
 ever beautiful a young lady may be otherwise, if her 
 eyes are crossed that beauty is marred; and if she is oth- 
 erwise unprepossessing, crossed eyes could but render her 
 more so. A young man afflicted with esotropia cannot 
 be so handsome as he would be if his eyes were straight. 
 A girl or boy, a woman or man with esotropia is at a de- 
 cided disadvantage from a cosmetic point of view; and if 
 there was no other reason for operating, this one would 
 be sufficient.
 
 ESOTROPIA. 539 
 
 An objective symptom that should never be neglected 
 in the study of any case of esotropia is the turning* in of 
 the good eye when under the cover, at which time the 
 fellow eye must become the fixing eye. The secondary 
 esotropia should be equal to the primary; but if the 
 secondary esotropia is greater than the primary, it 
 points to paretic, and not to comitant, esotropia. 
 
 COMPLICATIONS OF ESOTROPIA. These are errors 
 of refraction; hypertropia, single or double; catatropia, 
 single or double; hypertropia of one eye and catatropia 
 of the other; and cyclotropia, either plus or minus. Hy- 
 pertropia, catatropia, and cyclotropia will be studied 
 farther on in this chapter. Here it may be said that 
 these errors, if unassociated with esotropia, would often 
 be phorias, and not tropias. Nevertheless, before operat- 
 ing for esotropia, it is important to know if these errors 
 exist; it is also important, before operating for esotro- 
 pia, to study well the refraction of the two eyes, and to 
 correct those errors (hyperopia and hyperopic astig- 
 matism) that are not only complications of esotropia, 
 but act as causes also. Another condition which com- 
 plicates esotropia is amblyopia, which is also a result of 
 esotropia. 
 
 TREATMENT OF ESOTROPIA. 
 
 Hyperopia and hyperopic astigmatism, often a compli- 
 cation of esotropia, are just as often causative of this
 
 540 ESOTROPIA. 
 
 condition. A very few cases of esotropia have, for their 
 chief causes, these errors of refraction. It is only a case 
 of this kind that eventually recovers spontaneously; but 
 spontaneous recoveries are rare. Nor should these cases 
 be allowed to wait for such a recovery, which would be 
 years in coming-; but they should be cured at the earliest 
 possible moment. The only treatment needed for such 
 cases is the full correction of the hyperopic error, and at 
 the earliest time possible. Such a patient, if only two 
 years old, will wear the correcting" lenses kindly, because 
 of the relief experienced. If the spectacles are not given 
 to the little fellow promptly after his morning toilet, he 
 will call for them. It is often interesting- to experiment 
 with such a case by having him look at some distant ob- 
 ject one moment through the lenses, when the eyes will 
 be straight, and then a moment without the lenses, when 
 the eyes will cross. The repeated raising and lowering 
 of the lenses will show alternate crossing and straight- 
 ness. One who has seen these changes cannot reasonably 
 doubt the effectiveness of convex lenses in the treatment 
 of esotropia. 
 
 There are two reasons for the early adjustment of 
 convex lenses in the treatment of esotropia. One is that 
 it is in the earliest years of life that the power of mental 
 suppression of images in the deviating eye is acquired. 
 To prevent this amblyopia is to cure the esotropia; or,
 
 ESOTROPIA. 541 
 
 if the habit of suppression has already been formed, the 
 early correction of the esotropia gives the patient a 
 chance to recover the lost vision with greater ease than 
 would be possible in later years. The other reason for 
 the early correction of the hyperopic error that has 
 caused the esotropia is the relief the lenses give to the 
 brain-center that supplies power to the ciliary muscles. 
 With the convex lenses on, this brain-center is no longer 
 over-stimulated, and consequently the third conjugate 
 center is no longer over-excited. The extra nerve force 
 that must be expended by these centers, if the hyperopic 
 error remains uncorrected, must be at the expense of 
 nerve force needed by other centers. 
 
 Every little child whose eyes are crossed should be 
 given the chance of a cure by means of spectacles. If 
 the hyperopic error is the whole cause of the esotropia, 
 the lenses will certainly effect a speedy cure; if the hy- 
 peropia is only one factor, while esophoria is the other 
 factor, in the production of esotropia, the early correc- 
 tion of the focal error will often make it impossible for 
 the esophoria to continue to transform itself into esotro- 
 pia. The eyes can be straightened, in some of these cases, 
 by means of convex lenses, but the esophoria will remain. 
 Later, because of nervous symptoms, the esophoria may 
 demand treatment, either surgical or non-surgical. To 
 do any kind of surgery for the cure of an esotropia that
 
 542 ESOTROPIA, 
 
 has for its sole cause a hyperopic error must result in 
 harm. In early life no case of esotropia that is hyper- 
 opic should be subjected to operation until it becomes ev- 
 ident that convex lenses cannot straighten the eyes,. It 
 is doubtful if the almost universal practice of keeping- 
 such eyes under the influence of atropine is helpful, but 
 certainly both eyes should be under the influence of either 
 atropine or homatropine at the time the measurements 
 are taken, and the full error thus found should be cor- 
 rected. Worth is correct in his advocacy of atropine in 
 the good eye only after the convex lenses have been giv- 
 en, and the reason for this is not far away: it allows the 
 child to use the better eye for distance, but forces him 
 to use the deviating eye for near objects a very good 
 way for curing the amblyopia. For the same reason 
 atropine could be used in the good eye when there is any 
 other form of heterotropia. 
 
 If in a month or two convex lenses do not cause the 
 eyes to swing straight, surgery should be resorted to, 
 however young may be the patient. By "surgery" is 
 meant the right kind of surgery partial tenotomies of 
 the interni, with or without shortenings of the externi. 
 A complete tenotomy in the case of a child should never 
 be done, and advancements should be avoided. Very 
 slight operations, if done in early life, will accomplish 
 as much as more extensive operations done in later years;
 
 ESOTROPIA. 543 
 
 but an esotrope never grows sufficiently old to justify 
 complete tenotomies. 
 
 If the refraction of the eyes is myopic, this error can- 
 not have been a factor in the production of the esotropia; 
 hence the correcting 1 lenses cannot aid in the cure. Sur- 
 gery alone can bring 1 these eyes straight. Such a case of 
 esotropia can never recover spontaneously. An esotrope 
 who is emmetropic can be cured only by surgery. Atro- 
 pine used in the good eye will help after surgery has 
 been resorted to. 
 
 Esotropic patients who have been allowed to go for 
 years without treatment, whatever may have been the 
 cause or causes, become more or less amblyopic in the 
 deviating 1 eye. In many of these cases the correction of 
 the hyperopia, if it had been given early, would have 
 speedily straightened the eyes; but if this correction is 
 withheld until the suppression habit has become estab- 
 lished, the cure, if it can ever be effected by the convex 
 lenses, is much more tedious. Nevertheless, a fair trial 
 of the lenses should be given, a great aid to which will 
 be the forced use of the deviating- amblyopic eye, for 
 a short while, several times a da} 7 . This is done b} T 
 placing- a flap before the g-ood eye, thus compelling the 
 mind to receive the impression of the images on the ret- 
 ina of the bad eye. At such time, and at all times, the 
 correcting lenses should be worn. At first only large
 
 544 ESOTROPIA. 
 
 objects in the distance should be observed; later, pic- 
 tures or large print should be looked at. If the pa- 
 tient is old enough, he will observe the improved state 
 of his vision from week to week, and will thus be en- 
 couraged to continue; if the patient is a child, the exer- 
 cise should be enforced, for the little one cannot appre- 
 ciate the results. This practice at first may be con- 
 tinued only a few minutes from ten to thirty; later, it 
 should be prolonged for an hour or more; and, in either 
 case, it should be repeated two or more times daily. 
 The training of the mind to use the amblyopic eye is the 
 best means for the beginning of the development of the 
 fusion power. Whether a child or a grown person, the 
 use of atropine in the good eye will help to train the mind 
 to use the bad eye. 
 
 This training of the mind to use the amblyopic eye is 
 necessary even in those cases that must be subjected to 
 operations, else binocular single vision may not be ob- 
 tained. The chief object in view in the treatment of 
 esotropia, whether by lenses or by operations, or by 
 both, is the establishment of binocular single vision. 
 There should be fewer failures in this direction in the 
 future than in the past. The forced use of the ambly- 
 opic eye will make success more certain. 
 
 After a few months of training, as set forth above, 
 the stereoscope can be brought into use. At first the
 
 ESOTROPIA. 545 
 
 two pictures used should be unlike, but of such a nature 
 as to be easily combined. The best example is the pic- 
 ture of a bird before one eye and the picture of a cage 
 before the other. The bird, at first outside the cage, will 
 be observed by the child to approach and enter it, finally 
 resting 1 on the perch. Other pictures that can be asso- 
 ciated should be provided. Later, cards may be used, 
 on one end of which is drawn one part of an object; on 
 the other end, the remaining- part of the object. If the 
 complete object is seen, the retinal images have been 
 fused. Later, the pictures ordinarily used in the stereo- 
 scope may be given. To be certain that these pictures 
 have been fused, it becomes necessary to make some 
 change in each at different parts; for example, cut off 
 the upper left-hand corner of one picture and the lower 
 right-hand corner of the other. If an unmutilated pic- 
 ture is seen, the two retinal images have been fused. 
 Many other changes, such as placing different kinds of 
 marks on the pictures, would readily suggest them- 
 selves. When the esotropia is of high degree, training 
 by means of the ordinary stereoscope is impossible. 
 
 The best means for training the fusion power is, prob- 
 ably, the Worth reflecting stereoscope, or amblyoscope, 
 shown in Fig. 75. This instrument can be used in any 
 and all cases of esotropia; but before undertaking the 
 training of the fusion faculty by this means, the ambly-
 
 546 
 
 ESOTROPIA. 
 
 opia of the deviating eye should be treated in the manner 
 already set forth. As shown in the cut, the Worth in- 
 strument consists of two symmetrical halves; each half 
 is made by uniting- two tubes, a long and a short one, at 
 an angle of one hundred and twenty degrees, and the 
 two halves are joined by the hinge shown at A. These 
 
 halves are further connected by the brass arc D-K-F, in 
 which are two slots, and by means of which the distal 
 ends of the tubes may be made to vary the distance be- 
 tween them. At D and F are binding screws for "fix- 
 ing" the proper relationship of the tubes, when it has 
 been attained, for any given pair of esotropic eyes. By
 
 ESOTROPIA. 547 
 
 placing 1 the binding* screws at the inner ends of their re- 
 spective slots the instrument is in adjustment for sixty 
 degrees of esotropia, and by moving- these screws to the 
 outer ends of their respective slots the instrument will 
 be in adjustment for thirty degrees of exotropia. 
 
 At G-H of each tube there is an arrangement for the 
 insertion of translucent picture slides. At A-X of each 
 tube there is an oval mirror. At the ocular ends A-B 
 there are lenses of a certain power, which may be sup- 
 plemented by other lenses that may be needed by any 
 individual case, for making sharp the outline of the im- 
 ages reflected from the mirrors. 
 
 In using this instrument for training the fusion facul- 
 ty, images that differ, and yet can be associated, should 
 be placed in the distal ends of the tubes. The best ex- 
 ample is the picture of a cage for one tube,- and that of 
 a bird for the other. The tubes must be related corre- 
 sponding to the degree of deviation of the esotropic eye, 
 so that the reflected image of the one picture may fall on 
 one macula, while that of the other falls on the other 
 macula. At first the patient may see only the cage, and 
 not the bird, or vice versa. By increasing, relatively 
 the intensity of the light entering the tube that is before 
 the squinting eye, the bird is finally seen in the cage. 
 Any two pictures that can be associated may be used, 
 but none can be better than those of the bird and the
 
 548 ESOTROPIA. 
 
 cage. Later, one may place in the tubes pictures that 
 represent different parts of an object, the fusion of the 
 two making- the thing- represented in parts appear as 
 a whole. A very great variety of such pictures should 
 be on hand, so as to make the exercise interesting- to the 
 little patient. 
 
 These exercises should not be undertaken until treat- 
 ment has relieved, to a considerable extent, the ambly- 
 opia of the deviating eye. It would be well if the fusion 
 faculty could be trained before operating, if circumstances 
 will allow, and certainly before the final operations are 
 done, if the best results are to be expected. 
 
 BAR-READING. Perhaps one of the best means for 
 perfecting the fusion faculty is bar-reading. A strip of 
 card-board, half an inch wide or even a pencil, though 
 this is hardly wide enough should be held between the 
 eyes and the printed page, about four inches from the 
 latter. This will obscure some of the words for each 
 eye, and will thus interfere with the reading, unless both 
 eyes are being used. The words obscured for one eye 
 are seen by the other, in binocular vision; therefore the 
 bar does not hinder the reading; and, since this is so, 
 the bar-reading exercise may be continued for hours at a 
 time. There can be no question as to its value. 
 
 Treatment of the amblyopia is by excluding the good 
 eye, by the adjustment of lenses that correct hyperopic
 
 ESOTROPIA. 549 
 
 errors; by the use of atropine in the good eye, forcing 
 the near use of the other; by the training of the fusion 
 faculty with the simple stereoscope or the reflecting ster- 
 eoscope, and, later, by bar-reading these are non-opera- 
 tive means that should be applied to all cases of esotro- 
 pia, even to those that must be subjected to operations. 
 
 OPERATIVE TREATMENT OF ESOTROPIA. 
 
 If all cases of esotropia could be treated at the earliest 
 possible time that is, when the condition first shows 
 itself probably not more than twent}^-five per cent of 
 them could be cured by non-operative means. Of this 
 twenty-five per cent, a fair proportion would require, 
 later in life, operations for the relief of the esophoria, 
 which had been one of the causes, probably the chief 
 cause, of the esotropia. A cure of esotropia, in the 
 strictest sense, would mean that every causative factor 
 has been removed. Convex lenses, given for the correc- 
 tion of hyperopic errors, remove only one factor; but in 
 doing this much, they sometimes render inoperative the 
 esophoric factor. However, the latter can be removed 
 only by exercise or by operations. 
 
 It cannot be emphasized too strongly that complete 
 tenotomies are not indicated in esotropia, even though 
 the error should be high in degree; and if complete te- 
 notomies should not be done, it goes without the saying
 
 550 ESOTROPIA. 
 
 that the "check ligaments," so-called, should never be 
 severed. It must be granted that some cases on whom 
 complete tenotomies have been done have resulted in a 
 cure of the esotropia, but it must be conceded also that 
 a greater number have not been cured. One does not 
 have to theorize as to the possibility of an esotropia's be- 
 ing- converted into an exotropia by complete tenotomies of 
 the interni, for this unfortunate result has been observed 
 in a multitude of cases. In every complete tenotomy the 
 control that comes from anchorag-e is lost. Uncut fibers 
 of the tendon constitute the best anchorage; but if by 
 accident all the fibers of a tendon should be cut, the 
 divided tendon should be anchored to the globe by means 
 of a stitch. Otherwise, the dang-er is great that the 
 muscle may retract too far, and thus become a crippled 
 muscle. 
 
 The only complete tenotomy that can be said to be at 
 all safe is that advised by Panas. In this operation the 
 hook is passed beneath the tendon (of the internus in eso- 
 tropia), and by it the eye is rotated outward until the cor- 
 nea is almost hidden behind the external canthus. This 
 done, the force is relaxed and the tendon is completely 
 divided. The element of safety lies in the fact that the 
 over-stretched muscle has been rendered paretic, and, 
 therefore, does not retract so far as it otherwise would 
 do. The cut tendon becomes adherent to the globe be-
 
 ESOTROPIA. 551 
 
 fore the muscle recovers from its paresis; hence its new 
 attachment is as favorable for normal action of the mus- 
 cle as it is possible for it to be after a complete tenot- 
 omy. The element of safety in the Panas operation is 
 not sufficient to justify its adoption, in the face of the 
 fact that there are safer operative means for the treat- 
 ment of esotropia. 
 
 If advancements are done in connection with complete 
 tenotomies, the latter become even more hazardous. 
 
 Landolt's method of treating 1 esotropia by advance- 
 ments of the externi alone is much to be preferred to 
 complete tenotomies of the interni; for it is not attended 
 by the danger of converting 1 an esotropia into an exotro- 
 pia, and it offers a better chance for the giving* of binoc- 
 ular single vision in all parts of the field. 
 
 As in all other matters, so in operating for esotropia, 
 extremes should be avoided. "The golden mean" is 
 not an inapt expression. One extreme in the treatment 
 of esotropia is complete tenotomies of the interni and the 
 cutting of the check ligaments, "without shortenings or 
 advancements of the externi; the other extreme is ad- 
 vancements of the externi, without interfering in any way 
 with the interni. 
 
 By the one method the strong muscles are made weak 
 by setting them back (and, as already shown, the danger 
 lies in the probability that they will be set back too far) ;
 
 552 ESOTROPIA. 
 
 by the other method the weak muscles are made strong 
 by bringing 1 their attachments farther forward, with but 
 little danger of bringing them too far. If enough could 
 be accomplished by the advancements, in all cases, it 
 would be almost the ideal operation. 
 
 The ideal operation for the cure of esotropia and its 
 complications consists of advancements of both externi, 
 or, if in young 1 children, shortening's of both externi, to 
 make them stronger, and partial tenotomies of both in- 
 terni to make them weaker. The object in view is to 
 bring the strength of the externi up to the normal both 
 as to abduction and abversion, and to reduce the strength 
 of the internt only to the normal both as to adduction 
 and adversion. There is practically no danger of over- 
 reaching the limit in either of the two directions. 
 
 There are a few cases of esotropia, as will be shown 
 farther on, in which it would not be correct to do any- 
 thing primarily but advance the externi and depress their 
 planes of rotation. 
 
 The two effects that can be accomplished by advance- 
 ments are an increase of tension and a change of the 
 plane of rotation. The former must always be accom- 
 plished, while the latter should be accomplished in some 
 cases, but avoided in others. The two effects that can 
 be accomplished by partial tenotomies are diminution of 
 tension and a change of the plane of rotation. The
 
 ESOTKOPIA. 553 
 
 former must always be attained, while the latter must 
 be accomplished in some cases, but avoided in others. 
 
 Before operating on any case of esotropia it must be 
 decided whether the tension alone shall be altered, or 
 whether, in connection with altering 1 the tension, the 
 plane of rotation shall be changed. To alter only the 
 tension of the muscles, when their planes also should be 
 changed, would be to fail to cure the case. In all cases 
 in which the deviating eye is not totally blind it may be 
 known beforehand just what kind of an operation should 
 be done. If the deviating eye is totally blind, there can 
 be no indication for a change of plane, and all that 
 should be done for such a case would be to alter the 
 tension. * 
 
 The operative treatment of uncomplicated esotropis 
 should be applied primarily to the deviating eye, with 
 the view of leaving some of the error to be corrected by 
 means of operations on the other eye. The externus of 
 the deviating eye should be well advanced, straight-for- 
 ward, so as to increase its tension without changing its 
 plane of rotation, and at the same time a central partial 
 tenotomy of the opposing internus should be done, the 
 operator always being careful to leave uncut a sufficient 
 number of fibers above and below to act as stay-cords. 
 By this partial tenotomy the tension is reduced, but the 
 plane is not changed. These two operations, done at the
 
 554 ESOTROPIA. 
 
 same time, will usually enable the patient to fix with this 
 eye, the other eye now becoming slightly crossed. 
 
 After an interval of two or more weeks a central par- 
 tial tenotomy of the internus of the good eye should be 
 done, with the view of lessening its tension without 
 changing its plane. If it appears that the effect of this 
 partial tenotomy is not enough, the externus of this eye 
 should be shortened, straight-forward, at once; or, if a 
 still greater effect is needed, this muscle should be ad- 
 vanced straight-forward. In either case the tension of 
 the muscle would be increased, but its plane would not 
 be changed. At the time the partial tenotomy is done, 
 if there is doubt as to whether enough has been accom- 
 plished, nothing more should be done at that time. 
 Later, if found necessary, the externus should be short- 
 ened. 
 
 In all uncomplicated cases of esotropia that cannot be 
 cured or greatly helped by non-operative means, three 
 operations advancement of the externus, a partial te- 
 notomy of the internus of the deviating eye, and (a little 
 later) a partial tenotomy of the internus of the good 
 eye should be done; and a fourth operation shorten- 
 ing or advancement of the externus of the good eye- 
 may be demanded. If these operations are carefully 
 done, the result should be a restoration of the power of 
 binocular single vision.
 
 ESOTROPIA. 555 
 
 If esotropia is complicated by a hypertropia of one eye 
 and catatropia of the other and there is no cyclotropia, 
 the operations for the cure of the esotropia should be 
 done as if there were no complication that is, by alter- 
 ing- the tension of the lateral recti in such a way as not 
 to make the slightest change in their planes of rotation. 
 Later, or even simultaneously, the vertical error should 
 be treated as will be set forth in connection with the 
 study of the vertical deviations. 
 
 If esotropia is complicated by cyclotropia, the opera- 
 tions done for altering tension should be so done as to 
 change the planes of rotation also. In esotropia with 
 plus cyclotropia, but no hypertropia, the partial tenot- 
 omies of both interni should be marginal, including all 
 of the lower and central fibers, and equal in extent, 
 leaving uncut the upper fibers, thus altering tension and 
 elevating the planes of rotation; and the shortenings or 
 advancements, equal in extent, of both externi should be 
 done so as to give them a lower attachment, unless it is 
 shown by tests that the marginal tenotomies of the in- 
 terni, which should always be done first, have fully cor- 
 rected the plus cyclotropia. If the plus cyclotropia has 
 been cured by the marginal tenotomies of the interni, the 
 remaining part of the esotropia should be treated by 
 straight-forward advancements or shortenings of the 
 externi.
 
 556 ESOTROPIA. 
 
 If esotropia is complicated by plus cyclotropia of both 
 eyes and right hypertropia and left catatropia, the fol- 
 lowing plan of operating should be adopted: First, an 
 advancement of the externus of the right eye so as to 
 lower its plane of rotation. This would counteract, in 
 part, the esotropia, the cyclotropia, and the right hyper- 
 tropia; for the muscle, by means of its new attachment, 
 would pull the eye toward the temple, draw it down, 
 and tort it in. The second operation should be done on 
 the internus of the left eye, and it should be a partial 
 teuotomy, including all the lower and central fibers and 
 leaving uncut only the fibers at its upper margin. By a 
 reduction of the tension of this internus, the externus 
 will draw this eye toward the temple, while the upper 
 uncut fibers of the internus will pull the eye up and tort 
 it in. Thus the esotropia will be further corrected, and 
 the plus cyclotropia and the catatropia will be wholly, 
 or in greater part, corrected. Any remaining esotropia 
 must be counteracted by a central partial tenotomy of 
 the right internus, and, if necessary, a straight-forward 
 advancement of the left externus, for the reason that if 
 by the first two operations the vertical heterotropia and 
 the plus cyclotropia have been cured, the remaining eso- 
 tropia would be uncomplicated and should be so treated, 
 and for the further reason that should there still remain 
 some of both complications after the first two opera-
 
 ESOTROPIA. 557 
 
 tions, elevation of the plane of the right internus would 
 increase the hypertropia while lessening- the plus cyclo- 
 tropia, and lowering the plane of the left externus 
 would increase the catatropia, while lessening the plus 
 cyclotropia. In such a case, therefore, the planes of ro- 
 tation of the right internus and the left externus should 
 not be changed, although it may be necessary to alter 
 their tension. Any vertical heterotropia and plus cyclo- 
 tropia remaining after the first two operations, should be 
 corrected by a partial tenotomy of the superior rectus of 
 the right eye, including all of its nasal fibers and as 
 many of its central fibers as might be necessary. Should 
 there still remain some of the left catatropia and plus 
 cyclotropia, a partial tenotomy of the left inferior rectus 
 should be done, including all the temporal fibers and as 
 few as possible of the central fibers. The six operations 
 performed in the order named, and done with proper 
 care, should cure the worst case of this kind. The only 
 remaining operations that should be done in such a case 
 are: advancement of the nasal margin of the right in- 
 ferior rectus and advancement of the temporal margin 
 of the left superior rectus, the indication for which 
 would be some remaining plus cyclotropia with right 
 hypertropia and left catatropia. The first four opera- 
 tions usually accomplish everything that could be de- 
 sired. To ignore the vertical heterotropia when com-
 
 558 ESOTROPIA. 
 
 plicated by plus cyclotropia, or to ignore the plus cyclo- 
 tropia when it is the only complication, in operating" for 
 esotropia, is to fail to cure the patient. 
 
 By far the most troublesome cases of esotropia the 
 incurable cases, under the old methods of operating 
 are those complicated by plus cyclotropia and double 
 h} 7 pertropia. The primary deviation is in and up, and 
 the eye is torted out; likewise, the secondary deviation 
 is in and up, and the eye is torted out. In these cases 
 the double hypertropia and the plus cyclotropia are both 
 caused by over-action of the inferior obliques, while the 
 whole of the esotropia is caused by over-action of the 
 two interni, a large part of this over-action of the in- 
 terni being in the nature of spasm. In some of these 
 cases a division of the two inferior obliques will cure 
 the double hypertropia, the plus cyclotropia, and the 
 esotropia; and this was doubtless the operation done 
 by the quack, Taylor, referred to in the first part of 
 this chapter. The author has done this operation once, 
 recently, and with gratifying results. These cases al- 
 ways carry their heads high, but they should be care- 
 fully studied otherwise than as to the pose of the head. 
 In the more aggravated cases of this character, cutting 
 across the inferior obliques by means of a Graefe knife, 
 being careful not to injure the infraorbital vessels and 
 nerves, is probably the best method of procedure. If
 
 ESOTROPIA. 559 
 
 the inferior obliques are not to be cut in these cases, the 
 first two operations should be done on the superior recti, 
 at the same time, and should consist of a division of all 
 the nasal and central fibers of each, leaving- uncut only 
 the temporal margins. These operations would lower 
 the two eyes, and the uncut temporal fibers would tort 
 both eyes in. In some of these cases these two opera- 
 tions go far toward curing, not only the double hyper- 
 tropia and the plus cyclotropia, but also the esotropia. 
 The next two operations, to be done at the same time or 
 with a short interval between, are advancements of both 
 externi. These operations should be done to increase 
 the tension of these muscles, so as to counteract the eso- 
 tropia, and lower their new attachments, so as to still 
 further correct the double hypertropia and the plus cy- 
 clotropia. Usually nothing else will have to be done. 
 Should there remain, after these four operations, some 
 of the double hypertropia and plus cyclotropia, the nasal 
 margins of both inferior recti should be advanced. Any 
 remaining esotropia should be corrected by a central par- 
 tial tenotomy of one or both interni, in such a way as not 
 to change the plane of rotation; for to elevate the plane 
 would be to increase any uncorrected nypertropia, while 
 lessening any uncorrected plus cyclotropia . 
 
 Since minus cyclotropia, as a complication of esotro- 
 pia, is so very rare, it is only necessary to say that, in
 
 560 EXOTROPIA. 
 
 operating 1 on the interni, their planes should be de- 
 pressed; and in operating 1 on the externi, their planes 
 should be elevated, this being- the very reverse of what 
 should be done when there is plus cyclotropia. 
 
 If a patient should be unwilling to undergo all the 
 operations that might be necessary for correcting his 
 comitant esotropia, he may have the reflex nervous symp- 
 toms relieved by submitting to one operation namely, 
 a partial tenotomy of the internus of the fixing eye. 
 This would relieve the nervous tension of the externus 
 of this eye, without risk of interfering with the comi- 
 tant movements of the two eyes, but it would not correct 
 the esotropia. 
 
 EXOTROPIA. 
 
 This condition, the opposite of esotropia, shows itself 
 in such a deviation of one eye that its visual axis, instead 
 of intersecting the visual axis of the fixing eye at the 
 point of view, deviates from it. It is generally taught 
 that myopia is one of the factors in its production. As 
 taught in a previous chapter, pseudo-exophoria manifests 
 itself only in the near; so it would appear that myopia, 
 on which pseudo-exophoria depends, could have nothing 
 to do directly in the causation of an exotropia that shows 
 itself when the point of view is in the distance. My- 
 opia does cause exotropia to be greater in the near than 
 in the far. The true cause of exotropia is intrinsic ex-
 
 EXOTROPIA. 561 
 
 ophoria. In a myope the exotropia first shows itself in 
 the near, when the pseudo-exophoria is grafted on the 
 intrinsic exophoria, the two tog-ether producing- the exo- 
 tropia. Beginning- in the near, the exotropia will show 
 itself later in the distance also, for the reason that the 
 mind, learning- to disreg-ard, in near work, the images on 
 the retina of the deviating- eye, becomes able to suppress 
 the images of distant objects, and this suppression leads 
 to the conversion of the exophoria into exotropia. In 
 this way myopia does contribute to the production of 
 exotropia. An early cure of the pseudo-exophoria, by a 
 full correction of the myopia, prevents an exotropia in 
 the near that does not exist in distant vision, and the 
 intrinsic exophoria may remain unchanged throug-h life. 
 If myopia were as common as hyperopia, exotropia would 
 be found as often as esotropia; for intrinsic exophoria 
 exists in fully as many cases as does intrinsic esophoria. 
 Exotropia may depend only on the excessive strength 
 of the externi as contrasted with the interni. This dif- 
 ference in relative streng-th may be due to hyper-devel- 
 opment of the externi or subnormal development of the 
 interni, or to the fact that the externi have a more 
 advantag-eous attachment to the globe than have the in- 
 terni. Associated with either the one or the other of 
 these conditions, there may be a deficiency in the third 
 conjug-ate innervation center. While the chief cause
 
 562 EXOTROPIA. 
 
 the sole cause in most cases may be in the excessive 
 strength of the externi, the obliques may also enter 
 into the causation, and that, too, without there being 
 any imbalance of the obliques. If the obliques are hy- 
 per-developed, or if they are attached too far behind the 
 equator, or if they are too short' and tense, they will 
 help the too strong externus to turn the eye out. If, in 
 any case of exophoria, disease or injury should greatly 
 reduce the vision of one eye, it will become exotropic in 
 time. In anisometropia, if there is exophoria, the worse 
 eye eventually will turn outward, in many cases. A 
 congenitally low state of vision in one eye, when there is 
 exophoria, will favor its transformation into exotropia. 
 It is doubtful if "antipathy to binocular single vision" 
 is as often a cause of exotropia as it is of esotropia. 
 
 The chief cause of many cases of exotropia has been 
 traumatism; and, unfortunately for science, it has been 
 operative traumatism. "Straightening crossed eyes in 
 a minute " has most often resulted in a perpetual out- 
 turning. But in the past, complete tenotomies of the 
 interni for esotropia, performed by both general and 
 ophthalmic surgeons, because they had been taught to 
 do so by such masters as Dieffenbach and Graefe, re- 
 sulted often, in a year or two, in an exotropia that was 
 not comitant. Such a disaster has happened to every 
 surgeon who has made many complete tenotomies of the
 
 EXOTROPIA. 563 
 
 interni, even when he was most careful not to cut the 
 check ligaments. It is true that exotropia has not fol- 
 lowed all the complete tenotomies of the interni that 
 have been made, else surgeons would have ceased, long- 
 ago, to attempt thus to relieve patients of one deformity 
 simply to bring 1 on them another, even more objectiona- 
 ble. Thanks to the long- and strong- insistence of Lan- 
 dolt, that advancements should supplant tenotomies, the 
 days of complete tenotomies of the interni are numbered. 
 Even Panas' operation cannot long- delay the total aban- 
 donment of complete tenotomies for the relief of esotro- 
 pia or any other form of heterotropia. Then no case of 
 exotropia will result from surgery. 
 
 While comitant exotropia may show itself in only one 
 eye, it is, nevertheless, a binocular trouble, which should 
 not be forgotten at the time treatment is instituted. 
 Exotropia always begins later in life than esotropia. 
 Exotropia may be alternating early in the history of a 
 case, but it soon becomes the fixed habit of one eye, usu- 
 ally the one that has conditions most favorable to mental 
 suppression of images a habit that is acquired by exo- 
 tropes as well as by esotropes. 
 
 The complications of exotropia are errors of refraction 
 (myopic refraction helps to cause exotropia) ; double hy- 
 pertropia and double catatropia; hypertropia of one eye 
 and catatropia of the other; and symmetrical or non-
 
 564 EXOTROPIA. 
 
 symmetrical cyclotropia. Treatment of the complica- 
 tions must constitute a part of the treatment of the 
 chief condition, and, for this reason, they should not be 
 ignored in any case. 
 
 The amount of exotropia can be determined readily, 
 by any one of the methods resorted to for measuring 
 esotropia, by a reversal of every step. 
 
 SYMPTOMS. The symptoms of exotropia are objec- 
 tive and subjective. The only objective symptom is 
 the disfigurement, which is greater or less, in pro- 
 portion to the extent of the outward turning-. Am- 
 blyopia, in many cases, is the only subjective symp- 
 tom; and this in some cases, at least has been 
 acquired by the power of mental suppression. Exo- 
 phoria is attended, practically always, by reflex symp- 
 toms, as already shown; but reflex symptoms are rare 
 in exotropia. The reflex symptoms found in a case 
 of exotropia are due either to the nervous tension of 
 the internus of the fixing- eye or to some one or more of 
 the complications. Exotropes who have been made so 
 by complete tenotomies of the interni are more liable to 
 show reflexes, and for the reason that the out-turned 
 eye cannot move comitantly with its fellow. It is the 
 generation of the excessive impulse the unbalanced im- 
 pulse to force comitant movements that cannot be 
 forced, which brings about the reflex disturbances. To
 
 EXOTROPIA. 565 
 
 illustrate: Suppose that the right internus has been cut, 
 resulting* in a non-comitant exotropia. When the eyes 
 are made to move to the right, there must be abnormal ac- 
 tion of the fourth conjugate center; for the left internus, 
 being- opposed by an uncrippled externus, will require a 
 greater impulse for a certain movement of its eye to the 
 right than will the externus of the right eye, which is 
 opposed by a crippled internus. It is the fourth conju- 
 gate brain-center that effects this rotation, and it cannot 
 act normally under such a condition. In such a case, 
 when the eyes are rotated toward the left, it must be 
 through the fifth conjugate brain-center, which will at- 
 tempt the impossible task of making the crippled right 
 internus move its eye comitantly with the fellow eye 
 whose externus is not crippled. The impossibility of 
 accomplishing the task does not prevent the brain-center 
 from undertaking it. Disturbance of one brain-center 
 can excite sympathetic disturbance in any other brain- 
 center. 
 
 One of the worst neurotic conditions that the author 
 has ever seen was in a patient who had a non-comitant 
 exotropia which had resulted from a complete tenotomy 
 of his right internus, performed many years before. His 
 case was diagnosed as an organic brain disease, and he 
 was treated accordingly for two or more years without 
 improvement. That his troubles were all reflex, and
 
 566 EXOTROPIA. 
 
 that the cause was his non-comitant exotropia, cannot be 
 doubted, for he recovered quickly after the enucleation 
 of his exotropic eye, which operation was done at his 
 own earnest solicitation ; he even demanded that it 
 should be done, believing-, as he did, that this was his 
 only chance. His belief that his troubles were referable 
 to the condition of his right eye was based on temporary 
 relief which he experienced two years previously from 
 an advancement operation on the right internus, per- 
 formed by the author, with an incomplete result as to 
 position and movement. Later, an operation was done 
 on the right superior rectus for a complicating hypertro- 
 pia, with renewed relief of some of the symptoms that 
 had again become prominent. Later, the author ex- 
 pected, and promised, to bring the right internus, atro- 
 phied as it was, still farther forward. The symptoms 
 became aggravated again, and the patient returned for 
 the promised operation. A colleague, Dr. J. A. Wither- 
 spoon, of Nashville, skilled in neurology, was called in 
 consultation. The Doctor pronounced the case one of or- 
 ganic brain disease, the author agreeing with him. No 
 other operation was attempted. The patient was placed 
 entirely in the hands of the consultant, who treated 
 him without results. In a few months the patient 
 was induced to go to Battle Creek Sanitarium, where 
 he remained for nearly two years without any marked
 
 EXOTROPIA. 567 
 
 change in his condition, either for better or worse. It 
 was while there that he insisted on the operation of enu- 
 cleation, which was done. 
 
 The above case is thus fully reported to emphasize the 
 point that a comitant heterotropia of one kind should 
 never be converted into a non-comitant heterotropia of 
 another kind, to avoid which one should be careful never 
 to do a complete tenotomy of any rectus muscle for any 
 condition. 
 
 In this connection it may be said that, in all probabil- 
 ity, Dr. John Dunn, of Richmond, Va., was the first 
 operator to enucleate one eye in which there was good 
 vision, to relieve the patient of severe nervous symptoms 
 caused by what was considered a hopeless muscle im- 
 balance. The operation cured the patient. This case 
 has not been reported. 
 
 Another case may be referred to also, somewhat like 
 the two preceding cases as to results, though the method 
 of obtaining them was unlike that resorted to in the 
 other cases. This case was that of a young lawyer who 
 suffered so much with his head and eyes that he contem- 
 plated giving up his profession, having failed to get re- 
 lief from cylinders which he needed, from prisms which 
 he did not need, and from ceiling-to-floor and wall-to- 
 wall exercise, which, for some reason, he was unable to 
 do for even one minute without suffering. There was
 
 568 EXOTROPIA. 
 
 no heterophoria, but the muscles were "balanced in 
 weakness," as shown by the fact that his abduction was 
 two degrees; his adduction, less than ten degrees; his 
 sub-duction and superduction, one degree. The vision 
 of his rig-lit eye was ||; that of the left eye, |. Every 
 means that had been suggested by any one of the several 
 ophthalmic surgeons whom he had consulted had been 
 tried, and failure had resulted from all. At last the 
 author advised him to have his left eye rendered useless. 
 He consented, and the left lens, already slightly opaque, 
 accounting for the reduced vision, was carefully needled, 
 so as to render it densely opaque without effecting its 
 solution. The comfort which he had been seeking came 
 as a result of this operation. It has been one year and 
 a half since the operation was done, and there has been 
 no return of his symptoms. Nothing else than making 
 the one eye blind, or removing it, could have cured him, 
 except the shortening of all the recti muscles, and it 
 is doubtful if that would have done it. These shorten- 
 ings the author would have advised if the lens in his left 
 eye had been perfectly transparent and vision had been 
 good. 
 
 These three cases are reported here, though not prop* 
 erly connected, because of the results that followed so 
 radical operations, after all other means had failed. 
 These three patients, operated on by three different men,
 
 EXOTROPIA. 569 
 
 would agree that it is better to go through life with only 
 one eye than to have two eyes that would be a constant 
 source of suffering. If relief can be obtained short of 
 sacrificing one eye, so repulsive an operation as enuclea- 
 tion should be avoided. 
 
 TREATMENT OF EXOTROPIA. 
 
 The correction of myopia early in the history of an 
 exotropia that is, when there is exotropia in the near, 
 but none in the far by removing the pseudo-exophoric 
 factor, may correct the exotropia, reconverting the exo- 
 tropia into an intrinsic exophoria. But the correction of 
 the exotropia by means of the concave lenses is not a 
 cure, in the proper sense; the intrinsic exophoric factor 
 must also be removed, and this can be done, in such a 
 case, only by partial tenotomies of the externi or by 
 shortenings or advancements of the interni. 
 
 In simple uncomplicated exotropia, at least three op- 
 erations should be performed. Two operations on the 
 deviating eye should be done first. One of these should 
 be a partial tenotomy of the externus, so done as to les- 
 sen its tension without changing its plane of rotation a 
 central partial tenotomy; and at the same time the oppos- 
 ing internus should be either shortened or advanced, and 
 in such away as to increase its tension without changing 
 its plane a straight-forward shortening or a straight-
 
 570 EXOTROPIA. 
 
 forward advancement. At any time after one week, a 
 partial tenotomy of the externus of the fellow eye should 
 be made, and in such a way as to lessen its tension without 
 changing its plane a central partial tenotomy. If these 
 three operations do not properly relate the eyes, a fourth 
 operation should be done, at any time after two to four 
 weeks. This operation should be a shortening or an ad- 
 vancement of the internus of the good eye, and it should 
 be so done as to increase its tension without changing its 
 plane a straight-forward shortening or a straight-for- 
 ward advancement. A very slight simple exotropia may 
 be cured by central partial tenotomies of the two externi, 
 performed at the same time; but most cases will require 
 three, if not four, operations. If these operations have 
 been performed in the order and after the manner set 
 forth above, the operator need have no fear that his case, 
 which w r as comitant exotropia before the operations, will 
 become non-comitant esotropia later; nor need he have 
 any fear that a torsioning of the eyes will result. In 
 exotropia of medium or high degree, the operation on the 
 weak interni must be an advancement, for a shortening 
 cannot produce enough effect. 
 
 An exotropia complicated with a double hypertropia, a 
 double catatropia, or a hypertropia of one eye and a cata- 
 tropia of the other, would require for its relief the same 
 kind of operations as if there were no complication
 
 EXOTROPIA. 571 
 
 that is, the partial tenotomies of the extern! should be 
 central, so as to lessen tension without a change of 
 plane; and the shortenings or advancements of the in- 
 terni should be straight forward, so as to increase ten- 
 sion without a change of the plane of rotation. In the 
 course of the treatment, the vertical heterotropia should 
 be relieved in the manner to be shown in the study of hy- 
 pertropia and catatropia, uncomplicated by cyclotropia. 
 
 If exotropia is complicated by plus cyclotropia only, 
 the order of operating, as well as the method, should be 
 changed. The two operations to be done first, and in 
 immediate succession, should be performed on both ex- 
 terni, and should consist of a marginal tenotomy of each, 
 the cut including the upper and central fibers, the lower 
 fibers to remain intact. These operations would lessen 
 the tension of both externi, and would lower their planes 
 of rotation, so that, in their new relationship, they would 
 tort the eyes in. This change of plane would also cause 
 a double cataphoria. The operative effect on the two 
 muscles should be as nearly equal as possible, so as to tort 
 both eyes in alike and depress them equally. After these 
 two operations, if some of the plus cyclotropia, as well as 
 some of the exotropia, should remain, both interni should 
 be shortened or advanced equally, and in such a manner 
 as to elevate their planes of rotation. The amount of 
 increase of tension and the extent of the elevation of the
 
 572 EXOTROPIA. 
 
 planes would have to be gauged according to the best 
 judgment of the operator. The end in view should be 
 perfect control of the visual axes and the paralleling of 
 the vertical axes with the median plane of the head. If 
 the two marginal tenotomies should correct the whole of 
 the plus cyclotropia, the remaining exotropia should be 
 corrected by straight - forward shortening or advance- 
 ment first, of the internus of the deviating eye; and 
 later, if necessary, of the internus of the good eye. 
 
 If exotropia is complicated with plus cyclotropia, right 
 hypertropia, and left catatropia, the operations on the lat- 
 eral recti should be done so as to alter their tension and 
 change their planes of rotation, the latter only up to the 
 point of a full correction of the plus cyclotropia. The 
 operations should be done in the following order, with two 
 or more weeks intervening: The first operation should be 
 a marginal partial tenotomy of the externus of the hyper- 
 tropic eye, including the upper and central fibers. The 
 effect of this would be (1) to lessen its tension, so that the 
 internus might draw the eye in; (2) lowering the plane so 
 as to tort the eye in, to counteract the plus cyclotropia, 
 and at the same time (3) turn the eye down for counteract- 
 ing the right hypertropia. The second operation should 
 be a shortening or an advancement of the left internus, 
 so as to increase its tension and elevate its plane; and, 
 that this may be done, not over half of the correction of
 
 EXOTROPIA. 573 
 
 the main error and its complications should be attempted 
 in the first operation. The effect of the second opera- 
 tion would be (1) to increase its tension so as to enable 
 it to draw the eye in; (2) to tort the eye in, b}^ means of 
 the elevation of the plane, so as to counteract, if possible, 
 the remaining plus cyclotropia; and (3) to elevate the eye, 
 to still farther and, if possible, entirely relieve the re- 
 maining part of the left catatropia. If, for the farther 
 relief of the exotropia (whether or not there may have 
 remained from the first two operations some of the plus 
 cyclotropia), it becomes necessary to operate on the in- 
 ternus of the right eye and the externus of the left eye, 
 each of these operations would have to be done so as to 
 alter tension without changing the plane of rotation 
 that is, the shortening or the advancement of the right 
 internus would have to be straight-forward, and the par- 
 tial tenotomy of the left externus would have to be cen- 
 tral. The reason for this is clear: To elevate the plane 
 of the right internus would help to correct any remain- 
 ing plus cyclotropia, in itself desirable, but this would 
 also elevate the eye a thing not to be desired; to depress 
 the plane of the left externus \vould correct any remain- 
 ing plus cyclotropia, in itself desirable, but it would de- 
 press still farther the eye that is already too low. 
 
 It is so very rare that a minus cyclotropia is found com- 
 plicating an exotropia, it is only necessary to say that,
 
 574 EXOTROPIA. 
 
 when it does exist, both the order of operating and the 
 method of doing- each operation, looking toward a change 
 of the muscle plane, should be the reverse of what has 
 been advised when plus cyclotropia is the complication. 
 
 When exotropia is complicated by a double hypertro- 
 pia and plus cyclotropia, it is probable that both compli- 
 cations are caused by the inferior obliques, and that these 
 muscles have also entered largely into the causation of 
 the exotropia. The operation most plainly indicated is a 
 division of the inferior oblique of both the deviating eye 
 and the fixing eye. If it were possible, in doing these 
 operations, to leave some of its fibers uncut, it would be 
 better. But a hook and scissors cannot be used, and the 
 division must be effected by passing a Graefe knife above 
 and beyond the muscle and between its origin and the 
 course of the infraorbital vessels and nerves, with the 
 cutting edge of the knife looking toward the orbital 
 floor, then, bringing the knife down, dividing every struc- 
 ture between it and the orbital floor. Again, the author 
 will say that he has done this operation on only one case, 
 and the result was highly satisfactory. He would not 
 hesitate to do it again in a case so well marked. 
 
 If the case is not sufficiently exaggerated to justify a 
 complete division of the inferior obliques, or if these have 
 been divided, but some of the main error with both of its 
 complications remains, a marginal tenotomy of both ex-
 
 SXOTROPIA. 
 
 terni should be done, including the upper and central 
 fibers. This would lessen their tension, so as to allow 
 the eyes to be drawn toward each other by the intern i, and 
 the lower uncut fibers \vould depress the eyes and would 
 tort them in. To make shortenings or advancements of 
 the interni with the view not only of increasing their 
 tension, but also of changing their planes of rotation 
 would be wrong; for elevating these planes would raise 
 the eyes still higher, while counteracting the plus cyclo- 
 tropia hurtful in one result, while helpful in the other. 
 It is clear, therefore, that, in such a case, if the tension 
 of the interni must be increased to still further correct 
 the exotropia, the shortenings or advancements should 
 be straight-forward. 
 
 At the meeting of the American Medical Association in 
 Atlantic City, N. J., in 1900, L. Webster Fox, of Philadel- 
 phia, read before the section of ophthalmology a paper, 
 entitled ' 'A Simple Operation for Divergent Strabismus. ' ' 
 He stated in this paper that he had put to a test the vari- 
 ous accepted methods for correcting this error, and that 
 he had noted the difficulties and many failures in his own 
 practice, such as had been experienced by others. This 
 led him to devise the method which he wished to de- 
 scribe, and for the reason that, through a period of 
 eight years, it had given him satisfaction. At the au- 
 thor's request, Dr. Fox has furnished the cuts to illus-
 
 576 EXOTROPIA. 
 
 trate the text. The method of procedure will be given 
 in Fox's own words: 
 
 "The operation is divided into three parts, and is per- 
 formed under cocaine: (1) tenotomy of both external recti 
 muscles and stretching* of conjunctiva and Tenon's cap- 
 sule; (2) making- the elliptical opening- either on one eye 
 or both; (3) suturing this opening-. 
 
 "The details of operation are carried out as follows: 
 "1. Tenotomy of both external recti muscles, making 
 an opening- through the conjunctiva, over the insertion of 
 the tendons. I then stretch Tenon's capsule until the 
 cornea is well into the inner canthus; this is done on 
 both eyes. Panas' method is to insert the hook under the 
 muscle and apply pronounced traction, at the same time 
 burying the cornea in the outer or inner canthus [inner, 
 in exotropia]. The operation is performed under ether 
 or chloroform, while in this method cocaine only is used. 
 The stretching of Tenon's capsule is an important part 
 of the operation. My method is as follows: The stra- 
 bismus hook (which is a large one), flat on its side, is 
 inserted in the opened conjunctiva and Tenon's cap- 
 sule, and with considerable traction all the tissues are 
 stretched inward until the cornea is buried in the in- 
 ner canthus. The stretching of the upper tissue has, 
 as can be readily understood, a tendency to rotate the 
 eyeball to a certain degree and leave the conjunctiva
 
 EXOTROPIA. 
 
 577 
 
 and Tenon's capsule intact below; to equalize the 
 stretching, the point of the hook is reversed, and the 
 lower conjunctiva and capsule stretched. In Panas' 
 method the hook being- placed under the external or 
 internal muscle prevents rotation of the eyeball. 
 
 " 2. With the retractor forceps I grasp the conjuctiva 
 verticallv, midway between the cornea and caruncle and 
 
 Fig. 76. 
 
 directly over the internal muscle, and draw upward the 
 conjunctiva and as much of Tenon's capsule as I can. I 
 raise the forceps two or three times to take up as much 
 of the redundant tissue as my judg-ment dictates, and by 
 this means one apparently is always successful in sepa- 
 rating- conjunctiva and overlying 1 tissue from the muscle, 
 if it be still present; then with curved scissors I cut
 
 578 
 
 EXOTROPIA. 
 
 with one long 1 sweep the upraised conjunctiva and cap- 
 sule close to the eyeball, making 1 an elliptic opening, ex- 
 posing, at times, the attenuated muscle, and, if no mus- 
 cle be present, then the clear sclerotic. 
 
 Fig. 77. 
 
 ' ' This opening now extends in a vertical direction, be- 
 ginning below the lower level of the cornea to a point 
 above the same, its width over the muscle is about one 
 full centimeter at its greatest diameter. The conjuctiva 
 is then separated around this elliptic wound from its sub-
 
 EXOTROPIA. 579 
 
 conjunctival tissues at all points even around the cor- 
 nea, if possible. 
 
 " 3. The elliptic opening is brought together with four 
 sutures. The upper suture is inserted through conjunc- 
 tiva and Tenon's capsule and across under conjunctiva 
 and Tenon's capsule midway between the insertion of 
 the superior rectus muscle and the margin of the cornea; 
 
 Fig. 78. 
 
 a similar suture is passed through the lower margin of 
 the conjunctiva and brought out midway between the 
 insertion of the inferior muscle and the margin of the 
 cornea; this thread is then tied, and, in like manner, the 
 upper thread; two more sutures are passed through the 
 margin of the lips of the wound and united. 
 
 ' ' This constitutes the details of the operation. The 
 object of the operator should be to produce from one to 
 four millimeters of convergence, which disappears during
 
 580 3XOTROPIA. 
 
 cicatrization. When the defect is not more than two or 
 three millimeters, I have performed an external tenotomy 
 on both and stretched Tenon's capsule, with excellent 
 results, without taking- out the elliptic section, especially 
 in those cases where the eyes could be held by the patient 
 at fixed convergence at ten inches." 
 
 Fox's operation has been thus described, in his own 
 words, for the reason that it is probably the equal of 
 Panas' operation, if not superior to it, for exotropia. 
 While it may be comparatively safe in exotropia, it cer- 
 tainly would be very dangerous in esotropia; but even 
 in exotropia there is danger that a complete tenotomy 
 may cripple the comitant lateral movements of the eyes 
 a danger never encountered when the stronger muscle is 
 partially divided, without any stretching, and the weaker 
 muscle is shortened or advanced. 
 
 The form of exotropia that most urgently demands 
 relief is the non-comitant exotropia which has resulted 
 from complete tenotomies for esotropia. In these cases 
 the externi, which were never possessed of too much 
 intrinsic strength, should not be even partially cut, but 
 the whole effect should be accomplished by advancement 
 of the internus that had been allowed to retract too 
 far. In these cases all the complications must be con- 
 sidered, and the advancements should be governed ac- 
 cordingly.
 
 HYPERTROPIA AND CATATROPIA. 581 
 
 HYPERTROPIA AND CATATROPIA. 
 
 These conditions practically always exist as compli- 
 cations of either esotropia or exotropia, and not infre- 
 quently are associated with cyclotropia. Hypertropia 
 may be double, and catatropia may be double, or there 
 may be a hypertropia of one eye and a catatropia of the 
 other. If there is double hypertropia without cyclo- 
 tropia, the error is caused by the conjoined action of the 
 superior recti and the inferior obliques, both of which 
 elevate the eye, while the in-torting action of the supe- 
 rior rectus is counteracted by the out-torting- action of 
 the inferior obliques. 
 
 If there is double hypertropia with minus cyclotropia, 
 the chief factors in its production are the superior recti, 
 aided, possibly, by interni whose attachments are too 
 high. 
 
 If there is double hypertropia with plus cyclotropia, 
 the chief factors are the inferior obliques, aided, possi- 
 bly, by externi that are attached too high. 
 
 Double catatropia, if caused by both the inferior recti 
 and the superior obliques, will show no cyclotropia; if 
 caused by the inferior recti alone, or with the aid of in- 
 terni that are attached too low, there will be plus cyclo- 
 tropia also; if caused by the superior obliques alone, or 
 with the aid of externi whose attachments are too low, 
 there will be minus cyclotropia also.
 
 582 HYPERTROPIA AND CATATROPIA. 
 
 When there is hypertropia of one eye with catatropia 
 of the other, there will be no cyclotropia if the hyper- 
 tropia is caused by the conjoined action of the superior 
 rectus and the inferior oblique, and the catatropia is 
 caused by the united action of the inferior rectus and 
 the superior oblique. 
 
 If the hypertropia of the one eye is caused by the 
 superior rectus alone, or with the aid of a too high in- 
 ternus, there will be minus cyclotropia; and if the cat- 
 atropia of the other eye is caused by the inferior rectus 
 alone, or with the aid of a too low internus, there will 
 be plus cyclotropia the two eyes together would have 
 parallel cyclotropia. 
 
 If the hypertropia of the one eye is caused by the infe- 
 rior oblique alone, or with the aid of an externus that is 
 attached too high, there will be also a plus cyclotropia; 
 and if the catatropia of the other eye is caused by the 
 superior oblique alone, or with the aid of an externus 
 that is attached too low, there will be also a minus 
 cyclotropia the two eyes together would show parallel 
 cyclotropia. 
 
 If there is hypertropia of one eye with catatropia of 
 the other, and the complication is plus cyclotropia of 
 both eyes, the cause of the hypertropia is the inferior 
 oblique, and the cause of the catatropia is the inferior 
 rectus; or, if the complication is minus cyclotropia, the
 
 HYPERTROPIA AND CATATROPIA. 583 
 
 cause of the hypertropia is the superior rectus, and the 
 cause of the catatropia is the superior oblique. 
 
 The cause of the vertical heterotropias is in the mus- 
 cles that are concerned in elevating- and depressing- the 
 eyes, aided in some cases by the lateral muscles that are 
 attached too high or too low. For the first year or two 
 the want of harmony between these muscles is shown by 
 some form of vertical heterophoria, which, especially 
 when associated with some form of imbalance of the 
 laterally acting 1 muscles, becomes transformed into a 
 vertical heterotropia at the same time that the lateral 
 heterophoria becomes transformed into lateral hetero- 
 tropia. Hypertropia and catatropia rarely exist alone. 
 They are comitant in character, except when they are the 
 result of operations or caused by paralysis. 
 
 The disfigurement of the individual is the objective 
 symptom; and the subjective symptoms are those al- 
 ready mentioned in connection with the study of the 
 lateral heterotropias. Reflex neuroses are not often 
 connected with the comitant form; but when they do 
 exist, their cause is abnormal nervous tension of the 
 weaker muscle of the fixing eye. But the non-comi- 
 tant hypertropia or catatropia nearly always the lat- 
 ter, for the reason that a complete tenotomy of a su- 
 perior rectus for a hyperphoria is more often done 
 than a complete tenotomy for a cataphoria often causes
 
 584 HYPERTROPIA AND CATATROPIA. 
 
 severe reflexes; besides, a non-comitant catatropia, re- 
 sulting' from a complete division of a superior rectus 
 for a hyperphoria, in an adult, is always attended by 
 diplopia. At that age mental suppression is impossible. 
 These errors can be measured more easily by the pho- 
 rometer than by any other method, but the perimeter 
 and the tape methods (the graduated tape to be held 
 vertically) can be resorted to. 
 
 TREATMENT OF VERTICAL HETEROTROPIA. 
 
 In the discussion of the treatment of esotropia and ex- 
 otropia it has been shown that, when hypertropia and 
 catatropia are the only complication, each condition 
 must be treated as thoug-h the other -did not exist that 
 is, every offending- muscle must have its tension altered 
 without a chang-e of plane. In the same manner must 
 uncomplicated vertical heterotropias be treated. If the 
 error is a double hypertropia, a central partial tenotomy 
 of each superior rectus should be done. The effect 
 should be equally divided between the muscles, so as to 
 lower the eyes the same number of degrees. If the con- 
 dition is an uncomplicated double catatropia, a central 
 partial tenotomy of both inferior recti should be done; 
 but care should be taken not to do too much, for the 
 reason that a slight double catatropia is much to be pre- 
 ferred to a very slight double hypertropia.
 
 HYPERTROPIA AND CATATROPIA. 585 
 
 A double hypertropia complicated by plus cyclotropia 
 is caused by the inferior obliques. If these two errors 
 are very high in degree, and especially if there is want 
 of converging- power, the conditions would be better cor- 
 rected by cutting 1 both inferior obliques. These opera- 
 tions would correct not only the double hypertropia and 
 the plus cyclotropia, but would also g-ive an increase of 
 converging- power. If these combined errors are not so 
 high in degree, or if high in degree and there is little or 
 much esotropia, a division of the inner and central fibers 
 of both superior recti would be indicated; for these op- 
 erations would correct the double hypertropia and the 
 plus cyclotropia and at the same time would lessen con- 
 vergence. 
 
 A double hypertropia complicated by a minus cyclo- 
 tropia is caused by the two superior recti, and the oper- 
 ation to be done is a marginal tenotomy of both these 
 muscles, dividing the temporal and central fibers. In 
 such a case there is practically always some esotropia 
 also, which will be slightly increased by these opera- 
 tions; but the latter can be treated as set forth under 
 the head "Esotropia." 
 
 A double catatropia complicated by a plus cyclotropia 
 is caused by the inferior recti alone, and should be re- 
 lieved by a division of the temporal and central fibers of 
 both these muscles. If in such a case there is want of
 
 586 HYPERTROPIA AND CATATROPIA. 
 
 converging power, this would be helped by these opera- 
 tions; but if there is an excess of convergence, this will 
 be made greater. How to deal with such a case has 
 been set forth alread}-. 
 
 The most common form of vertical heterotropia is hy- 
 pertropia of one eye and catatropia of the other. If 
 there is no complicating cyclotropia, the first operation 
 should be a central partial tenotomy of the superior 
 rectus of the hypertropic eye, the aim being to accom- 
 plish more than half the correction, rather than less; and 
 the second operation, after from two to four weeks, should 
 be a central partial tenotomy of the inferior rectus of the 
 catatropic eye, with the view of placing the visual axes 
 in the same plane. These operations will result only in 
 lessening the tension of the muscles that are too strong. 
 If some of the old errors should remain, the third opera- 
 tion should be a straight-forward shortening of the in- 
 ferior rectus of the hypertropic eye. These three oper- 
 ations should correct the most aggravated vertical error; 
 but a fourth operation could be done viz., a straight- 
 forward shortening of the superior rectus of the cata- 
 tropic eye. 
 
 Hypertropia of one eye and catatropia of the other, 
 complicated by a plus cyclotropia, should be corrected by 
 a marginal partial tenotomy, including the nasal and 
 central fibers, of the superior rectus of the hypertropic
 
 CYCLOTROPIA. 587 
 
 eye; and a marginal partial tenotomy, including- the 
 temporal and central fibers, of the inferior rectus of the 
 catatropic eye. 
 
 Hypertropia of one eye and catatropia of the other, 
 complicated by parallel cyclotropia plus in one eye and 
 minus in the other would require one method of pro- 
 cedure if the hypertropic eye had the plus cyclotropia, 
 and a very different method if the hypertropic eye had 
 the minus cyclotropia. In the former case the marginal 
 tenotomy of the superior rectus of the hypertropic eye 
 should include the nasal and central fibers, and the 
 marginal tenotomy of the inferior rectus of the cata- 
 tropic eye should include its nasal and central fibers; 
 while in the latter case the tenotomy would include the 
 temporal and central fibers of the superior rectus of the 
 hypertropic eye and the temporal and central fibers of 
 the inferior rectus of the catatropic eye. 
 
 CYCLOTROPIA. 
 
 Cyclotropia is an actual loss of parallelism between 
 the vertical axes of the eyes and the fixed median plane 
 of the head. This condition probably never exists alone, 
 though it is often found in connection with other forms 
 of heterotropia, as has been shown already. It may be, 
 however, the chief condition in some cases, the lateral or 
 vertical deviations of the visual axes being complications;
 
 588 CYCLOTROPIA. 
 
 but far more often the cyclotropia is a complication of the 
 vertical and lateral deviations. 
 
 There are two classes of cyclotropia namely, similar 
 and dissimilar. In the former class the cyclotropia is 
 plus or minus in both eyes, while in the latter class the 
 error is plus in one eye and minus in the other. The 
 former might be termed "non-parallel cyclotropia" 
 that is, the vertical axes are either divergent or conver- 
 gent; the latter might be termed " parallel cyclotropia " 
 that is, the vertical axes are inclined one toward, and 
 the other from, the median plane. Cases of parallel cy- 
 clotropia are not often found; and of the non-parallel 
 class, plus cyclotropia is far more common than minus 
 cyclotropia. 
 
 In parallel cyclotropia, if the minus error is in the 
 right eye and the superior oblique is the cause, in the 
 sense of being too strong, the complication for that eye 
 will be catatropia; but if the superior rectus is the cause, 
 the complication will be hypertropia. The plus cyclo- 
 tropia of the left eye will be complicated with hypertro- 
 pia if the inferior oblique is the cause, and catatropia will 
 be the complication if the inferior rectus is the cause. 
 In esotropia, which may complicate parallel cyclotropia, 
 the internus of the right eye, if attached too high, will 
 aid in the production of the minus cyclotropia, and, in 
 some cases, may be the chief cause of the minus cyclo-
 
 CYCLOTROPIA. 589 
 
 tropia; while the internus of the left eye, if its attach- 
 ment is too low, will aid in the production of the left 
 plus cyclotropia. A too low right externus would be a 
 causative factor of the minus cyclotropia, and a too hig-h 
 left externus would help to cause the plus cyclotropia of 
 this eye. 
 
 In plus cyclotropia of both eyes, the error is caused by 
 both inferior obliques or by both inferior recti. If the 
 inferior obliques cause the error, the necessary complica- 
 tion will be double hypertropia; and if the inferior recti 
 are the cause, the necessary complication will be double 
 catatropia. The interni, \vith their attachments too low, 
 can help the inferior recti in the development of plus cy- 
 clotropia; and the externi, with their attachments too 
 high, can aid the inferior obliques in the causation of the 
 plus cyclotropia. 
 
 Minus cyclotropia of both eyes can be caused by the 
 superior obliques alone, when the complication will be 
 double catatropia; it can also be caused by the superior 
 recti, when the complication will be double hypertropia. 
 Externi that are too low can help the superior obliques 
 in the production of minus cyclotropia, and interni that 
 are too hig-h can aid the superior recti in the production 
 of minus cyclotropia. 
 
 Plus cyclotropia of one eye, with hypertropia, is 
 caused by the inferior oblique; plus cyclotropia of the
 
 590 CYCLOTROPIA. 
 
 other eye, with catatropia, is caused by the inferior 
 rectus. 
 
 Cyclotropia, of whatever kind, can be detected and 
 measured by means of the cyclo-phorometer, used as in 
 the investigation of cyclophoria. Because of the am- 
 blyopia that usually exists in one eye, the red glass 
 should be placed in the cell behind the rod that is before 
 the better eye. The prism of five degrees should be 
 placed in the cell behind the rod that is in front of the 
 amblyopic eye, base either up or down in the former 
 position, if this eye is hypertropic; in the latter position, 
 if it is catatropic. If the red streak of light is below, 
 and the two streaks converge at the ends corresponding 
 to the red glass, there is plus cyclotropia; if they con- 
 verge at the other ends, there is minus cyclotropia. 
 Turning the rods in the directions that will parallel the 
 streaks, and at the same time make them appear to be 
 horizontal, measures the error; and the pointing of the 
 index also names the error. If the two stand in the nasal 
 quadrant, the error is plus; if they stand in the tem- 
 poral quadrant, the error is minus. 
 
 Cyclotropia, like the other forms of heterotropia, is 
 alternating that is, the fixing eye, whichever it may 
 be, will have its vertical axis parallel with the median 
 plane of the head, while the vertical axis of the other 
 eye will be torted out or in, as the case may determine.
 
 CYCLOTROPIA. 591 
 
 It is also comitant, the angle being- the same in all posi- 
 tions of the eyes. 
 
 Cyclotropia, caused by paralysis, or paresis, and oper- 
 ations, is non-comitant, and will be attended by most 
 annoying- symptoms. The symptoms of comitant cyclo- 
 tropia are those common to the other forms of comitant 
 heterotropia, including- the loss of vision in one eye, 
 caused by mental suppression. Reflex symptoms are 
 caused by nervous tension of the weaker oblique of the 
 fixing- eye, that the vertical axis may be made parallel 
 with the median plane of the head. 
 
 TREATMENT OF CYCLOTROPIA. 
 
 When cyclotropia is a complication of esotropia, exo- 
 tropia, hypertropia, and catatropia, it should be treated 
 as has been set forth already. Here it is necessary to 
 speak of the treatment of cyclotropia when it is the 
 chief error; it rarely exists alone. If there is much 
 plus cyclotropia, complicated by double h}'pertropia, 
 but no marked lateral error exists, the operative effect 
 should be equally divided between the two eyes. Either 
 the two inferior obliques should be divided completely 
 (for the reason that a partial division of these muscles 
 seems impossible) with the Graefe knife; or a marginal 
 tenotomy of both superior recti should be done, con- 
 sisting- of a division of the nasal and central fibers of
 
 592 CYCLOTROPIA. 
 
 each, leaving- uncut the temporal fibers. The results 
 of the operation on the superior recti would be the 
 same in kind, if not in degree, as those done on the in- 
 ferior obliques namely, the two eyes would be partly, 
 if not wholly, relieved of the outward torsion, and they 
 would be relieved more or less of the double hypertropia. 
 In the absence of any lateral deviation, the only remain- 
 ing muscles to be subjected to operations are the inferior 
 recti, whose nasal fibers should be shortened or advanced 
 equally. The operations on the inferior recti would 
 correct more or less of the plus cyclotropia and the 
 double hypertropia. 
 
 Plus cyclotropia complicated by hypertropia of the 
 rig-tit eye and catatropia of the left eye, should be treated 
 first by one or the other of two operations on the rig-ht 
 eye that is, either the inferior oblique should be cut, or 
 a marginal partial tenotomy, including 1 the nasal and 
 central fibers, should be done on the superior rectus. 
 Either of these operations would correct wholly or in 
 part both the plus cyclotropia and the hypertropia of 
 this eye. The next step would be to divide the temporal 
 and central fibers of the inferior rectus of the left eye, 
 which would correct wholty or in part both the plus cy- 
 clotropia and the catatropia of this eye. If, after these 
 operations have been done, there should remain some of 
 both the plus cyclotropia and the hypertropia of the rig-ht
 
 CYCLOTROPIA. 593 
 
 eye and catatropia of the left eye, one other operation 
 should be done on each eye namely, the nasal margin of 
 the right inferior rectus and the temporal margin of the 
 left superior rectus should be either shortened or ad- 
 vanced. 
 
 Plus cyclotropia uncomplicated by any other deviation, 
 should be relieved by either a nasal marginal tenotomy 
 of both superior recti or by a nasal marginal advance- 
 ment or shortening of both inferior recti; or, in cases de- 
 manding it, both operations should be done on each eye. 
 Since a double catatropia would result, necessarily, from 
 either marginal tenotomies of the superior recti or mar- 
 ginal shortenings or advancements of the inferior recti, 
 the former operation should be preferred, for the reason 
 that it is both more easily done and less annoying after- 
 wards to the patient. In those cases in which sub-duction 
 is greater than normal (more than three degrees), after 
 the nasal marginal tenotomies of the superior recti have 
 failed to correct the plus cyclotropia, temporal marginal 
 tenotomies of the inferior recti should take the. place of 
 the nasal marginal shortenings or advancements. 
 
 Minus cyclotropia complicated or uncomplicated is so 
 rare that its treatment may be dismissed with the state- 
 ment that the part of a superior or inferior rectus that 
 should be cut for plus cyclotropia should be advanced or 
 shortened for a minus cyclotropia, and the part of these
 
 594 CYCLOTROPIA. 
 
 muscles that should be advanced or shortened for a plus 
 cyclotropia should be cut for a minus cyclotropia. The 
 same holds true also as to operations that might be indi- 
 cated on the lateral recti, when errors of these mus- 
 cles complicate minus cyclotropia. The superior oblique 
 has probably never been divided, nor should this be done, 
 for a minus cyclotropia. 
 
 In the discussion of the treatment of the various forms 
 of heterotropia, much has been taught in this chapter 
 that cannot be appreciated by the reader who is not 
 well grounded in the principles set forth in Chapter I. 
 In this department of ophthalmology theory directs 
 practice and practice sustains theory. Every operation 
 on the extrinsic ocular muscles should be done with the 
 view of enabling the superior and inferior recti to plane 
 the visual axes, the interni and externi to so control 
 these axes in this plane as to make them intersect at the 
 point of view, and the obliques to parallel the vertical 
 axes of the eyes with the median plane of the head. In 
 accomplishing these aims, operations should be so done 
 as not to reduce below the normal the duction and ver- 
 sion power of a single muscle.
 
 CHAPTER XL 
 
 PARALYSIS AND PARESIS OF THE OCULAR 
 
 MUSCLES. 
 
 A BRIEF review of the nerve supply is essential to a 
 clear understanding- of paralysis or paresis affecting- one 
 or more of the ocular muscles. 
 
 THE THIRD NERVE (mortor oculi). This nerve sends 
 fibers to the superior, inferior, and internal straight mus- 
 cles, and to the inferior oblique; it also supplies the 
 muscle that elevates the upper lid; and throug-h the 
 medium of the ciliary g-ang-lion it sends fibers to the 
 sphincter of the iris and to the ciliary muscle. Its 
 nucleus of origin is in the posterior part of the floor of 
 the third ventricle, and in the floor of the aqueduct of 
 Sylvius. There is a nucleolus of origin for those fibers 
 of this nerve that finally must terminate in the indi- 
 vidual muscle to be controlled by it. Of these nucleoli 
 the most anterior one is connected with the sphincter of 
 the iris; the one nearest it is connected with the ciliary 
 muscle; and the next one, in order, is connected with 
 the internal rectus. The order of the nucleoli that are 
 
 (5951
 
 596 PARALYSIS AND PARESIS 
 
 connected with the other muscles supplied by the third 
 nerve is not so well understood. Some optic nerve 
 fibers these doubtless come from the macula are con- 
 nected with the nucleus of origin of the oculo-mortor 
 nerve, and thus is established the reflex relationship 
 between the retina and the muscles supplied by the 
 third nerve. From each of these nucleoli, fibers go, 
 through the internal capsule, to higher brain-centers, 
 and are there connected with fibers from nucleoli in the 
 nucleus of origin of the other nerve of the pair. 
 
 To illustrate: The first conjugate brain-center the 
 one that causes both superior recti to rotate the eyes 
 up must have connected with it fibers that come from 
 the nucleolus on the right side, which is connected with 
 the right superior rectus, and the nucleolus on the left 
 side, which is connected with the left superior rectus; 
 likewise the nucleoli the one on the one side of the 
 brain; the other, on the other side connected with 
 their respective internal recti, must each send fibers to 
 the third conjugate brain center (the center of conver- 
 gence). Thus the connection of all the conjugate brain- 
 centers with corresponding nucleoli at the base of the 
 brain might be traced. It appears evident that some 
 of these connecting fibers, on their way to the higher 
 centers the conjugate centers must cross from one 
 side of the brain to the other.
 
 OF THE OCULAR MUSCLES. 597 
 
 THE FOURTH NERVE. This supplies only one mus- 
 cle, the superior oblique. Its nucleus of origin is im- 
 mediately behind that of the third nerve. With this 
 nucleus there is connected, most likely, some optic nerve 
 fibers, to establish the reflex relationship between the 
 retina and the superior oblique. From these nuclei 
 the one on the one side of the brain; the other, on the 
 other side fibers must go to form a common connection 
 with the sixth conjugate brain-center; and from the 
 right nucleus, fibers must go to form a common connec- 
 tion, in the eighth conjugate brain-center, with fibers 
 from the nucleolus controlling the left inferior oblique; 
 likewise fibers must go from the nucleus for the fourth 
 nerve on the left side to connect, in the ninth conjugate 
 center, with fibers from the nucleolus on the right side 
 that controls the right inferior oblique. Again, it is 
 evident that, to reach these conjugate centers, some 
 fibers must cross from one side of the brain to the other. 
 
 THE SIXTH NERVE. This supplies only one muscle, 
 the external rectus of the corresponding side. This 
 nucleus is behind that of the fourth nerve, and is sepa- 
 rated from it by the nucleus of origin of the fifth nerve. 
 Fibers from the nucleus controlling the right externus 
 must go to the fourth conjugate brain-center, to connect 
 with fibers from the nucleolus that controls the left in- 
 ternus; and, in like manner, fibers from the nucleus that
 
 598 PARALYSIS AND PARESIS 
 
 controls the left externus must connect, in the fifth con- 
 jugate brain-center, with fibers from the nucleolus that 
 controls the right internus. Again, it appears that some 
 fibers must cross from one side of the brain to the other, 
 that these connections ma}* be formed. It is reasonable 
 to suppose that some optic nerve fibers are also con- 
 nected with the nucleus of the sixth nerve, to establish 
 the reflex relationship between the retina and the ex- 
 ternus. 
 
 CAUSES. Paralytic or paretic heterotropia may be 
 caused by disease or injury of the muscle, or muscles, 
 affected; by disease or injury involving the nerve trunk; 
 by disease of the nucleus at the base of the brain; by dis- 
 ease in the internal capsule or corona radiata; and by dis- 
 ease or injury of a conjugate brain-center in the cortex. 
 
 Occasionally children are born with paralysis of one 
 or more ocular muscles. 
 
 The disease that most often causes paralysis or pare- 
 sis of the ocular muscles is syphilis. The muscles most 
 frequent!}* involved, when syphilis is the cause, are those 
 supplied by the third nerve; but the superior oblique 
 and the external rectus may suffer from the same cause. 
 The history of the case will show whether syphilis is 
 the probable cause. Ocular paralysis is one of the re- 
 mote results of syphilitic infection. 
 
 Rheumatism affecting the muscle itself or involving
 
 OF THE OCULAR MUSCLES. 599 
 
 the nerve in its course is not infrequently the cause of 
 ocular paralysis or paresis. The external rectus is the 
 muscle that most frequently suffers from this cause. 
 
 A cold contracted from undue exposure to dampness, 
 to a draught, or any other causative agent, may cause, 
 in some inexplicable way, paresis or even paralysis of 
 any one of the ocular muscles. 
 
 Tumor, or other disease of the internal capsule and 
 the corona radiata, will cause paralysis of conjugate 
 'movements, but not paralysis of the muscles ; duction 
 power, which is reflex in character, will not be involved, 
 but the verting power, which is volitional, will be im- 
 paired or lost. In such cases, symptoms referable to 
 other parts are always associated with the eye symp- 
 toms. 
 
 Injury or disease of the cortex, involving an}- one of 
 the nine conjugate centers, will result in paralysis or 
 paresis of one muscle connected with each eye; but the 
 paralysis will show itself in the absence of verting 
 power, with no loss of duction power. To illustrate: If 
 the third conjugate center alone is involved, there can 
 be no convergence, but because of freedom from disease 
 of the fourth and fifth conjugate centers the two eves 
 can be made to turn harmoniously to the right or to the 
 left; and adduction, which is reflex, will be unimpaired. 
 
 Disease or injury of the orbit involving tbe parts
 
 600 PARALYSIS AND PARESIS 
 
 around the sphenoidal fissure, disease in the orbital 
 cavity behind the eye, and disease or injury of the mus- 
 cles themselves, can cause paralysis of any one or sev- 
 eral of the orbital muscles. 
 
 INDIVIDUAL FORMS OF PARALYSIS. 
 
 (1) THE THIRD NERVE. If the cause is in the nu- 
 cleus or in the course of the nerve before it divides into 
 its several branches, the following- conditions will be 
 present: () Ptosis; (b) the eye will be turned out more 
 or less by the unopposed externus, and it cannot be 
 rotated in; (c) the eye will be turned slightly down and 
 will be torted in by the unopposed superior oblique; the 
 eye cannot be turned upward, for both elevators the 
 superior rectus and the inferior oblique are involved, 
 and it can be turned downward only slightly by the 
 superior oblique, for the chief depressor the inferior 
 rectus is powerless; (d) the pupil will be dilated and 
 the accommodation will be suspended. There will be 
 neither headache, nausea, nor dizziness; for the fallen 
 lid cuts off the light from the eye, and the brain-cen- 
 ters the fusional centers are not excited. 
 
 If the disease involves only one branch after it leaves 
 the main nerve, only one muscle will be affected. If the 
 diseased branch is the one supplying the muscle that 
 elevates the upper lid, the only symptom will be ptosis.
 
 OF THE OCULAR MUSCLES. 601 
 
 If the involved branch is the one supplying 1 the internus, 
 both adduction and adversion \vill be impaired or abol- 
 ished, the eye being- turned out; and because of the ab- 
 sence of ptosis there will be crossed diplopia, associated 
 with headache, nausea, and dizziness, due to excitation of 
 brain-centers. If the affected branch is the one supply- 
 ing- the inferior rectus, sub-duction will be impaired or 
 absent, and sub-version by the superior oblique will be 
 only slig-ht; and, for the same reason g-iven above, there 
 will be diplopia in the lower field, headache, nausea, and 
 dizziness. If the involved branch is the one supplying- 
 the superior rectus, superduction will be impaired or 
 lost, and superversion by the inferior oblique will be only 
 slig-ht; and there would be diplopia in the upper field, 
 headache, nausea, and dizziness. If the branch affected 
 is the one supplying 1 the inferior oblique, superduction 
 (by the superior rectus) will probably be unimpaired, 
 and superversion will be only slightly lessened; and there 
 will be diplopia in the upper field, headache, nausea, 
 and dizziness on attempting- to look up, as would be 
 true, also, when the superior rectus is paretic. The 
 symptoms caused by paresis of the inferior rectus (and 
 by paresis of the superior oblique, as will be shown later) 
 are always more pronounced, for the reason that we look 
 down more than we look up. If the branch implicated is 
 the one going to the ciliary g-ang-lion, thence to the
 
 602 PARALYSIS AND PARESIS 
 
 ciliary muscle and the sphincter of the iris, there will 
 be complete loss of accommodation and full dilatation of 
 the pupil ; but if the ciliary ganglion itself is the involved 
 part, there will be complete loss of accommodation, but 
 the pupil will not be fully dilated. Both the sphincter of 
 the iris and the dilator fibers will be paralyzed, hence 
 partial dilatation, but complete inactivity of the pupil. 
 The symptoms will be: Dread of light, inability to see 
 near objects well, and pain referable to the eye. 
 
 (2) THE FOURTH NERVE. Since this nerve supplies 
 only the superior oblique, the symptoms are the same, 
 whether the disease is at the nucleus of origin, or in 
 the course, of the nerve. The eye is torted out by the 
 unopposed inferior oblique ; sub-version is limited, but 
 sub-duction is probably not much impaired. There is 
 always diplopia in the lower field. Nausea, vomiting, 
 dizziness, and headache are nearly always pronounced. 
 
 (3) THE SIXTH NERVE. Since this nerve supplies 
 only the external rectus, the symptoms are alwa} T s the 
 same, whether it is diseased at its nucleus or in its 
 course. The eye will be turned in, and both abduction 
 and ab version will be abolished. There will be homony- 
 mous diplopia. There being no ptosis to cut off light 
 from the affected eye, the cortical centers will become 
 excited, and there will be headache, nausea, and dizziness 
 when attempting to look toward the corresponding side.
 
 OP THE OCULAR MUSCLES. 603 
 
 It is only when there is extensive disease at the base 
 of the brain, or disease involving- all the structures in 
 the sphenoidal fissure, or extensive disease in the orbit 
 itself, that paralysis of all the muscles of one eye is 
 possible. The symptoms of such a condition \vould be 
 immobility of the eye in any direction; protrusion of the 
 eye, even when the disease causing* it is not in the orbit, 
 for there would be relaxation of all the external muscles; 
 diplopia would be pronounced in all directions (unless 
 the optic nerve has been involved in the disease process 
 within the cranium), were it .not for the fact that the 
 upper lid usually falls far enough down to cover the 
 pupil; the ptosis would be complete, were it not modified 
 by the protrusion of the globe; and, finally, the accom- 
 modation would be suspended and the pupil dilated. An 
 ophthalmoplegia externa, without associated parah r sis of 
 the ciliary muscle and sphincter of the iris, is incon- 
 ceivable, and that, too, whether the disease causing it is 
 intracranial or intraorbital. On the contrary, paralysis 
 of the muscles within the eye may be unassociated with 
 paralysis of the external muscles. 
 
 DIAGNOSIS. There can never be any doubt as to what 
 rectus muscle is involved when the paralysis is complete; 
 but when there is paresis, it is often a difficult matter 
 to determine to which eye the affected muscle belongs 
 and what muscle is involved, for in some of these cases
 
 604 PARALYSIS AND PARESIS 
 
 there is no perceptible squint, and apparently no limita- 
 tion of movement. The unfailing- test for paresis and 
 (were it necessary) for paralysis is the diplopia test. 
 This test will always be responded to in the direction of 
 action of the affected muscle, and it invariably deter- 
 mines the eye to which the affected muscle belongs 
 and unerringly points to the paretic muscle. For the 
 laterally acting- muscles the following- rule may be formu- 
 lated: The candle will appear sing-le in the left field if 
 the affected muscle is a right vertor, but will be doubled 
 in the right field, and vice versa if the affected muscle 
 is a left vertor; the eye to 'which the affected muscle be- 
 longs will see the candle that is farthest removed {the 
 false candle}, and the affected muscle is on that side of 
 this eye corresponding" to the direction of doubling-. If 
 the doubling is to the right, the paretic muscle is a right 
 vertor, and is, therefore, either the right externus or the 
 left internus. If the right eye sees the candle farthest 
 removed, it is the right externus; but if the left eye 
 sees the false light, it is the left internus. Nothing 
 could be more easily accomplished than the complete 
 diagnosis of paresis of a right vertor or a left vertor. 
 
 Although there are two sub-vertors and two super- 
 vertors for each eye, the determination of the question, 
 "To which eye belongs the paretic muscle?" is as easy 
 as can be; and the difficulty in the way of finding the
 
 OF THE OCULAR MUSCLES. 605 
 
 involved muscle is only apparent. If the affected mus- 
 cle is a sub-vertor, the candle will appear single above, 
 but double below, the horizontal plane, and vice versa 
 if the affected muscle is a supervertor. The following 
 is the rule for finding- the eye to which the affected 
 muscle belongs and for locating 1 the paretic muscle: The 
 eye to "which the paretic sub-vertor or supervertor be- 
 longs sees the candle that is farthest removed (cither 
 above or belovS) from the horizontal plane, and the 
 direction of the leaning' of the false candle determines 
 "whether it is a straig-ht or an oblique muscle that is 
 involved. If the doubling- is below the horizontal 
 plane and the false candle leans toward the same side, 
 the inferior rectus is the paretic muscle; if it leans 
 toward the opposite side, the superior oblique is the 
 paretic muscle; but if the doubling is above the hori- 
 zontal 'plane and the false candle leans toward the 
 corresponding- side, the inferior oblique is paretic; if it 
 leans toward the opposite side, the superior rectus is 
 paretic. 
 
 The accompanying- cuts illustrate perfectly the rules 
 g-iven above. In the cuts illustrating- paresis and paraly- 
 sis of the right and left vertors, the doubling- is repre- 
 sented as existing" when the vertical plane has been 
 reached, the distance between the false and the true 
 candles increasing as the candle is carried farther in the
 
 606 
 
 PARALYSIS AND PARESIS 
 
 direction of action of the affected muscle. This is always 
 true in paralysis, but in paresis the doubling' may not 
 occur, in passing- from the field of fusion into the field of 
 diplopia, until the vertical plane has been passed. Like- 
 wise, in the cuts representing paralysis and paresis of 
 the sub-vertors and supervertors, the doubling- is repre- 
 sented as having- occurred before reaching- the horizontal 
 plane, in passing- from the fusion field into the field of 
 diplopia. 
 
 a -f 
 
 A -A 
 
 
 
 Fig- 79- 
 
 Fig-. 79 illustrates paralysis or paresis of a right 
 vertor, either the rig-ht externus or the left internus. 
 If the rig-ht eye sees candle b, the affected muscle is 
 the right externus; but if the left eye sees candle b, the 
 affected muscle is the left internus. A red glass before 
 either eye shows quickly which eye it is that sees the 
 false candle; covering either eye with a card will also 
 show which eye it is that sees candle b. 
 
 The false candle may be above or below the true, or 
 of the same height as shown in the cut, depending on 
 the state of imbalance or balance of the vertically acting
 
 OF THE OCULAR MUSCLES. 607 
 
 muscles. A leaning of the false candle will appear 
 whenever there is a cyclophoria. 
 
 Fig. 80 illustrates paralysis or paresis of a left vertor, 
 either the left externus or the right internus. If the left 
 eye sees candle b, the affected muscle is the left externus; 
 but if the right eye sees candle b, it is the right internus. 
 
 The false candle in paralysis of a right or a left 
 vertor is not always parallel with the true candle. 
 When this is true, the direct antagonist of the paralyzed 
 
 
 
 Fig. 80. 
 
 muscle has not an ideal attachment to the globe; its at- 
 tachment is either too high or too low. When the healthy 
 muscle is an internus, if the false candle leans toward 
 the side of the affected eye, its attachment is too high, 
 or there is minus cyclophoria ; but if the false candle 
 leans toward the opposite side, its attachment is too low, 
 or there is a plus cyclophoria. Just the opposite is true 
 when the healthy muscle is an externus. 
 
 The false candle may be higher or lower than, or 
 even with, the true, depending on the state of imbalance 
 or balance of the vertically acting muscles.
 
 608 
 
 PARALYSIS AND PARESIS 
 
 # 
 
 Fig. 81. 
 
 Fig. 81 and Fig. 82 illustrate paralysis 
 of a sub-vertor muscle of either one eye or 
 the other. Below, in parallel columns, 
 will be shown the significance of each cut. 
 Inclination toward the opposite side points 
 to the superior oblique, while inclination 
 toward the same side points to the inferior 
 rectus: 
 
 Fig. 82 is illus- 
 trative of paralysis 
 of either the supe- 
 rior oblique or the 
 inferior rectus of 
 the eye that sees 
 
 Fig. 81 is illus- 
 trative of paralysis 
 of either the supe- 
 rior oblique or the 
 inferior rectus of 
 the eye that sees 
 candle b. If the 
 right eye sees it, 
 the affected muscle 
 is the inferior rec- 
 tus; but if the left 
 eye sees it, the af- 
 fected muscle is the supe- 
 rior oblique. 
 
 candle b. If the 
 right eye sees it, 
 the affected muscle 
 is the superior ob- 
 lique; but if the 
 left eye sees it, the 
 affected muscle is 
 ferior rectus. 
 
 
 
 D 
 
 * 
 
 ^ 
 r 
 
 * 
 
 Fig. 82. 
 
 the in- 
 
 In either case the false candle may be to the right or 
 left of the true, depending on the relationship between 
 the lateral recti muscles.
 
 OF THE OCULAR MUSCLES. 
 
 609 
 
 4 
 
 Fig. 83 and Fig. 84 illustrate paralysis 
 of a supervertor muscle of either one eye 
 > \ or the other. Below, in parallel columns, / 
 \J will be shown the significance of each cut. ;[J 
 & Inclination toward the opposite side points 
 to the superior rectus, while inclination to- 
 ward the same side points to the inferior 
 
 oblique: 
 
 Fig. 83 is illus- 
 trative of paralysis 
 of either the supe- 
 rior rectus or the 
 inferior oblique of 
 the eye that sees 
 candle b. If the 
 right eye sees it, 
 the affected mus- 
 cle is the superior 
 rectus; but if the 
 Fig - 83 ' left eye sees it, the 
 affected muscle is the in- 
 ferior oblique. 
 
 Fig. 84 is illus- 
 trative of paralysis 
 of either the supe- 
 rior rectus or the 
 inferior oblique of 
 the eye that sees 
 candle b. If the 
 right eye sees it, 
 the affected mus- 
 cle is the inferior 
 oblique; but if the 
 left eye sees it, the 
 affected muscle is the su- 
 perior rectus. 
 
 Fig. 84. 
 
 As in paresis or paralysis of the sub-vertors, the false 
 candle may be to the right or left of the true, depending 
 on the relative strength of the laterally acting muscles.
 
 610 PARALYSIS AND PARESIS 
 
 In making a diagnosis of paralysis or paresis of the 
 ocular muscles, by means of the diplopia test, the candle 
 need be carried only in the four cardinal directions that 
 is, the head should be erect; and in testing- for paresis of 
 the right and left vertors, the candle should be carried 
 only along the extended horizontal plane of the head di- 
 rectly to the right and left of the vertical plane; and in 
 testing for paresis of the sub-vertors and supervertors, 
 the candle should be carried only in the extended median 
 plane of the head, above and below the horizontal plane. 
 
 For detecting paralysis or paresis of the sub-vertors 
 and supervertors, nothing serves better than a horizontal 
 line at a distance of twenty feet. If the sub-vertors are 
 at fault, elevating the head, while still looking at the 
 line, will cause it to double, the false line appearing be- 
 low the true. If the false line leans toward the corre- 
 sponding side, the affected muscle is the inferior rectus; 
 but if it leans toward the opposite side, the affected mus- 
 cle is the superior oblique. 
 
 When a right vertor or a left vertor is paralyzed, the 
 resulting deviation might be mistaken for comitant lat- 
 eral heterotropia. This may be avoided in two ways 
 first, by a test of the verting power, when the affected 
 eye will always lag behind its fellow if the two eyes are 
 turned in the direction of action of the paretic muscle, 
 whereas, in comitant squint, the deviating eye moves
 
 OF THE OCULAR MUSCLES. 611 
 
 always through as great an arc as the fixing- eye; sec- 
 ondly, by covering 1 the eyes alternately, the secondary 
 deviation will always be greater than the primary, when 
 there is paralysis. But in comitant squint the secondary 
 and the primary deviations are always the same. 
 
 In paralytic squint there is always diplopia in one 
 part of the field, with binocular sing-le vision in the op- 
 posite part; while in comitant squint there is no diplo- 
 pia in any part of the field. 
 
 A very good diagnostic feature is the pose of the head 
 in cases of paralysis of an orbital muscle. In paralysis 
 of a lateral rectus muscle, the face is always turned in 
 the direction of action of the affected muscle that is, 
 if a left vertor is paralyzed, the face will be turned to 
 the left in the interest of binocular single vision, and 
 vice versa if a right vertor is paralyzed; if a sub-vertor 
 is paralyzed, the face will be depressed; and if a super- 
 vertor is paralyzed, the face will be elevated. 
 
 In "paralysis of motion, rather than of muscle," duc- 
 tion power, which is reflex in the sense that it is not vo- 
 litional, is not involved. This statement covers all the 
 conjugate brain-centers from the first to the fifth, inclu- 
 sive those centers that are concerned with the recti 
 muscles. Since there is no voluntary action of the ob- 
 liques, the cortical centers (if there be such) governing 
 them must act independently of the will. These centers
 
 612 PARALYSIS AND PARESIS 
 
 are the sixth, seventh, eighth, and ninth. That these 
 conjugate centers for the obliques may be involved in 
 pathologic changes must be conceded Since the object of 
 the sixth and seventh centers is to prevent diplopia, on 
 looking down and up, respectively, these correspond per- 
 fectly in action with the reflex centers of the recti that 
 are also concerned with the prevention of diplopia when 
 images are displaced by prisms; therefore they ought not 
 to be affected in disease of the cortex. The eighth and 
 ninth centers are not concerned with the prevention of 
 diplopia; but, what is probably of as much importance, 
 they are concerned with the steadying of all objects in 
 the field of vision whenever the eyes are voluntarily 
 moved in an oblique direction. For instance, when the 
 gaze is directed up and to the right, or down and to 
 the left, the eyes would be torted to the right, were it 
 not for the eighth conjugate center, when all objects 
 would be made to appear to incline to the left from their 
 real position, their inclination corresponding precisely 
 with the degree of torsioning. This is prevented by 
 the eighth conjugate center, which maintains the paral- 
 lelism between the vertical axes of the eyes and the me- 
 dian plane of the head in such a voluntary rotation. It 
 appears, therefore, that disease of this center would be 
 attended by a wheel-like movement of objects whenever 
 the visual axes are made to move up and to the right, or
 
 OF THE OCULAR MUSCLES. 613 
 
 down and to the left, which appearance would not be if 
 the gaze were directed up and to the left, or down and 
 to the right. But if the ninth conjugate center were in- 
 volved in pathologic change, the wheel-like movement of 
 objects would be observed only when the gaze is up and 
 to the left, or down and to the right. In neither case 
 would there be diplopia. 
 
 Should the sixth conjugate center be involved, on look- 
 ing down at a candle it would appear double, the one 
 seen by the right eye leaning to the left and the one seen 
 by the left eye leaning to the right; the diplopia would 
 be attended by dizziness and nausea. In the upper field 
 there would be no diplopia. 
 
 Should the seventh conjugate center become diseased, 
 the diplopia would be in the upper field, and the candle 
 seen by the right eye would lean to the right, and the 
 one seen by the left eye would incline to the left. It ap- 
 pears that each oblique muscle is connected by individual 
 nerve fibers with three centers one center, basal; the 
 two others, probably cortical. The former center has 
 connected with it fibers from only one muscle, but each 
 of the latter has connected with it fibers from two ob- 
 lique muscles, one of these belonging to one eye and the 
 other to the other eye; and, therefore, they are conjugate 
 centers. All the fibers from these three centers come 
 together and form the trunk of the nerve, a disease of
 
 614 PARALYSIS AND PARESIS 
 
 which suspends the independent and conjugate action of 
 the muscle supplied by it; and the muscles of the fellow 
 eye are not involved. The right superior oblique is con- 
 nected with the sixth conjugate center, as is also the left 
 superior oblique; the right superior oblique is also con- 
 nected with the eighth conjugate center, as is also the 
 left inferior oblique. Disease of the sixth center, as al- 
 ready shown, gives trouble only when looking directly 
 down; disease of the eighth center causes trouble, as 
 shown above, only when looking up and to the right, or 
 down and to the left. Disease of these two conjugate 
 centers would have no influence over the basal center 
 that gives duction or fusion power to either of the two 
 muscles mentioned that power that is exercised when 
 images are displaced by oblique astigmatism, natural or 
 artificial. 
 
 Each internus muscle is also connected with three cen- 
 ters one center, basal; the two others, cortical. The for- 
 mer is reflex; the latter, volitional. To illustrate: The 
 right internus has its reflex center the center giving it 
 duction or fusion power in the nucleus of the mortor 
 oculi; it is also connected with the third conjugate brain- 
 center, as is also the left internus; it is also connected 
 with the fifth conjugate center, as is also the left exter- 
 nus. All the fibers from these three centers for the right 
 internus form the bundle that constitutes the branch of
 
 OF THE OCULAR MUSCLES. 615 
 
 the third nerve, supplying it with its threefold power. 
 Disease of this branch suspends both the reflex (fusion) 
 and voluntary power of this muscle; it can neither ad- 
 duct, converge, nor advert the eye to which it belongs. 
 Disease of the third conjugate center involves only those 
 fibers that convey to the muscle the convergence impulse; 
 disease of the fifth conjugate center involves only those 
 fibers that convey the adversion impulse; likewise dis- 
 ease of the reflex nucleolus involves only those fibers 
 that convey the fusion impulse. Disease of the third 
 conjugate center would suspend, of course, the conver- 
 ging power of the left internus also; while disease of the 
 fifth conjugate center would affect the abverting power 
 of the left externus as well as the adverting power of 
 the right internus. Thus each muscle, with its several 
 centers, might be studied. 
 
 It only remains to speak of the symptoms that would 
 present themselves, should any one of the five conjugate 
 centers, controlling the recti, become diseased: 
 
 (1) Disease of the first conjugate center: inability to 
 
 supervert the eyes, but no diplopia. 
 
 (2) Disease of the second conjugate center: inability to 
 
 sub-vert the eyes, but no diplopia. 
 
 (3) Disease of the third conjugate center: inability to 
 
 converge the eyes, with diplopia in the near.
 
 616 PARALYSIS AND PARESIS 
 
 (4) Disease of the fourth conjugate center: inability to 
 
 rotate the eyes to the right, either cardinally or 
 obliquely, but no diplopia. 
 
 (5) Disease of the fifth conjugate center: inability to 
 
 rotate the eyes to the left, either cardinally or 
 obliquely, but no diplopia. 
 
 TREATMENT. 
 
 In any form of paralysis of muscle that is, when the 
 disease causing it is below the internal capsule the 
 diplopia should be prevented by covering the affected 
 eye, which will relieve all nervous symptoms, such as 
 headache, dizziness, and nausea. The affected eye 
 should be kept under cover until the disease has been 
 cured. In paralysis of the third nerve, nature supplies 
 the cover in the production of ptosis, and usually the 
 last muscle, supplied by the third nerve, to regain its 
 power is the elevator of the upper lid. If any case is 
 clearly rheumatic, it should be treated with large doses 
 of the salicylate of sodium or other anti-rheumatic rem- 
 edy; if the cause is syphilis, iodide of potassium in in- 
 creasingly large doses should be given after meals; if 
 the cause is not known, the case should be treated with 
 the iodide of potassium. Early in any case the admin- 
 istration of the fluid extract of jaborandi, in doses of 
 twenty drops at 9 A.M., 3 P.M., and 9 P.M., by pro-
 
 OF THE OCULAR MUSCLES. 617 
 
 moting absorption of effused serum, will greatly aid the 
 iodides in the work of hastening- the absorption of plas- 
 tic effusion. Bichloride of mercury in small doses may 
 also be given. 
 
 The above remedies should be continued until the 
 diplopia has entirely disappeared. This much having 
 been accomplished, the sulphate of strychnia in doses of 
 iro to 53 of a grain should be g-iven before each meal. At 
 this stag-e the interrupted current of electricity, used 
 once daily for ten minutes, will do g-ood. While there is 
 still diplopia, the strychnia and electricity would do 
 harm, rather than g-ood. 
 
 In old cases of ocular paralysis, when there can be no 
 long-er any hope of restoration of power to the paralyzed 
 muscle, surgery will do good, in that it will lessen the 
 field of diplopia and give to the patient a more natural 
 pose of the head. The operation should be either an 
 extensive shortening or advancement of the paralyzed 
 muscle, and never even a partial tenotomy of the antag- 
 onist. The muscle plane should be changed or not, 
 when making the shortening or advancement, as may be 
 indicated by the existence or non-existence of torsion.
 
 618 PARALYSIS AND PARESIS 
 
 LAGOPHTHALMOS. 
 
 The condition termed " lagophthalmos " was so named 
 because it gave to the human eye the appearance of the 
 eye of the hare always open, asleep or awake. The 
 cause of the condition is disease of the seventh nerve in 
 its course; or at its basal or cortical centers, or between 
 these two in the internal capsule or in the corona 
 striata. In either case there is a greater or less loss of 
 power on the part of the corresponding- orbicularis, and 
 usually the muscles of the face are also involved. The 
 location of the disease or injury determines the array of 
 symptoms to be presented in any case. 
 
 When the part involved is the basal center of the nerve, 
 or the body of the nerve as it finds its way out to be 
 finally distributed to all the muscles of the face, includ- 
 ing 1 the orbicularis of the corresponding" side, all these 
 muscles will be paralyzed, and the log^aphthalmos will 
 be only one of the symptoms. The skin of the forehead 
 on the affected side is smooth, as if "ironed out," and 
 the patient is wholly unable to throw it into wrinkles 
 for the reason that this half of the anterior part of the 
 occipito-frontalis is supplied by the diseased nerve; the 
 corrug^ator supercilii must also be inactive, therefore 
 the brow on that side cannot be drawn down; the vari- 
 ous muscles connected with the nose and mouth, action 
 of which gx>es so far to give agreeableness of expression to
 
 OF THE OCULAR MUSCLES. 619 
 
 the face, cannot receive a nerve impulse, therefore they 
 must be inactive, and the face, on that side, becomes 
 expressionless; the buccinator, which is also supplied by 
 the seventh nerve, loses its power and thus the mastica- 
 tion of food on that side becomes inconvenient almost 
 impossible for the reason that, when the tongue 
 presses the food between the teeth, the buccinator being 
 unable to make counter pressure, the food cannot be 
 kept between the grinders. Soon the patient learns to 
 do all his chewing on the unaffected side. The mouth 
 is always drawn toward the unaffected side, and a 
 laugh will be confined wholly to this side. The patient 
 drinks with difficulty and cannot whistle. All of these 
 symptoms will be associated with the inability to close 
 the eye. 
 
 Both parts the voluntary and the involuntary of 
 the orbicularis being involved, the eye will be wide open, 
 and there will be no power to close it. Any great effort 
 to close it will only cause the eye to move upward, as if 
 to hide behind the upraised lid. The lower lid will not 
 be held in contact with the globe, hence the punctum 
 will be displaced. The absence of the batting power 
 makes it impossible for the punctum of the upper lid to 
 carry off the tears; hence there must be an excess of 
 tears in the conjunctival sac. The unprotected eye 
 becomes irritable, as shown by conjunctival redness, ex-
 
 620 PARALYSIS AND PARESIS 
 
 cessive secretion of tears, and some dread of light. If 
 the eye is exposed too long and too severely, the cornea 
 may ulcerate, when the eye, of course, becomes painful. 
 By far the most common cause of lagophthalmos, as- 
 sociated with the other symptoms already described, is 
 inflammation of the middle ear, and the reason is not 
 hard to find. The seventh nerve, as it passes through 
 the aqueduct of Fallopius, in the inner bony wall of the 
 drum cavity, should be completely covered in by bone 
 structure. That this bone-covering is complete, in 
 many cases, is made evident by the fact that otitis media 
 is not attended by involvement of the seventh nerve ; 
 that it is incomplete, in some cases, is made equally evi- 
 dent because of the fact that in some cases even a very 
 slight otitis media is attended by paralysis of all the 
 muscles of the face. Whenever there is a break in the 
 bony covering, the mucous membrane lining the inner 
 wall of the drum cavity must lie directly in contact with 
 the sheath of the seventh nerve, hence the readiness 
 with which an inflammation of this membrane may in- 
 volve the -nerve. Catarrhal, as well as suppurative, 
 inflammation of the middle ear, in such cases, almost 
 always causes facial paralysis. When such is the cause 
 of facial paralysis, the usual symptoms of inflammation 
 of the ear are present namely: pain, fullness, and deaf- 
 ness, with some fever. The objective symptoms are
 
 OF THE OCULAR MUSCLES. 621 
 
 also present. If the inflammation causing- the paralysis 
 is between the basal center of the seventh nerve and the 
 point where the eighth nerve parts company with the 
 facial nerve, to find its terminals in the internal ear, the 
 resulting pressure will cause deafness, as well as pa- 
 ralysis of the facial muscles; but other symptoms and 
 signs of otitis media will be absent. In the latter case 
 the paralysis of the orbicularis will be as complete as in 
 the former. If the inflammation or injury of the facial 
 nerve is at some point between where it leaves the aque- 
 duct of Pallopius and the point where it divides into its 
 several branches, the facial paralysis will be complete; 
 but the hearing will not be involved, nor will there be 
 any other symptoms referable to the ear. In all of 
 these conditions the batting- power is lost. 
 
 When. the cause of the lag-ophthalmos is in the cortex, 
 the lids are not so widely separated, and their batting- 
 power, thoug-h modified, is not lost. The other muscles 
 of the face may not be involved. If the disease in the 
 cortex, in the internal capsule, or in the corona radiata is 
 extensive, other symptoms will be found in association 
 with the lag-ophthalmos. Such cases are not so likely 
 to recover full voluntary power over the orbicularis. 
 
 TREATMENT. 
 
 Whatever may be the cause, the eye should be pro- 
 tected by a flap until such time as the lids may have
 
 622 PARALYSIS AND PARESIS. 
 
 recovered their power; otherwise, the cornea may ulcer- 
 ate. If otitis media is the cause, this condition should 
 be so treated as to prevent suppuration, if possible ; but 
 if suppuration occurs, the disease should be so treated 
 as to bring it, as speedily as possible, under control. 
 In all cases the iodide of potassium and the bichloride of 
 mercury should be administered for promoting- absorp- 
 tion of inflammatory deposits within the sheath of the 
 nerve. In this work these drug's can be greatly aided 
 by the fluid extract of jaborandi, in twenty-drop doses, 
 three times a day for the first two weeks. Strychnia 
 should be given only when a return of voluntary power 
 to the facial muscles shows that the pressure of inflam- 
 matory deposits has been relieved more or less com- 
 pletely. When the cause of lagophthalmos is above the 
 basal, or reflex, center, sorbefacient treatment is indi- 
 cated; but, as already stated, recovery is both slow and 
 doubtful o
 
 CHAPTER XII. 
 
 MUSCLES OF THE IRIS AND OF THE 
 CILIARY BODY. 
 
 THE heading- of this chapter is intended to convey the 
 idea that the iris has more than one muscle-, and that in 
 the ciliary body there is more than one muscle. Both 
 anatomy and physiology g"ive evidence of the existence 
 of two muscles in the iris; anatomy shows two sets of 
 muscular fibers in the ciliary body, and there is also 
 physiologic evidence of the existence of two independent 
 muscles, each under a separate innervation. 
 
 MUSCLES OF THE IRIS. 
 
 At one time in the history of medicine it was taug-ht 
 that there was erectile tissue in the iris which, by be- 
 coming- filled with blood, would make the pupil small, 
 and, by ag-ain becoming- empty, would effect the dilatation 
 of the pupil. Other theories were offered from time to 
 time, accounting- for the chang-eableness of the pupil- 
 lary opening- in the iris, without taking- into account 
 the necessity for muscular contraction to effect these 
 
 (623)
 
 624 MUSCLES OF THE IRIS. 
 
 changes. As early as the tenth century an Arabian 
 physician announced his belief in the existence of mus- 
 cles in the iris, contractions of which varied the size of 
 the pupil, his only evidence being physiologic. In his 
 day theie were no means of investigation to determine 
 anatomically the existence of muscle structure so small. 
 Descartes, though neither an anatomist nor a physiolo- 
 gist, announced in one of his publications, in the seven- 
 teenth century, that muscles in the iris regulated the 
 pupillary opening. 
 
 The existence of radiating fibers was generally con- 
 ceded a long time before Berger announced, in 1701, 
 that orbicular fibers also existed in the iris. It was not 
 until 1812 that the microscope, under the eye of Mau- 
 noir, revealed the existence of circular fibers in the iris 
 of the bird. Prom that time to the present there has 
 been no one ready to deny the existence of the circular 
 muscle of the iris. The microscope has since demon- 
 strated the existence of the sphincter muscle of the iris 
 in man. It is known to be a circular muscle-band, about 
 one millimeter wide, at the pupillary margin of the iris 
 and nearer its posterior surface. 
 
 Radiating muscular fibers in the iris has been a mat- 
 ter of much discussion, but now the preponderance of 
 evidence is in favor of the existence of such fibers. 
 Grunhagen, Collins, and others have taught that there is
 
 MUSCLES OF THE IRIS. 625 
 
 elastic tissue in the iris that effects the dilatation of the 
 pupil whenever action of the sphincter is inhibited that 
 the dilatation is effected passively, and not actively. 
 Juler, at the eighth International Congress of Ophthal- 
 mology, in 1894, announced that, by a new method of 
 investigation, he had been able to show, under the 
 microscope, the radiating muscular structure of the iris. 
 This anatomic evidence, associated with the evidence 
 given by physiology, removes the question of the exist- 
 ence of a pupil-dilator muscle entirely from the domain 
 of doubt. Juler has demonstrated that the radiating 
 muscular fibers have their origin at the attached margin 
 of the iris, and pass to the pupillary margin, where they 
 become blended with the sphincter muscle. 
 
 Petit observed, in 1727, that a division of the cervical 
 sympathetic caused contraction of the pupil; and Biffi, 
 in 1846, showed that stimulation of the cervical sympa- 
 thetic effected dilatation of the pupil. By a similar 
 method of investigation, Mayo, in 1823, proved that the 
 sphincter muscle of the iris is supplied by the third 
 cranial nerve, a division of which dilates the pupil, 
 while stimulation of this nerve makes the pupil contract. 
 
 There is no room for doubting the existence of these 
 two muscles in the iris ; and that they are antagonistic 
 the one contracting the pupil, the other effecting its dila- 
 tation is as little open to doubt.
 
 626 MUSCLES OF THE IRIS. 
 
 Those fibers of the third nerve and of the cervical 
 sympathetic, that give power, respectively, to the pupil- 
 contractor muscle and the pupil-dilator muscle, pass 
 first to the ciliary ganglion, in which they are joined by 
 fibers from the fifth nerve. From this g-anglion the 
 several short ciliary nerves, each containing fibers from 
 the three different sources, make their way to the pos- 
 terior part of the eye, which they enter. They are 
 finally distributed to the ciliary body and the iris, giv- 
 ing sensation to these structures and power to their mus- 
 cular parts. 
 
 The function of the iris is to regulate the quantity of 
 light that enters the eye, and this it does reflexly. A 
 too-bright light makes it necessary for the pupil to be 
 made smaller, which is effected by an impulse sent from 
 the nucleolus of the third nerve-center that controls the 
 sphincter of the iris; a dim light takes the nucleolus of 
 the sphincter off its guard and allows the influence of 
 the cervical sympathetic on the radiating fibers of the 
 iris to effect the dilatation of the pupil. There should be 
 harmony in the antagonism of these two muscles, for 
 the purpose of properly regulating the quantity of the 
 light that enters the eye. The iris also serves to cut off 
 the peripheral rays of every cone of light, which enables 
 the refractive media to make a focus sharper than it 
 would be if spherical aberration were not thus prevented.
 
 MUSCLES OP THE IRIS. 627 
 
 In most cases the muscles of the iris do their work 
 well. There are cases, however, in which either the 
 sphincter muscle is too weak, because of poor develop- 
 ment or slight innervation, or the pupil-dilator muscle 
 is abnormally strong from hyper-development or over- 
 stimulation; as a result, the pupil is too large under 
 ordinary light and when shaded. Under the stimulus 
 of strong light it contracts; but if such exposure is pro- 
 longed, the contraction of the sphincter becomes painful. 
 Any one of several symptoms of eye-strain may be 
 caused by prolonged contraction of a weak sphincter of 
 the iris. Such patients cannot endure, with any com- 
 fort, prolonged exposure to bright light, whether nat- 
 ural or artificial. The author has observed a fairly 
 large number of such cases, and has had a fair degree of 
 success in managing them. A weak pupil-dilator mus- 
 cle is not likely to be the source of annoying symptoms. 
 A patient with weak pupil contractors should have these 
 muscles treated, regardless of what else must be done 
 for the relief of other conditions that may cause strain. 
 
 TREATMENT. 
 
 Patients with large pupils, who suffer when exposed 
 to bright light, may have their pupil contractors devel- 
 oped and strengthened by exercise. The method is as 
 follows : Before retiring at night, the patient should
 
 628 MUSCLES OF THE CILIARY BODY. 
 
 sit before a fairly bright lamp, holding- in one hand a 
 densely opaque cardboard which she should place be- 
 tween her and the light at regular intervals of two or three 
 seconds, looking all the time in the direction of the light. 
 Thus there would be alternate exposure of the eyes to 
 light and darkness, producing rhythmic contraction and 
 relaxation of the sphincter ol the iris. For this exercise 
 ten minutes will be sufficient; but should the e} T es be- 
 come fatigued, the exercise should cease sooner. The 
 exercise should be repeated every night for a long w r hile. 
 In the absence of the exercise treatment, the only 
 thing to be advised is the wearing of smoke lenses con- 
 stantly, or whenever the eyes are to be exposed to bright 
 light. These lenses allow the pupils to become more or 
 less enlarged, which means that the sphincters are 
 thereby rested. This method favors the muscle in its 
 weakness, and is not to be preferred to the exercise 
 treatment, for the latter means that the sphincter will 
 be made strong eventually. 
 
 MUSCLES OF THE CILIARY BODY. 
 
 It was not known until 1846 that there were any mus- 
 cular fibers in the ciliary body; but at this time Bowman 
 discovered, with the microscope, muscular fibers which 
 were parallel with the meridians of the eye, hence prop- 
 erly called them "meridional." These he considered as
 
 MUSCLES OF THE CILIARY BODY. 629 
 
 having" their origin in the anterior part of the ciliary 
 body and their insertion in the anterior part of the 
 choroid. He named this newly discovered muscle the 
 "tensor of the choroid," and in it he thought he had 
 found the secret of the power of accommodation. His 
 explanation was that this muscle, by making tense the 
 choroid, so compressed and changed the shape of the 
 vitreous as to force the lens forward, thereby increasing 
 the distance between the macula and the lens sufficiently, 
 he thought, to account for the phenomena of accommo- 
 dation. Before that time no theory of accommodation 
 had included the idea that there existed, in the ciliary 
 body, a muscle. So thoroughly satisfied was Bowman 
 that he did not pursue his investigations further, else he 
 would have discovered, also, the circular fibers which 
 were discovered later by H. Miiller. Long before the 
 discovery of either Bowman's muscle or Miiller's muscle 
 (that there are two muscles will be shown farther on), 
 Young had demonstrated an increase in the curvature of 
 the crystalline lens in the act of accommodation. Miil- 
 ler thought that, by contraction of the circular muscle 
 discovered by himself, direct pressure, by the ciliary 
 processes, on the periphery of the lens, caused the in- 
 crease in convexity; but Helmholtz had taught that the 
 increase in curvature was due to inherent elasticity of 
 the lens, which was allowed to manifest itself because of
 
 630 MUSCLES OF THE CILIARY BODY. 
 
 relaxation of the zonula, effected by the contraction of 
 Bowman's muscle. 
 
 It would seem that all authors are agreed that in the 
 ciliary body there are two sets of muscular fibers one 
 set running- parallel with the meridians, and another col- 
 lection of fibers forming a circle in the anterior part of 
 the ciliary body. There is universal agreement, also, 
 that one or the other of these muscles, or both, is the 
 active agent in accommodation. It is also universally 
 conceded that the accommodative muscle is supplied by 
 the third nerve. 
 
 The microscope has revealed the fact that there are 
 two muscles or, at least, two different arrangements of 
 muscular fibers in the ciliary body; the existence of two 
 independent muscles, each getting its nerve supply from 
 a separate source, appears to be shown by physiology. 
 Young, in 1801, demonstrated increased curvature of the 
 lens in accommodation; Helmholtz accounted for this in 
 relaxation of the zonula by a contraction of the muscle 
 of Bowman the so-called "tensor of the choroid " when 
 he could have accounted for it more easily in a contrac- 
 tion of the muscle of Miiller, which, by making more 
 narrow the zone between the ciliary processes and the 
 periphery of the lens, necessarily relaxed the suspensory 
 ligament of the lens, thus allowing the lens to manifest 
 its elasticity. By becoming' more convex, the lens would
 
 MUSCLES OF THE CILIARY BODY. 631 
 
 necessarily take up the laxness of the ligament. A fact 
 strongly favoring the idea that the muscle of accommo- 
 dation is Miiller's muscle is that Coccius has seen, in 
 eyes on which an iridectomy had been done, a narrowing 
 of the circumlental zone in the act of accommodation. 
 It is easier to understand how the circular muscle 
 (Miiller's) could relax the zonula, and thus enable the 
 lens to become more convex, than it is to understand how 
 Bowman's muscle could effect the same changes. In 
 fact, it would appear that, if Bowman's muscle is the 
 active agent in accommodation, the zonula would be 
 made more tense, and would, therefore, prevent the lens 
 from increasing in convexity; but, on the contrary, the 
 lens would be compressed toward its periphery. If 
 Bowman's muscle is the active agent in accommodation, 
 it is supplied by the third, or mortor oculi, nerve, and the 
 change of the lens would be more in position than in 
 curvature; the change in curvature would not be an in- 
 crease in spherical curvature, but it would be the forma- 
 tion of a lenticonus. There, then, could be no possible 
 use for the circular muscle of Miiller. If the Miiller 
 muscle is the active agent in accommodation, it is sup- 
 plied by the third, or mortor oculi, nerve, and the change 
 in the lens would not be in position, but wholly in curva- 
 ture; the change in curvature would be in an increase 
 of the sphericity of the lens a shortening of the radius
 
 632 MUSCLES OF THE CILIARY BODY. 
 
 of the anterior curve made possible by a narrowing of 
 the circumlental zone. If this is the work of the Miiller 
 muscle, there would still remain a work to be done by the 
 Bowman muscle, which will be set forth farther on. 
 
 The answer to the question, "Is the muscle of Bow- 
 man or the muscle of Muller the active agent in accom- 
 modation ? " must come from a study of the actual change 
 that occurs in the lens in the accommodative act. If 
 Bowman's muscle is the muscle of accommodation, 
 Tscherning's views as to the condition of the zonula and 
 the state of the lens in accommodation must be correct 
 that is, the zonula must be on the stretch, and the ante- 
 rior surface of the lens must assume the shape to which 
 he has given the name "lenticonus." If in accommoda- 
 tion the zonula is relaxed, a more rapid spherical curva- 
 ture of the lens is possible, and these changes can be ef- 
 fected only by the contraction of Miiller's muscle. Helm- 
 holtz would be correct, at least in part; he would be 
 wrong only in the thought that the narrowing of the 
 circumlental zone had been effected by Bowman's muscle. 
 
 Is the change in the lens the formation of a lenticonus, 
 according to Tscherning, or is it an increase in the 
 curvature of the anterior surface, according to Young, 
 Helmholtz, Bonders, and many others? One thing should 
 be conceded at the outset that is, there is in accommo- 
 dation a narrowing of the circumlental zone, the space
 
 MUSCLES OF THE CILIARY BODY. 633 
 
 between the ciliary processes and the periphery or equa- 
 tor of the lens. All writers agree that in the absence 
 of accommodation the two surfaces of the lens are spher- 
 ical. Now, suppose the eye of one individual to be em- 
 metropic, and the eye of another person to be hyperopic. 
 The emmetropic eye, without any accommodative effort, 
 has vision equal ^x, and that through a lens whose sur- 
 face must be conceded to be spherical. The person with 
 the hyperopic eye (say of 3. D), by the aid of his accom- 
 modative power, also has vision equal ||. Surfaces dif- 
 ferently curved cannot refract light in the same way. 
 If the emmetropic eye saw through a lens having a 
 spherically curved surface, the hyperopic eye, in the 
 act of accommodation for distant seeing, must have had 
 also a lens whose surface was spherically curved. If ac- 
 commodation of 3. D for distant seeing does not produce 
 a lenticonus, is it possible that accommodation of 3. D for 
 near seeing will do so? Again, suppose one person to be 
 emmetropic and sixty years old, but still possessing a 
 perfectly transparent lens; and suppose another person 
 emmetropic and sixteen years old. These two persons 
 will have equally good distant vision, without any accom- 
 modative effort on the part of either. At a distance of 
 thirteen inches the older person, not having any accom- 
 modative power, cannot see to read; while the younger 
 person, by the exercise of accommodation, sees every
 
 634 MUSCLES OP THE CILIARY BODY. 
 
 word and letter perfectly. On placing 1 a plus 3. D lens 
 before the eye of the older person, everything 1 on the 
 page becomes as clear and as distinct to him as it is to 
 the young-er person. The lens of the older person has 
 not lost its sphericity in changing* the point of view from 
 twenty feet to thirteen inches, for he has no accommoda- 
 tive power; but for him the plus 3. D spherical lens has 
 made divergent rays parallel, and these parallel rays are 
 easily and accurately focused on his retina by his own 
 spherically curved crystalline lens. If the two spher- 
 ically curved bodies the presbyopic lens and his crys- 
 talline lens have made the old man see perfectly, has it 
 been necessary for the surface of the crystalline lens in 
 the young 1 person to become changed to a lenticonus in 
 order that he might see distinctly at thirteen inches? 
 Either the surface of the crystalline lens in the young 
 person has not changed from a spherical curve, when 
 there was no accommodation, to a lenticonus, in accom- 
 modation, or a presbyopic lens should be a lenticonus, and 
 not spherical. In conclusion, this statement will be 
 made without fear of contradiction: Spherical refractive 
 surfaces, with the peripheral rays cut off by a perfo- 
 rated diaphragm, can reproduce perfectly, point for 
 point, an image of the object from which the rays of 
 light have come. 
 
 For the reasons given above, the logical conclusion is
 
 MUSCLES OF THE CILIARY BODY. 635 
 
 that in accommodation the zonula is relaxed by a nar- 
 rowing- of the circumlental zone, that this laxness is 
 taken up by an increase in the convexity of the elastic 
 crystalline lens, and that these changes can be effected 
 only by a contraction of Miiller's muscle. Since Miil- 
 ler's muscle is the active agent in accommodation, it is 
 supplied by the third nerve. 
 
 Since Tscherning published his views concerning- ac- 
 commodation, it has been demonstrated by Hess that the 
 zonula is relaxed in accommodation; and Priestly Smith 
 has claimed that it is possible for the anterior surface of 
 the lens to assume the lenticonus shape, in accommoda- 
 tion, when the zonula is relaxed. 
 
 As already stated, there is a use for the muscle of 
 Bowman, reg-ardless of the fact that it is not the active 
 agent in accommodation. There is a reason for believ- 
 ing- that this muscle, like the radiating- muscle of the 
 iris, is supplied by the cervical sympathetic, through the 
 medium of the ciliary ganglion. It is generally taught 
 that at least some of the meridional fibers extend from 
 the anterior part of the choroid through the ciliary bod}*, 
 terminating in the part occupied by the circular muscle 
 (Miiller's) in the region of the attachment of the zonula 
 to the ciliary processes. They pursue such a course and 
 are so related to the suspensory ligament that it appears 
 highly probable that it is through the active agency of
 
 636 MUSCLES OF THE CILIARY BODY. 
 
 these fibers (Bowman's muscle) that the crystalline lens 
 is made to assume a mathematically correct position in 
 its bed in the anterior part of the vitreous. This normal 
 and mathematically correct position the position that it 
 must occupy when there is no corneal astigmatism is 
 such that the antero-posterior axis shall coincide with 
 the visual axis, and that its equatorial plane shall be 
 parallel with the equator of the eye. In the process of 
 development the lens, in many instances, may passively 
 assume the proper position; and, if so, there would be 
 nothing" for Bowman's muscle to do; but in many in- 
 stances the passive position assumed by this lens in its 
 development would not be mathematically correct, hence 
 the need of some active agent for readjusting. This 
 agent could be, and doubtless is, Bowman's muscle, and 
 the medium through which this muscle could effect the 
 readjustment is the suspensory ligament the zonula. 
 The agent calling on Bowman's muscle to do this work 
 would be the guiding sensation of the retina, which is 
 the taskmaster of all the ocular muscles, intrinsic and 
 extrinsic. The time for effecting this readjustment 
 would be after birth, for before birth the guiding sensa- 
 tion must be dormant. The task of readjustment is, 
 doubtless, fully accomplished in infancy, or, at the latest, 
 early in childhood. It is not more wonderful that Bow- 
 man's muscle should be endowed with this unvolitional
 
 MUSCLES OF THE CILIARY BODY. 637 
 
 power than it is that Muller's muscle, likewise under 
 the control of the guiding sensation, should be endowed 
 with power to mathematically adjust vision for all dis- 
 tances. 
 
 If Bowman's muscle can readjust the lens in an eye 
 whose cornea is free from astigmatism, so that its posi- 
 tion shall be mathematically correct, is it not also pos- 
 sible that the same muscle may be the active agent in 
 producing a lenticular astigmatism at right angles to a 
 corneal astigmatism for the purpose of neutralizing it? 
 Suppose a case of corneal astigmatism of 2. D, with the 
 meridian of greatest curvature at one hundred and eighty 
 degrees; to correct this by a neutralizing lenticular astig- 
 matism, an impulse would have to be sent to a collection 
 of meridional fibers, either directly above or below the 
 lens, a contraction of which would tilt the lens on its hori- 
 zontal axis so as to increase the refractive power of its 
 vertical meridian to the extent of 2. D. Thus would the 
 corneal astigmatism be neutralized. It is well known 
 that the tilting of a lens increases its refractive power at 
 right angles to the axis of tilting. Tilting a lens forty- 
 five degrees practically doubles its strength at right an- 
 gles to the axis of rotation, without changing its power 
 in line with this axis; and in this way a spherical lens is 
 made to have an astigmatic effect. The strength of the 
 crystalline lens is so great that a very slight tilting
 
 638 MUSCLES OF THE CILIARY BODY. 
 
 would produce a considerable astigmatic effect. L/entic- 
 ular astigmatism cannot be effected by a contraction of 
 Miiller's muscle, but it can be easily effected by the ac- 
 tion of individual fibers cf Bowman's muscle. How the 
 guiding sensation can select and call into action a few 
 fibers of Bowman's muscle, yet allow all the balance 
 of this muscle to remain quiet, is not subject to expla- 
 nation. 
 
 The author does not have to suppose a case of corneal 
 astigmatism that, in some way or other, was neutralized 
 automatically, to a considerable extent, for many years. 
 His own corneal astigmatism is 2.50 D, and has been so 
 since 1889, when Swan M. Burnett, of Washington, meas- 
 ured it with Javal's ophthalmometer. The first attempt 
 at astigmatic correction by artificial means was made in 
 1882, under the influence of atropine. The correcting 
 cylinder for each eye was plus .65. In 1885, again under 
 a mydriatic, L. Webster Fox, of Philadelphia, found the 
 correcting cylinder for each eye to be plus .75. In 1887 
 a plus 1. cylinder for each eye was given. Again, in 
 1888, a plus 1.25 cylinder for each eye fully corrected the 
 manifest astigmatism, a mydriatic again being used this 
 time, homatropine, gr. viii. to water oz. i. Ten drops, 
 one every five minutes, were placed in each eye, and 
 at the end of half an hour the examination was made. 
 From that time until 1895 more astigmatism became
 
 MUSCLES OF THE CILIARY BODY. 639 
 
 manifest, but the stronger cylinder was not given until 
 that date. The cylinder then given was plus 2. D for 
 each eye. In 1900 the cylinder given for the right eye 
 was plus 2.25, and that given the left eye was plus 2.50 
 practically a full correction of the corneal astigmatism, 
 which during at least eleven years had remained the 
 same, as shown by the Javal ophthalmometer. 
 
 The author has thus related his own experience for the 
 purpose of giving emphasis to two points: (1) There was 
 a lenticular astigmatism that almost completely neutral- 
 ized the corneal astigmatism up to the age of twenty- 
 eight years; (2) the power that effected the neutralizing 
 lenticular astigmatism was not suspended by the repeated 
 use of mvdriatics, and this power, therefore, could not 
 have been given through the fibers of the third nerve 
 that come from the ciliary ganglion. The logical con- 
 clusion is that the lenticular astigmatism was produced 
 by fibers of Bowman's muscle, and that these fibers de- 
 rived their power from the cervical sympathetic. 
 
 A personal experience, similar to that through which 
 the author has passed, has been related by Edward Jack- 
 son, of Denver. What Jackson's explanation is, the au- 
 thor does not know. Doubtless many others have had 
 a similar personal experience; and it is not too much to 
 say that every observer has had such cases in his prac- 
 tice. Occasionally men of large experience have seen
 
 640 MUSCLES OF THE CILIARY BODY. 
 
 cases of astigmatism to be accounted for only by an as- 
 tigmatic condition of the crystalline lens. 
 
 It may be that, in some cases, a much higher degree 
 than 2.50 D of corneal astigmatism could be neutralized 
 by a lenticular astigmatism. It is true, nevertheless, 
 that, in many cases, even a low degree of astigmatism is 
 not always thus neutralized, the Bowman muscle being 
 unable, from some cause, to effect the necessary change 
 in the lens. 
 
 If a tilting of the lens by contraction of a single part 
 of Bowman's muscle is not the cause of the lenticular 
 astigmatism, the simultaneous and equal action of two 
 opposite parts of Bowman's muscle, by making tense the 
 corresponding parts of the zonula, could so compress the 
 part of the lens intervening as to increase its refractive 
 power, thus effecting lenticular astigmatism. It would 
 appear that, in one of these two ways, the muscle of 
 Bowman causes a neutralizing lenticular astigmatism. 
 If this change is caused by a tilting of the lens, it is 
 reasonable to suppose that the work of tilting could be 
 transferred from one part of the muscle to another part 
 directly opposite. For instance, in the production of a 
 lenticular astigmatism for neutralizing a corneal astig- 
 matism meridian of greatest curvature, vertical the 
 lens could be tilted on its vertical axis by contraction of 
 either the nasal or the temporal part of Bowman's mus-
 
 MUSCLES OF THE CILIARY BODY. 641 
 
 cle; for the effect would be the same, whether the nasal 
 part of the lens is thrown forward by contraction of the 
 temporal part of the muscle, or thrown backward by a 
 contraction of the nasal part of the muscle. Both of 
 these parts would have to contract simultaneously and 
 equally if the lenticular astigmatism is a result of change 
 in curvature, and not a change in position. In either in- 
 stance, the work done would be strain, and possibly one 
 of the worst forms of eye-strain. 
 
 After the foregoing study of the muscles located in 
 the ciliary body, this chapter may be concluded with a 
 study of the normal work required of each in some con- 
 ditions of refraction, and the abnormal work required of 
 them in other states of refraction. 
 
 THE FUNCTION OF THE MULLER MUSCLE. No mus- 
 cle of the eye is ever called on to do either normal or ab- 
 normal work for any other purpose than the improve- 
 ment of vision, and these calls are always made b} r the 
 guiding sensation, which resides in the macula, or, at 
 the farthest, within the retinal area of binocular fusion. 
 The contraction of Miiller's muscle is intended only to 
 increase the refractive power of the crystalline lens 
 equally in all of its meridians. This change in the re- 
 fractive power of the lens is effected by two agents, 
 Miiller's muscle being the active agent and the elasticity 
 of the lens being the passive agent. When the Miiller
 
 642 MUSCLES OF THE CILIARY BODY. 
 
 muscle is at rest, the zonula is tense, and, by its pressure 
 against the lens, suspends the elasticity of the latter, in 
 which state it has its minimum power of refraction. 
 When the guiding sensation calls for a sharper image 
 on the macula, the response comes in an impulse sent 
 through those fibers of the third nerve that end in the 
 muscle of accommodation (Miiller's). At once this 
 muscle contracts equally in its entire extent, relaxing 
 the zonula, the laxness of which is at once taken up by 
 an increase in the convexity of the lens by its own elas- 
 ticity. The degree of contraction of the muscle is reg- 
 ulated with mathematical precision, and the change in 
 refractive power of the lens is only enough to satisfy 
 the guiding sensation. 
 
 EMMETROPIA. In this condition of refraction, Miil- 
 ler's muscle is never called into action when the object 
 looked at is in the distance; but when the point of fixa- 
 tion is at thirteen inches, in response to a demand from 
 the guiding sensation, an impulse is sent to this muscle 
 sufficiently powerful to effect a contraction that will in- 
 crease the refraction of the crystalline lens by 3. D. At 
 nine inches a 4. D impulse must be sent to the muscle; 
 but when the point of fixation is at the distance of 
 1 M, only a 1. D impulse is needed. Looking again into 
 practical infinity any distance beyond twenty feet the 
 Miiller muscle goes into a state of rest, to be aroused
 
 MUSCLES OF THE CILIARY BODY. 643 
 
 into activity again only when the point of view is near 
 by. In distant seeing 1 , not only is the muscle of accom- 
 modation at rest, but all of the recti; and the obliques 
 should also be in a state of rest, and they will be in this 
 state if there is orthophoria. As shown elsewhere, the 
 brain-center controlling- the ciliary muscle (Miiller's) is 
 in some way associated with the third conjugate center 
 ( convergence center), so that for every dioptre of ac- 
 commodation there is a convergence of each visual axis 
 of nearly two degrees of arc, which would mean about 
 four degrees of prism a point not made clear in the 
 study of pseudo-esophoria. 
 
 In emmetropia and orthophoria everything is favorable 
 for comfort in the use of the eyes. Such eyes, under or- 
 dinary use, can give trouble only when in the emme- 
 tropic eye there is a weak muscle of accommodation or 
 when the orthophoria is asthenic. What should be done 
 for the asthenic orthophoria has already been set forth; 
 what should be done to strengthen a weak muscle of ac- 
 commodation will be shown farther on in this chapter. 
 
 In a normal condition, the strength of Miiller's muscle 
 varies with the age of the patient, until advancing years 
 deprive it of all power. The table showing the varia- 
 tion in strength, as given by Jackson, is probably as 
 nearly correct as any. The error, if any, is in the show- 
 ing of too much ciliary power after the age of thirty
 
 644 MUSCLES OF THE CILIARY BODY. 
 
 years. This table shows the relative or associated ac- 
 commodation, and is much greater than would be shown 
 if accommodation, unassociated with convergence, were 
 tested with concave lenses. Jackson's table is as fol- 
 lows: 
 
 
 Accommodation 
 
 Distance of Point 
 
 Age. 
 
 in Dioptres. 
 
 of Fixation Inches. 
 
 10 
 
 14. 
 
 2.81 
 
 15 
 
 12. 
 
 3.28 
 
 20 
 
 10. 
 
 8.94 
 
 25 
 
 9. 
 
 4.4 
 
 30 
 
 8. 
 
 4.9 
 
 35 
 
 7. 
 
 5.6 
 
 40 
 
 5.5 
 
 7.1 
 
 45 
 
 4. 
 
 9.84 
 
 50 
 
 2.5 
 
 15.75 
 
 55 
 
 1.25 
 
 31.5 
 
 60 
 
 .5 
 
 75.74 
 
 65 
 
 .0 
 
 .00 
 
 The above table shows that the amplitude of accom- 
 modation, which is the distance between the far and the 
 near points, grows less with advancing years, until, at 
 the age of sixty-five years, the near point has receded 
 so far that it becomes one with the far point. 
 
 The recession of the near point is due either to an ac- 
 tual weakening of Miiller's muscle or to a gradual loss of 
 elasticity of the lens, probably both. If the muscle could 
 be kept strong, the elasticity of the lens would doubtless
 
 MUSCLES OF THE CILIARY BODY. 645 
 
 be maintained longer. The method for keeping the cil- 
 iary muscle strong will be set forth in answer to the 
 question: ' ' Can presbyopia be deferred ? ' ' 
 
 HYPEROPIA AND HYPEROPIC ASTIGMATISM. In ei- 
 ther of these conditions of refraction the guiding sensa- 
 tion will call for activity of Miiller's muscle in both dis- 
 tant and near seeing. In hyperopia the accommodation, 
 unassociated with convergence, must effect just such 
 an increase of the refractive power of the lens, for dis- 
 tant vision, as will render sharp the image of the object 
 of fixation. This necessity for the exercise of the ac- 
 commodation for distant seeing disturbs the harmony be- 
 tween accommodation and convergence. For every di- 
 optre of accommodation for distance there is developed 
 nearly two degrees (of arc) of pseudo-esophoria, which 
 would be measured by a prism of nearly four degrees. 
 In the discussion of pseudo-esophoria this distinction be- 
 tween arc and prism degrees was not made; hence the 
 author would emphasize it here. Wherever the quantity 
 of pseudo-esophoria is given in the chapter on esophoria, 
 it should be read "of arc," or it should be multiplied by 
 two to read "of prism." 
 
 In manifest hyperopic astigmatism, simple or com- 
 pound, the guiding sensation must be satisfied when 
 Miiller's muscle has so accommodated as to place the 
 focal interval on the macula, for vision of astigmatics is
 
 646 MUSCLES OF THE CILIARY BODY. 
 
 best for all parts of an object when the anterior focus 
 is just as far in front of the retina as the posterior focus 
 is behind it. This is shown in the half-tone cut on 
 page 434. However, the muscle can accommodate so 
 as to place either the anterior or the posterior focus on 
 the macula in the first instance, sharpening 1 lines at 
 right angles to the meridian that is most curved; in the 
 second instance, sharpening lines that are parallel with 
 the most curved meridian. This irregular, zigzag con- 
 traction of Miiller's muscle is what occurs when hyper- 
 opic astigmatic eyes look at checked goods a very un- 
 pleasant thing for them to do. 
 
 This work of Miiller's muscle to sharpen images in 
 hyperopia and hyperopic astigmatism is abnormal, and 
 always develops a pseudo-esophoria. The pseudo-eso- 
 phoria manifests itself in one of three ways: First, it 
 shows an esophoria, when, intrinsically, there is ortho- 
 phoria; second, it shows a greater amount of esophoria 
 than really exists; third, it lessens an existing intrinsic 
 exophoria. In either instance, if the muscle of accom- 
 modation is not of subnormal development, the pseudo- 
 esophoria will be the same in both far and near vision. 
 
 In any case of hyperopia or hyperopic astigmatism, 
 the error must be considered not wholly with reference 
 to the muscle of Miiller, but the inherent condition of 
 the lateral recti muscles must also be taken into consid-
 
 MUSCLES OF THE CILIARY BODY. 647 
 
 eration. If there is lateral orthophoria, and especially so 
 if there is an inherent esophoria, the abnormal work re- 
 quired of the muscles of accommodation should be re- 
 lieved by a full correction of the focal error, and the 
 lenses should be worn for both far and near seeing. If 
 there is inherent exophoria, it would be better, in many 
 cases, especially those having- strong- muscles of accom- 
 modation, to correct the hyperopic astigmatism with 
 minus cylinders, and to leave uncorrected any low de- 
 gree of hyperopia, in order that the pseudo-esophoria 
 may neutralize, wholly or in part, the inherent exo- 
 phoria. In every case of hyperopic astigmatism a full 
 correction of all the error that can be made manifest 
 should be given, using either plus or minus cylinders, as 
 might be indicated by an associated study of the focal 
 error and the intrinsic state of the muscles. If minus 
 cylinders are used because of a complicating exophoria, 
 the hyperopic astigmatism, which is worse, is converted 
 into a simple hyperopia, which is better. How to deal 
 directly with any inherent muscle imbalance, has already 
 been set forth in preceding chapters. 
 
 MYOPIA AND MYOPIC ASTIGMATISM. When either 
 of these errors exists, the guiding sensation does not call 
 on Miiller's muscle to do any work when the object of 
 fixation is in the distance. If there is simple myopia of 
 3. JD, or more, the muscle of accommodation is not called
 
 648 MUSCLES OF THE CILIARY BODY. 
 
 into action, even in the near use of the eyes; so that in 
 such eyes the muscle remains inactive, whatever may be 
 the location of the point of view, unless it should be 
 brought nearer the eyes than their far points. If there 
 is manifest myopic astigmatism, the accommodative mus- 
 cle will be brought into activity only when the eyes are 
 used in near vision and for the purpose of placing the 
 focal interval on the macula. In compound myopic as- 
 tigmatism, the myopia being 3. D or more, the muscle of 
 Miiller will remain inactive, regardless of whether the 
 eyes are being used either in the far or in the near. In 
 nryopia of less than 3. D, with the page at thirteen inches, 
 the guiding sensation calls only for such accommodative 
 action as will increase the refractive power of the lens 
 to correspond, in dioptres, with the difference between 
 the number of dioptres of myopia and 3. D. This work 
 of the ciliary muscle to improve vision in the near when 
 there is myopic astigmatism, and to give the proper near 
 point when there is a low degree of myopia is abnormal 
 work, though less than is required when there is emme- 
 tropia. These refractive errors interfere in no way with 
 any intrinsic muscle condition, when the point of view is 
 in the distance; but in the near use of the eyes there is 
 a resultant pseudo-exophoria. This may show itself in 
 any one of three ways: First, there will be an exophoria 
 in the near, when, intrinsicall)', the lateral muscles may
 
 MUSCLES OF THE CILIARY BODY. 
 
 be well balanced; second, the manifest exophoria will be 
 more than the real; third, the pseudo-exophoria may 
 serve to lessen an inherent esophoria. 
 
 In any case, a full correction of a myopic error for the 
 purpose of distant seeing- should be given, since such a 
 correction will not excite into activity the muscle of ac- 
 commodation, nor will it interfere with any existing 
 state of the lateral muscles. There can arise no disad- 
 vantage from wearing the correcting lenses for distant 
 vision, and there is a very great source of pleasure given 
 in making sharp and well defined objects that are re- 
 mote. When the associated muscle condition is inherent 
 orthophoria, and especially when there is exophoria in 
 the near, myopes should wear their correcting lenses for 
 both far and near seeing; but when there is esophoria, 
 as will be shown in both the distant and the near tests, 
 the myope will have added comfort by removing his 
 lenses for all near work, in that the pseudo-exophoria 
 will lessen the intrinsic esophoria. In all cases, myopic 
 astigmatism should be corrected by a proper minus cyl- 
 inder when there is lateral orthophoria or exophoria in 
 the near, but by plus cylinders, to be worn only in read- 
 ing or in other near work, when there is a complicating 
 esophoria. So it appears that myopic errors must be 
 studied and treated by taking into consideration the 
 Miiller muscle and the lateral recti muscles.
 
 650 MUSCLES OF THE CILIARY BODY. 
 
 WEAKNESS OF MULLER'S MUSCLE. As already 
 shown, the amplitude of accommodation diminishes with 
 advancing- years. Whether this failing accommodation 
 is due to loss of power in the muscle, or whether it is 
 because the lens, growing- more dense, continually suf- 
 fers loss of elasticity, is still a subject for discussion. 
 Probably the two conditions enter as factors in the de- 
 velopment of presbyopia. The weakening- of the muscle 
 of accommodation may favor the loss of elasticity, and 
 the loss of elasticity may react on the weak muscle. 
 Presbyopia shows itself in a recession of the near point 
 until, finally, it has been removed inconveniently far. 
 Before this, however, the muscle may have become so 
 weak that its use in reading- or other near work bring-s 
 on fatig-ue, headache, or other symptoms of eye-strain. 
 In such cases one of two thing's should be done: The 
 muscle should be helped by increasing its strength by 
 exercise, or by supplementing its power. 
 
 Can presbyopia be deferred ? What the author wrote 
 in 1894, in answer to this question, so perfectly coincides 
 with his present views, that he reproduces it here: 
 
 ' ' That the leading cause of old sight is failure of cil- 
 iary power we think may be proved; and if this is true, 
 simple and scientific means for deferring the onset of 
 presbyopia may be brought into use. Rhythmic exer- 
 cise can be as readily effected in the ciliary muscle as in
 
 MUSCLES OF THE CILIARY BODY. 651 
 
 any of the extra-ocular muscles. Will this exercise de- 
 velop the power of these muscles that are under the 
 direct control of the guiding sensation, the common 
 master of all the ocular muscles ? 
 
 "That involuntary muscular fibers can be increased 
 in size and augmented in power as a result of effort to 
 overcome obstruction is a matter of common accept- 
 ance, so far as the heart and the bladder are concerned. 
 In mitral stenosis it is well known that the walls of the 
 left auricle become hypertrophied and more powerful, so 
 that it may send the blood through the narrowed open- 
 ing into the ventricle; in like manner, when there is 
 obstruction at the aortic opening, the walls of the ven- 
 tricle become hypertrophied and more powerful. 
 
 "When the prostate gland is enlarged or there is 
 stricture of the urethra, impeding the flow of urine, the 
 muscular fibers in the walls of the bladder are increased 
 in size, and become much more powerful, so as to be 
 able to force the flow. It will be conceded that this 
 muscle development in heart and bladder results from 
 effort to overcome obstruction. 
 
 "Displacement of images by prisms and blurred im- 
 ages by means of concave lenses are obstructions which, 
 if not too great, will be overcome by muscular action 
 the former, by action of the recti muscles; the latter, by 
 action of the ciliary muscles. Many observers have
 
 652 MUSCLES OF THE CILIARY BODY. 
 
 already acknowledged that rhythmic exercise of the 
 recti muscles, by means of prisms, and of the obliques, 
 by means of cylinders properly placed, not only in- 
 creases their power, but at the same time dispels the 
 nervous phenomena associated with and dependent on 
 their former weakness. If the ciliary muscles can be 
 developed by rhythmic exercise, then concave lenses, 
 not too strong 1 , used rhythmically, but not too long- at a 
 time, may be the means of deferring old sight to five or 
 ten, or even more, years beyond the now common age of 
 its onset about the age of forty-five years. 
 
 "As in developing the recti and obliques, so in the 
 development of the ciliary muscles, the power to over- 
 come obstruction should never be taxed to anything like 
 its fullest capacity. Gentle contraction and relaxation, 
 rhythmic in order, continued from five to ten minutes and 
 repeated once or twice every twenty-four hours, must 
 result in giving tone to the ciliary muscles. The time 
 of life for beginning the exercise, and the strength of 
 concave lenses to use, are matters that must be settled 
 by observation and experience. As a preliminary to the 
 treatment of failing accommodation, all existing focal 
 errors should be corrected, and this correction should be 
 worn behind the exercise lenses at each sitting. A mi- 
 nus .50 D. spherical lens, properly centered, will be the 
 most useful. The patient should be seated from fifteen to
 
 MUSCLES OF THE CILIARY BODY. 653 
 
 twenty feet from a lighted candle, lamp, or gas jet, and 
 should look at the same through the concave lenses five 
 seconds, and then raise them for a period of five seconds, 
 and so on to the end of the sitting. It is evident that, 
 with the focal correction on when needed, the image of 
 the flame is sharp, satisfying the guiding sensation 
 without ciliary action. The moment the weak concave 
 lenses are lowered the image is blurred, and at once the 
 ciliary muscles are called into action, to again return to a 
 state of rest the moment they are raised. Thus contrac- 
 tion and relaxation are easily induced. In this way the 
 nutrition of the muscle should be improved and its 
 power enhanced or maintained. The age at which to 
 begin the exercise, as a rule, need not be under forty 
 nor over forty-three years, and it should be continued as 
 long as the proper reading distance is preserved. 
 
 "The question would naturally arise in the mind of 
 the patient as well as that of the practitioner: ' Can any 
 injury come from the treatment?' The nutrition of the 
 ciliary body is from the blood that circulates in it. 
 Nothing is more reasonable than that gentle, rhythmic, 
 and periodic exercise of the ciliary muscle would im- 
 prove the nutrition of the ciliary body, just as the nutri- 
 tion of other muscles is improved by proper exercise. 
 No harm, then, could come to the muscle as a result of 
 the proposed gymnastic exercise. May we fear unfa-
 
 654 MUSCLES OF THE CILIARY BODY. 
 
 vorable change in the lens as a consequence of this exer- 
 cise of the ciliary muscle ? It is generally conceded that 
 the lens gets its nourishment, by the process of osmosis, 
 from the blood circulating in the ciliary body. It must 
 be acknowledged that the better the nutrition of the 
 lens, the more likely will it retain its two very impor- 
 tant properties, transparency and elasticity. It cannot 
 be denied that the better the nutrition of the ciliary 
 body, the healthier will be the crystalline lens. We 
 must conclude that, if the exercise would improve the 
 condition of the ciliary body, it would at the same time 
 have a tendency to improve the nutrition of the lens, 
 whereby the latter would be only the more certain to 
 continue both transparent and elastic. Thus not only 
 may old sight be deferred, but also the development of 
 cataract may be prevented." 
 
 It is now about eight years since the above was writ- 
 ten. During five of these years, beginning at the age of 
 forty-three years, the author faithfully "took his own 
 prescription," hardly a day passing that he did not exer- 
 cise his ciliary muscles with concave spheres. When the 
 exercise was commenced, there was already beginning 
 presbyopia, interfering somewhat with the finding of 
 foreign bodies in the cornea and with their removal. 
 There was hesitating vision in the more delicate opera- 
 tion on the eye. He commenced the exercise with a mi-
 
 MUSCLES OF THE CILIARY BODY. 655 
 
 nus .50 sphere and soon experienced increase of ciliary 
 power, as shown in both comfort and convenience experi- 
 enced in reading 1 and operative work. After a few months 
 a minus 1. sphere was substituted for the weaker lens, 
 and with this the exercise was continued until the age of 
 forty-eight years. Except for the hard work, by artifi- 
 cial light, incident on the writing of this book, he would 
 have continued the exercise longer, possibly until the 
 age of fifty years. Even now, in his forty-ninth year, 
 although he has been wearing a presbyopic lens (a 
 plus 1. D) for the past six months, he can see to read this 
 print easily at fifteen inches through his astigmatic cor- 
 rection only. If the three necessary factors for carry- 
 ing out this exercise time, patience, and perseverance - 
 could be kept compounded, much might be accomplished, 
 especially if the exercise were commenced before the 
 age of forty years. 
 
 If the exercise treatment is not resorted to, waning 
 ciliary power should be supplemented by convex lenses, 
 as soon as inconveniences arise in near work. There is 
 no reason why plus .50 D spheres might not be first used, 
 and as long as they give comfort. Whenever the ciliary 
 muscles begin to call for more, the presbyopic correction 
 should be increased by steps of .50 D. Finally, when all 
 ciliary power has vanished, artificial aid must be sub- 
 stituted for the lost ciliary power. To give an unneces-
 
 656 MUSCLES OF THE CILIARY BODY. 
 
 sarily strong presbyopic correction at the beginning 
 should be avoided, for by so doing the nutrition of both 
 the ciliary body and the lens might be interfered with. 
 Presbyopic lenses should always be correctly centered, 
 and they should be set before the eye so that the visual 
 axes would pass through the lenses at right angles. 
 
 WEAKNESS OF MULLER'S MUSCLE IN THE YOUNG. 
 Either from the want ol proper development of the 
 muscles or because of faulty innervation, the power of 
 accommodation in young people is often found below 
 par. In association with convergence, the printed page 
 may be seen, but prolonged use of the eyes for reading 
 fatigues the weak muscles and brings on headache or 
 other reflex nervous symptoms. If focal errors exist in 
 these cases, they should be corrected as might be indi- 
 cated by an associated study of the focal errors and in- 
 trinsic condition of the lateral recti muscles. In many 
 cases weakness of Miiller's muscle is the chief source 
 of trouble; and if comfort is ever to be given such a suf- 
 ferer, this condition must be treated. 
 
 A diagnosis of such a condition may be made easily by 
 means of the concave lenses in the refraction case, but 
 more easily and rapidly by means of two parallel bars 
 containing a series of concave spherical lenses, varying 
 in strength from .50 to 3. D, the difference in strength 
 between any two adjacent lenses being .50 D. These
 
 MUSCLES OF THE CILIARY BODY. 657 
 
 bars should be so connected above that the distance 
 between them may be regulated to suit the distance 
 between the pupillary centers of the eyes to be tested. 
 The minus .50 should be below; the minus .3D sphericals, 
 above. Beginning with minus .50 sphericals before the 
 two eyes, the patient all the while looking at the Snellen 
 letters made to be read at twenty feet, each pair of lenses 
 should be passed down in front of the eyes so long as 
 the patient is still able to see xx- If the muscles of ac- 
 commodation are weak, ciliary power, unassociated with 
 convergence, will be less than 3. D; in many cases it is 
 not more than 1. D. The standard of ciliary power, when 
 unassociated with convergence, may be placed at 3. D, for 
 the reason that a ciliary muscle that can overcome a 
 minus 3. D, when not converging, can easily accommodate 
 for the reading distance, in association with convergence. 
 Not much help, from a diagnostic standpoint, can come 
 from a test of the relative power of accommodation. 
 The test apparatus just described may be called a "cili- 
 ometer. " Except for the trouble and inconvenience, the 
 lenses from the trial case could be used for making these 
 tests. 
 
 Lucien Howe has devised a more complicated appa- 
 ratus for testing ciliary power, which he exhibited before 
 the Section of Ophthalmology of the American Medical 
 Association two or three years ago. As the author re-
 
 658 MUSCLES OF THE CILIARY BODY. 
 
 members the device, he thinks it would be easy to use 
 and fully worthy of trust. 
 
 Every protracted illness must weaken ciliary power, 
 which time and tonics will relieve. Such patients should 
 abstain from near work until the general health has 
 been fully restored 
 
 TREATMENT. The treatment of weakness of Miil- 
 ler's muscle is by exercise, after the method set forth in 
 the answer to the question: "Can presbyopia be de- 
 ferred?" The result of the exercise will depend largely 
 on the faithfulness with which it is carried out. In 
 cases of congenital weakness of the ciliary muscles, 
 strychnia, electricity, and other tonics can accomplish 
 but little. Rhythmic exercise by means of minus .50 to 
 minus 1 D spherical lenses will cure, usually in a few 
 months. The giving of convex lenses to supplement 
 the weak ciliary power should not be considered, for it 
 would be making the patient old while yet young. 
 
 BOWMAN'S MUSCLE: ITS NORMAL AND ABNORMAL 
 WORK. In non-astigmatic eyes, when the position of 
 the lens is ideal from the processes of development, the 
 Bowman muscle can have nothing to do, unless it be to 
 aid in steadying the lens in the act of accommodation by 
 Miiller's muscle. Such action, if it occurs, must be of 
 the entire muscle. 
 
 If a lens, as the result of the processes of develop-
 
 MUSCLES OF THE CILIARY BODY. 659 
 
 ment, is not ideally placed in a non-astigmatic eye es- 
 pecially if its equatorial plane is not parallel with the 
 equator of the eye, and probably if its antero-posterior 
 axis does not coincide with the visual axis the task of 
 correction of these errors must fall on Bowman's muscle, 
 and the work must be accomplished through the guiding 
 sensation of the retina, most likely in the earlier months 
 of infancy. This regulation of position must be effected 
 by action of a definite portion of the muscle, and it must 
 be kept up unless the suspensory ligament should un- 
 dergo such change as, in itself, would fix the lens. A 
 failure on the part of the muscle to act would give a 
 permanent lenticular astigmatism. Such work required 
 of Bowman's muscle would be abnormal, but essential. 
 
 When there is corneal astigmatism, there is necessity 
 for abnormal action of Bowman's muscle in a localized 
 part. The adjustment of the lens must be such as to 
 increase its refractive power in the part at right angles 
 to the plane of the meridian of greatest curvature of the 
 cornea. This can be effected in one of two ways first, 
 by a contraction of one single part of Bowman's muscle, 
 so as to rotate the lens on an axis that lies in the plane 
 of the meridian of the cornea that is most curved; second, 
 by the simultaneous and equal contraction of opposite 
 parts of the muscle so as, by pressure on the lens through 
 the tension of corresponding parts of the suspensory
 
 660 MUSCLES OF THE CILIARY BODY. 
 
 ligaments, to increase the curvature of that part of the 
 lens at right angles to the plane of the most curved cor- 
 neal meridian. While, in either instance, the corneal as- 
 tigmatism would be neutralized, in part or wholly, the 
 author inclines to the view that it is effected by the tilt- 
 ing- of the lens. This work is abnormal, rarely ever 
 perfectly effective, especially in the higher degrees of 
 astigmatism, and is probably one of the worst kinds of 
 eye-strain. As the patient grows older this astigmatic 
 accommodative power is less able to accomplish its work, 
 and a greater amount of the astigmatism becomes mani- 
 fest. There is no known drug that will suspend astig- 
 matic accommodation, else at the first examination the 
 whole error could be found, and should be corrected. 
 
 There are but two ways to deal with astigmatism: 
 First, correct only the manifest error, increasing the 
 strength of the cylinder from time to time, as the latent 
 error becomes manifest; second, give at once a full cor- 
 rection of the corneal astigmatism, as shown by the oph- 
 thalmometer, and thus force the suspension of the ac- 
 commodative astigmatic power, which would doubtless 
 occur in a short while. 
 
 The production of artificial astigmatism, unless indi- 
 cated by insufficiency of the superior obliques, should 
 always be avoided. To avoid thus calling into abnor- 
 mal action any part of Bowman's muscle, the correction
 
 MUSCLES OF THE CILIARY BODY. 661 
 
 of corneal astigmatism should be perfect, both as to 
 strength of cylinder and location of its axis; and when 
 minus spherical lenses are required for the correction of 
 myopia, or plus spherical lenses are given for the cor- 
 rection of hyperopia and presbyopia, they should be so 
 placed that the plane of each lens shall be parallel with 
 the equator of the eye by which it is to be used. 
 
 APPENDIX. 
 
 In the original Cyclo-phorometer, depicted on page 262, 
 the graduated semicircle is below. Those now made 
 have the degrees marked in the semicircle above. In the 
 former instrument, when the index stands in the lower- 
 nasal arc, in order to make the two streaks of light paral- 
 lel, the condition is plus cyclophoria; in the latter instru- 
 ment, when the index stands in the upper-temporal arc, 
 the condition is plus cyclophoria. In either instrument, 
 when testing for cyclophoria or cyclotropia, the upper- 
 temporal and lower-nasal arcs refer to the superior 
 obliques, and the upper-nasal and lower-temporal arcs 
 refer to the inferior obliques. 
 
 The duction arcs for the superior obliques are the 
 upper-nasal and lower-temporal; for the inferior obliques, 
 the upper-temporal and lower-nasal.
 
 INDEX. 
 
 ANTAGONISTS AND SYNERGISTS, 
 
 tables of 59, 62 
 
 ADVANCEMENT OPERATION, 
 
 to only alter tension 261 
 
 to alter tension and change plane 266 
 
 marginal 267 
 
 for esophoria 312 
 
 suggested by Querin 501 
 
 of Lagleize 269 
 
 ABEA, RETINAL, 
 
 of binocular fusion, and how measured 175 
 
 ANGLE GAMMA 528 
 
 how measured 532 
 
 Axis OF CARDINAL ROTATIONS, 
 
 how to find 16 
 
 AXES OF OBLIQUE ROTATIONS, 
 
 are only two 44 
 
 ACTION, 
 
 principal and subordinate, of a muscle 52 
 
 ASTIGMATISM, 
 
 oblique, why more annoying than the vertical 446 
 
 parallel 450 
 
 phenomena of, shown by experiments 459 
 
 metamorphopsia in, through correcting cylinders 462 
 
 hyperopic, how to correct 647 
 
 myopic, how to correct 649 
 
 (662)
 
 INDEX. 663 
 
 ASTIGMATIC ACCOMMODATION 637, 638 
 
 two points about 639 
 
 ANISOMETROPIA, 
 
 a cause of compensating hetcrotropia 492 
 
 ANTIPATHY 
 
 to binocular single vision, explained 520 
 
 ACCOMMODATION AND CONVERGENCE 279 
 
 Axis OF VISION 6, 8 
 
 Axis OF ROTATION 8 
 
 ACCOMMODATION, 
 
 change of lens in 629 
 
 Helmholtz' theory of 630 
 
 muscle of 631 
 
 Miiller's or Bowman's, which? 632 
 
 Tscherning's views of lens-changes in 632 
 
 presbyopic correction compared with 633 
 
 of the hyperope 633 
 
 conclusions about 635 
 
 normal power of, how determined 657 
 
 ABDUCENS 597 
 
 ADDUCTION, 
 
 the normal 153, 158, 197 
 
 ABDUCTION, 
 
 the normal 153, 158, 197 
 
 ADVERSION 169, 173, 201 
 
 ABVERSION 168, 172, 201 
 
 ADJUSTMENT OF CYLINDERS 486 
 
 BAXTEB'S CYCLO-PHOROMETER 161 
 
 BLACK 268 
 
 BREWER'S TORSIOMETER 161 
 
 BEARD 2G8 
 
 BERGER . G2 1
 
 664 INDEX. 
 
 BIFFI 625 
 
 BINOCULAB SINGLE VISION 104, 105 
 
 line (curve) of 99, 102 
 
 surface of 99 
 
 antipathy to 520 
 
 BINOCULAB ROTATIONS, 
 
 in the four cardinal directions 7, 21 
 
 in oblique directions ^ 58 
 
 BINOCULAB FUSION FIELD 174 
 
 BINOCULAB FIELD OF VISION 125 
 
 BINOCULAB FIELD OF VIEW 125 
 
 BINOCULAB SPACIAL POLE 124, 135 
 
 BINOCULAB SPACIAL MERIDIANS 126, 131 
 
 BINOCULAB SPACIAL PARALLELS 130 
 
 BRAIN CENTERS FOR BINOCULAR ROTATIONS, 
 
 how they control 77,78 
 
 demonstration of their existence 78-81 
 
 individual fusion centers 81 
 
 BROWN, MANNING 99 
 
 BOWMAN'S MUSCLE 628 
 
 nerve supply of 635 
 
 function of 636 
 
 how it may act 640 
 
 its normal and abnormal work 658 
 
 its work of adjusting the lens, after birth 659 
 
 its work in neutralizing corneal astigmatism 659 
 
 BURNETT, SWAN M 185, 402, 638 
 
 CARDINAL ROTATIONS 169 
 
 CATAPHORIA, 
 
 treatment of, by prisms 233 
 
 < See " Hyperphoria.")
 
 INDEX. 665 
 
 CATAPHORIA, DOUBLE, 
 
 causes of 353 
 
 treatment of, 
 
 by prisms 376 
 
 by exercise 378 
 
 by operations 378 
 
 CATATROPIA, DOUBLE, 
 
 without cyclotropia 581 
 
 with plus cyclotropia 581 
 
 the operations for 585 
 
 with minus cyclotropia 581 
 
 CENTERS, 
 
 the conjugate 69, 70 
 
 the fusion 71, 80-91 
 
 CHECK LIGAMENTS 503 
 
 CHECKED GOODS, 
 
 why annoying to astigmatics 646 
 
 CILIARY MUSCLES, 
 
 normal and subnormal 281 
 
 super-normal 282 
 
 CILIARY BODY, 
 
 muscles of 628 
 
 Bowman's 628 
 
 Miiller's 629 
 
 CILIOMETER 657 
 
 CHISOLM, J. J 329 
 
 CRITCHETT 502 
 
 CONJUGATE CENTERS, 
 
 disease of sixth, seventh, eighth, and ninth 612 
 
 disease of first, second, third, fourth, and fifth 614 
 
 COLLINS 624 
 
 Coccius . 631
 
 666 INDEX. 
 
 CONJUGATE INNERVATIONS 69, 70 
 
 CORRESPONDING RETINAL POINTS 451 
 
 CONVERGENCE, 
 
 angle of, and formula for calculating 140 
 
 angle of, and pupillary distance 141 
 
 size of angle of, how to find 144 
 
 CONVERGENCE AND ACCOMMODATION 279 
 
 CORNEA, 
 
 decentration of 493 
 
 imperfect images caused by 494 
 
 how to detect 494 
 
 CROSS-EYES 497 
 
 CULBERTSON, H 401, 407 
 
 CYCLO-PHOROMETER 161 
 
 how to use 162 
 
 CYCLO-DUCTION 163, 167, 198, 396 
 
 CYCLOPHOHIA, 
 
 history of 383 
 
 varieties of 384 
 
 causes of 384 
 
 tests for, 
 
 by Maddox prism 194, 389 
 
 by single prism 194, 392 
 
 by rotary prism 392 
 
 by the Stevens clinoscope 195, 393 
 
 by the cyclo-phorometer 195, 395 
 
 symptoms of 400 
 
 treatment of, 
 
 by exercise cylinders 237, 401 
 
 by rest cylinders 402 
 
 how to place axes of cylinders given for correction of astigma- 
 tism 405 
 
 by operations 248, 414
 
 INDEX. 667 
 
 CYCLOPHOBIA, 
 
 operations for, first suggested 402 
 
 uncomplicated, 
 
 the operations for 414 
 
 complicated by double hyperphoria, 
 
 the operations for 414 
 
 complicated by double cataphoria, 
 
 the operations for 414 
 
 complicated by right hyperphoria and left cataphoria, 
 
 the operations for 414 
 
 complicated by sthenic esophoria, 
 
 the operations for 414 
 
 complicated by sthenic exophoria, 
 
 the operations for 414 
 
 complicated by esophoria, right hyperphoria, and left catapho- 
 ria, 
 
 the operations for 415 
 
 complicated by exophoria, right hyperphoria, and left catapho- 
 ria, 
 
 the operations for 415 
 
 CYCLOTROPIA, 
 compensating, 
 
 history of the study of 419, 438 
 
 caused by oblique astigmatism 418 
 
 how retinal images are displaced 439 
 
 how the displaced images are fused 442, 458 
 
 treatment of, by correcting cylinders 466 
 
 annoyances following treatment of 466 
 
 why annoyances vanish sooner in some cases than in others. . . 467 
 
 Lippincott's method of applying correcting cylinders 469 
 
 the kind of cases requiring this method 469 
 
 the kind of cases not requiring this method 471 
 
 the gradual correction of, by displacing the axes of the fully 
 
 correcting cylinders 471 
 
 Steele rule for displacing cylinders 472 
 
 Steele rule corrected . 472
 
 668 INDEX. 
 
 CYCLOTBOPIA, 
 
 comitant 587 
 
 parallel and non-parallel 588 
 
 parallel, causes of 588 
 
 plus, causes of 589 
 
 minus, causes of 589 
 
 how detected and measured 590 
 
 plus, 
 
 complicated by double hypertropia, 
 
 the operations for 591 
 
 complicated by hypertropia of one eye and catatropia of the 
 other, 
 
 the operations for 592 
 
 uncomplicated, 
 
 the operations for 593 
 
 CYLINDERS, 
 
 adjustment of 486 
 
 distortion by displacement of 484 
 
 DANIEL, PBOF. JOHN 48 
 
 DEBCUM AND PABKEB'S EXPERIMENTS 210 
 
 DESCHWEINITZ 221 
 
 DEADY 231 
 
 DECENTBATION OF LENSES 302 
 
 DEGREES. 
 
 of arc and of prism compared 643, 645 
 
 DEVIATIONS, 
 
 primary and secondary 525 
 
 DJPLOPIA, 
 
 Nature's two methods of preventing 66, 498 
 
 DISTORTION BY CYLINDERS, 
 
 arcs of 474, 484 
 
 plates illustrating 475, 480, 485 
 
 a knowledge of, necessary 486
 
 INDEX. 669 
 
 DlEFFENBACH 499 
 
 BONDERS 279, 509 
 
 DOAK, R. S 363 
 
 DUANE 187 
 
 DUNN, JOHN 566 
 
 DUCTION POWER 197 
 
 standard of 176 
 
 value of 199 
 
 how determined by the Wilson phorometer 153 
 
 how determined by the monocular phorometer 157 
 
 EXTERNUS. 
 
 plane of action of 53 
 
 correct attachment of 53 
 
 high attachment of 53 
 
 low attachment of 53 
 
 operation on (see " Exophoria " and " Esophoria.") 
 
 EXERCISE, 
 
 ceiling-to-floor and wall-to-wall 177 
 
 EMMETROPIA, 
 
 Miiller's muscle in 642 
 
 convergence and accommodation in 643 
 
 with orthophoria 643 
 
 EXOPHORIA 314 
 
 pseudo, 
 
 causes of 318 
 
 treatment of, by concave lenses 328 
 
 treatment of, by under-correction of hyperopia 329 
 
 intrinsic 315 
 
 causes of 315 
 
 sthenic and asthenic 317 
 
 why variable 317 
 
 tests for, 
 
 by exclusion 322
 
 670 INDEX. 
 
 EXOPHORIA, 314 
 
 by red glass 323 
 
 by double prism 323 
 
 by single prism 323 
 
 by Maddox rod 324 
 
 by photometer 324 
 
 abduction, and abversion in 325 
 
 adduction and adversion in 326 
 
 complications of 326 
 
 symptoms of 327 
 
 treatment of, 
 
 by prisms for constant wearing 330 
 
 by exercise prisms 230, 334 
 
 by candle exercise 228, 332 
 
 by Gould or Deady method 232 
 
 how to adjust rest prisms in 331 
 
 sthenic, uncomplicated, 
 
 the operations for 336 
 
 complicated by hyperphoria and cataphoria only, 
 
 the operations for 337 
 
 complicated by plus cyclophoria only, 
 
 the operations for 337 
 
 complicated by hyperphoria and cyclophoria, 
 
 the operations for 338 
 
 asthenic, uncomplicated, 
 
 the operations for 338 
 
 complicated by hyperphoria and cataphoria only, 
 
 the operations for 339 
 
 complicated by cyclophoria only, 
 
 the operations for 339 
 
 complicated by hyperphoria and cyclophoria, 
 
 the operations for 339 
 
 ESOPHOBIA, 
 
 pseudo, 
 
 cause of 278 
 
 how it manifests itself . . 279
 
 INDEX. 671 
 
 ESOPHOBIA, 
 
 treatment of 297 
 
 intrinsic or inherent, 
 
 conditions that cause 273 
 
 sthenic, how determined 277 
 
 asthenic, how determined 278 
 
 tests for, when unreliable 284 
 
 by exclusion 286 
 
 by red glass 286 
 
 by double prism 287 
 
 by single prism 287 
 
 by Maddox rod 288 
 
 by the phorometer 291 
 
 the same, far and near 281 
 
 variable, greater in the far 280 
 
 complications of 293 
 
 symptoms of 294 
 
 treatment of, 
 
 by convex lenses 297 
 
 by rest prisms, and how to adjust 299 
 
 by exercise prisms 233, 304 
 
 sthenic, uncomplicated, 
 
 the operations for 308 
 
 complicated by hyperphoria and cataphoria only, 
 
 the operations for 308 
 
 complicated by cyclophoria only, 
 
 the operations for 309 
 
 complicated by plus cyclophoria and hyperphoria of one eye 
 and cataphoria of the other, 
 
 the operations for 310 
 
 asthenic, uncomplicated, 
 
 the operations for 310 
 
 complicated by hyperphoria and cataphoria only, 
 
 the operations for 311 
 
 complicated by plus cyclophoria only, 
 
 the operations for 311
 
 672 INDEX. 
 
 ESOTROPIA, 
 comitant 513 
 
 time of occurrence, and why 513 
 
 causes of 514 
 
 esophoria as a cause 515 
 
 hyperopia 516 
 
 hyperphoria and cataphoria 517 
 
 low visual acuity 519 
 
 faulty connection of the maculas with the brain 520 
 
 varieties of 524 
 
 tests for, 
 
 by phonometer 520 
 
 by perimeter 531 
 
 by tape 533 
 
 by linear method 535 
 
 by Hirschberg method 535 
 
 symptoms of 536 
 
 amblyopia 537 
 
 disfigurement 538 
 
 secondary deviation 539 
 
 headache and other reflexes 536 
 
 treatment of 539 
 
 by convex lenses 539 
 
 why these should be given only 540 
 
 by atropine in the good eye 543 
 
 by flap before the good eye 543 
 
 by the stereoscope 544 
 
 by the amblyoscope 545 
 
 by bar reading 548 
 
 the object of treatment 544 
 
 operative treatment of 549 
 
 by complete tenotomies, never 549 
 
 why Panas' complete tenotomy is safer than any other 550 
 
 by advancements 551 
 
 the two extremes in operating 551 
 
 by partial tenotomies, advancements, and shortenings, the 
 ideal operations 552
 
 INDEX. 673 
 
 ESOTROPIA, 
 
 the two effects that may be accomplished by any operation. . . . 552 
 comitant, uncomplicated, 
 
 the operations for 553 
 
 complicated by hypertropia and catatropia only, 
 
 the operations for 555 
 
 complicated by plus cyclotropia only, 
 
 the operations for 555 
 
 complicated by plus cyclotropia and hypertropia of one eye and 
 catatropia of the other, 
 
 the operations for 556 
 
 complicated by plus cyclotropia and double hypertropia, 
 
 the operations for 558 
 
 EXOTROPIA, 
 comitant, 
 causes of, 
 
 myopia 561 
 
 exophoria 561 
 
 defective third innervation center 561 
 
 the obliques may cause 562 
 
 traumatism (bad surgery on an internus) 562 
 
 is a binocular trouble 563 
 
 complications of 563 
 
 symptoms of 564 
 
 a case of non-comitant, with symptoms 562 
 
 comitant, uncomplicated, 
 
 the operations for 569 
 
 complicated by hypertropia, 
 
 the operations for 570 
 
 complicated by plus cyclotropia only, 
 
 the operations for 571 
 
 complicated by plus cyclotropia, hypertropia, and catatropia, 
 
 the operations for 572 
 
 complicated by plus cyclotropia and double hypertropia, 
 
 the operations for 574 
 
 simple, 
 
 the Fox operation for 575
 
 674 INDEX. 
 
 EYE, 
 
 the ideal 27-35 
 
 the non-ideal 27-35 
 
 FBAMES FOB EXERCISE CYLINDERS 411 
 
 FIXED PLANES OF THE HEAD 72 
 
 FIXATION, LINE OF 528 
 
 Fox's OPERATION FOB EXOTROPIA 575 
 
 FUSION, RETINAL AREA OF 175 
 
 GBAEFE 184, 500, 520 
 
 GAMMA, ANGLE 528 
 
 GOULD 231 
 
 GUIDING SENSATION 175, 641 
 
 GBTTNHAGEN 624 
 
 HALE, G. W 215 
 
 HELMHOLTZ 10, 15, 16, 25, 96, 630 
 
 HELMHOLTZ' FUNDAMENTAL ERRORS 14, 34 
 
 HELMHOLTZ AND THE AUTHOR, 
 
 eight points of disagreement 32-34 
 
 HELMHOLTZ' METHOD 
 
 of finding the fixed axis of a rotation 10-13 
 
 HESS 635 
 
 HETEROPHOBIA, 
 
 vertical 180 
 
 lateral 181 
 
 oblique 181 
 
 causes of 181 
 
 pseudo and intrinsic 188 
 
 tests for 188, 189 
 
 symptoms of 203
 
 INDEX. 675 
 
 HETEROPHOP.IA, 
 
 headache 204 
 
 vertigo and nausea 206 
 
 confubion of thought 206 
 
 chorea 207 
 
 epilepsy 208 
 
 catalepsy 212 
 
 hysteria 213 
 
 neurasthenia 213 
 
 visceral disturbances 214 
 
 asthenopia 216 
 
 treatment of, 
 
 by rest prisms 217 
 
 by rest cylinders 219 
 
 by exercise prisms 220 
 
 by operations 239 
 
 HETEROTROPIA, 
 
 compensating 489 
 
 caused by anisometropia 489 
 
 caused by prisms and decentered lenses 492 
 
 comitant, 
 
 varieties of 497 
 
 history of 499 
 
 Panas' operation for 503 
 
 classes of 510 
 
 treatment of (see " Esotropia," etc.) 
 
 how distinguished from paralytic heterotropia 512 
 
 HlRSCHBERG 538 
 
 HOROPTER 35-39, 94 
 
 HOTZ 419 
 
 HOWE 657 
 
 HYPERKIXESIS AND HYPOKIXESIS . .187
 
 676 INDEX. 
 
 HYPEBPHOBIA AND CATAPHOETA, 
 inherent, 
 causes of, 
 
 malformation of orbits 342 
 
 too high attachments of the lateral recti 349 
 
 other causes 350, 354 
 
 tests for 358 
 
 proof tests for 361 
 
 duction and version tests 366 
 
 complications of 366 
 
 symptoms of 367 
 
 tilting of head in 363 
 
 treatment of, 
 
 by prism exercise 233, 372 
 
 by rest prisms 375 
 
 uncomplicated, 
 
 the operations for 379 
 
 complicated by cyclophoria, 
 
 the operations for 380 
 
 HYPEBPHORIA, DOUBLE, 
 
 causes of 351 
 
 tests for 361 
 
 proof tests for 193, 361 
 
 treatment of, 
 
 by prisms 376 
 
 by straight-forward-to-floor exercise 377 
 
 by operations 377 
 
 HYPEBTBOPIA AND CATATROPIA 581 
 
 with no cyclotropia 582 
 
 with cyclotropia 582 
 
 the causes of 583 
 
 symptoms of 583 
 
 treatment of 584 
 
 uncomplicated, 
 
 the operations for 586
 
 INDEX. 677 
 
 HYPEKTEOPIA AND CATATROPIA 581 
 
 complicated by plus cyclotropia, 
 
 the operations for 586 
 
 complicated by parallel cyclotropia, 
 
 the operations for 597 
 
 HYPEBTBOPIA, DOUBLE, 
 
 without cyclotropia 581 
 
 with minus cyclotropia 581 
 
 with plus cyclotropia 581 
 
 uncomplicated, 
 
 the operations for 584 
 
 complicated by plus cyclotropia, 
 
 the operations for 585 
 
 complicated by minus cyclotropia, 
 
 the operations for 585 
 
 INTERNUS, 
 
 correct attachment of 52 
 
 high attachment of 52 
 
 low attachment of 52 
 
 plane of 52 
 
 operations on (see " Esophoria " and " Exophoria.") 
 
 INFERIOR OBLIQUE, 
 
 plane of 53 
 
 INNEBVATIONS, THE CONJUGATE 69 
 
 what they do 147 
 
 IBIS, 
 
 muscles of 624 
 
 nerves of 626 
 
 function of 626 
 
 weak sphincter of, how to treat 627 
 
 ISOGONAL CIRCLES, PRIMARY 104 
 
 ISOGONAL CIRCLES, SECONDARY 105 
 
 ISOGONAL CIRCLE 94, 97, 102
 
 678 INDEX. 
 
 ISOGONAL SURFACE 99, 102 
 
 IK SUFFICIENCY OF THE OBLIQUES 461 
 
 JACKSON, EDWABD 302 
 
 JOHNSON, W. B 538 
 
 JULER 625 
 
 KNAPP 26, 501 
 
 LAW, 
 
 of monocular rotations 57 
 
 of binocular rotations 109 
 
 of corresponding retinal points 64 
 
 of direction 65, 94 
 
 of direction subordinate to the law of corresponding retinal 
 
 points 456 
 
 LAGLIEZE'S OPERATION 269 
 
 LAGOPHTHALMOS 618 
 
 causes of 620 
 
 symptoms of 618 
 
 treatment of 622 
 
 LANDOLT 502, 554 
 
 LAWRENCE 535 
 
 LE CONTE 35, 38, 94, 95 
 
 LENS, 
 
 changes of, in accommodation 632 
 
 effect of tilting of 637 
 
 elasticity of, how suspended 642 
 
 how to set for presbyopia 656 
 
 LISTING'S PLANE 75 
 
 law 43 
 
 LINES OF DIRECTION 35 
 
 where they cross 31 
 
 where they do not cross 27-30
 
 INDEX. 679 
 
 LIPPINCOTT 469 
 
 LOWBY 430 
 
 MACULA, THE ROTATING POINT 6 
 
 MADDOX 46, 101, 102, 187, 302 
 
 MADDOX ROD 159 
 
 its legitimate use 160 
 
 single in testing for oblique astigmatism, but multiple when 
 testing for cyclophoria 465 
 
 MAY 303 
 
 MAUNOIE 624 
 
 MAYO 625 
 
 MACULA, 
 
 " new-formed," so-called 496 
 
 MEBIDIANS, 
 
 retinal 17 
 
 spacial, monocular 17 
 
 spacial, binocular 126, 131 
 
 METRE-ANGLE OF NAGEL 141 
 
 variable with pupillary distances 142 
 
 value of, in degrees 143 
 
 METAMOEPHOPSIA THROUGH CORRECTING CYLINDERS, 
 
 cause of 462 
 
 why it disappears more quickly in some cases than in others. . . 462 
 
 MICHEL, CHARLES E 226 
 
 MONOSCOPTEB 94 
 
 MOTOR NERVES, 
 
 the third 595 
 
 the fourth 597 
 
 the sixth 597 
 
 MUSCLES ARRANGED IN NINE PAIRS . 68
 
 680 INDEX. 
 
 MUSCLE INDICATOR 113 
 
 MUSCLE PLANE, 
 
 of the internus 52 
 
 of the externus 53 
 
 MULLEB'S MUSCLE 629 
 
 nerve supply of 635 
 
 function of 641 
 
 loss of power in 643 
 
 table showing 644 
 
 in emmetropia 642 
 
 in hyperopia 645 
 
 in hyperopic astigmatism 645 
 
 in myopia 647 
 
 in myopic astigmatism 648 
 
 weakness of, in the old 650 
 
 weakness of, in the young 652 
 
 diagnosis of 656 
 
 treatment of 658 
 
 NAGEL 141 
 
 NETTLESHIP ....'.... 407 
 
 NODAL POINT 27-35 
 
 NOMENCLATURE OF THE MUSCLES 185 
 
 NOTES 222 
 
 OPHTHALMOLPLEGTA EXTERNA. 
 
 symptoms of 603 
 
 causes of 603 
 
 OPERATIONS ON THE MUSCLES 240 
 
 to lessen tension 241 
 
 to lessen tension and change plane 242 
 
 to increase tension 243 
 
 to increase tension and change plane 244 
 
 objects of all operations 310 
 
 (See the various " phorias " and " tropias.")
 
 INDEX. 681 
 
 ORBITAL MALFORMATIONS 182 
 
 OBLIQUE MUSCLES, 
 
 history of the study of 184 
 
 simple function of 450 
 
 complicated function of 452 
 
 OBLIQUES, INFERIOR, 
 
 once thought to be advertors 504 
 
 possibly cut by Taylor 507 
 
 OPTIC Axis 10, 32, 528 
 
 ORIENTATION 59, 74 
 
 ORTHOPHORIA 146 
 
 lateral, tests for 149, 152, 157 
 
 vertical, tests for 150, 152, 3 57 
 
 oblique, tests for 154, 161, 163, 250 
 
 sthenic 176 
 
 asthenic 177 
 
 treatment of 177 
 
 PLANES OF REFERENCE 73 
 
 median fixed plane 73 
 
 horizontal fixed plane 73, 182 
 
 PLANE OF ROTATION, 
 
 how to construct 51 
 
 PLANE OF ROTATION OF INDIVIDUAL MUSCLES 51-57 
 
 PAN AS' OPERATION 503 
 
 PARALYSIS, 
 
 of the third nerve 600 
 
 symptoms of 600 
 
 causes of 598 
 
 treatment of 616 
 
 of the fourth nerve 602 
 
 causes of 598 
 
 symptoms of , 602
 
 682 INDEX. 
 
 PARALYSIS, 
 
 treatment of 616 
 
 of the sixth nerve 602 
 
 causes of 598 
 
 symptoms of 602 
 
 treatment of 616 
 
 of the seventh nerve 618 
 
 PARALYSIS AND PARESIS, 
 
 diagnosis of 603 
 
 rules for finding the affected muscle 604, 605 
 
 of a right-vertor 606 
 
 of a left-vertor 607 
 
 of a sub-vertor 608, 610 
 
 of a supervertor 609, 610 
 
 pose of the head in 611 
 
 PARALYSIS, 
 
 of motion, and not of muscle 611 
 
 symptoms of 615 
 
 PERIMETER, 
 
 for making version tests 168 
 
 PERRY, C. H 398, 428 
 
 PETIT 625 
 
 POLES 27-33 
 
 POLE, POSTERIOR 10, 17, 19, 20, 24, 25, 94 
 
 POLE, ANTERIOR 10, 19, 20, 25, 27-35 
 
 POLE, SPACIAL, MONOCULAR 17 
 
 POLE, BINOCULAR 124, 135 
 
 PRESBYOPIA, 
 
 causes of 644, 650 
 
 can it be deferred? 650 
 
 treatment by exercise 652 
 
 treatment by correcting lenses 655
 
 INDEX. 683 
 
 PStUDO-ESOPHOBIA, 
 
 how manifested 646 
 
 when desirable 647 
 
 when harmful 647 
 
 PSEUDO-EXOPHOBIA, 
 
 how manifested 648 
 
 PBISMS, 
 
 a cause of compensating heterotropia 492 
 
 PBICE'S CYCLO-PHOBOMETEB, 
 
 the first made 160 
 
 PBICE, GEOBGE H 253 
 
 PHOBOMETEB, 
 
 the Stevens 147 
 
 its capabilities 148 
 
 why objectionable 148 
 
 method of using 149 
 
 the Wilson, 
 
 its capabilities 152 
 
 why objectionable 148 
 
 method of using 152 
 
 the correct principle of construction of the 155 
 
 the Monocular 156 
 
 QUEBIN 511 
 
 RANNEY 209 
 
 RETINAL POINTS, 
 
 law of corresponding 64 
 
 RISLEY 182 
 
 ROTATIONS, 
 
 cardinal 7, 2i 
 
 oblique 58 
 
 monocular 39-63 
 
 binocular . 63-110
 
 684 INDEX. 
 
 ROTATIONS, 
 
 law of 57, 59 
 
 axis of i, 2, 5, 10, 44, 45, 51 
 
 plane of l, 2, 5, 13, 19, 51 
 
 by a single muscle 51 
 
 in the four cardinal directions 41, 77 
 
 in any oblique direction 41, 78, 79 
 
 ROTATING LINE 2, 4, 5, 6, 17 
 
 ROTATING POINT 4, 5, 6, 20 
 
 ROTATING POINTS, Two 7 
 
 RHYTHMIC EXERCISE OF THE MUSCLES 226 
 
 STRABISMUS 497 
 
 STEVENS' NOMENCLATURE 146 
 
 phororaeter 147 
 
 clinoscope 160 
 
 description of 164 
 
 tropometer 169 
 
 STEVENS 182, 184, 209, 225 
 
 STEELE, N. C 472 
 
 SMITH, PRIESTLEY 533, 635 
 
 SHORTENING OPERATIONS, 
 
 advantages of 257 
 
 to only increase tension 258 
 
 to alter tension and change plane 262 
 
 marginal 262 
 
 STROMEYEH 499 
 
 SUB-DUCTION, THE NORMAL 153, 158, 198 
 
 SUPERDUCTION, THE NORMAL 153, 158, 191 
 
 SUPERVERSION 169, 171, 202 
 
 SUB-VERSION 169, 172, 202 
 
 SQUINT ......... 497 
 
 SUPPRESSION, MENTAL 66
 
 INDEX 685 
 
 SYNERGISTS AND ANTAGONISTS, 
 
 tables of 59, 62 
 
 old table 59, 60 
 
 new table 62, 63 
 
 TAYLOR, THE SQUINT QUACK 505 
 
 TESTS FOR HETEROPHORIA 189 
 
 TENOTOMY, 
 partial, 
 
 central, to lower tension 251 
 
 marginal, to lower tension and change plane 256 
 
 TENDONOMETER 254 
 
 TSCHERNING 632 
 
 TORSION, 
 
 measured 47 
 
 table of 48, 50 
 
 how prevented 46 
 
 TROPOMETER, 
 
 description of 169 
 
 THORINGTON 303 
 
 VERSION POWER, 
 
 standard of 174 
 
 VERSION TEST, 
 
 value of 199 
 
 by tropometer 200 
 
 by perimeter 200 
 
 VISUAL Axis 8, 528 
 
 VISUAL LINES 14, 31, 35 
 
 WILSON, HAROLD 420 
 
 WORTH 545 
 
 YOUNG 629, 630 
 
 ZONULA, 
 
 how relaxed . 631
 
 Date Due 
 
 CAT. NO. 23 233 PRINTED IN U.S.A.
 
 A 000510439 
 
 WWU o 
 
 S263 o 
 1911 
 
 Savage, Giles C 
 
 Ophthalmic myology 
 
 wwUoo 
 
 S263 o 
 1911 
 Javage, Giles C 
 
 Ophthalmic myology . . . 
 
 MEDICAL SCIENCES LIBRARY