B M 31T 571 ,,GTIO^ end MUSCULAR liM:BALANGE ■ AS SIMPLrFIED )ugh.the use of the [^tom:eter wmmmmmti^^ aERKELEY LIBRARY UNfVE^SlTY OP CALlfORNlA Cos A Columbia (Hnitoer^ftp mtl)eCttp0f3amgork THE LIBRARIES OPTOMETRY LIBRARY DOITATED BY LEO HIRSCHBERG Optometry '17 Ski-optometer Master Model 215 Embodying in a Single Instrument, in Convenient Form, Cylindrical and Spherical Lenses, in Combination with Appliances for Testing and Cor- recting Miiscvdar Imbalance. Refraction and Muscular Imbalance As Simplified Through the Use of the Ski-optometer By DANIEL WOOLF / WOOLF INSTRUMENT CORPORATION New York: 516 Fifth Avenue r iCxvjJCC^ jL^/YtX^^ iERiCELSY \ UhkARY UNfVc«JlTY Of CALIfORNiA OPTOMETRY LIBRARY Copyright 1921 By WOOLF INSTRUMENT CORPORATION Published by Theodore S. Holbrook New York CONTENTS Chapter I Page SkI-OPTOMETER CoNSTRUCTrON 1 Convex Spherical Lenses... 2 Operates and Indicates Automatically 6 Concave Spherical Lenses 7 Chapter II Cylindrical Lenses 10 Obtaining Correct Focus 11 Why Concave Cylinders Are Used Exclusively 14 Transposition of Lenses >.• 14 Chapter III How THE Ski-optometer Assists in Refraction 17 The Use of the Ski-optometer in Skioscopy 17 A Simplified Skioscopic Method 20 Employing Spheres and Cylinders in Skioscopy.. 22 Use of the Ski-optometer in Subjective Testing.. 23 A Simplified Subjective Method 24 Procedure for Using Minus Cyhnders Exclusively 26 Constant Attention Not Required 29 Chapter IV Important Points in Connection with the Use OF THE Ski-optometer 30 Elimination of Trial Frame Discomfort 30 Rigidity of Construction 31 How to Place the Ski-optometer in Position 32 Cleaning the Lenses 33 Accuracy Assured in Every Test 34 Built to Last a Lifetime 35 CONTENTS— Continued Chapter V Page Condensed Procedure for Making Sphere and Cylinder Test with the Ski-op tometer 37 Subjective Distance Test 37 Subjective Reading Test 40 Chapter VI Muscular Imbalance 41 The Action of Prisms 42 The Phorometer 43 The Maddox Rod 44 Procedure for Making the Muscle Test 45 Binocular and Monocular Test 47 Chapter VII The Binocular Muscle Test 4S Made with the Maddox Rod and Phorometer... 48 Esophoria and Exophoria 50 Making Muscle Test Before and After Optical Correction 52 When to Consider Correction of Muscular Im- balance 53 Four Methods for Correction of Muscular Im- balance 54 The Rotary Prism 54 Use of the Rotary Prism in Binocular Muscle Tests 56 Chapter VIII The Monocular Duction Muscle Test 58 Made with Both Rotary Prisms 58 Locating the Faulty Muscle 58 Adduction 59 Abduction 61 CONTENTS— Continued » Page Superduction 62 Subduction 63 Procedure for Monocular Muscle Testing 64 Diagnosing a Specific Muscle Case 65 Chapter IX First Method of Treatment — Optical Correc- tion 70 Esophoria 70 Treatment for Correcting Esophoria in Children 72 How Optical Correction Tends to Decrease 6° Esophoria in a Child 74 Chapter X Second Method of Treatment — Muscular Exercise 75 Made with Two Rotary Prisms and Red Mad- dox Rod 75 Exophoria 75 An Assumed Case 78 Effect of Muscular Exercise 80 Home Treatment for Muscular Exercise — Square Prism Set Used in Conjunction with the Ski-optometer 82 Chapter XI Third Method of Treatment — Prism Lenses 84 When and How Employed 84 Prism Reduction Method 85 Chapter XII A Condensation of Previous Chapters on the Procedure for Muscle Testing with the Ski-optometer 87 CONTENTS— Crw///////^^/ • Page Four Methods of Treating an Imbalance Case when the Preceding One Fails 90 Prisms 92 Cyclophoria 92 Chapter XIII Cyclophoria 93 Made with Maddox Rods and Rotary Prisms.... 93 Chapter XIV Cycloduciton Test 99 Made with the Combined Use of the Two Mad- dox Rods 99 Treatment for Cyclophoria 102 Chapter XV Movements of the Eyeballs and their Ano- malies 105 Monocular Fixation 105 Binocular Fixation 106 Orthophoria ..• 107 Heterophoria 107 Squint 108 Varieties of Heterophoria and Squint 109 Chapter XVI Law of Projection H-l- Suppression of Image 115 Monocular Diplopia 115 Table of Diplopia 116 Movement of Each Eye Singly 117 Subsidiary Actions 118 Field of Action of Muscles 120 Direction of the Gaze 120 CONTENTS— Co//./«./^^/ Page Primary Position — Field of Fixation 121 Binocular Movements 121 Parallel Movements 122 Lateral Rotators 123 Eye Associates 124 Movements of Convergence 125 Movements of Divergence 125 Vertical Divergence 126 Orthophoria 126 Heterophoria 126 Subdivisions 126 Chapter XVII Symptoms of Heterophoria 128 Treatment 130 Destrophoria and Laevophoria 132 ^ I ''HE demands of the day for maximum efficiency in the refracting world are largely accountable for the inception, con- tinuous improvement and ultimate develop- ment of the master model Ski-optometer. The present volume, dealing w^ith the in- strument's distinctive operative features, has been prepared not only for Ski-optometer users, but also for those interested in the sim- plification of refraction and muscular im- balance. The author is indebted for invaluable counsel, to Louis J. Ameno, M.D., New York. E. LeRoy Ryer, O.D., New York. Jos. D. Heitger, M.D., Louisville, Ky. W. B. Needles, N.D., Kansas City, Mo. INTRODUCTORY 1 X 7H1LE in a measure the conventional trial case still serves its purpose, so much of the refractionist's time is consumed through the mechanical process of individually transfer- ring the trial case spheres and cylinder lenses, that far too little thought is given to muscular imbalance, notwithstanding its importance in all refraction cases. Dr. Samuel Theibold, of Johns Hopkins University, in a recent address before the American Medical Association, stated that the average ref ractionist was inclined to devote an excess of time to general refraction, completely overlooking the important test and correction of muscular imbalance. If the latter is to be at all considered, general refraction must be simplified — without impairing its accuracy — a result that is greatly facilitated through the use of the Ski-optometer. One must admit that tediously selecting the required trial-case lens — whether sphere, cyl- inder or prism — watching the stamped num- ber on the handle — continual wiping and in- serting each individual lens in a trial frame is a time-consuming practise. This is readily overcome, however, through the employment of the Ski-optometer. INTRODUCTORY In a word, the Ski-optomctcr is practically an automatic trial case, bearing the same rela- tion to the refracting room as the accepted labor and time-saving devices of the day bear to the commercial world. The present volume has accordingly been published, not alone in the interest of those possessing a Ski-optometer, but also for those interested in attaining the highest point of ef- ficiency in the work of refraction and muscu- lar imbalance. Ski-cptorneter Lens Battery [ahnost actual i/zf] shoiv- ing hoiv sphere and cyl- inder lenses are procured. Supple in e n t a r y Disk Handle and Indicator. Cylinders Register Here 1st — Turn this Single Reel to obtain all your spherical lenses, whether convex or concave. 2nd — Set this axis indicator, which automat- ically positions each cylinder lens at the axis designated. 3rd — Then merely turn this Single Reel to obtain your various cylinder lens strengths at that axis. After obtaining FINAL results, your prescription is automatically re- gistered, ALL READY for you to transcribe. Fig. 1 — The three time-saving moves necessary in the operation of the Ski-optometer. Chapter I SKI-OPTOMETER CONSTRUCTION A FAR better understanding of the instru- ment will be secured if the refractionist possessing a Ski-optometer will place it before him, working out each operation and experi- ment step by step in its proper routine. The three moves as outlined in Fig. 1 should first be thoughtfully studied and the method of obtaining the spheres and cylinders carefully observed. Fig. 2— To Obtain Piano. 1 — Set spherical indicator at "000" as illustrated above. 2 — Set cylinder indicator to "0". 3 — Set pointer of supplementary disk at "open". The instrument should then be set at zero or ''piano," a position indicated by the appear- [1] Refraction and Muscular Imbalance ance of the three ^'o o o'' at the spherical register, in conjunction with one ^'o," or zero, for the cylinder at its register, marked ^'CC Cyl." After this move, the supplementary disk's pointer should be set at ''open" (Fig. 2). sphere Ind'u /itor Fig. 3 — To obtain sphericals, turn this Single Reel as shown by dotted finger. This assures an automatic and simultaneous registration at sphere indicator of focus of lens appearing at sight opening. Convex Spherical Lenses A careful study will show that the Ski- optomoter's spherical lenses are obtained by merely turning the smaller reel (Fig. 3). The first outward turn of this reel, toward the temporal side of the instrument, draws into position in rcguhir order the spherical lenses [2] Refraction and Muscular Imbalance -f.25, +.50, +.75, and +1.D., as shown in Fig. 3a. 3-A — Outer spherical reel containing Cx. sphericals from .025 to l.OOD and a blank. 3-B — Inner spherical disk containing Cx. sphericals, automatically turns within 3-A. 3-C — Supplementary spherical disk. By means of a concealed tooth gear, an inner disk is automatically picked up, placing its first lens +1.25D in position (Fig. 3b). This + 1.25D spherical lens remains stationary while the outer disk again revolves, adding to it the original +.25, +.50, +.75 and +1.D., [3] Refraction and Muscular Imbalance Fig. 4 — With the reappearance of "00" at sphere indicator, a rapid increase or decrease of +1.25 is accurately and speedily attained, the latter totalling +2.25D. At this point, the instrument again automatically picks up its inner disk, thereby placing its second lens, +2. SOD, in position. Instead of using intermediate strengths in making an examination, it is frequently desir- able to make such extended changes as 1.2SD to 2. SOD. With the Ski-optometer, the re- fractionist will note that two white zeros ap- peared at the spherical register in connection with +1.2S, and again with +2. SO. A rapid outward turn of the spherical reel toward the temporal side to the point of the reappearance of the two zeros will show +3.7SD; or, if in- creased power is still desired, a rapid turn will draw +5. D. into position (Fig. 4). [4] Refraction and Muscular Imbalance Turning the reel inward toward the nasal side will likewise decrease its convex power. In brief, each one of these lenses, showing their foci in conjunction with the two white zeros, are signals indicating the rapid increase or decrease of one and one-quarter diopter. After continuing to +6D., the next turn auto- matically shows zero (or ^'plano"), the origi- nal starting point, which is again indicated by the three white zeros. Through the turn of the single reel — an ex- clusive Ski-optometer feature — all convex spherical lenses have now been attained in quarters up to -r6.D, practically covering ninety percent of all refraction cases. Fig. 5 — With supplementary disk pointer set at -j- 6 Sph., this places an additional + 6.D spherical lens at sight opening, extending instrument's total convex spherical power to +12. D. [5] Refraction and Muscular Imbalance Should still greater power be desired, the small pointer at the outer edge of the instru- ment should be set at +6 sphere (Fig. 5). This controls a supplementary disk (Fig. 3c) which places an additional +6D. lens before the original range of lenses previously referred to, thus increasing the maximum power to + 12D. If still greater strength is required, any additional trial case lens may be added, a cell being provided for that purpose on the forward plate of the instrument. Operates and Indicates Automatically As previously explained, in using the Ski- optometer, it is only necessary to remember that each outward turn of the single reel toward the temporal side of the patient in- creases the plus power, while the reverse turn toward the patient's nose decreases it. In fact, no attention need ever be given the register until the required sum-total is secured, it only being necessary to turn the single reel in order to be assured of the unvarying and accurate operation of the instrument. For convenience, the contour or upper edge of the plate covering the spherical reel has been made to fit the index finger (Fig. 3). Hence the operator should note that it requires but one complete turn from extreme side to [6] Refraction and Muscular Imbalance side, rather than a number of short turns, in order to bring each individual lens into posi- tion, thus obtaining the full advantage of the automatic spring-stop. This likewise permits the refractionist to operate the Ski-optometer even though the room is in total darkness. Concave Spherical Lenses Another simple and exclusive Ski-optom- eter advantage w^orthy of note is the method employed in obtaining concave, spherical lenses. Instead of employing a battery of con- cave lenses similar to the convex battery pre- viously described, the instrument's operation is greatly simplified through the use of a neu- tralizing process. In short, the Ski-optometer only contains two concave lenses to obtain its entire series — namely, a — 6.D and a — 12.D sphere (Fig. 3c) — first setting the pointer of the sup- plementary disk at — 6. sphere, then setting the indicator of the spherical battery at +6. Thus zero (or piano) is obtained, the plus neutralizing the minus. By merely turning the plus or convex spher- ical reel inward, or toward the patient's nose, the convex power is then decreased, naturally increasing the concave value or total minus lens power. For example, if the spherical in- [7] Refraction and Muscular Imbalance dicator shows +S.D, when the — 6D. lens is placed behind it, the lens value at the sight opening will be — ID (Fig. 6). If re- quired, the refractionist may continue on this plan until only the — 6D. lens remains. Fig. 6 — With this indicator of supplementary disk, set at — 6.D, Sph. and spherical indicator at +5.0 — lens value at sight opening is — l.D. Sph. This simple arrangement makes it possible to operate the Ski-optometer with but Single Reel for both plus and minus sphericals. Should concave power stronger than — 6D. be desired, by placing the pointer of the sup- plementary disk at — 12D. Sph. and proceed- ing to neutralize as before, all the concave powers up to — 12D. in quarters are similarly obtained. For the convenience of the opera- tor, all minus or concave spherical powers are indicated in red; while plus, or convex pow- ers, are indicated in white. [8] Refraction and Muscular Imbalance The instrument is also provided with an opaque or blank disk which is brought into position before the sight opening by setting the pointer of the supplementary disk at ''shut" (Fig. 3c.) Summing up, all plus and minus spherical powers have been attained from zero to 12D. in quarters, practically through the turn of the smgle reel — a simplicity of operation largely responsible for Ski-optometer supremacy. [9] Chapter 11 CYLINDRICAL LENSES TT is commonly admitted that setting each trial case cylindrical lens at a common axis is the most tedious part of refraction. The automatic cylinder, one of the Ski- optometer's latest and distinctly exclusive fea- tures, not only overcomes this annoyance but also avoids the need of individually trans- ferring each cylindrical lens according to the varying strengths. Fig. 7 — Once you set the axis indicator as shown by ciotted finders, each cylindrical lens in the instrument auto- matically positions itself exactly at that axis, as indi- cated by the arrow. By merely setting the Ski-optometer's axis indicator (Fig. 7), each cylindrical lens in the instrument automatically positions itself, [10] Refraction and Muscular Imbalance so that it will appear at the opening at the exact axis indicated. This is readily accomplished by placing the thumb on the small knob, or handle of the axis indicator, drawing it outward so as to release it from spring tension. The indicator may then be set at any desired axis; and, on releasing the handle, every cylinder in the in- strument becomes locked, making it impos- sible for any lens to appear at an axis other than the one specified by the indicator. This insures the absolute accuracy of the axis of every cylinder as it appears before the patient's eye. Subsequent shifting of the axis even to a single degree is impossible, al- though it is a common occurrence where trial- case lenses are employed. Obtaining Correct Focus After setting the axis indicator, the only re- maining move is to obtain the correct cylin- drical strength or focus. This is readily ac- complished by merely turning the Ski-optom- eter's larger or extreme outer single reel, which contains concave cylindrical lenses from .2SD to 2D in quarters (Fig. 8a). It should again be borne in mind that a down- ward turn increases concave cylinder power, while an upward turn decreases it. The oper- [11] Refraction and Muscular Imbalance ation of the cylinder reel is greatly facilitated by carefully noting position of thumb and in- dex finger (Fig. 8). Thus accuracy of result, simplicity of operation and the saving of much valuable time is invariably assured. Fig. 8A — Inner cog-wheel construction, showing arrange- ment of Ski-optometer cylinders. This simple construc- tion assures accuracy and avoidance of the slightest shifting of axes. As each cylinder appears before the pa- tient's eye, it simultaneously registers its focus at the indicator marked "CC CYL" shown in Fig. 8. Examinations of greater accuracy could not possibly be made than those obtained through the Ski-optometer, hence no refrac- tionist should hesitate to employ it throughout an eni'ire examination — wherever trial-case lenses are used. The range of the Ski-optometer's cylinder- lens battery includes up to 2D. in quarters. An axis scale and a cell is located at the back [12] Refraction and Muscular Imbalance of the instrument for insertion of an additional trial-case cylinder lens, when stronger cylin- Fig. 8 — Turn this Single Reel as shown by dotted finger to obtain cylindrical lenses, which simultaneously register their focus as they appear. Each lens also automatically positions itself at axis designated. drical power is required. For example, if an additional — 2D. cylinder is added, it will in- crease the range up to 4D. cylinder; or if twelfths are desired, an 0.12D. cylinder lens may be inserted. In this connection, it is in- teresting to note that considerable experiment- ing with twelfths in the Ski-optometer proved them to be needless, inasmuch as the instru- ment's cylindrical lenses set directly next to the patient's eyes overcome all possible loss of refraction, as explained in a later paragraph. [13] Refraction and Muscular Imbalance Why Concave Cylinders Are Used Exclusively The Ski-optometer contains only concave cylinders, as it is universally admitted that convex cylinders are not essential for testing purposes. In fact, concave cylinders should alone be used in making an examination, even where a complete trial-case is employed. To repeat one of the first rules of refraction: "As much plus or as little minus spherical power as pa- tients will accept, combined with weakest minus cylinder, simplifies the work of refrac- tion and insures accuracy without time- waste." After an examination with the Ski-optom- eter is completed, the total result of plus sphere and minus cylinder may be transposed if desired, though in most intances it is pre- ferable to prescribe the exact findings indi- cated by the instrument. This will also avoid every possibility of error, eliminating respon- sibility where one is not familiar with trans- position — since, after all, it is the duty of the optician to thoroughly understand that part of the work. Transposition of Lknses It is commonly understood that transposi- tion of lenses is merely change of form, but not of value. [14] Refraction and Muscular Imbalance For example, a lens +1.00 sph. = — .50 cyl. axis 180° may be transposed to its equivalent, which is -r .50 sph. == 4- .50 cyl. axis 90^ The accepted formula in this special instance is as follows : Algebraically add the two quan- tities for the new sphere, retain the power or the original cylinder, but change its sign and reverse its axis 90 degrees. Applying this rule, a lens -r .75 sph. = — .25 cyl. axis 180°, is equivalent to + .50 sph. = + .25 cvl. axis 90°. Similarly, a lens +1.00 sph. = — 1.00 cyl. axis 180° is equivalent to +1.00 cyl. axis 90°. One of the difficulties in transposing is in reversing the axis. In such cases, it is well to m_emorize the following simple rule : To reverse the axis of any cylindrical lens containing three numerals — add the first two together and carry the last. For example, from 105 to 180 degrees, etc.: 105° Add — one and "0" equals 1 Then carry the 5 = 15° 120° Add— one and two equals 3 Then carry the = 30° 130° Add — three and one equals 4 Then carry the = 40° 150° Add — live and one equals 6 Then carry the ^ 60° 165° Add — six and one equals 7 Then carry the 5 = 75° 180° Add — eight and one equals 9 Then carry the ^ 90° To transpose where there are but tivo numerals, 90° should be added. In using the Ski-optometer, it is absolutely unnecessary to transpose the final result of an examination; merely write the prescription as [15] Refraction and Muscular Imbalance instrument indicates. The idea that plus sphere combined with minus cylinder, or the reverse, is an incorrect method of writing a prescription, has long since been disproved. [16] Chapter III HOW THE SKI-OPTOMETER ASSISTS IN REFRACTION ^"T^HE construction of the Ski-optometer has now been fully explained, and the reader realizes that since the instrument contains all the lenses necessary in making an examination, greater operative facility is afforded through its use than where the trial-case lenses are em- ployed. The Ski-optometer is ^'an automatic trial- case" in the broadest sense of the term, wholly superseding the conventional trial-case. It should therefore be employed throughout an entire examination, wherever trial-case lenses were formerly used. To fully realize its labor saving value in obtaining accurate ex- amination results, it is only necessary to recall the tedious method of individually handling and transferring each lens from the trial-case to the trial-frame, watching the stamped num- ber on each lens handle, wiping each lens and in the case of cylindrical lenses setting each one at a designated axis — all being needless steps where the Ski-optometer is employed. The Use of the Ski-optometer in Skioscopy In skioscopy, the Ski-optometer offers the refractionist assistance of the most valuable character. [17] Refraction and Muscular Imbalance For example, assuming that extreme motion in the opposite direction with plane or con- cave mirror is obtained with a +1 .2SD. spheri- cal lens before the patient's eye; by quickly turning the Ski-optometer's single reel until the two white zeros again appear, +2. SOD is secured, as explained in the previous chapter. If this continues to give too much ''against motion," the lens power should be quickly in- creased to +3.75 or +S.OOD if necessary (Fig. 4) . Should the latter reveal a shadow in the reversed direction, the refractionist is as- sured that it is the weakest lens that will cause its neutralization. Practically but few lenses have been used to obtain the final result prov- ing the instrument's importance and time-sav- ing value in skioscopy, and demonstrating the simplicity with which tedious transference of trial-case lenses is avoided. Furthermore, it should be noted that where the Ski-optometer is used in skioscopy, it is not necessary to remove the retinoscope from the eye or to constantly locate a new reflex with each lens change. This permits a direct comparison of the final lens and eliminates the usual difficulty in mastering skioscopy. The chief cause of this difficulty is due to the fact [18] Refraction and Muscular Imbalance that the transferring of the trial-case lenses makes it practically impossible for the student to determine whether the previous lens caused more 'Svith" or ''against" motion. Where the indirect method is employed in skioscopy, best results are secured through the use of the Woolf ophthalmic bracket and con- Fig. 9 — The Woolf ophthalmic bracket. A convenient and portable accessory in skioscopy and muscle testing; can be used with or without Greek cross. centrated filament lamp, together with an iris diaphragm chimney. The latter permits the reduction or increase of the amount of light entering the eye, as it is agreed that a large pupil requires less light, a small pupil re- quiring more light. The bracket referred to permits the operator to swing the light into any desired position (Fig. 9), while the iris diaphragm chimney serves as a shutter. This apparatus may also be employed for [19] Refraction and Muscular Imbalance muscle testing, as described in a subsequent paragraph. A Simplified Skioscopic Method In using the Ski-optometer, instead of working forty inches away from the patient in skioscopy and deducting I.D., the refrac- tionist will find it more convenient to work at a twenty-inch distance, deducting 2.D. This working distance may be accurately mea- sured and maintained by using the reading rod accompanying the instrument. Instead of deducting 2.D. from the total findings, however, it is preferable to insert a +2.D. trial case lens in the rear cell of the instru- ment directly next to the patient's eye. After determining the weakest lens required to neu- tralize the shadow in both meridians, the ad- ditional +2.D. lens should be removed and the total result of the examination read from the instrument's register. To illustrate a case in skioscopy where spherical lenses are employed to correct both meridians, assume that the vertical shadow requires a +1.2SD lens to cause its reversal, while the horizontal recjuires +2.00D. Em- ployment of the customary diagram, illus- trated in Fig. 10, would show the patient re- quired M.2S sph. -~ +.75 cyl. axis 90, which [20] Refraction and Muscular Imbalance when transposed is equivalent to +2.00 Sph. = —.75 cyl. axis 180°. -I- ZOO Fig. 10 — Where spherical lenses are employed in Ski- oscopy, above indicates patient requires -1- 125 Sph. = + 75 Cyl. Axis 90° or + 2 Sph. = — 75 Cyl. Axis 180° It should be noted that the total spherical power is +2.00D, as the Ski-optometer's register shows, while the difference between the two meridians is 75, which is the required strength of the cylinder. By then turning the cylinder reel to .75, and setting the axis indi- cator at 180° (because by using minus cylin- ders, the axis must be reversed) the patient should read the test type with ease if the ski- oscopic findings are correct. Thus with the Ski-optometer, it is not even necessary to learn transposition, since the instrument automati- cally accomplishes the work, avoiding all pos- sibility of error. [21] Refraction and Muscular I w balance Employing Sphlrhs and Cylinders in Skioscopy Another commonly used objective method may be employed with even greater facility through the combined use of both the Ski- optometer's spherical and cylindrical lenses. As previously suggested, insert the +2.00 spherical trial-case lens in the rear of the in- strument, working at a twenty inch distance, then proceed to correct the strongest meridian first. It was assumed that it required a +2.00 spherical to neutralize the strongest, or hori- zontal meridian, as shown in Fig. 10. The re- fractionist should then set the axis indi- cator therewith, which is the axis of the cylin- der, or 180°. It is then merely a matter of increasing the Ski-optometer's cylindrical lens power until the reversal of the shadow in the weakest meridian is determined. Assuming this proves to be — .75 cylinder, axis 180°, the patient's complete prescription +2.00 sph. = — .75 cyl. axis 180°, would be registered in the Ski-optometer without any further lens change other than the removal of the +2.00 working distance lens. However, regardless of the method em- ployed, the Ski-optometer greatly simplifies [22] Refraciion and Muscular Imbalance skioscopy. In fact, the instrument was origi- nally intended to simplify retinoscopy or skio- scopy, as the subject should be termed, the name ''Ski-optometer" having been derived from the latter. Use of the Ski-optometer in Subjective Testing In subjective refraction, especially where the "better or worse" query must be decided by the patient, it is commonly understood that the refractionist is compelled to first increase and then decrease a quarter of a diopter before the final lens is decided. With the Ski-opto- meter, the usual three final changes are made in far less time than it takes to make even one lens change from trial-case to trial-frame. For example : Assuming, with a +1.2SD spherical lens before the patient's right eye, he remarks that he "sees better" with a +1.D. while +.75D is not as satisfactory. The refractionist can then quickly return to +1.D., simply turning the Ski-optometer's single reel outward to in- crease, or backward to decrease, the lens strength. So rapidly have these lens changes been made, that the patient quickly sees the difTference of even a quarter diopter, and quickly replies, "better" or "worse." This is made possible because the eye does [23] Refraction and Muscular Imbalance not ''accommodate" as quickly as the lens change made with the Ski-optometer. It should also be noted that the eye receives an image on its retina within one-sixteenth of a second; otherwise, the patient is forced to ac- commodate, making it difficult to see the dif- ference of even a quarter dioptre. On the other hand, in transferring trial-case lenses, with its slow, tedious procedure, the patient, being unable to detect the slight difference of only a quarter diopter, unhesitatingly replies, *^no difference," merely because they are com- pelled to accommodate. A Simplified Subjective Method The following simplified method of pro- cedure is suggested for subjective testing with the Ski-optometer, although as previously ex- plained, the refractionist may employ his cus- tomary method, overcoming the annoyance of transferring trial-case lenses and the setting of each cylinder individually. The Ski-optom- eter has been constructed and based upon the golden rule of refraction : ''As much plus or as little minus spherical, combined with as little minus cylinder power as the patient accepts." By applying this rule as in the above method and starting with +5.D. spherical, watching [24] Refraction and Muscular Imbalance the two zeros (Fig. 4) and rapidly reduc- ing + 1.25D each time, we will assume that + 1.25D gives 20/30 vision; as a final result + 1.D. will possibly give 20/25 vision. The patient's attention should next be di- rected to the most visible line of type, pre- ferably concentrating on the letter ''E" or the clock dial chart^ — either of which will assist in determining any possible astigmatism. Since the Ski-optometer contains concave cylinders exclusively, the next move should be the set- ting of its axis indicator at 180°, commonly understood as "with the rule." One should then proceed to determine the cylinder lens- strength by turning the reel containing the cylindrical lenses (Fig. 8). Should the pa- tient's vision fail to improve after the — .50D. cylinder axis 180° has been employed, the re- fractionist, in seeking an improvement, should then slowly move the axis indicator through its entire arc. With the cylinder added, regardless of axis, poor vision might indicate the absence of astigmatism. If astigmatism exists, vision will usually show signs of improvement at some point, indicating the approximate axis. Once the latter is ascertained, the re- fractionist may readily turn the Ski-optom- eter's cylinder reel and obtain the correct cyl- [25] Refraction and Muscular Imbalance inder lens strength, after which the axis in- dicator should be moved in either direction in order to obtain the best possible vision for the patient. The refractionist should always aim to ob- tain normal (or 20/20) vision with the weak- est concave cylinder, combined with the strongest plus sphere, or weakest minus sphere. Procedure for Using Minus Cylinders Exclusively For the benefit of those who have never used minus cylinders exclusively in making their examinations, we will assume that the patient requires O.U. fl.D Sph. = — ID cyl. axis 180° for final correction; the latter, in its trans- posed form, being equivalent to +1.D. cylin- der axis 90°. Unquestionably the best method is the one that requires the least number of lens changes to secure the final result. To obtain this, the following order of lens change should be made: First, +r.D. sphere is finally determined and allowed to remain in place. Concave cylinders are then employed in quarters until the final results of +1.D. spherical, combined with — l.D. cylinder axis 180° is secured. This necessitates the change of but four cylindrical lenses as shown in rou- tine ''A" as follows: [26] Refraction and Muscular Imbalance ROUTINE "A" ROUTINE "B" (Made with minus cylinder) (Made with plus cylinder) Sph. +1.D. Cvl. Axis Sph. +1.D. Cyl. Axis Step 1 +1.D. — —25 ax. 180° equal to +.75 = +.25 ax. 90° Step 2 +1.D. = —50 ax. 180° equal to +.50 = +.50 ax. 90° Step 3 +1.D. = —75 ax. 180° equal to +.25 = +.75 ax. 90° Step 4 +1.D. = —1 ax. 180° equal to +1 ax. 90' In brief the method of using minus cylin- ders exclusively in an examination, as ex- plained in routine ''A", necessitates the change of the cylinder lenses only after the strongest plus sphere is secured. On the other hand, notwithstanding in- numerable other methods where plus cylin- ders are used, routine "B'' shows that the best spherical lens strength the patient will accept, is also first determined. Then both spheres and cylinders are changed in their regular order by gradually building up in routine, by increasing plus cylinder and next decreasing sphere, a quarter dioptre each time, until the final result is secured. While it is conceded that both routine "A" and "B" are of themselves simplified meth- ods, by comparing routine ^^A" where minus cylinders are used with routine ^'B" where plus cylinders are used in their corresponding steps, the ref ractionist will note by comparison that one is the exact equivalent and transposi- tion of the other. Where plus cylinders are [27] Refraction and Muscular Imbalance employed, eight lens changes are made be- fore final results are secured; while but four lens changes are necessary where minus cylin- ders are used. The refractionist should also note by com- parison that the use of minus cylinders re- duces focus of the plus sphere, but only in the meridian of the axis. It has not made the pa- tient myopic. Furthermore, a plus cylinder will bring the focal rays forward, while minus cylinders throw them backward toward the retina. This is but another reason for the exclusive use of minus cylinders in refraction. The method of using minus cylinders exclu- sively in an examination, necessitates the change of the cylinder lenses only. On the other hand, the method of using plus cylinders makes it necessary to change spheres and cyl- inders in routine. In brief, since using the minus cylinder is merely a matter of mathematical optics, their use even in a trial-case examination is strongly urged. The maximum value of the Ski-optometer is fully realized only when the advantages of using minus cylinders exclusively in every ex- amination is clearly understood. [28] Refraction and Muscular Imbalance Constant Attention Not Required With the Ski-optometer, when the examina- tion is completed, the sum-total of final re- sults — whether spherical, cylinder, axis, or all combined— are automatically indicated or registered ready to write the prescription. Until then, the foci of the various lenses that may be employed are of no importance. In short, in using the Ski-optometer, it is not necessary to constantly watch the registra- tions during examinations. The automatic operation of the instrument is an exclusive fea- ture, so that the refractionist should unhesi- tatingly employ it. Hence, by eliminating the perpetual watch on the lenses in use, the re- fractionist is enabled to give his undivided at- tention to the patient rather than to the trial lenses. Where a special dark-room is used for ski- oscopic work, an additional wall bracket or floor-stand will necessitate only the removal of the instrument itself. This enables the refrac- tionist to use the Ski-optometer for subjective or objective work, without disturbing the pa- tient's correction. [29] Chapter IV IMPORTANT POINTS IN CONNECTION WITH THE USE OF THE SKI-OPTOMETER ^T^HE Ski-optometer is equipped with an adjustable head-rest, permitting its lenses to be brought as close as possible to the eye without touching the patients lashes, a matter of importance in every examination. in- Fig. 11 — The nasal lines of the Ski-optqmeter fit the contour of face with mask-like perfection, patient re- maining in comfortable position. Elimination of Trial Frami: Discomfort Where the Ski-optometer is correctly fitted to the face, the patient invariably remains in a comfortable position (Fig. 11). The in- strument is shaped to fit the face like a mask, [30] Refractioti and Muscular Imbalance so that even with a pupillary distance of but SO m/m (that of a child) there still remains, without pinching, ample room for the widest nose of an adult. Before making an examination, the correct pupillary distance should always be obtained by drawing an imaginary vertical line down- ward through the center of each eye from the 90° point on the Ski-optometer axis scale. The pupillary distance will then register in milli- meters on the scale of measurements for each eye separately. If the Ski-optometer is cor- rectly adjusted, the patient is securely held in position, the cumbersome trial-frame being entirely eliminated. Rigidity of Construction Illustration on following page (Fig. 11a) shows the reinforced double bearing arms which hold the Ski-optometer lens batteries at two points. This eliminates possibility of the instrument getting out of alignment, and pre- vents wabbling or loose working parts. The broad horizontal slides shown in the cut, move in and out independently so that the pupillary distance is obtained for each eye separately by turning the pinioned handle on either side of the instrument. The scale de- notes in millimeters the P.D. from the median [31] Refraction and Muscular Imbalance line of the nose outward, the total of both scales being the patient's pupillary distance. Fig. 1 1 a also serves to show the staunch con- struction of the base of the Ski-optometer. Handles Controlling Pupillary Distance for Each Eye Separately Fig. 11 A — Showing staunch construction of Ski-optometer. base. How TO Place the Ski-optometer in Position The patient should be placed in a comfort- able position with "chin up," as though look- ing at a distant object. The instrument should then be raised or lowered by the adjustable ratchet wheel of the bracket. The wall bracket gives best results when suspended from the wall, back of the patient, as shown on page 135. This bracket should be placed about ten inches above the head of the aver- [32] Refraction and Muscular Imbalance age patient. When the Ski-optometer is placed in position for use, its lower edge will barely touch the patient's cheeks. It is some- times advisable to request the patient to light- ly press toward the face the horizontal bar supporting the instrument. Particularly good results are secured where a chair with a head-rest is employed in conjunction with the Ski-optometer. (See illustration of Model Refraction Room, Page 112). Cleaning the Lenses The time-waste of perpetually cleaning lenses is overcome where the Ski-optometer is employed. For the convenience of the opera- tor and protection of Ski-optometer lenses, the latter are concealed in a dust-proof cell, overcoming all dust and finger-print annoy- ances. When not in use, the instrument should be covered with the standardized hood form- ing part of the equipment. The instrument should not be taken apart under any circumstances. To clean its lenses, not a single screw need be removed, as the lens- es of each disk may be cleaned individually through the opening of the other disks. These openings are conveniently indicated by the white zeros (Fig. 2). The Ski-optometer contains but eleven spherical and eight cylin- [33] Refraction and Muscular Imbalance drical lenses on each side, so that the actual work of cleaning should not require over ten minutes at the most, cleaning the lenses every other week proving quite sufficient. Accuracy Assured in Every Test Loss of refraction is completely eliminated through the use of the Ski-optometer. The most casual examination of the trial-frame or any other instrument shows that the construc- tion necessitates the placing of the spherical lens next to the eye with the cylinder lens out- ermost — a serious fault wholly overcome in the Ski-optometer. Not only do the cylindrical lenses of the Ski-optometer set directly next to the patient's eye, thus overcoming any possible loss of re- fraction, but the strong spherical lenses of the supplementary disk are set directly next to the cylinder. There is apparently but a hair's distance between these lenses; the two disks containing the spherical lenses of the Ski-op- tometer likewise setting close together. In a word, the Ski-optometer's cylinder lenses set directly next to the patient's eye, fol- lowed by the stronger sphericals, so that the weakest spherical or +.25 (the lens of least importance) sets farthest away. This is 3i/< m/m closer than any trial frame manufac- [34] Refraction and Muscular Imbalance tured, however, and at least 10 m/m closer than any other instrument — another reason for implicitly relying on the Ski-optometer for uniformly accurate results. Built to Last a Lifetime The Ski-optometer is built on the plan of 1/lOOC, insuring absolute rigidity and accu- Fig. 12— (A. and B.)— This unique, patented split-spring device of screwless construction, securely holds all movable parts. In case of repair, they may be removed with the blade of a knife. racy and a lifetime of endurance. Particular and detailed attention has been given to the novel means of eliminating screw^s vs^hich either bind, create friction or continually w^ork loose, causing false indications of find- ings on scales of measurements; hence correct and accurate indications are insured in the [35] Refraction and Muscular Imbalance Ski-optometer by means of a split spring- washer construction similar to that of an auto> mobile tire's detachable rim (Fig. 12). This patented spring-washer construction securely holds the phorometer lenses, the ro- tary prism and the revolving cylinder lens cells. Whenever necessary, or in case of repair, these parts may be readily removed with the blade of a knife. [36] Chapter V CONDENSED PROCEDURE FOR MAKING SPHERE AND CYLINDER TEST WITH THE SKI-OPTOMETER ^J^OTWITHSTANDING various meth- ods employed, for both subjective and objective refraction, the following synopsis of the previous chapters will unquestionably prove most valuable to the busy refractionist, enabling him to make error-proof examina- tions in practically every case without resort- ing to the transference of trial case sphere or cylinder lenses. A careful reading of chapters one and two should be made how- ever, so that one may gain an understanding as to how spheres and cylinders are obtained with the Ski-optometer. Subjective Distance Test 1st — Place Ski-optometer in position, em- ploying spirit level, thus maintaining instru- ment's horizontal balance. 2nd — Adjust the pupillary distance for each eye individually, by drawing an imaginary vertical line downward through the center of each eye from the 90° point on the Ski-optom- eter's axis scale. The opaque disk should be placed before the patient's left eye by setting the supplementary disk handle at ''shut." [37] Refraction and Muscular Imbalance 3rd — The Ski-optometer lens battery before the patient's right eye should be set at "open" (figure 2), whereupon the first turn of spher- ical lens battery toward the nasal side places a +6.D sphere in position. This should blur vision of average patient. 4th — It is now only necessary to remember that an outward turn toward temporal side of the instrument increases plus sphere power, while a nasal turn decreases it. Therefore con- rnue to reduce convex spherical lens power until the large letter ''E" on the distant test card is clear. Then request patient to read as far down as possible, — a rapid turn of a quarter dioptre being readily accomplished with the Ski-optometer (Fig. 4). 5th — In the event of working down to "zero" with spheres, the supplementary disk handle or indicator should next be set at — 6.D sphere, while the spherical reel should be turned toward the nasal side — thus building up on minus spheres (Fig. 6). In short, the strongest plus sphere or weakest minus sphere should always be determined before employing cylinders. 6th — With the best spherical lens that the patient will accept left in place, direct at- tention to the letter E or F in the lowest line of type the patient can see on the distant test [38] Refraction and Muscular Imbalance letter chart. Then set axis indicator at 180° (Fig. 7). 7th — Next increase concave cylinder power until vision is improved. If vision is not im- proved after increasing cylinder strength to — .50 axis 180°, merely reverse the axis to 90°. If vision is improved, cylinder lens strength should be increased. If not, it should be de- creased (Fig. 8). 8th — Slowly move axis indicator through entire arc of axis, thus locating best possible axis (Fig. 7). 9th — After sphere and cylinder test of right eye has been made, place supplementary disk handle at "shut." Then repeat procedure in testing left eye. 10th — After completing examination for each eye separately, then, with both of the patient's eyes open, direct attention to lowest line of type he can see, concentrating on the E or F, simultaneously increasing or decreasing spherical power before both eyes. The re- fractionist merely recalls that by turning the Ski-optometer's single reel toward the tem- poral side, convex spherical power is in- creased, by turning toward the nasal side for either eye, spherical power is decreased. Cyl- inder lens strength may be changed in a like manner before both eyes simultaneously. [39] Refraction and Muscular Imbalance Uth — After making the distance test, then only is it necessary to copy the result of the examination as recorded by the Ski-optom- eter. Subjective Reading Test Tilt Ski-optometer forward in making read- ing test. The wide groove in the horizontal bar supporting the instrument, permits it to be slightly tilted. 12th — Place Ski-optometer reading rod in position with card at about 14 inches. Close off one eye. Direct patient's attention to the name ^'Benjamin" printed at top of card. 13th — Leave cylinder lens in place. Pro- ceed as in distance test with +6.D sphere, fog- ging down until the first word ''laugh" on the reading card, in line 75M, is perfectly clear, this being slightly smaller than the average newspaper type. 14th — After completion of examination for each eye separately, then with both eyes direct patient's attention to word "laugh." Move reading card in or out a few inches either side of 14 inch mark. This will de- termine any possibility of an over-correction. Then record prescription just as Ski-optom- eter indicates. For a detailed description of above, as well as for objective testing with the Ski-optometer, read chapter three. [40] T Chapter VI MUSCULAR IMBALANCE 'HE purpose of the present chapter is to acquaint the refractionist with the opera- tion of the Ski-optometer as "a scientific in- strument for muscle testing" — the subject being treated as briefly and comprehensively as is practicable. As the reader progresses in the subject of muscular anomalies, he may carry his work to as high a plane as desired, increasing his professional usefulness to an enviable degree. Through the use of the Ski-optometer, muscle testing may be accurately accom- plished in less time than a description of the operation requires. Furthermore, tedious ex- aminations may be wholly overcome through the discontinuance of the consecutive trans- ference of the various degrees of prisms from the trial case. In fact, the latter method has long been quite obsolete, owing to the possi- bility of inaccuracy. The muscle action of the eye is usually quicker than the result sought through the use of trial-case prisms; hence muscle testing with the Ski-optometer is ac- complished with far greater rapidity and ac- curacy, thus making the instrument an invalu- able appliance in every examination. [41] Refraction and Muscular Imbalance The Action of Prisms Students in refraction — and one may still be a student after years of refracting — are some- times puzzled as to just what a prism does when placed before an eye. They refer to every available volume and are often confused between ductions and phorias, finally drop- ping the subject as an unsolvable problem. In view of this fact, it is suggested that the ref rac- tionist should read the present volume with the actual instrument before him. Before proceeding, one should first under- stand the effect of a prism and what it ac- complishes. To determine this, close one eye, looking at some small, fixed object; at the same time, hold a ten-degree prism base-in before the open eye, noting displacement of the object. This will clearly show that the eye behind the prism turns toward the prism apex. To carry the experiment further, the fol- lowing test may be employed on a patient. Covering one eye, direct his attention to a fixed object, placing the ten degree prism be- fore the eye, but far enough away to see the patient's eye behind it. As the prism is brought in to the line of vision, it will be seen that the eye turns towards the apex of the [42] Refraction and Muscular Imbalance prism. When the prism is removed, the eye returns to its normal position. Similar experiments enable the refraction- ist to make the most practical use of treating phorias and ductions, as well as to compre- hend all other technical work. Fig. 13 — An important part of the equipment for muscular work. The Phorometer As previously stated, it is practically impos- sible to accurately diagnose a case of muscular imbalance with trial case prisms. For this reason the phorometer forms an important part of the equipment for muscle testing in the Ski-optometer, having proven both rapid and [43] Refraction and Muscular Imbalance accurate. It consists of two five-degree prisms with bases opposite, each reflecting an object toward the apex or thin edge. The patient whose attention is directed to the usual muscle-testing spot of light, will see two spots. Aside from the instrument itself, and in further explanation of the phorometer's prin- ciple and construction, when two five-degree prisms are placed together so that their bases are directly opposite, they naturally neutral- ize; when their bases are together, their strength is doubled. Thus while the prisms of the phorometer are rotating, they give prism values from piano to ten degrees, the same be- ing indicated by the pointer on the phoro- meter's scale of measurments. As a guide in dark-room testing, it should be noted that the handle of the phorometer in a vertical position is an indication that the vertical muscles are being tested; if hori- zontal, the horizontal muscles are undergoing the test. The Maddox Rod The Maddox rod (Fig. 14) consists of a number of red or white rods, which cause a corresponding colored streak to be seen by the patient. This rod is placed most conveniently on the instrument, being pro- [44] Refraction and Muscular Imbalance vided with independent stops for accurately setting the rods at 90 or 180 degree positions. Fig. 1-1 — The Maddox Rod, a valuable aid in making muscular tests. The Maddox rod has proven of valuable as- sistance in detecting muscular defects, par- ticularly when used in conjunction with the phorometer. Thus employed, it enables the patient to determine when the streak seen with one eye crosses through the muscle-testing spot-light observable by the other eye, as here- after described. Procedure for Making the Muscle Test The Ski-optometer should be equipped with two Maddox rods, one red and one white. Their combined use is of the utmost import- ance since they assist in accurately determin- ing cyclophoria and its degree of tortion as [45] Refraction and Muscular Imbalance designated on the degree scale, and fully de- scribed in a later chapter. When the Maddox rods are placed in a vertical position, it is an indication that the vertical muscles are being tested; when placed horizontally, the horizontal muscles are being tested. It should be particularly noted that the streaks of light observable through the Maddox rods always appear at right angles to the position in which they lie. The Ski-optometer should be placed in a comfortable position before the patient's face with the brow-rest and pupillary distance ad- justed to their respective requirements. The instrument should be levelled so that the bub- ble of the spirit level lies evenly between its two lines, thus insuring horizontal balance. The muscle-test light should be employed at an approximate distance of twenty feet on a plane with the patient's head. Best results in muscle testing are secured through the use of the Woolf ophthalmic bracket, with iris diaphragm chimney and a specially adapted concentrated filament electric lamp (Fig. 9). This gives a brilliant illumination which is particularly essential. The test for error of refraction should be made in the usual manner, using the spherical and cylin- drical lenses contained in the Ski-optometer, [46] Refraction and Muscular Imbalance thus obviating the transference of trial-case lenses and the use of a cumbersome trial frame. The time-saving thus effected enables the refractionist to include a muscle test in every examination and without tiring the pa- tient — a consideration of the utmost import- ance. Binocular and Monocular Test The test for muscular imbalance may be divided in tw^o parts. First, binocular test, or combined muscle test of the two eyes ; sec- ond, monocular test, or muscle test of each eye separately. The latter does not signify the shutting out of vision or closing off of either eye, since muscular imbalance can only be determined when both eyes are open. These two tests are fully explained in the fol- lowing chapter. [47] Chapter VI 1 THE BINOCULAR MUSCLE TEST Made with the Maddox Rod and Phorometer T\ IRECTING the patient's attention to the usual muscle testing spot of light, the red Maddox rod should be placed in operative position before the eye, with the single white line or indicator on red zero (Fig. IS). The rods now lie in a vertical position. Fig. 15 — The Maddox rods placed vertically denote test for right or left hyperphoria, causing a horizontal streak to be seen by patient. The pointer of the phorometer should like- wise be set on the neutral line of the red scale, causing the handle to point upward (Fig. 16). A distance point of light and a red streak laying in a horizontal position should now be seen by the patient. [48] Refraction and Muscular Imbalance Fig. 16— The phorometer handle placed verticaUy, de- notes vertical muscles are undergoing test for right or left hypherphoria — as indicated by "R. H." or "L. H." Instead of memorizing a vast number of rules essential where trial case prisms are employed for testing ocular muscles, the pointer of the phorometer indicates not only the degree on the red scale, but the presence of right hyperphoria (R. H.) or left hyper- phoria, (L. H.). Fig. 17— The horizontal streak caused by Maddox rod bisecting muscle testing spotlight for vertical imbalance, as patient should see it. Assuming that the patient finds that the streak cuts through the point of light, the re- [49] Refraction and Muscular Imbalance Fig. 18 — The Maddox rods placed horizontally test eso- phoria or exophoria, caudng a vertical streak to be seen by the patient. fractionist instantly notes the absence of hy- perphoria. Should the point of light and the red streak not bisect, prism power must be added by rotating the phorometer's handle to a position that will cause the streak to cut through the light (Fig. 17). While testing for hyperphoria, the red scale should alone be employed, the white scale being totally ignored. ESOPHORIA AND ExOPHORIA The next step is to set the white lines of the red Maddox rod either at white zero, or 180° line, with the rods in a horizontal position (Fig. 18) and the phorometer on the white neutral line, with handle horizontal, (Fig. 19), thus making the test for esophoria or [50] Refraction and Muscular Imbalance exophoria, technically known as lateral devia- tions. The red streak will now be seen in a verti- cal position. Should it bisect the spot of light, it would show that no lateral imbalance ex- ists. Should it not bisect, the existence of either esophoria or exophoria is proven, ne- cessitating the turning of the phorometer handle. Should the refractionist rotate the handle in a direction opposing that of the ex- isting imbalance, the light will be taken fur- ther away from the streak, indicating that the rotation of the prisms should be reversed. At the point of bisection (Fig. 20), the phorometer will indicate on the white scale Fig. 19 — The phorometer handle placed horizontally de- notes horizontal muscles are undergoing test for eso- phoria or exophoria indicated by "Es." or "Ex." [51] Refraction and Muscular Imbalance whether the case is esophoria or exophoria and to what amount. In testing esophoria (ES) or exophoria (EX), the white scale is alone employed, no attention being given to the red scale. Fig. 20 — The vertical streak bisecting muscle testing spot- light for horizontal inmbalance, as patient should see it. Making Muscle Test Before and After Optical Correction It is considered best to make the binocular test before regular refraction is made, mak- ing note of the findings; and again repeating the test after the full optical correction has been placed before the patient's eye. This enables the refractionist to definitely deter- mine whether the correction has benefited or aggravated the muscles. Furthermore, by making the muscle test before and after the optical correction, a starting point in an ex- amination is frequently attained. For ex- [52] Refraction and Muscular Imbalance ample, where the phorometer indicates eso- phoria it is usually associated with hyper- opia, whereas exophoria is usually asso- ciated with myopia, thus serving as a clue for the optical correction. Assuming for example that the binocular muscle test shows six degrees of esophoria without the optical correction, and with it but four degrees, it is readily seen that the im- balance has been benefited by the optical cor- rection. Under such conditions it is safe to believe that the optical correction will con- tinue to benefit as the patient advances in years, tending to overcome muscular defect. When to Consider Correction of Muscular Imbalance In correcting an imbalance, it is also a good plan to adhere to the following rule: In case of hyperphoria, either right or left, consider for further correction only those cases that show one degree or more. In exophoria, those showing three degrees or more. In eso- phoria, correct those showing five degrees or more, except in children, where correction should be made in cases showing an excess of 3° of esophoria. These rules are naturally sub- ject to variation according to the patient's [53] Refraction and Muscular Inihalan ce refraction and age, but they are generally ac- cepted as safe. Four Methods for Correction of Muscular Imbalance There are four distinct methods for correct- ing muscular imbalance, each of which should be carried out in the following routine: 1. Optical correction made with spheres or cylinders, or a combination of both. 2. Muscular exercising or "ocular gym- nastics." This is accomplished on the same principle as the employment of other forms of exercises, or calisthenics. 3. The use of Prisms: When the second method fails, prisms are supplied, with base of prism before the weak muscle, for rest only. 4. Operation : If the above three methods, as outlined in the following chapters, have been carefully investigated, nothing remains but a tetonomy or advancement, or other op- erative means for relief and satisfaction to the patient. The Rotary' Prism The rotary prism of the Ski-optometer, (Fig. 21) consists of a prism unit, having a total equivalent of thirty degrees. It is com- posed of two fifteen-degree prisms, back to [54] Refraction and Muscular Imbalance back, so that the turn of its pinion or handle causes each of its lenses to revolve, one on the other. When its bases are opposite, they neu- tralize; when directly together, they give a total value of thirty degrees. While revolv- ing from zero to maximum strength, they give prism values w^hich are indicated on the scale of measurements, the red line denoting the total prism equivalent. Fig. 21 — Turning rotary prism's pinioned handle gives prism value from zero to 30° as indicated by prism's red line indicator. It is obviously essential to know^ where the base of the rotary prism is located. Therefore if prism in or out is desired, the zero gradua- tions should be placed vertically and the red line or indicator set at the upper zero (Fig. 21). A rotation inward to 10 would give a prism [55] Refraction and Muscular Imbalance equivalent of ten degrees, base in. A rotation from zero to 10 outward would give a prism equivalent of ten degrees, base out, etc. With zero graduations horizontal and the red. line or indicator set therewith, a rotation upward to ten on the scale would give a prism equi- valent of ten degrees, base up. A rotation from zero downward to 10 would give a prism equivalent of ten degrees, base down. An understanding of the foregoing will show that a rotation of the red line, or indica- tor, will give prism value from zero to 30, with base up, down, in or out. Use of the Rotary Prism in Binocular Muscle Tests Should a case be one of esophoria, exceed- ing the ten degree range of the phorometer, the rotary prism should be brought into opera- tive position with cypher (0) graduations vertical (Fig. 21), while the red line or indicator should be set at 10 on the outer or temporal scale. The phorometer's indicator should again be set on the center or neutral line on the white scale. The rotary prism will then add ten degrees to the esophoria reading indicated on the phorometer. Should the case be one of exophoria, exceed- ing ten degrees, the indicator should be set [56] Refraction and Muscular Imbalance at ten degrees upon the inner or nasal scale and the indicator of the phorometer should then be set at the white center or neutral line, as in the previous test. Should prism power ever be required to supplement the phoro- meter in hyperphoria, the rotary prism should be employed with zero graduations horizontal, and the red line or indicator set at ten degrees on upper or lower scale, as required. [57] Chapter VIII THE MONOCULAR DUCTION MUSCLE TEST Made with Both Rotary Prisms AXT'HILE the previously described binocular muscle test made with the phorometer and Maddox rod, only determines the existence and amount of esophoria, exophoria, and hyperphoria, neither the faulty nor the deviat- ing muscle is located, hence a monocular muscle test is essential in order to determine whether the muscles of the right or left eye are faulty. Furthermore, an imbalance may possibly be due to either a faulty muscular poise, or lack of nerve force in one or both eyes. A "duction test" should accordingly be made of each muscle of each eye separately, followed by a comparison of the muscular pull of both eyes collectively. These tests are commonly termed adduc- tion, abduction, superduction and subduc- tion, and are defined in the order named. They include tests of the vertical and horizontal muscles of each eye, made in- dividually by means of the rotary prisms, each being placed before the eye undergoing the test. Locating the Faulty Muscle The phorometer and the Maddox rod [58] Refraction and Muscular Inibalan a should be removed from operative position, discontinuing the use of the muscle-testing spot-light, employed in the previously de- scribed binocular test. The optical correction, if one is required, should be left in place, while the patient's attention should be directed, W\\h both eyes open, to the largest letter on the distant test chart; or if preferable, the Greek cross in the Woolf opthalmic chimney may be used. Either one, however, should be located on a plane with the patient's head. As a guide for the operator, it might be well to remember that when the handle of the rotary prism is in a horizontal position, the lateral or horizontal muscles are being tested. On the other hand, when the handle is in a vertical position, the vertical muscles are undergoing the test. Adduction Adduction, or relative convergence, is the power of the internal muscles to turn the eyes inward; prism power base out and apex m, is employed. To test adduction of the patient's right eye, the rotary prism should be placed in position before the right eye, the red line or prism in- dicator being registered at zero upon the prism upper scale. The two cyphers (0) should be placed in a vertical position with [59] Refraction and Muscular Imbalance Fig. 22 — To test adduction, base out is required. Rotary prism's line or indicator should be rotated from zero out- wardly. To test abduction, base in is required. Indi- cator should be rotated inwardly from zero. the handle pointed horizontally (Fig. 21). The rotary prism should then be rotated so that its red line or indicator is rotated out- ward from zero until the large letter — pre- ferably the largest letter, which is usually ''E" — on the distance test-type or the Greek cross previously referred to, first appears to double in the horizontal plane. The reading on the scale of measurements should ac- cordingly be noted. This test should be re- peated several times, constantly striving for the highest prism power that the patient will accept without producing diplopia. The prism equivalent thus obtained will indicate [60] Refraction and Muscular Imbalance the right adduction and should be so re- corded, as designated in Fig. 24. The amount of adduction ranges from 6 to 28, prism di- optres, the normal average being 24. Abduction Abduction is the relative power of the ex- ternal muscles to turn the eyes outward. Prism power base in and apex out is em- ployed. To determine abduction, or the amount of divergence of the external rectus muscle of the right eye, prism power with base in or toward the nasal side should be employed. The rotary prism will therefore remain in the same relative position as in making the adduction test (Fig. 22), with the two cyphers (0) or zero graduations vertical, but the indicator or red line should be rotated inward from zero, or towards the patient's nose. With the patient's attention again directed to the large letter ''E," or the Greek cross, this inward rotation should be continued until diplopia or double vision occurs. Like the former, this test should be repeated several times, the ref ractionist continuing to strive for the highest prism power which the eye will ac- cept. This will indicate abduction of the right eye and should be so recorded as designated in [61] Refraction and Muscular Imbalance Fig. 24. The amount of abduction ranges from 3 to 10 prism dioptres. The normal av- erage is 8. The ratio of adduction to abduction is nor- mally rated at about three to one. In other words, it is conceded that the power of the eye to converge is normally three times as great as its power to diverge, the usual mea- surements being eight to twenty-four respec- tively. While applicable in most instances, this may vary in different cases. SUPERDUCTION Superduction, sometimes termed sursum- duction, is the relative power of the superior recti to turn the eyes upward. Prism power base down and apex up is employed. To test superduction, the rotary prism should be placed in position with the two cyphers lying horizontally, with the handle pointed vertically (Fig. 23). The patient's atten- tion should again be directed to the large letter "E'\ and the indicator or red line should be rotated downward from zero. The highest prism power that the patient will ac- cept before the object appears to double in the vertical plane will indicate the degree of right superduction. This should be recorded accordingly. Conditions of this kind do not [62] Refraction and Muscular Imbalance usually exceed two or three degrees. The test, however, should be repeated several times before the final result is recorded, as indicated in Fig. 24. The amount of super- duction ranges from 1 to 4 prism dioptres. The normal average is 2. Fig. 23— To test superduction, base down is required. Rotary prism's line or indicator should be rotated down- ward from zero. To test subduction, base up is required. Indicator should be rotated upward from zero. Subduction Subduction, sometimes termed infraduc- tion or deorsumduction, is the relative power of the inferior recti to turn the eyes downward. Prism power base up and apex down is em- ployed. To test subduction, the rotary prism should be operated with zero graduations [63] Refraction and Muscular Imbaland placed horizontally, as in the superduction test (Fig. 23), but the indicator should be slowly rotated in the reverse direction, or up- ward from zero. With the patient's attention again directed to the large letter ''E," or the Greek cross, the strongest degree prism thus se- cured without diplopia will indicate the right subduction. The amount of subduction ranges from 1 to 4 prism dioptres. The normal av- erage is 2. Any difference between superduction and subduction, usually denoting the existence of hyperphoria, should be given careful con- sideration. Procedure for Monocular Muscle Testing As previously explained, after a duction test of each of the four muscles of the right eye, the rotary prism before that eye should be placed out of position and the procedure for adduction, abduction, superduction and subduction repeated by means of the rotary prism before the left eye. In case of an ex- isting imbalance, after testing the muscle of both right and left eyes, the refractionist can quickly determine which muscle or muscles may be lacking in strength (Fig. 24). In practically every instance muscle exercises or correcting prisms may then be prescribed [64] Refraction and Muscular Imbalance with definite knowledge of requirements, as further described in the following para- graphs. A binocular muscle test made with the phorometer, Maddox rod and distant mus- cle - testing point of light might quickly indicate six degrees of exophoria, both be- fore and after the optical correction is made. While this would doubtless be the correct amount of the manifest imbalance, it would be a difficult matter to ascertain which mus- cles caused the disturbance. To determine this important question, the monocular or duction test should be invariably employed. Diagnosing a Specific Muscle Case Assuming, for example, a specific case where six degrees of exophoria was deter- mined in the binocular test that the muscle findings in the duction test show right adduc- tion of twenty-four degrees, with an accom- panying abduction of eight degrees; likewise a superduction and subduction of two degrees for each eye. With the aid of a chart or diagram— which should be made in every case — a comparison of these figures would indicate an exophoria of approximately six degrees, with a corresponding weak left internus (Fig. 24). This not only shows [65] Refraction and Muscular Imbalance the muscle pull of each eye individually, but a comparison of the two eyes as indicated by the dotted lines. Thus the relationship of the two eyes, and their corresponding muscles is quickly indicated. Equal RIGHT Z UUCTIOV EYE SUP. CHART LEFFlrE 2 SUP. (5/9^,^-"^ Z4/JJ). /8/}£). ^^~-- Sf}B~'^ Equal \ jro / / \ / \ / \ / \ / \ f\ / \ / \ / \ / \ / / '' or / ^^ Normal \ 1 &-'£XOPHCf?/fl RflT/O Fig. 2A — Duction chart should be made in every case. Above readily shows existence of muscular imbalance and proves subduction and superduction for both eyes are equal; other- wise hypherphoria would be disclosed. Also note ab- duction for both right and left eye are equal, otherwise esophoria would be disclosed. Also note adduction for right eye is 24° while left is but 18°, proving a case of 6° of exophoria with a left weak internus. A glance at the above diagram discloses the following three important facts, all of which should be known to the refractionist before a single thought can be devoted to the correcting of the case: 1. 6° exophoria is the amount of the in- sufficiency. 2. 18° adduction (which should be 24°). 3. Left weak internus. [66] Refraction and Muscular Imbalance As previously stated, the power to con- verge is normally rated 3 to 1, or 8 to 24, as shown above, while the power of the eye to look upward, is equal to the power to look downward. The diagram accordingly proves that the muscles of the right eye are in perfect balance, having equal muscular energy. A comparison of the left eye shows adduc- tion of 18 degrees with an abduction of 8 de- grees, proving a lateral insufficiency because the ratio is less than 3 to 1 ; and the muscles of the left eye are at fault. The power of 2 degrees superduction and 2 degrees subduc- tion, proves that no weakness exists in the ver- tical muscles. After making the duction test for each eye individually, a comparison of both eyes in re- lationship to each other may be more readily determined by following the dotted lines (Fig. 24). As previously stated, it is the inability of the two eyes to work together that causes the imbalance, so that if both eyes were normal, the adduction, abduction, superduction and subduction of the two e^^es would agree. The duction chart (Fig. 24.) also shows that the corresponding muscles of each eye agree — with the exception of the adduction [67] Refraction and Muscular Imbalance of the right eye and the left eye. This proves that the left internus is weak, measuring only 18 degrees instead of 24 degrees; it further proves the 6 degrees of exophoria in the monocular test, as w^as quickly and more readily determined in the binocular test. Likewise, in cases of esophoria, hyper- phoria, or cataphoria, the making of definite muscle measurements independently through the prescribed method would show through the merest glance at a similar diagram which muscle or muscles were relatively out of bal- ance. Heterphoria of almost any type, or tendencies other than normal, may be fully investigated by making a thorough and sepa- rate test of each muscle. Where an imbalance exists, a rapid test may be employed to distinguish a pseudo or false condition from a true condition. This is ac- complished by first placing the two Maddox rods (both the red and white) so that the rods lie in a vertical position. If the two lines fuse, we have determined the existence of a false condition caused by a possible error of refrac- tion or nerve strain. If the lines separate, we have determined a true muscular condition, and then only should the second method of muscular treatment follow. [68] Same as Model 2i^ but Automatic Cylinder Arrange- ment omitted. Ski-optometer Model 205 Embodying: Spherical Lenses Combined with Appliances for Testing and Correcting Muscular Imbalance. [69] T Chapter IX FIRST m?:thod of treatment _ OPTICAL CORRECTION ^HE mere determination of the degree of an imbalance, or even the diagnosis of a patient's trouble, is not sufficient. If relief is to be secured, something more must be ac- complished. As previously stated, muscular imbalance may be corrected through one of the four fol- lowing rules or methods, each explained in their relative order: 1 — Optical Correction 2 — Muscular Exercise 3 — Use of Prism Lenses -Operative Methods ESOPHORIA To correct a case of muscular imbalance, where six degrees of esophoria has been de- termined, the first rule of making the test for optical correction with the Ski-optometer's spherical and cylindrical lenses, would be in the line of routine. The binocular test made with the phorometer and combined use of the red Maddox rod would have determined the six degrees of esophoria. [70] Refraction and Muscular Imbalance The reason for making the binocular muscle test before and after the optical correction is because an imbalance is often aggravated or benefited by the correcting lenses. The optical correction frequently eliminates the need for further muscular treatment. For example, we will assume that the optical correction tends to decrease the degree of esophoria from six degrees to four degrees. According to the previously mentioned rule for correcting cases exceeding one degree in hyperphoria, three degrees in exophoria and five degrees in esophoria, the condition would indicate that of being "left alone." Just what is taking place should be fully understood — its cause as well as its efifect. Perfectly centered L pupil Centered pupil and decentered lens Centered lens and decentered pupil Fig. 25 — Comparative diagram showing how a decentered lens before a centered eye has the same effect as a centered lens before a decentered eye. When not otherwise specified, accurately centered lenses are of primary importance. The pupil of the eye should be directly be- hind the center of each lens (Fig. 25). [71] Refraction and Muscular Imbalance Figure ''A" of the latter sketch illustrates a perfectly centered lens — its center indicated by a cross, the circle representing an eye di- rectly behind it. Figure "B" illustrates a per- fectly centered pupil behind a prism, with its center designated by a cross. To ascertain how the centered spherical lens takes the place of a prism. Figure ''C" should be compared with Figure ''B"; this will show that the eye is decentered, while the lens is centered. A further comparison will prove that the results in Figures "B" and ''C" are identical, the correcting lenses having practically the same effect through the decentration of the eye as if a prism were prescribed, nature supplying its own decentration. Treatment for Correcting Esophoria in Children In case of esophoria, regardless of amount, slightly increased spherical power is fre- quently prescribed for children. This will naturally blur or fog the patient's vision, but in their effort to overcome the blur, accommo- dation is relaxed, usually tending to correct the muscular defect. In such cases, as a rule, a quarter diopter increased spherical strength may frequently be added for each degree of esophoria as de- [72] Refraction and Muscular Imbalance termined before the optical correction was made. In a case of 6 degrees of esophoria, the refractionist may prescribe +1.50 dioptre spherical added to the optical correction, which, let us assume, is +1.00 sph. = — 1.00 cyl. ax. 180°, so that the treatment glasses would be +2.50 sph. = —1.00 ax. 180° (See Pro- cedure on Page 74). At the end of each three months' period, the patient should be requested to return, when the binocular and the duction test should again be made, comparing results with the work pre- viously accomplished. An improvement tend- ing to build up the left weak externus will possibly permit of a decrease of the excessive spherical power, so that excessive spherical power is reduced until completely removed, in all probability overcoming the muscular defect. Esophoria is almost invariably a false condition and frequently is outgrown under this treatment as the child advances in years. On the other hand, esophoria uncared for in the child may tend to produce exophoria in the adult. [73] o 5: 'I- I X X X 5 S" Oh o w is^i w -f M •^ 00 o < Ol W o: o o V w Q d _o o ^-J H o C/3 Q /?; o tq H (U ^ 55 (P o cS h s o _^ (£j m u 0) u ■'-' o ^ U o w h-9 :3 < E U h u a, -2 o :2 o 03_73 C";^ ;^ OJ Ol C QJ ^S^fJ. O X ^ -J "it o £ rt ,— ( r^ ) eg (>} ++ + + o ci o a m abduction. In this to original correc- d have required six -thus consuming 18 ft : lenses eqi has increa or 0.25 X -escribed t w ---^ c ?; CO 3 a;<(_i ^ increa equals reatmen bductio f 5 Es. ction, 1 ment ] w 8° educed is WOL apart- 3 w d : ^".-^ : tj O i'.C K a>'^+j 03 o a; 03 r> fH r- e a quarter diop imbalance or 0.25 ^d date) prescribe hs later) assumin howing difference ed to -optical co U: ■) assumin fference o] ptical con equal: ^ months t Id left eye t lenses a -100 X 180. three mo 0) "5 ^ m ct ? !« hs la wing ed to lense ry th right •eatm .00 = lens le. Xi- ^^^■'z3~^o,z, a. i;-4 >< 6 = 1>4°) for each eye — base in — or esophoria base out, hy- perphoria base up on eye affected. 2nd. Advise patient to call every three months and make duction test (Fig. 24). If no improvement in condition, after wearing prisms six months, operative means is suggest- ed. Assume a case is benefited, reduce prism power according to rule; J/4D prism for each degree of imbalance. Cyclophoria This work being of a technical nature, it is deemed best for the reader to study Chapter XIII and XIV. [92] Chapter XIII CYCLOPHORIA Made with Maddox Rods and Rotary Prisms /^YCLOPHORIA, a condition affecting the oblique muscles of the eye, is caused by its rotation. It is detected in the following manner by the combined use of the red and white Maddox rods and the rotary prism. Fig. 29 — Position of rotary prism for producing diplopia in testing cyclophoria with prism placed at 8° base up. Darken the room and direct the patient's attention to the usual muscle-testing spot of light, located approximately twenty feet away and on a direct plane with the patient's eye. The optical correction, if one is required, should always be left in place — just as in mak- ing other previously described muscle tests. [93] Refraction and Muscular Imbalance The rotary prism should then be brought be- fore the patient's right eye with the handle- pointing upward and with zero graduations horizontal. The indicator or red line should then be rotated upward from zero to eight upon the prism scale, creating the equivalent of a prism of 8 diopters with base up (Fig. 29) . This normally caused diplopia, although in some cases it may be necessary to place the prism at 10 or 12 degrees before diplopia is produced. A B Fig. 30 — (A. and B.) — First position of both Maddox rods used in conjunction with Fig. 29 for determining cyclophoria. The red Maddox rod should then be brought into operative position before the pa- tient's left eye (Fig. 30a) and the white Mad- dox rod before the patient's right eye, (Fig. 30b) setting each one so that the rods lie in [94] Refraction and Muscular Imbalan ce a vertical position with their white line on the large red zero (0). The patient should now see two separate and distinct streaks of light, one appearing below the other. DETERMINING CYCLOPHORIR /?/GHn £r£ ^Eirr £/£ Fig. 31 ^'9. 34 A/O CrCLO/^HO^/ff /VO CYCLOPHO/?//^ Fuj. 32 crcL op/io/^/ff Fw- 35 ■hCYCLOPHOP/ff Fig. n crcLOH/- 3 M-43 Either eye inward (eso- phoria, esotropia.) Either eye outward (exophoria, e x o t r o- pia.) Right eye up or left eye down (right hyperpho- ria, right hypertropia, left hypotropia.) Right eye down or left eye up (left hyperpho- ria, left hypertropia, right hypotropia.) Image of right eye as compared with that of the left is On the right On the left Below Above Name of diplopia Homony- mous Heterony- mous (or - crossed) 'Right .Left |BJ3JBT 1BDI}J3A [116] Refraction and Muscular Imbalance monocular diplopia, or the condition in which the patient sees double with one eye alone. This occurs as the result of astigmatism, plus spherical aberration and other conditions found occasionally in squint. It can readily be differentiated by the fact that binocular diplopia disappears when the patient shuts either eye; while monocular diplopia, of course, does not. Movement of Each Eye Singly The movements of each eye individually are effected as follows : The external rectus moves the eye directly outward ; the internal rectus, directly inward. The primary action of the superior rectus is to raise the eye. Because of the way in which the muscles run, obliquely from within outward, its lifting action increases when the eye is abducted and diminishes to little or nothing when the eye is adducted. The inferior rectus carries the eye down. Owing to the oblique direction of the muscle, its depressing action increases as the eye is ab- ducted and decreases to zero as the eye is adducted. The inferior oblique is inserted back of the equator of the eye. Hence it pulls the back part of the eye down and consequently throws [117] Refraction and Muscular Imbalance the front part up. It is thus an elevator of the eye, reinforcing the action of the superior rectus. Owing to the way in which it runs, from the front backward and outward, its ele- vating action is greatest when the eye is ad- ducted, and diminishes to little or nothing when the eye is abducted. The superior oblique, so far as its action on the eyeball is concerned, may be regarded as arising from the trochlea. From this point it runs backward and outward and is inserted back of the eq^uator of the eye. It there pulls up the back part of the eye and consequently throws the front part down. It is thus a de- pressor, reinforcing the action of the inferior rectus. Owing to the oblique way in which it runs, its depressing action is greatest when the eye is adducted, and diminishes to little or nothing when the eye is abducted. Subsidiary Actions Besides these actions, rightly regarded as the main action of the ocular muscles, there are various subsidiary actions, due to the oblique way in which the superior and in- ferior recti and the two obliques run. Thus, both the superior and inferior recti adduct the eye, their action being most pronounced when the eye is already adducted. The two [118] Refraction and Muscular Imbalance obliques, on the other hand, abduct the eye and do so most effectively when the eye is already abducted. The superior rectus and superior oblique ro- tate the top of the vertical meridian of the eye inw^ard (intorsion) ; while the inferior oblique and inferior rectus rotate it outward (extor- sion) . The superior and inferior recti act thu3 on the vertical meridian mainly when the eye is adducted; the oblique, on the other hand, when the eye is abducted. Hence the eye is adducted by the internal rectus, assisted toward the end of its course by the superior and inferior recti. It is ab- ducted by the external rectus, assisted toward the end of its course by the two obliques. It is carried straight up by the superior rectus and inferior oblique, up and out by the su- perior rectus and external rectus (the inferior oblique helping to carry it out, but not up; and in, mainly by the inferior oblique and in- ternal rectus). The superior rectus assists in carrying it in, but hardly up at all. The eye is likewise carried straight down by the inferior rectus and the superior oblique ; down and out by the inferior and external recti, and down and in by the superior oblique and internal recti. [119] Refraction and Muscular Imbalance Field of Action of Muscles As will be seen, each muscle acts most en- ergetically in some special direction of the gaze, termed field of action of that particular muscle; thus the external rectus acts most powerfully when the eye is directed outward, and acts little or not at all when the eye is directed inward, except by purely passive trac- tion. Likewise the superior rectus acts main- ly when the eye is directed down. Further- more, its action is limited to the upper and outer field ; for in the upper and inner field elevation is performed chiefly by the inferior oblique. This is also true of all the other muscles. Direction of the Gaze There are six cardinal directions of the gaze, each corresponding to the field of action of one of the six ocular muscles as follows : Cardinal Direction: Muscles Specially Active: Straight out External rectus . Straight in Internal rectus Up and out Superior rectus (as an elevator) Up and in Inferior oblique (as an elevator) Down and out Inferior rectus (as a depressor) Down and in Superior oblique (as a depressor) It is to be noted that the action of each mus- cle does not absolutely stop at the middle line, but extends somewhat beyond it. Thus the action of the right externus extends not only [120] Refraction and Muscular Imbalance throughout the whole right half of the field of vision, but also some fifteen to twenty de- grees to the left of the median line; and that of the superior rectus extends not only above the horizontal plane but also somewhat below. Primary Position — Field of Fixation Under normal conditions, when the head is erect and the eye is directed straight forward — that is, when its line of sight is perpendicu- lar to the line joining the centres of rotation of the two eyes in the horizontal plane — the mus- cles are all balanced. This is called "the posi- tion of equilibrium" or the primary position. It is this position which must be assumed by the patient in conducting tests for balance of the muscles. From the primary position, the eye may make excursions in every direction so that the patient can look at a whole series of objects in succession without moving the head. This portion of space, occupied by all the objects that may thus be seen directly by moving the eye without moving the head, is called "the field of fixation." Binocular Movements While either eye alone may move in all pos- sible directions, one cannot move independent- ly of the other eye. Under ordinary circum- [121] Refraction and Muscular Imbalance Stances, those movements only are possible which are regularly required to subserve bi- nocular vision, hence, binocular single vision, as well. These movements are as follows: Parallel Movements When one eye looks at a distant object the other is also directed to it, so that the lines of sight of the two eyes are parallel ; if the distant object is moved about, the lines remain paral- lel, one moving as fast and as far as the other. These parallel movements of the two eyes are executed with considerable freedom in all di- rections, either eye being able to move read- ily to the right, left, up, down, or obliquely, provided the other eye moves precisely with it. In executing any parallel movement, each eye is acted upon by at least three and some- times by as many as five muscles. At times, but one of these muscles is required to pro- duce any great movement of the eye, the others simply serving to steady it in its course. Thus when we look up to the right, although there are five muscles really acting upon each eye, the right eye is moved mainly by the external rectus and the left eye by the internal rectus. Similarly, when we look up and to the right, although other muscles take part, the superior rectus is the chief muscle that moves the right [122] Refraction and Muscular Imbalance eye up, and the external rectus the chief one that moves it to the right; while for the left eye the interior oblique and the internal rec- tus are the efficient muscles. A careful study of the action of the indi- vidual muscles will make it clear that these facts hold good for each of the cardinal direc- tions of the gaze. Furthermore, if we attentively consider the action of the twelve muscles moving the two eyes, we see that they may be divided into three groups, viz; four lateral rotators, four elevators and four depressors. Right rotators L. Internal rectus R. External rectus Lateral Rotators I fLeft rotators -{ R. Internal rectus I L. External rectus to Elevators Right-handed elevators (acting mainly when the eyes are directed to the right) R. Superior rectus L. Inferior oblique Right-handed depressors (acting mainly when the eyes are directed to the right) R. Inferior oblique L. Superior oblique Left-handed elevators (acting mainly when the eyes are directed to the left) R. Inferior oblique L. Superior rectus Depressors Left-handed depressors (acting mainly when the eyes are directed to the left) R. Superior oblique L. Inferior rectus. Each group, it will be seen, comprises two pairs of muscles; one pair acting solely when [123] Refraction and Muscular Imbalance the eyes are directed to the right, the other when they are directed to the left. It will further be noted that of the two muscles con- stituting any one pair, one is situated in the right eye, the other in the left. Eye Associates The muscles forming any one pair are called associates. Any two associates acting together will move their respective eyes in precisely the same direction and to the same extent. Thus the right superior rectus moves the eye up to the left and rotates its vertical meridian to the left; and its associate, the left inferior oblique, moves its eye up to the left and rotates its vertical meridian to the left. This likewise applies to each of the other five groups of associates. If one eye fails to keep pace with the other in executing parallel movements, diplopia en- sues. If the eyes are moved in all directions and the point noted where the patient just be- gins to see double, we delimit the field of bi- nocular single vision. Normally, however, the two eyes maintain parallelism to the very limit of their excur- sion, so that diplopia occurs only at the ex- treme periphery of the field of vision, if at all. In fact, the field of binocular single vision [124] Refraction and Muscular Imbalance usually extends not less than 40 degrees from the primary position in every direction. Each of the various parallel movements of the eye appear to be governed by a distinct nerve mechanism, there being one centre for movements to the right, one for movements to the left, one for movements up, etc. Movements of Convergence In order to see an object at a nearby point, the eyes have to converge — a movement af- fected by a simultaneous and equal contrac- tion of both internal recti. This movement may be combined with a vertical, lateral or oblique parallel movement. Thus, when we wish to look at a near object situated twenty degrees to our right, we first turn both eyes twenty degrees to the right, then converge both equally, turning the left a little more to the right and the right a little back toward the left. Convergence is governed by a distinct mechanism of the nerves, the source of which has not been determined. Movements of Divergence In passing from a position of convergence to a position of parallelism, the lines of sight separate or diverge. This movement of diver- [125] Rcfnictioii and Muscular Iiuhalance gence is a simultaneous, equal contraction of both externi; or, probably, of both actions combined. The eyes may even diverge some- what beyond parallelism, as in overcoming prisms, base in, when looking at a distant ob- ject. Vertical Divergence The amount by which the lines of sight can separate in a vertical direction is very lim- ited^ — at most but one or two degrees. Orthophoria The term orthophoria is used to denote an absolutely normal balance of the extrinsic muscles, just as the term emmetropia denotes a normal refractive condition. They are equally rare. Heterophoria The term heterophoria includes all those conditions in which there is a tendency to de- part from normal balance, but which nature is able to compensate for; while the term also includes the conditions in which nature has been unequal to the task and an actual turn- ing or squint has occurred. Subdivisions The subdivisions of these terms at first read- ing appear complicated, but prove simple [126] Refraction and Muscular Imbalance enough on closer study, indicating only the di- rection of the turning or tendency to turn. For instance : Esophoria signifies imvard tendency Exophoria signifies outivard tendency. Hyperphoria signifies upivard tendency. Hypophoria signifies doivriivard tendency. Cyclophoria signifies tendency to torsion. Esotropia signifies imvard turning. Exotropia signifies oi/tivard turning. Hypertropia signifies upivard turning. Hypotropia signifies doivntvard turning. Cyclotropia signifies actual torsion. Combinations are describable in similar terms. A tendency of the right eye to turn up and inward, is a ''right hyperesophoria" ; the left eye to turn down and out, a ''left hy- perexophoria," etc. Tendencies of both eyes together are denoted by the terms which fol- low: Anaphoria signifies an upivard tendency. Kataphoria signifies a doivnivard tendency. Dextrophoria signifies a riff/it tendency. Laevophoria signifies a left tendency. [127] Chapter XVII SYMPTOMS OF HETEROPHORIA npHESE depend on the kind of error pres- ent as well as the degree and widely vary. In general, they may be said to fall into three classes — (1) defective vision, (2) pain of greater or less degree — (3) reflex symp- toms. Defective Vision. The first class may be present, even though each eye has a normal visual acuity; since, even when compensation is very good, the brain gets the impression of two objects, nearly, though not quite fused; and vision may be considerably worse with both eyes together than with either eye singly. When compensation is considerably im- paired, the diplopia becomes more and more persistent, till the brain finally makes choice of one image as more satisfactory, entirely suppressing the other. Visual acuity may not suffer in either eye; but vision being no longer binocular, everything is seen in the flat, the judgments of depth and distance being regu- larly more or less defective. While this is a tremendous disadvantage in many occupa- tions, people gradually and not infrequently become accustomed to these visual defects and are not conscious of the handicap. [128] Refraction and Muscular Imbalance Pain. It is quite different with the second set of symptoms, which are always accompan- ied with pain. In fact, the character of the subjective symptoms in refractive errors and muscular imbalance is so similar that it is practically impossible to differentiate in many cases. In muscular asthenopia, however, in addi- tion to becoming easily tired, the patient often complains that letters seem to jump or run together or he may contend that he sees double for an instant; or again that he can "feel his eyes turn" involuntarily in their sockets. These pains or conditions are sometimes pres- ent only during actual use of the eyes. At other times they persist for hours. In some cases, after days or weeks of overstimulation, an explosion in migraine form occurs at ir- regular intervals. This condition often lasts a day or two. Reflex Symptoms. In the third and last case, there are other reflex symptoms — such as dizziness, nausea, fainting, indigestion, in- somnia and pains in other portions of the body — sometimes stimulating organic diseases. The possibility of heterophoria as a factor in chorea, migraine, neurasthenia and other diseases which may be primarily due to un- stable nerves, equilibrium is not to be forgot- [129] Refraction and Muscular Imbalance ten. It is a notable fact that when the fusion compensation fails so completely that one image is entirely suppressed, or the diplopia is so great as to be overlooked, the symptoms often cease entirely. Treatment The treatment of heterophoria depends on a careful study of each individual case, but it cannot be too strongly emphasized that in the great majority of cases the sub- jective symptoms disappear after a full cor- rection of the refraction is made. In many cases, if the visual acuity in each eye be made normal, the fusion impulse alone W\\\ be sufficient to restore compensation. Many cases of csophoria result from over- stimulation of the centers for convergence and accomodation, made necessary by hyperopia and astigmatism, entirely disappearing when glasses abolish the need of accomodation. Cases of exophoria are sometimes due to the abnormal relaxation of accomodation and con- vergence which secures the best distant vision in myopia. Likewise the correction of my- opia, by increasing the far point, may dimin- ish the amount of convergence necessary for near vision. [130] Refraction and Muscular luihalance Prisms for constant use are often prescribed, so placed as to help the weak muscles and counteract the strong. For instance, in eso- phoria we find the prism which, base in, will produce orthophoria for distance and pre- scribe a quarter of it, base in, before each eye. While this is very successful in some cases, the tendency in others is for the externus to increase slightly from constant exercise in overcoming the prism, while the internus de- creases in proportion to the amount of work of which it is relieved. Prisms for perma- nent use are very beneficial in vertical devia- tions, since when the images are brought on the same level they require much less efifort to secure fusion; and when prescribed base up or down, the effect secured is commonly an unchanging one. We sometimes take advantage of this ten- dency when we prescribe for constant use weak prisms with the apex over the weak muscle, which gradually becomes strong from the exercise of overcoming it. This plan is effective only in patients who have a strong fusion impulse, and the prism selected must be weak enough to be easily overcome. We can accomplish the same effect by decentering the patient's refraction lenses. For instance, a convex lens so placed that [131] Refraction and Muscular Imbalance the visual line passes the reverse will be the case if the lens is concave. The amount of prismatic action depends on the strength of the lens and the amount of decentering, the rule being that every centimeter of displace- ment causes as many prism dioptres as there are dioptres in that meridian of the lens. Thus + 1 sphere, or cylinder axis 90, decentered one centimeter outward, is equivalent to adding a one degree prism dioptre lens, base out. Destrophoria and Laevophoria These are terms denoting a condition in which both eyes are capable of abnormal rotating toward the right or left, as the case may be. The movement in the opposite di- rection is most common. The patient can often rotate his eyes 60 degrees toward the right, and to perhaps only 40 degrees to the left. His position of rest is parallel with his visual lines, but to the right, in looking at objects directly in front, he is much more comfortable with his head turned slightly to the left. It is difficult to account for, except on the theory that definite movement of the eyes is rather to the right than to the left in most occupations. The position of the paper in writing at a desk tends toward dextrophoria; in reading, we move our eyes steadily from [132] Refraction and Muscular Imbalance left to right and then begin a new line by a single brief movement to the left; the things that a man uses most — whether he be laborer or student — are kept within reach of the right hand, and in referring to them the eyes are constantly turned toward the right. However, when these conditions result from other imbalances, they must be treated more carefully. For instance, a patient whose right internus is paralysed or congenitally defec- tive on looking to the left, has a cross diplopia which vanishes to the right; as a result, he soon assumes a habit of carrying his head in this position. Ordinarily, this will cause no dis- comfort; but if the left internus is so weak that it cannot follow the right externus to its posi- tion of greatest ease, the visual lines are evi- dently different and the case must be treated as an exophoria. If, on the other hand, the left internus over- balances the right externus, the condition is an esophoria and must be treated as such. Similar reasoning applies to the conditions known as Anaphoria and Kataphoria, in which the visual lines are parallel to each other but directed up or down with regard to the horizontal plane of the body. In the first, owing to congenital abnormali- ties, the eyes usually tend upward and the in- [133] Rcf raft ion and Muscular Imbalance dividual must go about with his chin on his chest, so that his eyes may look in front and yet remain in the position of rest. In the second, the chin is held in the air and the body arched backward. But, unless extreme, neither of these condi- tions causes more than cosmetic difficulty and both should be undisturbed owing to the ex- treme difficulty of securing the same opera- tive effect on both eyes. Suitable prisms are much more likely to be beneficial. 34] Supports for Holding The Ski-optometer Floor Stand Choice may be made from any of the above. The Wall Bracket is recom- mended, unless re- fractionist is provided with a specialist's chair, to which the Chair Attachment with Upright may be attached. [135] 14 DAY USE RETURN TO DESK FROM WHICH BORROWED OPTOMETRY LIBRARY he exp This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. ■ pio LD21— 32m— 1/75 (S3845L)4970 General Library University of California Berkeley . ill m^m^SB.!-^'' LIBRARIES coes'iMaits t