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The Trial Case 
 and How to Use It 
 
 A Practical Treatise For 
 Optometrists 
 
 Illustrated 
 Second Edition 
 
 By 
 R. M. LOCKWOOD 
 
 Author of Principles of Optometry, Some Experiments in Optics, 
 Subjective Tests for Difficult Cases, Etc. 
 
 NEW YORK 
 
 FREDERICK BOGER PUB. CO. 
 I Maiden Lane 
 
 X 
 
OPTOMFTRY 
 
 Copyright i 904 
 
 by 
 
 Frederick Boger Pub. Co. 
 
 I Maiden Lane 
 
 New York 
 
 V 
 
 PRESS OF 
 
 (^t)C <©ptical Journai 
 
OPTOMETRY 
 LIBRARY 
 
 LIST OF ILLUSTRATIONS. 
 
 PAGE 
 
 The Eye 8 
 
 A Normal Eye lo 
 
 Emmetropic Eye 14 
 
 Myopic Eye 14 
 
 Hypermetropic Eye 14 
 
 Test Types 20 
 
 Clock Dial Chart 21 
 
 Types of Lenses 21 
 
 Cylinders 22 
 
 Prisms 23 
 
 Pin-hole Disc 25 
 
 Stenopeic Slit 25 
 
 Maddox Rod 26 
 
 Double Prisms 2y 
 
 Cobalt Blue Disc 28 
 
 Trial Frame 30 
 
 ^Measuring Card 3^ 
 
 Trial Case 33 
 
 Test Types 34 
 
 Children's Test Types 35 
 
 Prav's Letter Chart 36 
 
 Fan Chart 37 
 
 A Landscape Out of Focus 44 
 
 A Landscape in Focus 45 
 
 An Adjustable Outfit 53 
 
 Lenticular Lenses 67 
 
 Toric Curves 69 
 
 Removing the Cinder 7^ 
 
 Tool for" Removing Cinders 77 
 
V 
 
PREFACE TO THE SECOND EDITION. 
 
 The very cordial reception which has been accorded to this 
 work whereby the first edition becomes exhausted in six months, 
 is extremely gratifying to the author, who feels that the series of 
 practical works of which the present volume is the second really 
 fills a want among those who make eye testing a profession. He 
 feared that optometrists might not care to freshen up on the 
 details of their work, but the result has proved this not to be 
 true. In the first volume of the series, "Principles of Optome- 
 try," he presented the principles as against the science of optom- 
 etry ; in the present volume he gives the routine practice for 
 ordinary cases as he follows it, while in "Subjective Tests for 
 Difficult Cases" he presents a great many practical methods for 
 those cases where the routine method is undesirable or where a 
 re-examination is necessary. 
 
 The author has carefully prepared the text of this second 
 edition. He has made a few corrections and slight additions to 
 give greater clearness, but otherwise the work remains the same 
 as in the first edition. 
 
CHAPTER I. 
 
 THE EYE AND SOME OF ITS FUNCTIONS. 
 
 THE EYE. — The eye is the same as a photographic camera 
 so far as its image-producing power is concerned, and corresponds 
 to a lens of something less than an inch focus. It differs from a 
 camera in the fact that it is not a simple lens or a combination of 
 simple lenses forming an image in the air at a certain dis- 
 tance to the rear, but rather a succession of transparent refracting 
 living substances forming altogether one solid whole. Com- 
 mencing at the front is the cornea, the transparent portion of the 
 eye which is exposed to the outside world. Behind this comes 
 the aqueous chamber, so called because of the watery-like fluid 
 which it contains; next the crystalline lens, which is bi-convex 
 in form, then the vitreous, a jelly-like, transparent medium, and 
 finally the retina, or the screen of the eye, on which the image 
 made by the succession of transparent bodies just specified forms 
 a copy of external objects. The retina is really an expansion 
 of the optic nerve which consists of hundreds of thousands of 
 individual fibres, entering the ball of the eye from the rear and 
 then spreading out on the inner surface of its hindermost por- 
 tion to form the retinal screen. This retinal screen is very com- 
 plex ; is made up of nine distinct layers, all transparent, but the 
 deepest one of all considered to contain those peculiar organs, the 
 rods and cones, which are now supposed to fulfill the function of 
 responding to the waves of light in such a way that the vibrations 
 which they transmit to the fibers of the optic nerve are carried by 
 
8 THE TRIAL CASE AND HOW TO USE IT. 
 
 the latter to tlie visual centers uf the brain, there to be interpreted 
 in that mysterious way which we call vision. 
 
 The eye is a globe, or almost one, of a diameter of about one 
 
 S. — The sclerotic. 
 
 V. — The viti'eous humor. 
 
 Oh. — The choroid. 
 
 Y. — The macula lutea. 
 
 Figure 1.— THE EYE. 
 A. — The aqueous humor. 
 
 R. — The retina. 
 I. — Iris. O. — Optic nerve. 
 
 T.. — The crystalline lens. C. — The cornea. 
 
 M. — The ciliary muscle. P. — The pupil. 
 
 X. — The centre of rotation of the eye. 
 J he dotted circle shows the departure of the normal eye from a spherical form 
 
THE EYE AND SOME OF ITS FUNCTIONS. 
 
 inch. Its outer coat is very tougli, far more so than it looks, and 
 this outer coat consists of three distinct layers. The inner one, 
 the retina, has already been referred to. Next to and outside of it 
 is the choroid, which is thin and dark purple, and contains most 
 of the blood vessels which feed the eye and carry off the products 
 of decay, for the eye is a physiological instrument and like all the 
 other organs of the body it is continually wearing out and being 
 renewed, or in other words there is a continual circulatory current 
 in the eye, and in all parts of the eye, which constantly brings 
 in new food and carries away waste products. It is true that it is all 
 transparent, or rather so in health, but at the same time this circu- 
 lation is absolutely necessary, and its cessation for any reason 
 means blindness in a few hours, while a partial choking up of 
 the ducts is very apt to seriously interfere with vision and ulti- 
 mately destroy it. Immediately outside of the choroid is the 
 sclerotic coat, which is white and very tough. At the front of the 
 eye this coating becomes transparent and then is known as the 
 cornea. 
 
 In the center of the cornea is the pupil, which is merely the 
 central portion not covered by the iris. It looks black, but is 
 really transparent. The reason we cannot see through it ordina- 
 rily is that to see anything through a transparent substance there 
 must be something more or less lighted up behind it, but in the 
 case of the eye the only way for the retina to be lighted up is 
 through the pupil, and this will never occur so long as our head is 
 in the way of the light, which it will always be when we attempt to 
 look inside. By reflecting light into the eye from a mirror, in 
 the center of which there is a tiny hole, through which we look, 
 we will then see the back of the eye, and the pupil will appear 
 bright red, or orange, instead of black, this due to the capillary 
 
10 THE TRIAL CASE AND HOW TO USE IT. 
 
 network of blood vessels of the choroid showing through the 
 transparent retina. 
 
 The eye is subject to many diseases, with very few of which 
 the optometrist can have any concern. The main thing that he 
 should know in this connection is to detect opacities, whether due 
 to cataract or to some other cause ; and to be able to tell by 
 simple inspection whether there is anything abnormal in the visible 
 portions of the eye. For this purpose a condensing lens, the 
 concave mirror and the ophthalmoscope are used. 
 
 Fig. 2.— a normal EYE. 
 
 One in which parallel rays of light focus on the retina when the eye is in a 
 
 state of physiological rest. 
 
 A NORMAL EYE. — From the point of view of the optome- 
 trist a normal eye is one which when it is in a state of physio- 
 logic rest it can look upon far distant objects and see them dis- 
 tinctly ; that is, the image of the distant object formed on the retina 
 will be without the slightest diffuseness of image. Such an eve is 
 extremely rare, but it serves as a standard of comparison by 
 which we may express the dioptric condition of any eye wdiich is 
 under test. Such an eye is said to be emmetropic. When the eye 
 is abnormal from an optical point of vicw^ we call it ametropic. 
 
THE EYE AND SOME OF ITS FUNCTIONS. 11 
 
 It is the sphere of optometry to supply f;lasses to anietropic eyes 
 to bring- them as near to emmctropia as the physiological and 
 optical conditions will permit. 
 
 ACCOMMODATION.— Just back of the iris where it meets 
 the sclerotic is a small circular muscle attached to a membrane, 
 to the center of which is fastened the crystalline lens. Although 
 the eye is a camera, there is one important point in which it 
 differs from all others cameras. Its screen is fixed, and in order 
 to see distinctly for all distances it must change its magnifying 
 power. With an ordinary lens, the nearer the bright object on one 
 side of the lens, the farther away must be the image on the other 
 side of the lens, but with the eye there can be no movement of the 
 screen which receives the image, hence the power of the lens 
 itself is altered. The more the crystalline lens swells in the center 
 the greater its strength, and the greater its strength the nearer the 
 object must be to be seen distinctly. It is the function of the small 
 circular muscle to produce these changes in convexity by loosen- 
 ing up the membrane, so that as this loosening occurs the crystal- 
 line lens swells. This property of the eye is called its accommo- 
 dation. It is strongest in childhood, but steadily diminishes in 
 power as we grow older until at about 65 years of age there is 
 no more accommodation, and the eye is only in focus for just 
 one point. This ocular process is called presbyopia and all hu- 
 man beings without exception, are subject to it. As a result of 
 it all persons, except a few very near-sighted ones, must wear 
 glasses eventually to read, while others must also wear glasses to 
 see well at a distance. 
 
 FAR AND NEAR POINTS.— These are the two points 
 which express the limits of the accommodative power of the 
 
13 THE TRIAL CASE AND HOW TO USE IT. 
 
 individual. In the case of a myope they have an actual existence, 
 and the same is the case with an emmetrope. In the former case 
 the two points will be within infinity, one being the greatest dis- 
 tance at which the eye can see clearly and the other the nearest 
 point at which it can see clearly. In the case of the emmetrope one 
 will be at infinity, but with a hypermetrope only one of the 
 points, the near point, can have an actual existence, and where 
 the hypermetropia is high both points may be beyond infinity; 
 that is to say, they will have no actual existence, the eye not 
 being able to focus any rays on the retina whether near or far. In 
 this case they may be said optically to be behind the patient's back. 
 
 HYPERMETROPIA.— When the eyeball is deficient in 
 depth, or the dioptric power of the crystalline lens of the eye is 
 too low, then we have a condition called hypermetropia or hyper- 
 opia. In this ocular condition the ciliary muscle must act to 
 increase the powder of the crystalline lens so that the image of the 
 distant object instead of blurring on the retina may form there 
 a clear and distinct image. This puts a great deal of work on the 
 delicate ciliary muscle as compared wath that of the emmetropic 
 eye, in which there is no strain at all on this muscle. The pos- 
 sible results of this condition are several. First the eye will 
 show presbyopia before it would were the eye strictly normal. 
 Usually with the normal eye, glasses are needed for reading about 
 42 years of age, but with an eye which is hypermetropic to a high 
 degree this necessity may arise many years sooner, while in some 
 extra high cases the glasses are needed in childhood. The aver- 
 age eye has just about so much ciliary power, and if, as is the case 
 with a hypermetropic eye, half of this is used to overcome the 
 optical abnormality of the eye, then only half of it is left for a 
 
THE EYE AND SOME OF ITS FUNCTIONS. 13 
 
 reserve, which will of course be used up long before the tra- 
 ditional age of 42. The second difficulty which arises with 
 hypermetropic eyes is headache and eyestrain. Each individual 
 has a certain amount of nervous force, and while there are some 
 who can give up the amount demanded by the ciliary muscle in 
 hypermetropia, there are others which even with a very small 
 amount of it will suffer from headache, especially after sight- 
 seeing, as well as from eyestrain, and in some extraordinary 
 cases from several remote nervous reflexes. Finally the ciliary 
 muscle may take on a condition of "spasm" or "cramp," in which 
 as the result of overwork the muscle may suddenly contract into 
 a fixed position and simulate myopia. There is considerable 
 difference of opinion as to the nature of this spasmodic condition, 
 some claiming that it a persistent spasm hard to break up, others 
 that it is only effective when the eye is in use, and that by "fog- 
 ging" the spasm will relax. Tscherning dismisses the whole 
 subject with the statement that "all spasm of the accommodation 
 will relax promptly in the dark room." If this is true then cer- 
 tainly "fogging" is all that is necessary. In any event the op- 
 tometrist must be constantly on his guard not to be deceived and 
 prescribe the wrong lenses. 
 
 MYOPIA. — When the eyeball is too long, or the dioptric 
 power of the crystalline lens of the eye is too strong, then we 
 have a condition of myopia. In order that the image of a given 
 object shall come clear on the retina, the power of the crystalline 
 lens must weaken, but there is a limit to this, which is reached 
 when the ciliary nuiscle is entirely relaxed. Myopes cannot see 
 at a distance, but do not have to wear reading glasses so soon as 
 emmetropes and hypermctropes ; in fact, some of them never have 
 
14 THE TRIAL CASE AND HOW TO USE IT. 
 
 to wear them. For a normal eye in a young person the range of 
 vision may be from 6 inches to infinity, while in a myope it may 
 only be from 4 to 13 inches. In both case the eyes have about 
 equal accommodative powers. It was laid down by Bonders, and 
 many others hold the same opinion, that a myopic eye is always a 
 diseased eye, and that the myopia is usually progressive and is 
 due to civilization ; that eves were not meant for such close work 
 
 Fig. 3. 
 (a) Emmetropic eye. {b) Myopic eye. (e) Hypermetropic eye. 
 
 as is common in schools, though of late years this opinion given out 
 by Bonders has been somewhat modified. It is now held that 
 there are two sorts of myopia; one, non-malignant, which is the 
 result of school life, and which runs to a certain point and there 
 stops, and the other the true malignant variety, which has noth- 
 ing to do with school. Germany is the home of the myope and the 
 condition arouses much concern there. 
 
 ASTIGMATISM. — The eye is far from being optically per- 
 fect and one of its most common defects, found alike in emme- 
 tropia and ametropia, is astigmatism. This means that ocidar 
 condition in which the different meridians of the eye have not the 
 same power. If we put before such an eye a narrow slit, first 
 vertical, then horizontal, and then in several other different direc- 
 tions, we will find one direction in which it shows a greater power 
 than the others, and we will find another in which the power is 
 
THE EYE AND SOME OF ITS FUNCTIONS. 15 
 
 less than all the others. The two directions, one having the 
 strongest power and the other having the least, are the two prin- 
 cipal meridians of the eye. Before w-e can get the clearest image 
 possible on the retina we must make all the meridians of equal 
 power. Astigmatism is extremely common, but in most cases of 
 so little amount that the owner has become used to it, and in fact 
 is better satisfied with it uncorrected than the contrary, but where 
 the condition is at all marked it often gives rise to the same symp- 
 toms as hypermetropia and is accompanied with poor vision. 
 
 USE OF CORRECTING LENSES.— The lenses used for 
 the correction of hypermetropia are those which, by adding diop- 
 tric power to the eye, force the ciliary muscle to give up an equal 
 amount, and thus bring about a normal state of rest. These are 
 plus lenses, those which have a magnifying power. For myopia 
 minus lenses are given, those which have a minifying power. 
 Their effect is to so decrease the total dioptric power of the eye and 
 lens together that the images of distant objects will come clear 
 upon the retina. For astigmatism we must use cylinders, either 
 plus or minus, as the case may require. These are lenses having 
 their curvatures all in one direction. If a plus cylinder is used its 
 greatest power is so placed that it corresponds with the weakest 
 meridian of the eye and thereby makes the two meridians equal, 
 or else if a minus lens, its greatest power is placed at right angles 
 to the highest meridian of the eye, or what is the same thing, paral- 
 lel and coincident with the meridian of lowest power. The result 
 in either case is the same ; all the meridians are made alike and the 
 combination acts as a sphere. For compound troubles, such as 
 hypermetropia combined with astigmatism, we must give a cylin- 
 der combined with a sphere. These form wdiat are called sphero- 
 cylinders. 
 
16 THE TRIAL CASE AND HOW TO USE IT. 
 
 The retinal image of an astigmatic eye is not correct but for 
 one meridian at a time, and advantage is taken of this in testing for 
 astigmatism. The eye under test is fogged, that is, a plus lens is 
 placed in front of it which blurs distant object. Then the patient 
 is directed to look at a set of black radiating lines, of which he 
 will see those in one direction the best. This direction is one 
 of the principal meridians of his astigmatism. The other is at 
 right angles to it. The direction of a cylinder in which there is 
 no power is called its axis. 
 
 PRISMS. — Prisms, though having no magnifying power, are 
 usually included under the general name "lenses" when all the 
 transparent media employed in the correction of refraction are con- 
 sidered together. They are used in some cases of heterophoria, 
 where this cannot be dissipated by the correction of the ametropia, 
 or where the case is not severe enough to demand an ocular opera- 
 tion. 
 
 DIOPTRIC SYSTEM.— Lenses are now numbered as fol- 
 lows: A lens forming on a screen an image of the sun at a dis- 
 tance of 40 inches is of i diopter ; a lens twice as strong, or one 
 forming an image of the sun at 20 inches is a 2 diopter lens ; a 
 lens which is three times as strong, forming an image of the sun 
 at 13 inches, is a 3 diopter lens, etc. The lenses in the trial case 
 are numbered in this way. To find the value of two or more of 
 them together combine the values as shown on their handles. 
 The old system was based on French inches, which are not ex- 
 actly the same as English inches, but one system may be turned 
 into the other, accurately enough for all practical purposes, by the 
 following rule : To change from diopters to inch system divide 
 
THE EYE AND SOME OF ITS FUNCTIONS. 17 
 
 40 by the value in diopters and the quotient will be the value in 
 the inch system. To change from the inch system to the diop- 
 tric method divide the number in inches into 40, and the quotient 
 will be the corresponding value in diopters. The reason we use 
 40 is that the dioptric system is based on the meter which is 
 39.37 inches, and 40 is so close to this that it is universally used. 
 
 AMBLYOPIA. — This means poor vision due to physiologi- 
 cal or pathological reasons ; something wrong with the retina, the 
 optic nerve or the visual brain centers. It cannot be corrected by 
 lenses during the test. 
 
 EXTERNAL MUSCLES OF THE EYE.— These are six 
 in number, four pulling the eye (lightly) back against the cap- 
 sule in which it rests, and two others acting with the check liga- 
 ments to pull the eye forward, thus keeping the organ in a state of 
 equilibrium. These muscles act harmoniously together, so that in 
 a normally functioning eye it may take any position required for 
 good vision with correctness and ease. Where this is not the case, 
 then we have a condition of heterophoria or muscle imbalance 
 which may result in headaches, eyeaches or other disagreable 
 symptoms ; or else the eye may give up the struggle and squint. 
 Heterophoria is difficult to treat ; prisms, muscle exercises and 
 operations being the means used. 
 
 ASTHENOPIA.— This may be of two kinds, muscular or 
 accommodative. In the first case there is strain on the external 
 muscles of the eye ; in the latter it is strain upon the ciliary muscle. 
 In either case the symptoms are about the same ; eyeache, diffi- 
 culties with vision, and sometimes nervous aflfections, more or 
 
18 THE TRIAL CASE AND HOW TO USE IT. 
 
 less hard to discover and cure, whose connection with the eyes is 
 hard to trace. Usually lenses and cylinders properly applied in 
 spectacles will correct accommodative asthenopia, while for the 
 muscular form we must have recourse to prisms, muscle exercises, 
 or even operations. 
 
 PHOTOPHOBLA. — This is an intolerance of light, more or 
 less pronounced. It may be due to sluggishness of the iris, undue 
 sensitiveness or inflammation of the retina, and is common in al- 
 binos, or where the eyes have been subjected to a dazzling light, 
 as well as in diseased conditions. It is properly a case for the 
 oculist, though tinted glasses are sometimes prescribed by the op- 
 tometrist to rest the retina. Only smoked glasses should be pre- 
 scribed for this purpose. 
 
CHAPTER II. 
 
 TESTING AND MEANS EMPLOYED. 
 
 METHODS OF TESTING.— There are two general 
 methods of testing eyes, the subjective and the objective. In the 
 former we depend upon what the patient says in response to our 
 questions as we apply our various tests. In the latter we judge 
 for ourselves by what we actually see. Both methods have their 
 place in optometry, but the subjective test with the trial case is al- 
 ways the court of last resort, and everything is checked up by it. 
 
 TEST TYPE FOR DISTANCE.— Twenty feet has come to 
 be the standard distance for testing eyes for all uses except near 
 work. The rays of light coming from this distance are so nearly 
 parallel that the slight error is disregarded. The letters on the 
 chart are usually black on a white ground, and figured for defin- 
 ite distances, the distance for which the different sizes are calcu- 
 lated being marked above each line. These types may be tised at 
 less than the regular distance of twenty feet, but in this case al- 
 lowance must be made for the decrease in distance. With these 
 types we are able to express the visual acuity either with lenses 
 or without. In doing this wx make use of the fractional method, 
 the numerator being the distance of the type and the denominator 
 the size. A child, corrected, if necessary, with lenses, should 
 have a visual acuity of 20/15; an adult under the same circum- 
 stances 20/20; an elderly person 15/20. Where this result can- 
 not be reached, the eye is below normal. Sometimes a better re- 
 
20 
 
 THE TRIAL CASE AND HOW TO USE IT 
 
 suit can be obtained, and in this case the eye is above normal, but 
 these cases are somewhat rare. 
 
 TEST TYPE FOR NEAR.— There are two varieties of this 
 type, one Jaeger's, which is nothing more than ordinary type from 
 the printer's font graded from the very finest up. and the other 
 Snellen's, which is similar to the distance type, but decreased pro- 
 
 Ul 
 
 
 E 
 
 3 III 
 
 
 T B 
 
 E Ul 3 
 
 
 D L N 
 
 E a Ul m 
 
 
 P T E B 
 
 UISEniA 
 
 
 rSBIlI! 
 
 
 
 OIKITQ 
 
 
 - 
 
 
 Fi 
 
 (i. 4. — Test Tyin 
 
 'S. 
 
 portionately in size to correspond with the short distances at which 
 it is used. With this type we find the reading point and the acuity 
 of vision for a short distance. Normal eyes should read the very 
 finest type on the chart at a distance of 13 inches. Many eyes can 
 do even better than this when pro{)crly corrected with glasses. 
 This chart may also be used in finding tlie amplitude of the ac- 
 commodation. 
 
TESTING AND MEANS EMPLOYED. 
 
 21 
 
 CLOCK DIAL CHART.— This consists of a scries of radiat- 
 ing lines with outer circles and Roman numbers arranged to cor- 
 respond closely with the dial of a clock. It is used in connection 
 with cylinders for the detection and correction of astigmatism. 
 
 Fig. 5.— Clock Dial Chart. 
 
 The Roman figures are used to name the radiating lines, those 
 which are vertical being called the XII to VI lines ; those which 
 are horizontal being called the lines from IX to III, etc. The 
 values of the lines are sometimes also read off in degrees ; the IX 
 
 A 
 
 Fig. 6. — Types of Lenses. 
 
 being zero, X 30, XI 60, XII 90, I 120, II 150, and III 180. This 
 numbering is in the contrary direction from that of the trial frame, 
 but this is necessary to make the two agree, since they are used 
 facing in different directions. There are many other line-tests 
 for astigmatism, but they are all based on the same principle. 
 
22 
 
 THE TRIAL CASE AND HOW TO USE IT. 
 
 PLUS LENSES. — These are magnifying^ glasses. They 
 converge the rays of Hght, and if the object is far enough away, 
 they will bring all the rays of light from this object to a focus, 
 where they will form an image, a duplicate of the object in form 
 and color, but inverted. In the trial case there are many of these 
 plus lenses arranged on the dioptric system and graded from the 
 weakest to the strongest. Their values are marked on the handles, 
 the fact that they are plus being shown by a cross stamped in the 
 metal. 
 
 MINUS LENSES. — These are minifying glasses. They di- 
 verge the rays of light, and do not form an image of the illu- 
 
 FiG. 7. — Cylinders. 
 
 minated object, no matter how near or far away it may be. These 
 lenses are arranged in the trial case in the same way as the plus 
 lenses, their handles being usually stamped with a minus, and also 
 gilded. 
 
TESTING AND MRANS EMPLOYED. 23 
 
 CYLINDERS. — These are glasses which arc ground in one 
 direction only. Look at the chimney of an argand gas lamp which 
 is cylindrical. The outer surface of this will show the curved sur- 
 face of a plus cylinder, while the inner surface will show the 
 curved surface of a minus cylinder. One of the surfaces of 
 the cylinders of the trial case is piano. These cylindrical lenses 
 are marked on their handles in the same way as the plus and 
 minus spherical lenses, but in addition their surface for a short 
 distance near the periphery, and parallel to the direction in w^hich 
 there is no curvature, is frosted. This shows the direction of the 
 axis of the cylinder. Referring again to th^ argand burner chim- 
 ney, the axis corresponds with the long way of the chimney. 
 
 Fig. 8. — rrisms. 
 
 PRISMS. — These are wedges of glass which have neither 
 magnifying nor minifying power, their two surfaces being plane. 
 Rays of light in passing through a prism are bent tow^ards the 
 thickest part of the w^dge, called the base, the thicker the wedge 
 
24 THE TRIAL CASE AND HOW TO USE IT. 
 
 the more the bending, while the eye looking through a prism in 
 order to see an object in any selected direction must turn from the 
 direct line of sight towards the sharp edge, or apex, of the prism. 
 Under these circumstances the eye is looking around an angle. 
 Prisms are usually marked with a figure follow^ed by a little tri- 
 angle to show the number of degrees of arc between the two sur- 
 faces of the wedge. There are other ways of marking prisms, 
 called the prism diopter and centrad. They are both scientific in 
 theory, but are not in common use. They will not be discussed 
 here. In many cases there are both circular and square prisms in 
 the trial case, the former to be used with the trial frame and the 
 latter with the fingers. 
 
 OPAQUE DISC. — This is a solid piece of metal or rubber, 
 circular in form, to fit the trial frame. It is used to shut ofif one 
 eye while the other is being tested. All modern optometry is 
 based on testing each eye separately, and while this is being done 
 the other eye should remain open so as not to tire out the patient. 
 The opaque disc produces this result. 
 
 GROUND GLASS DISC.— This is used for the same pur- 
 pose as the opaque disc, but the operator can see the eye through 
 the outside, which in certain cases is an advantage. 
 
 PIN-HOLE DISC. — This is the same as the opaque disc, 
 but with one modification. Its center is pierced with a very fine 
 hole through which the patient must look. It has the same efifect 
 as cutting down the size of the pupil and this results, in cases 
 of ametropia, in reducing the circles of diffusion formed on the 
 retina, with the result that the outlines of the object looked at 
 become much clearer. It is true that at the same time there is 
 
TESTING AND MEANS EMPLOYED. 2r. 
 
 much loss of light, due to the smallness of the hole, but the clear- 
 ness of form attained more than offsets this. Any eye that can be 
 improved by this test can always be improved by lenses. There 
 is no exception to the rule. 
 
 STENOPEIC DISC— This is an opaque disc in tne center 
 of which there is cut a narrow slit. With it we can test any 
 meridian of the eye. It is used in some cases to detect and cor- 
 rect astigmatism. It has one objection; the size of the pupil of 
 the eye varies with the amount of light which passes through it 
 
 Fig. 0. — Pin-hole Disc and Stenopeic Slit. 
 
 to the retina. Since the stenopeic slit cuts off a large part of tne 
 light, the pupil will dilate unduly and the peripheral part of the 
 lens will come into play. As this peripheral portion is sometimes 
 of a different power from the center, a false finding may be the 
 result. 
 
 MADDOX ROD.— This is used to uncover heterophoria. 
 It consists of a glass rod attached parallel and in front of a sten- 
 
26 THE TRIAL CASE AND HOW TO USE IT. 
 
 opeic slit. The small glass rod acts as a strong cylinder, thus 
 causing a light, such as a candle, to appear as a long streak about 
 the width of the flame. The difference in the appearance of this 
 from the candle flame itself deceives the eye, and if there is a ten- 
 
 FlG 
 
 Multiple ISIaddox Rod. 
 
 dency to heterophoria the weak muscle will take a position of com- 
 fort, since the mind fails to realize that the two bright objects, as 
 seen by the two eyes, one with the rod in front of it and the other 
 not, are one and the same, hence the fusion sense is not in play. 
 
 DOUBLE PRISM. — This is a solid piece of glass made in 
 the form of two prisms, base to base. It is placed over the eye 
 so that one-half of the pupil is behind one prism and the othtr half 
 behind the other prism. This causes the eye to see the light 
 double. By using a red glass over the other eye, or even without 
 any such glass, the patient will see three lights, the upper and 
 lower ones being the two images on one retina, caused by the 
 double prism, and the central one coming from the other eye. 
 The result here is the same as with the Maddox rod. The eye is 
 deceived and the muscles take a position of comfort. The po- 
 
TESTING AND MEANS EMPLOYED. 27 
 
 sition which the central Hght seems to take with relation to the 
 outer ones is the measure of the heterophoria, if such exist. 
 
 > 
 
 Fig. 11.— Double Prism. 
 
 TINTED PLANOS. — These are graded as to the obscurity 
 of the tint, and have been used as sufficient in cases of photo- 
 phobia, but this practice is decreasing, since photophobia has come 
 to be looked upon as rather a serious symptom. Where the optom- 
 etrist does prescribe them, the tints should be "smoke," no colors, 
 as the latter are bad for the eyes. It seems to be necessary for 
 the proper functioning of the retina that it should receive white 
 light ; that none of the spectrum colors should be missing. Colored 
 glass cuts off some of these colors, smoke tint does not, only de- 
 creasing the amount of each color entering the eye. 
 
 PLANO LENSES.— There is little call for these in opto- 
 metrical practice, but sometimes they are used to detect maling- 
 erers; for instance, children who want glasses just for looks. 
 These pianos are also used in testing eyes of marked acuity, where 
 a lens which is correct will seem to be not as good as the naked 
 
28 THE TRIAL CASE AND HOW TO USE IT. 
 
 eye because the glass absorbs some of the hght and therefore 
 makes the test card apparently not so clear. In these cases when 
 a lens is tried it must be used in conjunction with a piano, so that 
 conditions of illumination of retina may be equal. 
 
 COLORED GLASS DISCS.— These are generally red and 
 green. Either may be used in the Maddox rod test and the two 
 can be used together in the FRIEND test for malingerers. In 
 cases of marked hyperphorias the colored glass discs alone, the red 
 or the green, over one eye will be sufficient to show that the con- 
 dition exists, though the Maddox rod is the best in routine prac- 
 tice for this purpose. 
 
 COBALT BLUE GLASS.— This is a special test based on 
 the supposition that if the rays of light from a source of illumina- 
 
 FiG. 12.— Cobalt Blue Glass. 
 
 tion are cut down to the red and the blue, the accommodation will 
 relax and thereby permit the ocular condition to be diagnosed by 
 the appearance of the light. The glass used for the purpose is 
 apparently blue, but really allows both red and blue to freely pass 
 
TESTING AND MEANS EMPLOYED. 29 
 
 while all the other colors are almost entirely cut off. Since red 
 and blue are unequally refrangible, there will be two images of 
 the flame formed, one blue and the other red, the blue being nearer 
 to the crystalline lens. If the retina of the eye corresponds with 
 the focus of the blue rays then there will be a clear blue image on 
 which is superimposed the red image, but diffused. This will give 
 the appearance of a blue center with a red border. The contrary 
 will be the case if the retina corresponds with the focus of the red 
 rays, while for an intermediate point the two images will both be 
 slightly diffuse and will coincide in size. By these different ap- 
 pearances of the two colors the refraction of the eye is known. 
 Astigmatism is knowai by the change in the shapes of the two 
 colors. This test is perfectly reliable where there is no accommo- 
 dation, but otherwise is more or less uncertain. 
 
 SCHEINER'S TEST.— This is a very old test. It consists 
 of an opaque disc pierced by two very small holes close together. 
 The eye under test must look through both holes at the same time, 
 the light used being small and bright. The appearance of this 
 light, sometimes single, sometimes double, will give the refraction 
 of the eye. The test is moderately reliable, but difficult to apply, 
 as it is not alw^iys certain that the patient is looking through both 
 holes at the same time, and this is necessary for the success of the 
 test. 
 
 TRIAL FRAME.— This is a pair of spectacles made espe- 
 cially for testing. By suitable adjustments it may be made to fit 
 any eve, and by its calibration, if this is correct, the size of the 
 spectacles to be worn can be read oft*. It contains over each eye 
 two or three "cells" or receptacles for holding the lenses and vari- 
 
30 
 
 THE TRIAL CASE AND HOW TO USE IT. 
 
 oils tests from the trial case, one or more of these cells being" so ar- 
 ranged that the lens or test placed in it may be revolved. This is 
 
 Fig. 13. — Scheiner's Test. 
 Trial Frame. 
 
 Fig. 14. — Measuring Card. 
 
TESTING AND MEANS EMPLOYED. 31 
 
 especially for cylinders. On account of the weight of the trial 
 frame it is an instrument of torture for many people, and its use in 
 these case must be cut down to the smallest space of time pos- 
 sible. It does not usually give satisfaction in taking facial meas- 
 urements, due to errors in the calibration, to loose joints, and to 
 the fact that very often the round trial frame case lenses cannot be 
 put in the same position that the lenses of the spectacles or eye- 
 glasses are to occupy. Facial measurements are usually and pref- 
 erably taken with a small ruler divided into millimeters on one 
 edge and thirty-seconds of an inch on the other. 
 
CHAPTER III. 
 THE CONTENTS OF THE CASE. 
 
 The complete trial case for optometrical work usually con- 
 sists of the following : A graded assortment of bi-convex and bi- 
 concave spherical lenses of from 0.12 diopters to 20 diopters; a 
 similar assortment in plus and minus cylinders : a graded set of 
 prisms, both circular and square, marked by their apex angles, of 
 from 0.12 to 20 degrees or more; a three-cell trial frame; and the 
 following special testing discs : piano lens, tinted piano lenses, Nos. 
 I to 6; ground glass disc, opaque disc, pin-hole disc, stenopeic 
 disc, red glass, green glass, cobalt blue glass, Maddox rod and 
 double prism, the latter for muscle tests. Sometimes there are 
 special discs, such as Scheiner's and the cone prism test. Such a 
 case will cost $75.00 or more. 
 
 At the other end of the scale we find the pocket case. This 
 contains a limited number of lenses and discs, varying somewhat 
 with the dififerent dealers, but the following will be found to be a 
 good selection : plus and minus spheres in pairs, sizes 0.25, 0.50, 
 0.75, I., 1.50, 2., 2.50, 3., and 4 diopters; minus cylinders in pairs, 
 .25, .50, I., 1.50, 2.25 and 3 diopters; five testing discs; ground 
 glass, pin-hole, stenopeic slit, Maddox rod and red glass. With 
 this outfit and a plain three-celled trial frame, ninety per cent, or 
 more of all cases may be fitted provided the optometrist is a good 
 mathematician, since combinations with so limited an assortment 
 will usually have to be figured. Such a pocket case may be pur- 
 chased, including the plain three-cell trial frame, for about $15.00. 
 
THE CONTENTS OF THE CASE. 
 
 33 
 
 By adding to the outfit a few high power spheres, plus and minus, 
 the percentage of cases which may be treated will be still higher. 
 Between the two extremes above mentioned there are all 
 grades of trial cases, at all sorts of intermediate prices. Each one 
 must decide for himself just how far he can go, bearing in mind 
 
 Fig. 15. — Trial Case. 
 
 always that the more complete the trial case the more professional 
 it will seem, and the less the optometrist will have to make mathe- 
 matical calculations. 
 
 The method of trial case routine in this work will be so pre- 
 sented that the tests may be made with any variety of outfit within 
 the limits of price stated. 
 
34 
 
 THE TRIAL CASE AND HOW TO USE IT. 
 
 TEST CARDS. 
 
 To properly meet all emergencies, the assortment of test cards 
 should be as complete and varied as possible. There ought to be 
 one or more of Snellen's distance test cards, each lettered differ- 
 ently from the others, and if possible a special form of this chart 
 in which the letters on each line are of decreasing size. Also 
 
 n 
 
 m 
 
 
 tl jC Jtt 
 
 ^0 r jtr jc 
 
 u i t w fe 
 
 1 galctg 
 
 J .p.r^M 
 
 lu a E PI n 
 
 Fig. 16. — Test Types. 
 
 there should be a Snellen's test card for distance in German let- 
 ters; the E illiterate chart; the picture chart for young children, 
 and the clock dial and other astigmatic charts. For reading dis- 
 tance there should be the Jaeger or the Snellen near chart. For 
 testing the ocular muscles for close work there should be the red 
 and black Maddox near test, to be used with a single prism. This 
 
THE CONTENTS OF THE CASE. 35 
 
 latter chart is figured for a distance of lo inches, and it would be 
 well to also have one figured for i6 inches. For taking facial 
 measurements there should be either a properly marked ruler, or 
 else some of the special devises used for this purpose and to be 
 had of the various dealers, or possibly, what is better still, a set of 
 sample frames containing piano lenses and marked with a scratch 
 to show their geometrical centers. For measuring out the glasses 
 
 
 B & % 
 
 # Jit li e 
 
 « 1^ o • 
 
 •r V ♦ t 
 
 Fig. 17.— Test Types for Little Children. 
 
 on their return from the prescription house a protractor card, and 
 for quick w^ork a lens measure, are also needed. 
 
 The optometrist who must limit his purchases in these direc- 
 tions can get along, if he has to, with the distance letter chart, a 
 near chart and the clock dial chart. 
 
 The usual distance at which trial case tests are made is sup- 
 posed to be 20 feet. This distance is often stated to be the same 
 practically as infinity, so far as fitting glasses is concerned. This 
 is not correct. If an eye is fitted exactly for an infinite distance, 
 
36 THE TRIAL CASE AND HOW TO USE IT. 
 
 such as a brig-ht star, by a chart at a distance of 20 feet it is mis- 
 fitted to the extent of about 1-6 of a diopter, so that it will some- 
 times be found necessary to allow the nearest to this in the trial 
 case, which is 1-8 D. Then again it is not always possible to get 
 20 feet of space. In this case the optometrist must get along with 
 less, but should never forget that in the prescription a suitable 
 dioptric allowance is to be made to make the correction ri^ht for 
 
 ^^ f\ "t// 
 
 d^ V a 
 ^^^ ^^"^^ iA\ 
 
 Fig. 18. — Pray's Astigmatic Letter Chart. 
 
 infinity, the same to be in the form of an increase for minus 
 glasses and a decrease for plus. Where the distance is ten feet 
 or a little less a good plan is to use the reversed letter charts with 
 a mirror. These also may be had of all the dealers. 
 
 The distance letter charts should be brightly illuminated. 
 There is a rather general belief that the chart should receive only 
 moderate illumination, so that it may correspond more closely 
 
THE CONTENTS OF THE CASE. 
 
 37. 
 
 with natural, cvcry-day conditions. This sccnis plausihlc enough, 
 and yet there is no logic in it. In the first place, there is no stand- 
 ard of every-day illumination, and, secondly, what we are pri- 
 marily seeking to do is to find the dioptric condition of the eye, 
 and this can be best done by bright illumination, the brighter the 
 better within reasonable limits, that is, within the dazzling point. 
 The light which shines upon the distant reading charts should be 
 shaded so that the eye of the patient may receive little light, and 
 this light should also be arranged, as a matter of convenience, so 
 
 Fig. 19. — Fan Chart for Astigmatism. 
 
 that the screen in front of it may be removed and the light itself 
 used for testing muscle imbalance, if so desired. The trial case 
 also should be sufficiently illuminated so that the numbers and 
 marks on the handles of the lenses may be easily read. To see the 
 scale of degrees on the trial frame there should either be a hang- 
 ing electric light, which could be readily swung into position, or 
 else a mirror could be used to reflect the light to the desired point. 
 The astigmatic clock dial, as well as all other tests for astigmatism, 
 when used, should be exactly at right angles to the line of sight. 
 Where the charts are movable and so arranged that they can be 
 
38 THE TRIAL CASE AND HOW TO USE IT. 
 
 brought ill and uiit (jf sight fruin hchiiul a scivcii, there should be 
 counterweighted cords running across the ceihng and down to 
 the optometrist's hand. Back of the patient and convenient to 
 the eye of the optometrist there should be small cards which are 
 duplicates of the distant test charts, so that he may know whether 
 his patient is making mistakes or not, without needing to turn and 
 look across the room. When we are testing a patient, we should 
 be relieved of all possible inconveniences, so we may keep our 
 minds constantly on the test itself; and for this reason it is 
 necessary to have everything arranged conveniently. We can 
 often make out without all this special preparation and arrange- 
 ment of apparatus, but we are also liable at the critical moment to 
 forget some little point which may later cause us considerable 
 annoyance, as well as loss. To do good work in the refracting 
 room, everything should be arranged systematically, and kept so. 
 
CHAPTER IV. 
 
 THE PRELIMINARY TESTS. 
 
 There are certain points, as many of which as possible ought 
 to be cleared up before the optometrist can advantageously begin 
 to apply his subjective tests with the trial case apparatus. These 
 will be given here in a routine order. 
 
 GENERAL INSPECTION.— In the first place, the patient 
 should always remove his or her hat, or else the optometrist may 
 be put to considerable inconvenience. This being done, throw a 
 light on the eye from the side. If the eye is inflamed, or secre- 
 tions of any kind are present, it will be necessary to politely but 
 firmly refuse to take the case. Sore eyes are usually contagious 
 and some of them are of a very serious nature. In case of slight- 
 est doubt, no chances should be taken of carrying infection by 
 means of the trial frame either to the optometrist himself or suc- 
 ceeding patients. If no inflammation or secretions be present, 
 which will usually be true, then the pupillary reaction should be 
 noted. To this end the light should first be pushed back so that 
 the patient's eyes are in darkness, and then it should be brought 
 forward so as to shine directly into the eye, but a little to one 
 side. The pupils of the eyes, under the stimulus of the light, 
 should contract promptly and rapidly. If there is no contraction, 
 or it is very slow, the optometrist will often have the reason at 
 once why there are certain troublesome symptoms, such as photo- 
 phobia, retinal fatigue, and consequent nervous reflexes. 
 
40 THE TRIAL CASE AND HOW TO USE IT. 
 
 The cornea and iris and adjoining parts slionld now be no- 
 ticed to see if there are any malformations present which would 
 tend to reduce the visual acuity, or, in other words, normal vision. 
 
 Some claim that the shape of the head and the face will tell 
 the nature of the optical imperfection, but for this the writer will 
 not vouch. He will simply state here what is claimed in this re- 
 gard : "Flat face, hypermetropic eye ; long face, myopic eye ; 
 non-symmetrical face, astigmatism; large and prominent eyes, 
 myopia; small eyes, hypermetropia." 
 
 THE HISTORY OF THE CASE.— This is one.pf the most 
 important points. There are some optometrists who consider 
 themselves belittled if they ask the patient any preliminary ques- 
 tions. They take the ground that it is their place to find out the 
 ocular condition by the use of their optical appliances alone. We 
 can take a little instruction on this point from the physicans. 
 Those of us who are familiar with the work of the medical prac- 
 titioner and student know how much stress is laid on the "history 
 of the case," and how much time is given to it. There are several 
 things, which, if possible, we should find out by interrogating the 
 patient. 
 
 Why does he wish glasses, and has he ever worn them be- 
 fore? If so, for how long and with what results? 
 
 What particular ocular symptoms does he notice? Is there 
 dimness of vision, either permanent or temporary? 
 
 Does he see double, and in which direction, or do dark spots 
 ever seem to come before his eyes? 
 
 Does he have hard work to read, and does the print ever seem 
 to dance or swim? 
 
 Are there headache, eyeache, or burning sensations in the 
 eyes, and when? 
 
THE PREOMINARY TESTS. 41 
 
 Arc there excessive winking, or flow of tears, or sore-eyes in 
 the morning? 
 
 Is a bright light troublesome ? Can he see better at night or 
 in the daytime? 
 
 Has he ever had eye disease of any kind, and has any one put 
 drops in his eye recently? 
 
 To ask categorically all of the above questions would be an 
 unnecessary waste of time, but the patient should be skillfully led 
 to give the information, or as much of it as the inspection of the 
 eyes would seem to make necessary, though there should be no 
 rambHng allowed; this being courteously kept in check. Mean- 
 time the preliminary tests, as here described, should be going 
 on. Should the patient be churlish, we must get what informa- 
 tion we can. Still one more point is essential, especially with 
 presbyopes, and that is to get and measure out the power of the 
 lenses previously worn. Because a patient has a certain amount 
 of either presbyopia or ametropia, it does not follow that full cor- 
 rection should be prescribed. With a knowledge of what the 
 patient has last worn, the question of what to have him wear next 
 is more easily settled. When this information cannot be had, we 
 may unknowingly give the patient what he already has. This he 
 will soon discover when he tries on the new pair and compares 
 them with the old pair at home ; then he will return to investigate, 
 which will not always be pleasant. To get the strength of the 
 glasses which he has previously been wearing is just as necessary 
 as it is for a physician to know what medicine the patient has 
 previously been taking. It is true that he can often get along 
 without the knowledge, but he will do better with it. In fact, he 
 might unwittingly give his patient the same old prescription with 
 the same old taste, which he will recognize, with corresponding 
 loss of confidence. 
 
42 THE TRIAL CASE AOT) HOW TO USE IT. 
 
 LOOKING IN THE EYE FOR OPACITIES.— This is a 
 rapid test, mainly for the purpose of discovering if there are any 
 signs of cataract. It is made with the regular concave retino- 
 scopic mirror at a distance of about 24 inches from the eye under 
 test. Let the light be about one meter distant; have the patient 
 look in a little towards the nose ; nt)w reflect the light into his eye, 
 and the red fundus will immediately come into view. If there are 
 any opacities present, either corneal, lenticular or in the vitreous, 
 they will appear as black spots against the red background of the 
 fundus. Where the observer's own eyes cannot accommodate for 
 a distance of 24 inches, he should attach such a lens behind the 
 concave mirror, as will enable him to do so. The object of this is 
 to cut down the corneal reflex to the smallest possible size, and this 
 will be the case when the observer's eye accommodates properly 
 for this image; otherwise it will be blurred and therefore occupy 
 an increased space on his retina, thus hiding, perhaps, some 
 opacity. 
 
 Where the pupil of the patient's eye is very small so that the 
 fundus cannot be seen it will be necessary to put a strong plus lens 
 in the trial frame. 
 
 THE COVER TEST FOR HETEROPHORIA.— Direct 
 the patient to look steadily at a small light across the room. HoFd 
 a card before one eye and watch it from behind the card. Now 
 move the card to cover the opposite eye. Repeat in the reverse 
 direction. Do not be too quick to make the transfer of the card. 
 Wait a few seconds for the eye to become fixed. If, when the 
 card is removed from in front of either eye, there is a jumping 
 movement of the pupil, then there is heterophoria present. Should 
 the cover test develop any motion of this kind, then the following 
 
THE PRFXiMINARY TESTS. 43 
 
 muscle test should be made: Place over the right e)e oi the 
 patient the Maddox rod disc, and over the left eye a red glass, 
 unless the Maddox rod is made of red glass, when a green glass 
 should be used instead. At the opposite side of the room have a 
 gas or lamp flame, in front of which is a screen pierced by a hole 
 one inch in diameter. Let the patient sit at a distance from this 
 flame of 9 feet 6 inches. Turn the test in the trial frame until 
 the rod is horizontal. Now cover first one eye and then the other 
 until he has found both lights, one being the one-inch flame col- 
 ored green and the other a long streak of light. Take away the 
 card altogether and he will see the two forms of light at the same 
 timxC, though at first he may have a little trouble in this r-egard, 
 but this soon passes. Now let him describe to you the relative 
 positions of the tw^o lights ; how far to one side the streak is, and 
 on which side. Have him express their distance apart in terms 
 of the diameter of the flame. If the distance from center of 
 streak to center of flame is one inch, the diameter of the flame, 
 then he will have heterophoria to the extent that a one-degree 
 prism will correct ; that is, for every diameter of the flame that the 
 centers of the two lights are apart, there W'ill be required one de- 
 gree of prism to correct the heterophoria. This applies, as stated, 
 to a one-inch flame at a distance of 9 feet 6 inches. Make the 
 distance half of this and the flame would have to be but one-half 
 inch in diameter. The optometrist will find that the heterophoria 
 can be discovered by this m.ethod in less time than it has taken to 
 explain it. Every one is familiar with an inch, and when the pa- 
 tient is told that the flame is one inch wide, and then asked how 
 many inches the centers of the circle and disc are apart, he will 
 answer correctly. 
 
 With the jNIaddox rod, as stated, over the right eye, if the 
 
44 
 
 THE TRIAL CASE AND HOW TO USE IT. 
 
 vertical streak should also he to the rii^ht of the center of the circle 
 of light, then there is esophoria ; if to the left, exophoria. Now 
 turn the Maddox rod the other way, vertically, which makes the 
 streak of light horizontal, and test for hyperphoria. The Mad- 
 
 FiG. 20. — Before Correction. 
 
 dox rod being still before the right eye, if the streak is above the 
 circle, then the right eye looks down, or what is the same thing, 
 the left eye looks up, and we have hyperphoria, while if the 
 streak is below the center of the ring of light, then there is right 
 
THE PRELIMINARY TESTS. 45 
 
 hyperphoria. The method of making one inch at a distance of 
 9 feet 6 inches correspond to a one-degree prism (not a prism 
 diopter) is practically correct to 20 degrees. Above that there is 
 a steadily and rapidly increasing error. It is not absolutely nec- 
 
 FiG. 21. — After Correction. 
 
 essary to use a green glass ; no glass at all will do, but the green 
 glass is easier on the patient's eyes, but where the Maddox rod is 
 white a red glass over the other eye may be used. 
 
 VISUAL ACUITY FOR DISTANCE.— Visual acuity de- 
 pends on several factors, "^he size of the objects looked at, the 
 
46 THE TRIAL CASE AND HOW TO USE IT. 
 
 contrast in color between the objects and their surroundings; the 
 illumination ; the width of the pupil of the observing eye ; the con- 
 dition of the retina, the optic nerve and the visual centers of the 
 brain ; and finally upon the perfectness of the eye as an optical 
 instrument. The standard used for optometrical work is the 
 Snellen's chart when under a bright illumination. This the nor- 
 mal eye should see distinctly at the distances as marked on the 
 chart. The patient should be directed to look at the letters and to 
 read down as far as he can with both eyes, and then with each eye 
 singly. A record is to be made of the result for future compari- 
 son. This is with the naked eye. In making this record the fol- 
 lowing method is used : express the visual acuity as a fraction, 
 the numerator being the number of feet which the patient is dis- 
 tant from the chart and the denominator being the number of the 
 type. 20/20 means that 20- foot type can be read at 20 feet ; 
 10/15 that 15-foot type can be read at 10 feet only; 20/60 partly, 
 means that part of the 60-foot type could be read at 20 feet, but 
 not all the letters. In using the test letter chart it will be noticed 
 that some letters are easier to distinguish than others. The Snellen 
 chart has its letters all drawn to scale, the various parts of the let- 
 ters being one minute of arc wide, and the letter as a whole occu- 
 pying" 5 niinutes of arc. This is the size which a normal eye is 
 supposed to be just able to make out. The letter O is, however, 
 much more readily distinguished, 3 minutes of arc usually being 
 sufficient, while the letter L can often be made out with 2 minutes 
 of arc. Then, again, young people as a rule will see better than 
 normal, say 20/15, while aged persons can rarely do better than 
 15/20. Where these visual acuities are reached it is sometimes 
 assumed that there is neither myopia nor astigmatism present, un- 
 less there should also be present eyestrain or other nervous reflex 
 symptom. 
 
THE PRELIMINARY TESTS. 47 
 
 VISUAL ACUITY FOR CLOSE WORK.— This test 
 should be made with the near type, either the Jaeger or Snellen. 
 The patient should be allowed to hold the printed matter at any 
 distance he chooses, and the record should show this distance as 
 well as the smallest size of type that he can read. The two eyes 
 should be tested together first and then each eye separately. 
 Records can be made similar to the following : No. I at 20 
 mchcs ; No. 7 at 8 inches, etc. It would, of course, be better to 
 use the same notation as with the distance chart, but usually the 
 near test charts are not marked on the Snellen basis. 
 
 THE FAR POINT IN MYOPIC EYES.— Hold the near 
 type at a distance of six feet or so from the patient and then draw 
 gradually nearer until the letters come clear. If at the distance of 
 six feet the letters are blurred, but come out clear when the chart 
 is brought nearer, then there is myopia present, and the point at 
 which the letters are first clear is the far point for that particular 
 eye. 
 
 TO FIND THE NEAR POINT IN ALL EYES NOT 
 TOO HYPEROPIC— This is found in the same way as in the 
 previous paragraph, excepting that the chart is brought farther 
 forward, until the letters begin to blur again. Where the eyes 
 are myopic this will give us both the far and near point; the far 
 point when the letters come clear and the near point when they 
 begin to blur again. By measuring the distance from the eye in 
 each case and expressing the result as diopters, we can get the 
 amplitude of accommodation, which will be the difference be- 
 Uveen the two values. Furthermore, the far point itself, ex- 
 pressed in diopters, will be the measure of the myopia. Where 
 
48 THE TRIAL CASE AND HOW TO USE IT. 
 
 the eye is too hyperopia and presbyopic there will be no actual 
 near point. As a check on the above method, the following- may 
 be used : Hold the near test chart close to the eyes and gradually 
 withdraw it The near point will be the point where the type first 
 comes clear. 
 
 THE AUTHOR'S SPECIAL METHOD OF MAKING 
 THE NEAR TEST. — It is not always an easy matter to get the 
 exact near point by means of the near reading chart, for the patient 
 is often liable to read by pseudo-accommodation, the power of 
 reading slightly blurred images. Some patients will pronounce 
 the letters perfectly clear when they may be out of focus as much 
 as a whole diopter. To meet this difficulty the author has devised 
 a special form of near test which is extremely accurate. It con- 
 sists of a ruler on which there is freely movable a cardboard 
 slider containing three vertical targets, on each of which are 
 drawn three fine black vertical lines, the distance between targets 
 being two inches, though this distance may be made less. To 
 use the device, rest the ruler against the cheek bone under the 
 patient's eye and push the slider up as close to the eye as it will 
 go. Usually the lines on all three targets will be blurred ; if not 
 they may be made so by placing a suitable lens before the eye. 
 Next the apparatus should be withdrawn slowly until the lines on 
 the two outer targets become perfectly clear, while the inner one 
 remains blurred. The near point will then be marked by the 
 middle target if the patient is young, and by the point midway be- 
 tween the two if he is presbyopic. 
 
 THE PATIENT'S READING DISTANCE.— This does 
 not mean the distance at which he reads when he comes to have 
 
THE PRELIMINARY TESTS. 49 
 
 his eyes examined, but rather that point where considering his 
 length of arm and other anatomical points, it will be the right 
 place for him to read when he takes an easy position. The con- 
 dition of his eyes after fitting will also have something to do with 
 it. It is often assumed that the reading distance should be ex- 
 actly 13 inches, but for the reasons above stated this is not always 
 the case. Have the patient, with a piece of blank paper in his 
 hand, take that position which is most comfortable for him. 
 Measure this distance from the eye, and make a note of the same. 
 
 CHAPTER V. 
 TESTS FROM THE TRIAL CASE. 
 
 When the preliminary tests have been completed the optom- 
 etrist will usually have a pretty close idea of the patient's ocular 
 condition, and what is left for him to do is to determine that con- 
 dition with accuracy. To this end he should proceed method- 
 ically and according to some chosen system. As to what system 
 shall be followed in routine cases, that is a point on which there is 
 apt to be some difference of opinion. The method given here is 
 the one which the author has found in his own experience to be 
 the most satisfactory in ordinary cases. In the extraordinary 
 ones he has always been prepared to use some other special test,* 
 whichever one seemed to best fit the circumstances of the case. 
 The regular routine, then, will be as follows: 
 
 ♦Subjective Tests for Difficult Cases; Frederick Boger Publishing 
 Co., I Maiden Lane, New York. 
 
50 THE TRIAL CASE AND HOW TO USE IT. 
 
 ARTIFICIAL FAR AND NEAR POINT.— If the case is 
 one of myopia, as shown by the tests already made, it will not be 
 necessary to test for the artificial far and near point, since the in- 
 formation sought has already been gained. When this is not true, 
 however, a plus 4 diopter spherical lens should be placed in the 
 single cell trial frame over the right eye. (As a matter of routine 
 it is best to always commence with the right eye in all tests and 
 examinations.) The use of the plus 4 diopter lens is not only to 
 get the artificial far point, but also in cases of spasm of the accom- 
 modation to unlock the spasm, which wdll take place in a few 
 moments after the lens has been put in place. Now take the read- 
 mg chart, or the author's special test, suitably illuminated from a 
 light from behind and a little to one side of the patient. Move 
 the chart away from the eye to be tested until the letters on it are 
 all a blur, and then bring it gradually nearer until the print be- 
 comes clear. This will be the artificial far point with a plus 4 
 diopter lens. Measure the distance from the eyes, convert it into 
 the corresponding dioptric value by dividing into 40, and sub- 
 tract the result from plus 4 diopters. The answer will be the 
 approximate correction for distant vision. When we put a plus 
 4 lens before an emmetropic eye, the far point is brought from 
 infinity up to 10 inches or less. If we find with this lens that the 
 artificial point is not 10 inches, then the eye is not emmetropic. 
 If this far point is at 13 inches, which corresponds to plus 3 
 diopters, then to bring it up the remaining distance to 10 inches, 
 or 4 diopters, we would have to add the difference between plus 3 
 and plus 4, or plus i diopter, which is therefore the approximate 
 measure of the ametropia. If, on the contrary, with the plus 4 
 diopter lens we find the artificial far point to be at 9 inches, which 
 corresponds to 4.50 diopters, then the eye may be .50 diopters 
 
TESTS FROM THE TRIAL CASE. 51 
 
 myopic, though often this will not be true, since the sense of 
 nearness will often induce a certain amount of ciliary spasm. 
 
 After the artificial far point has been noted, then the read- 
 ing chart would be brought still nearer until it blurs again, this 
 time because it has been brought within the nearest point at which 
 it can be made out with all of the accommodation in force ; by now 
 moving the chart a little back again the point will be found within 
 which the letters will blur. This is the artificial near point for 
 this particular eye with a plus 4 diopter lens. Note this distance 
 and convert it into the corresponding diopters as before. 
 
 A large proportion of the patients will have no difficulty in 
 making out the smallest type on the test chart both for this arti- 
 ficial far and near point, but there will be others who will not be 
 able to do this. Such a result would argue amblyopia, or astig- 
 matism, and note should be made accordingly. To suit these 
 cases, attention should be called to the smallest type that can be 
 made out. 
 
 AMPLITUDE OF ACCOMMODATION.— This is the ex- 
 tent to which the ciliary muscle can contract expressed in diopters. 
 To find out how much it is, we deduct the far point from the near 
 point expressed in diopters. For instance, if the artificial far 
 point is found to be at 16 inches and the artificial near point at 5 
 inches from the eye, then the amplitude of accommodation for near 
 which is usually a little different than for distance will be 5>4 
 diopters, for 16 inches corresponds to 2J/2 diopters and 5 inches 
 corresponds to 8 diopters, and the difference between the two will 
 be as above stated. The amount of the amplitude of accommoda- 
 tion will vary with the individual and his age. The table by Don- 
 ders as given below, will apply to most cases, and where the actual 
 
 I 
 
52 THE TRIAL CASE AND HOW TO USE IT. 
 
 amount in any case as tested out is less, then there will be a sus- 
 picion of paralysis of the accommodation, or spasm of accommo- 
 dation, or a mistake in the age of the patient. 
 
 ears. 
 
 Amplitude in D. 
 
 Years. 
 
 Amplitude in D. 
 
 lO 
 
 14- 
 
 45 
 
 3-50 
 
 15 
 
 12. 
 
 50 
 
 2.50 
 
 20 
 
 10. 
 
 55 
 
 1.75 
 
 25 
 
 8.50 
 
 60 
 
 I. 
 
 30 
 
 7. 
 
 65 
 
 0.75 
 
 35 
 
 5.50 
 
 70 
 
 0.25 
 
 40 
 
 4-50 
 
 75 
 
 0.00 
 
 DEVELOPMENT OF THE MERIDIAN OF GREAT- 
 EST POWER. — The correction of astigmatism is the greatest 
 difficulty which stands in the path of the optometrist. To be cer- 
 tain in this branch of testing requires constant watchfulness. 
 There are two theories as to the way in which an astigmatic eye 
 sees. One is that it accommodates for an intermediate position 
 between the two principal meridians, so as to reduce the difficulty 
 to a minimum, and undoubtedly in some cases this is true. The 
 other is that the eye first adjusts for one meridian and then for 
 the one at right angles. This action is assumed to be extremely 
 rapid, the two images being continually superimposed. If this 
 latter theory is correct, we have a good explanation of two im- 
 portant points ; one being why so many astigmatic eyes see so 
 much better than ought to be the case as compared with emme- 
 tropic eyes, and the other why small errors of astigmatism pro- 
 duce in some cases such marked eyestrain and reflex symptoms. 
 In any event, no matter which theory is correct, one thing is cer- 
 tain ; the accommodation is usually in abnormal play, and unless 
 
TESTS FROM THE TRIAL CASE. 
 
 53 
 
 ^ 
 
 Fig. 22.— An Adjustable Outfit. 
 
54 THE TRIAL CASE AND HOW TO USE IT. 
 
 we force this to relax we stand little chance of getting the true 
 principal astigmatic meridians. But this is not all. Where the 
 meridians are oblique the prescription is apt only too often to be 
 wrong, either because of an error on the part of the optometrist, 
 or because the glasses are set wrong in the frame, usually the for- 
 mer. A sphero-cylinder with axis 120° wnll become 60° if turned 
 the wrong side out in the frame. Also it is quite evident that with 
 oblique meridians it will not do for the spectacle eyes to be re- 
 versed in the frames, since a right lens with axis 60°, for instance, 
 would not be correct if put in the left eye wire. To show that 
 the optometrist may readily make an error in the case of oblique 
 axes and meridians, let him try the following experiment: Hang 
 the clock dial chart on the wall. On a table on the opposite side 
 of the room place a trial frame just as it would be were it on a 
 patient's face, or it may be placed on some one's face. Now look 
 at the clock dial and select the lines from V to XI ; decide with 
 what degree of the trial frame these lines correspond. Now take 
 a ruler, place it over the lines from V to XI ; then holding it 
 rigidly in this direction, carry it across the room to the frame and 
 see if it marks the number of degrees decided upon at first as cor- 
 rect. N^ot every one will get it right, since the lines from V to 
 XI will be found to correspond to 60° and not to 120°. and the 
 lines from IV to X will correspond to 30° and not to 150°. 
 
 The first step, then, in the correction of astigmatism is to 
 properly locate the principal meridians, and this cannot be done 
 with any certainty unless the accommodation is relaxed during the 
 test ; neither will the result be attained the most smoothly unless 
 the patient receives first such explanation as will give him some 
 idea of what you are trying to do. 
 
 Remove the plus 4 diopter lens from before the patient's eye 
 
TESTS FROM THE TRIAL CASE. 65 
 
 and let him examine the clock dial chart in his hands. Call his 
 attention to the fact that it is arranged somewhat like a clock. 
 Have him notice that in each direction there are three parallel 
 black lines with two white spaces between. Next estimate his 
 approximate correction for one meter. This is obtained from the 
 artificial far point, as already shown. Put the appropriate lens in 
 the adjustable trial frame, properly centered, turn the letter chart 
 to the wall, hang the clock dial in position, so that it is on a level 
 with the eye to be tested. Ask the patient if he sees all the black 
 lines with intervening white spaces equally distinct, and if all their 
 edges are sharply defined. Do not ask "which line is the blackest." 
 Some people's idea of a black line takes into consideration not only 
 the intensity of the blackness^ but the retinal area of its image as 
 well. Now increase the power of the lenses, if plus, or decrease 
 the power, if minus, until all the lines on the chart are blurred. 
 Then take the clock dial from the wall and holding it with the VI 
 to XII lines, exactly vertical, steadily approach the patient. Di- 
 rect him to tell you which series of lines come out clear the first. 
 These will always show the meridian of greatest power, and by 
 noting the point where they become clear, while the lines in the 
 other direction are still blurred, an idea may be gained of the re- 
 fractive condition of the eye so far as that meridian is concerned. 
 This is discovered by converting the distance from the eye at 
 which the first lines come clear into diopters, and subtracting the 
 same from the power of the lens which happens to be in the frame. 
 Place the clock dial back on the wall, and decrease the power 
 of the lens in the frame just enough if a plus; or increase it, if a 
 minus, until the patient again sees the lines of the most defective 
 meridian clearly, while all the others are more or less blurred. 
 Now apply minus cylinders with axes at right angles to the black- 
 
56 THE TRIAL CASE AND HOW TO USE IT. 
 
 est line, which is always the most defective meridian, until all 
 the sets of radiating lines are alike. 
 
 Should the method of procedure as stated above develop no 
 difference in the lines, then there is no appreciable astigmatism in 
 that particular eye. 
 
 CHECKING UP ON THE LETTER CHART.— Leaving 
 all lenses in place, remove the clock dial, and direct the patient's 
 attention to the letter chart. Let him read down as far as he can. 
 Now shift the axis of the cylinder, if the previous test has shown 
 astigmatism, from side to side, to see if vision can be improved. 
 It will sometimes happen that the axis is off a few degrees and 
 this procedure will disclose the fact. Next, in cases of medium 
 and high cylindrical corrections, call the patient's attention to the 
 chart as a whole and ask if it seems perfectly rectangular, or 
 whether it appears slanting. Shift the axis of the cylinder again 
 if necessary until this appearance disappears. The usual final test 
 in cases of astigmatism is the ability to best read the smallest 
 letters possible but where rectangular objects seem on the slant, 
 this must be cleared even at the sacrifice of a little acuity. 
 
 THE FINAL COMPARATIVE TEST.— The optometrist 
 may be sure that the finding as above given is the right correction 
 so far as the cylinder is concerned, and a succession of tests with 
 intervening periods of time will always, in case of healthy eyes, 
 give the same result. It now remains, however, to get the spheres 
 exactly right. For this we should first change the letter chart,, 
 since by this time many patients will have memorized the letters. 
 We are to depend on the sense of contrast, which is an ex- 
 tremely discriminative ocular faculty. Take in one hand a 
 
TESTS FROM THE TRIAL CASE. 57 
 
 piano, and in the other a phis .50 sphere. First hold the piano in 
 front of the correction already in place in the frame, wait a 
 few seconds, and then substitute the plus 50, and ask if the latter 
 has caused a slight blur, making sure first, however, that the 
 patient knows what you mean by the word "blur." If the plus 
 50 does not blur, then take in one hand a plus .50 and in the other 
 a plus I. and repeat the test. Whenever the increase of .50 
 as stated above, produces a blur in the chart, then the correction 
 which does not blur is the one desired. Should the plus .50 
 in the first case blur, then try a piano in comparison with a 
 minus .50, trying the latter first. If necessary compare a minus 
 I. and a minus .50 in the same way, the minus i. to be tried 
 first. The reason why a piano should be used as described 
 is that with patients of sharp vision the chart will be pronounced 
 blurred because of a slight dimness caused by the absorption of 
 light by the glass of the lens itself. Glass absorbs light, and 
 with very sharp eyes this fact should be reckoned with. The 
 point will be, perhaps, better realized by the following experiment : 
 Look first through an open window and then through the win- 
 dow glass. The difference will be quite noticeable, no matter 
 how well cleaned the window glass may be. Should the test 
 as made seem to show that even with the piano lens the patient 
 is confusing this dimness with blurring, then a tinted piano may 
 be used to make sure. 
 
 In some cases it will be possible to do finer work than the 
 above; that is, where the visual sharpness is unduly acute, the 
 comparative test may be made with differences of .25 D., or even 
 in some cases with .12 D. On the contrary, where the visual sharp- 
 ness is low, the test may have to be made with differences of power 
 of I D. or even more. 
 
58 THE TRIAL CASE AND HOW TO USE IT. 
 
 CHECKING UP AT THIRTEEN INCHES.— In cases of 
 doubt the following may be added to the above. Combine a plus 
 3 with the correction for distance already in the frame. This 
 should make the artificial far point at about 13 inches, and if on 
 testing with the near chart for the artificial far point, this does 
 not prove to be the case, then something is wrong; either a mis- 
 take has been made, or else latent hyperopia has not been all made 
 manifest. 
 
 A DOUBLE CHECK TEST.— When the eye has been fitted, 
 and the full correction for distance is still in place, hold a plus 
 .25 sphere in front of the other lenses in the frame. The type 
 should blur a little. Next w^ith the plus .25 still in place bring 
 in front of it with the other hand a minus .25 sphere. The type 
 should come clear and sharp at once. A plus and minus .50 may 
 be used in the same way for eyes of sub-normal acuity. 
 
 THE PIN-HOLE TEST.— Whenever the visual acuity can- 
 not be brought up to normal this test should be used. With it 
 the test letters will never look so bright and clear, but where the 
 subnormal vision is due to optical defects of the eye alone the 
 patient will be able to make out smaller letters on the chart with 
 the pin-hole disc than without it. This is due to the fact that the 
 very small hole in the opaque disc cuts down the angle of aper- 
 ture so much that diffusion circles on the retina are made ex- 
 tremely small, thus permitting outlines to be more easily fol- 
 lowed. Where subnormal vision is due to some physiological or 
 other similar condition, then vision through the pin-hole will not 
 be improved but usually will be made w^orse. In placing the pin- 
 hole disc before the eye be sure that it is properly centered for the 
 
TESTS FROM THE TRIAL CASE. 59 
 
 pupil, it will be found mure satisfactory with intellig-ent patients 
 to have a special holder- with a handle for the pin-hole disc, so that 
 the patient may adjust it for himself. Where the visual acute- 
 ness is very poor it is a good plan to use the pin-hole disc as the 
 very first test so as to get some idea of the correction by lenses 
 as soon as possible. 
 
 CHAPTER VI. 
 
 TESTS FROM THE TRIAL CASE (Continued) 
 
 THE LENS PRESCRIPTION.— After the dioptric con- 
 dition of the eyes has been determined, the next question is what 
 to prescribe. The rule followed by some is very simple : Give 
 the full correction and insist that the patient wear it through thick 
 and thin until it becomes acceptable and comfortable. This 
 method takes no account of previous physiological habits. It is 
 based on implicit obedience on the patient's part and often fails, 
 for the reason that the average individual in wearing glasses will 
 reach a decision as to their fitness at the end of a very short time, 
 long before he has had a chance to "get used to them." In de- 
 ciding this question he has no consideration for anything but his 
 own feelings ; he does not compare his old visual acuity with his 
 new ; he forgets all about it ; but simply knows that the glasses are 
 uncomfortable, which was not the case with the old ones, and 
 hence he rejects them and visits some other optometrist who may 
 not be so fixed in his ideas as to the necessity of always giving 
 a full correction. The scientific fitting of lenses to the eye, with 
 
60 THE TRIAL CASE AND HOW TO USE IT. 
 
 due regard to acquired and natural ocular functions, is a delicate 
 problem which must be settled separately for each case. The 
 points to be known are the dioptric condition of the eye; the 
 glasses previously worn, if any, and the rules of physiological 
 habits. Especially is this true in medium and high defects and in 
 anisometropia. In the first place, with adults, when astigmatism 
 requires only .50 cylinder for correction, and there are no trouble- 
 some symptoms, it will usually be best to disregard the cylinder 
 altogether. In the second place, while no regular rule can be laid 
 down to fit all cases, it will be good routine practice for the first 
 pair of glasses to allow the eye muscles to do a portion of the 
 work, and in the succeeding ones to gradually cut down the 
 amount of this work if the circumstances seem to require it. 
 Where one of the eyes is amblyopic it will sometimes be best to 
 let one eye be fitted and disregard the other, though recently 
 quite a movement has arisen to first correct the best eye with 
 one pair of glasses for ordinary use, and then by special lenses to 
 develop the poor eye, unless the difference between them optically 
 be too great. To this end a special pair of glasses is given in 
 which only the poorer eye is corrected ; these practice glasses 
 to be used at regular intervals, say three times daily, the good 
 eye meantime being stopped off. Later, if the poor eye can be 
 worked up to the other in visual acuity with proper correction, a 
 pair of glasses is given correcting both eyes. Again, in cases 
 of anisometropia the question is whether to have one eye for 
 reading and the other for distance, or to try to make both eyes 
 work together. Where the difference between the two eyes does 
 not exceed i D., the latter method can eventually be used, but 
 where the difference is greater than i D. this method will usually 
 prove impracticable. In any event, if the attempt is made to get 
 
TESTS FROM THE TRIAL CASE. 61 
 
 the two eyes to work together the first glasses prescribed should 
 only allow for one-half of the difference of the two eyes, to be 
 followed later by a correction with the full difference. In each 
 case the patient must wear the glasses constantly, or the method 
 will be of no use. One objection to fitting cases of anisometropia 
 in this way is that the patient becomes dependent on his glasses, 
 and if by any mishap they are broken, he will be put to a great 
 deal of annoyance until they are repaired. In the case of high 
 myopes it will be found often that the power of accommodation is 
 more or less diminished from non-use ; hence the glasses prescribed 
 should not throw the near point out too far, but the lenses should 
 be made as strong as possible consistent with comfort, and the 
 patient should return later for a stronger pair. Eventually and 
 as soon as possible the full amount of the myopia should be cor- 
 rected. This is the consensus of opinion of most optometrists 
 and oculists. 
 
 THE BINOCULAR TEST FOR DISTANCE.— This, of 
 course, would be omitted in the case of one-eyed patients, of which 
 the optometrist will occasionally have a case. After each eye has 
 been fitted separately, the binocular test should be made. Have 
 the correction selected for distance, in accordance with the pre- 
 vious paragraph, in place. Let the patient look at the smallest 
 letters on the distant chart that he can make out. Now with a 
 pair of plus .25 lenses see if the glasses will be more acceptable 
 with this addition; try the same thing with plus .50 and with 
 minus .25 and minus .50 spheres. It will usually be found that 
 there will be no need to make any change where the eyes are 
 alike. Where this is not true, however, whether because of dif- 
 ferences in refractive power or in the axes of meridians of astig- 
 
62 THE TRIAL CASE AND HOW TO USE IT. 
 
 matism or both, it may be necessary to make some changes in the 
 relative strength. For this purpose use the lenses as given above, 
 also similar cylindrical powers, not over the two eyes together, 
 but over each in turn. For instance, suppose there is aniso- 
 metropia of I D., and suppose we have decided to make a differ- 
 ence in the two glasses of but .50 D., arguing that the eye muscles 
 are to be half relieved of the discrepancy. We may find that we 
 will have to cut the difference down to .25, or, on the other hand, 
 we may be able to go up. Each individual case is a law unto 
 itself in this regard. 
 
 GLASSES FOR COS^^IETIC PURPOSES.— These are 
 given in the case of the blind, either in one eye or both, where the 
 misfortune is noticeable. For a person totally blind, blue or 
 smoke glasses are usually given, but ground glass lenses will be 
 less conspicuous. In the case of a shrunken eye, it is advisable 
 sometimes to fit with a strong glass, which by its magnifying 
 power will make the two eyes look of the same size. 
 
 READING LENSES. — The usual method is to estimate the 
 reading correction from the finding for distance on the basis of 
 the age of the patient, and then modify the correction, if neces- 
 sary, until the patient is satisfied. It is usually assumed that the 
 prescription of glasses for reading is an easy matter, but in alto- 
 gether too large a proportion of these cases the result in the end is 
 not satisfactory. To correct theoretically a case of presbyopia is 
 simple enough, but to do so to the satisfaction of the wearer of 
 the glasses is quite another matter. Suppose we take the case of 
 an emmctrope, or one who is nearly so. The patient has had to 
 hold the print farther and farther from his eyes, until at last his 
 
I 
 
 TESTS FROM THE TRIAL CASE. 63 
 
 arms are too short for the purpose. Under these circumstances 
 he is forced to come at last to the optometrist for glasses. The 
 latter makes his tests and finds the distant correction, asks the 
 patient's age, and then figures the near correction on the basis of a 
 reading and working distance of 13 inches. Apparently the lenses 
 are excellent, the patient is delighted and feels that now his trou- 
 bles are over, but in a few days he returns. He reports that he 
 can see all right so far as clearness of vision is concerned. But 
 that he simply cannot wear the glasses prescribed ; that they are 
 not his fit ; that some one has made a mistake. The cause of the 
 trouble is this: He has been fitted for 13 inches. As a result 
 of previous presbyopic experience he has learned, unconsciously, 
 that to see at this short distance he must make a tremendous 
 ocular effort ; and in spite of his new glasses he still tries to make 
 it ; the result being eyestrain. To relieve the disagreeable symp- 
 toms he pushes the print farther back, as he used to, but this 
 makes the type either blurred or not so distinct, and so he brings it 
 back to 13 inches again, regardless of the eyestrain, until he loses 
 patience and comes back to get the "right fit." These symptoms 
 also are accentuated by the strain put upon his convergence, a con- 
 vergence which he has not used to such an extent for years. So 
 common is this experience in a more or less marked degree, that 
 there are many optometrists who, when asked which are the most 
 difficult cases to fit, will answer promptly ''presbyopic ones." 
 
 In prescribing glasses for reading and working, to get the 
 greatest satisfaction, there are several points to be taken into con- 
 sideration; the near point with the distance correction in place; 
 the amplitude of accommodation ; the point at which the patient 
 should read to be in the most comfortable position ; the point at 
 which he has previously been reading ; and most important of ah, 
 
64 THE TRIAL CASE AND HOW TO USE IT. 
 
 the glasses which he has been wearing, if any. The distance at 
 which the patient ought to read ordinarily depends upon his build, 
 unless amblyopia be present, but when he has been reading with 
 arms too far outstretched, it will be necessary at first to select a 
 new point only a little inside of this, even if it does seem too far 
 away. Later he will have to return and get stronger lenses which 
 will bring his reading point to the right place. 
 
 Where the presbyopic patient has been wearing reading 
 glasses which have become unsatisfactory, it will usually be be- 
 cause of increasing age and consequent loss of accommodation, 
 though it may be due to incipient cataract or retinal failure. In 
 these cases it is an open question whether it is always necessary to 
 go through the complete routine of examination. If the patient 
 has normal vision and no eyestrain or defects of vision for the 
 working distance, except that his glasses are no longer strong 
 enough, it may not be necessary to do anything more than to add 
 on the + .50 or + I. diopter required, but where the vision is not 
 normal then a rigid examination is usually best, though if the test 
 with the concave retinoscopic mirror reveals opacities the difficulty 
 is probably cataract, in which event the best and simplest way 
 is to decline the case and strongly advise the eye surgeon. 
 
 THE BINOCULAR TEST FOR NEAR.— With the near 
 correction in place have the patient take in his hand the near read- 
 ing chart and hold it at the reading distance for his case. Now 
 cover first one eye and then the other, to see if one eye sees better 
 than the other. In case one eye is better, alter the correction by 
 an additional plus or minus .25 or more to try to make both eyes 
 alike. Try tlit^ same method on the other eye, if necessary. If 
 there should prove to be considerable difiference in refraction of 
 
TESTS FROM THE TRIAL CASE. 65 
 
 the two eyes try the following: Have the patient watch the 
 smallest letters of the reading chart ; then by minus lenses of low 
 power before one eye, or plus lenses of low power before the other 
 (in addition to the correction already in place) see whether there 
 is any difference in the comfortable feeling of the eyes by slight 
 changes in the power of either eye. It will usually be found that 
 where the difference between the eyes is more than .25 D., that 
 this will have to be at least halved. The reason why there should 
 be a difference in the eyes at short distance and not at distance 
 is that the accommodation of the two eyes does not always work 
 in harmony. Where there is a difference between the two eyes 
 at the working distance, and it can not be corrected by lenses, then 
 it is due to an impairment of vision and the patient should be 
 so told, though the difference will often be so slight that no fur- 
 ther attention needs to be given to the matter. 
 
 THE TEST FOR SPECIAL DISTANCE.— Patients must 
 sometimes be fitted for special distances, as, for instance, musicians 
 and printers ; for the former the test chart should be musical notes 
 of various sizes. If these cases are simply presbyopic then the 
 matter is easily arranged, but where there is recent amblyopia due 
 to physiological changes, then trouble may be expected, for 
 it will be found that when the very best correction is in place, 
 whether for type or musical notes, as the case may be, the patient 
 will not see sufficiently well for his purpose. To get a patient of 
 this class to work at closer range than the specified distance is 
 usually impossible, and yet stronger lenses cannot be prescribed 
 unless the work is to be held closer. The optical rule is very 
 simple ; the more powerful the lens, the closer the print must be, as 
 is quite clear when we consider magnifying glasses. The patient, 
 
66 THE TRIAL CASE AND HOW TO USE IT. 
 
 however, as described here, will not accept any such dictum, but 
 demands glasses that will give him what he wants. He will 
 claim that this is what optometrists are for. Of the same general 
 nature as the above is the patient who insists on reading at a 
 certain distance when the condition of his eyes, usually amblyopic, 
 requires that he read at a shorter point. When the optometrist 
 gets a patient of this kind, and cannot convince him of the natural 
 limitations of lenses, he should decline to have anything further 
 to do with the case. 
 
 FITTING FOR CLOSER THAN THIRTEEN INCHES. 
 — It sometimes happens in cases of amblyopia, often due to 
 cataract or abnormally small pupils, that the patient must be fitted 
 for a much closer distance than 13 inches. Sometimes it has to 
 be as low as 4 inches or less. It is doubtful as to whether the 
 optometrist should touch these rare cases, but if he does it is 
 better to fit one eye only, so as to avoid extraordinary strain of 
 undue convergence. The writer has fitted a case of this kind, 
 high myopia combined with extensive cataract, for a distance 
 of 2 inches. 
 
 CHAPTER VII. 
 
 VARIOUS LENSES USED IN GLASSES. 
 
 A^ARIETIES OF LENSES.— The standard lenses for firsi- 
 class work are periscopic, the concavity in plus lenses being on 
 a minus curve of 1.25 D. of power, the concavity to be placed next 
 the eye. Where there is a minus cylinder present and the axis is 
 
VARIOUS LENSES USED IN GLASSES. 67 
 
 horizontal, the cylindrical side of the lens is placed towards the 
 eye. In glasses for myopia, however, which have a plus curve 
 of 1.25 D., it is the concave side which is placed next the eye. 
 In other cases the lenses are so set that the side which interferes 
 the least with the up and down motion of the eyebrows is on 
 the inside. Occasionally periscopic lenses are unsatisfactory, and 
 it is then necessary to give some other form, such as plano- 
 concave, bi-concave, plano-convex or bi-convex, as the case may 
 be. Why these should be accepted as comfortable, and the others 
 not, is not at all clear. It is usually stated that there is a "glare" 
 with the periscopic form which does not exist with the others, 
 though why so few of the vast number of those who wear the 
 periscopic form should notice this "glare" is a puzzle. Some 
 specialists go so far as to never prescribe periscopics. 
 
 LENTICULAR LENSES.— In cases of high ametropia, 
 where the weight of the lenses prescribed becomes an important 
 factor because of their pressure on the nose, "lenticular" lenses 
 are prescribed. These have a small center of the required diop- 
 
 Fig. 23. — Lenticular Lenses. 
 
 trie power, while the balance of the lens is ground down to a thin 
 glass plate, thus reducing the weight considerably. It is true that 
 they restrict the field of view, but this does not seem to be noticed 
 by those who wear them. 
 
 BIFOCALS.— Where the patient must wear corrections for 
 both far and near vision, two pairs can be described, or else 
 bifocals. There are several forms of these, as may be seen in 
 
68 THE TRIAL CASE AND HOW TO USE IT. 
 
 any dealer's catalogue, but the form most in use is the ''cement," 
 these having proved practically to be the most satisfactory. It 
 takes a patient some little time to get used to bifocals, as the 
 portion corrected for reading is apt to get in the way when the 
 [)atient looks down. This is especially troublesome when he is 
 going downstairs ; in fact, the patient should be cautioned in 
 regard to this. Once, however, accustomed to bifocals, those 
 who wear them are usually pleased and unwilling to take any 
 others. 
 
 CLERICAL LENSES.— These are the ordinary style of 
 lenses, periscopic or otherwise, as the case may be, with the 
 tops ground off. They take the place of a bifocal where the 
 patient is emmetropic, or nearly so, so that glasses for dis- 
 tance are not needed. Sometimes, in the case of myopes, they 
 are ground the other way, the bottoms off. Occasionally it is 
 also necessary to cut off the top of lenses to allow them to set 
 under projecting eyebrows. These lenses take their name from 
 the fact that they are used principally by clergymen in the pulpit. 
 
 COQUILLES, TORICS AND INVISIBLE BIFOCALS.— 
 These are three forms of lenses of considerable expense, which 
 for those who can afford them are rapidly coming into use. The 
 coquille lens is a shell-shaped glass. For a plus i. D. it might 
 have a minus curve of 6 diopters on one side and a plus 7 on 
 the other. The outer surface of these lenses, acting as a rather 
 strong convex mirror, produces an effect of brilliancy which gives 
 a peculiar charm and distinctiveness to the face of the wearer. 
 
 THE TORIC LENS.— This is similar to the coquille, but 
 corresponds optically to a sphero-cylinder. On one surface there 
 
VARIOUS LENSES USED IN GLASSES. 
 
 69 
 
 is a high spherical curve, while on the other the curvature is 
 that of a tore. Such a surface v^hen tested v^ith a lens measure 
 will show different power in different meridians on the same 
 
 Fig. 24. — Toric Curves. 
 
 surface. With both the coquilles and the toric lenses there are 
 sometimes complaints, similar to those in regard to periscopic 
 lenses ; hence it is necessary sometimes to give sphero-cylinders 
 instead. ■ 
 
 THE INVISIBLE BIFOCALS are recent. They are made 
 of three pieces of glass, two crown glass, and the third flint 
 glass, so made that the wafer which adds the power for near 
 vision is entirely inside the combination. These lenses take the 
 place of the usual bifocal. They will stand rougher usage and 
 make a better appearance. 
 
 TINTED LENSES AND PLANOS.— Photophobia or in- 
 tolerance of light is usually a symptom of some pathological condi- 
 tion, and hence the cases are hardly optometrical. Nevertheless 
 there are cases where the patients demand these glasses, and will 
 have them. Under these circumstances ''tinted" glasses will be 
 prescribed. There have been many colors and tints tried for this 
 special purpose in the past, but in view of the nature of the 
 
70 THE TRIAL CASE AND HOW TO USE IT. 
 
 retina in reference to the waves of light, smoke is the only tint 
 that should be used. The retina is adapted for the reception 
 of all the component parts of white light, and smoke glasses do 
 not cut any of these off, but simply reduce the intensity. On the 
 contrary, tinted glass deprives the retina of the stimulus of the 
 color which it cuts ofif, or absorbs, and this produces retinal 
 fatigue, and if the wearing of the colored glass is persisted in 
 there will be permanent retinal fatigue. To understand what is 
 meant by retinal fatigue for colors, take a piece of blue paper 
 and place it in the center of a sheet of white paper in a bright 
 light. Stare at the blue paper steadily for about half a minute, 
 then, with the eyes fixed, withdraw the blue paper. In a moment 
 or so a strong after image will appear on the white paper where 
 the blue piece had been placed. This will be of reddish color 
 and very vivid. It means that the white light from the card 
 which falls on that spot of the retina, in this case the macula lutea, 
 where the image of the blue had previously been, is not all seen. 
 We do not see the blue in it, for the eye is tired for blue. What 
 we see is the white with the blue left out, which is reddish. This is 
 the effect that wearing colored glasses will have. Those of us 
 who have gone to the theatre and seen the play of the calcium 
 lights will recall that while the beauty of it was striking, still the 
 return of the while light was always a relief. 
 
 PRISMS. — These are prescribed sometimes in heterophoria. 
 A large percentage of cases of heterophoria disappears after the 
 correction of the ametropia. Some authorities claim that all 
 heterophorias are due to refractive errors, and that prisms should 
 never be used ; others do not go so far as this, but in any event 
 the first thing to do in heterophoria is to correct the ametropia, 
 
VARIOUS LENSES USED IN GLASSES. 71 
 
 and then wait a few weeks. In other cases the heterophoria is not 
 noticed ; it gives no trouble, and therefore no attempt should be 
 made to correct it. Aside from the above-mentioned cases, there 
 are some where the heterophoria persists, and with these prisms 
 should under certain circumstances be prescribed. These cases 
 will not be discussed here. 
 
 KEEPING RECORDS.— If the method of partial correc- 
 tion at first, and the gradual increase to full correction later, is 
 followed, as recommended here, then records must be kept, not 
 only of the lenses which are prescribed, but of the dioptric con- 
 ditions on which such prescriptions are founded. As to the style 
 of record to be kept each one should devise his own. In it there 
 should be all the points that have been described here, including 
 a brief history of the case. Such a record, properly indexed, may 
 save a great deal of future trouble, as well as the necessity of 
 re-examinations. 
 
 CHAPTER VIII. 
 SOME USEFUL INFORMATION. 
 
 CHILDREN AND SCHOOL LIFE.— It is an open question 
 as to whether the eyes of many children are equal to the demands 
 of modern civilization. When we consider the age of the world, 
 and then the development of modern printing and its use in 
 schools, we feel that it is going to take many thousands of years 
 before all eyes will be fully altered to fit the continuance of pres- 
 ent school conditions. Fine print and sewing are bad enough, 
 especially when they are made part of a kindergarten course, but 
 
72 THE TRIAL CASE AND HOW TO USE IT. 
 
 when we add to this musical notes written in small type it is 
 not at all strange that eyestrain should be so prevalent. 
 
 In the case of books used in schools, there has been a steady 
 improvement, which has, however, for economical reasons, not 
 yet gone far enough. Every school book should be in large type, 
 well spaced, with narrow columns, and not on glazed paper. This 
 will reduce the strain on the vision to the lowest point. But 
 the reform should not stop there. There is the question of desks. 
 Every child should have a desk to fit him, and these are to be 
 had in the market. Some schools use them. Where the desks do 
 not fit, then the body, not being properly supported, the muscles 
 begin to droop ; the child to be comfortable comes too near to his 
 work, and eye troubles are the result. In other cases, however, 
 the weariness of the effort is the n;ain point, and the child ceases 
 to be a scholar. 
 
 Child nature has been studied a great deal, but the limi- 
 tations of children's endurance is as yet not one of the courses 
 given to teachers. A child should have frequent periods of rest ; 
 a great deal of their work, especially in arithmetic, should be done 
 standing at blackboards on which dustless crayon is used ; when 
 small they should have no home tasks at all ; in the grammar 
 schools these tasks should be light and few, though beyond that 
 point they seem to be an unavoidable part of modern school life ; 
 the light in the schools should be of the right kind and from the 
 correct direction — from the left ; under no circumstances should 
 their eyes face the light. The teacher should keep records of the 
 eyesight of the pupils ; not scientific records, but simple ones which 
 will not require on her part more than an hour of study to under- 
 stand and possibly two or three hours of the whole session to 
 make and keep. In the case of those children who fail on the 
 
SOME USEFUL INFORMATION. 73 
 
 au. pie sight tests given, notices should be sent to the parents, 
 and where these notices are not noticed they should be fol- 
 lowed up. 
 
 MYOPIA — This is the scientific name for near-sightedness. 
 A near-sighted child can see well near by, but not at a distance. 
 Such a child does not like to play with his fellows, as he is always 
 the one "caught." Myopia in school children tends to grow stead- 
 ily worse. The myopia may develop into cases of disease, and 
 where this is not the case the child is robbed of most of the enjoy- 
 ment of life. IMyopic children are usually unchildishly sober in 
 demeanor. 
 
 WHEN SHOULD A CHILD WEAR GLASSES ?— In the 
 first place, any child old enough to study, and who does have to 
 study, should wear glasses if his eyes are not normal. This will 
 be shown in several ways: DifBculty in seeing either near or 
 far ; pains in the eyes ; headaches. School life is an important 
 piece of business, and since almost the only sense used in schools 
 is the eye, and this sense is used to excess, every child's eyes 
 without exception should, before commencing school life, be exam- 
 ined in order to see to what extent he is prepared to take up 
 the work. Knowledge under modern conditions is an absolute 
 necessity, but so is vision, hence no chances should be taken. The 
 idea that all eyes are right and more or less alike is about as true 
 as to say that all people should be of the same height or weight, or 
 color of hair, or state of health. 
 
 OVERWORKING THE EYES.— It is strange how some 
 people will overwork their eyes. They will rest their backs when 
 tired, but for a tired eye they have no mercy. They will not 
 
74 THE TRIAL CASE AND HOW TO USE IT. 
 
 subject their voices to exercise, by screaming, for instance, but 
 they will read on the cars, or read when sleepy, or do fine work, 
 not because they have to, but because they take pleasure in it, 
 though the eyes are rebelling all the time. They will read poor 
 type, and small type, though their eyes are meantime on a con- 
 tinual strain. None of these things ought to be done, as they 
 force the owner of the eyes to wear spectacles sooner than would 
 otherwise be the case, yet every one with normal eyes must wear 
 glasses for reading sooner or later. That is the order of nature. 
 But though no one likes the idea of putting on glasses, still he 
 will do those very things which make the wearing of glasses 
 unduly early a necessity. When such a one is forced to come at 
 last to the optometrist, and wonders why, the reason is simple. 
 He has overworked his eyes and must pay the penalty. 
 
 WHEN SHOULD GLASSES BE WORN?— When one 
 does not recognize his friends on the street ; when he has to turn 
 the light very high to see to read ; when he has to hold the print 
 too far away from his eyes ; when he has to hold the print under 
 his nose ; when his eyes ache or water ! when he has headaches 
 which headache powders won't cure; when things look misty or 
 double; when his eyes trouble him in this way it is time for 
 him to have them examined. 
 
 DROPS IN THE EYES.— This is the expression used 
 when atropine or similar substance is put in the eye. Atropine 
 is a powerful poison. It is the alkaloid from belladonna just 
 as morphine is the alkaloid from opium. We should no more 
 think of having this powerful drug put in our eye than we would 
 to take chloroform or ether. Both ether and atropine have their 
 
SOME USEFUL INFORMATION. 75 
 
 places, but intelligent people should be slow to consent to their 
 use. It is true that those who make use of atropine belittle its 
 effects; nevertheless it is dangerous, and sometimes produces 
 untoward results. 
 
 PARAFFIN INJECTIONS TO IMPROVE THE SHAPE 
 OF THE NOSE. — The ey€ is an organ* with a circulatory system. 
 If the circulation stops, the eye will grow blind. There is danger 
 in the modern practice of injecting paraffin under the skin for 
 cosmetic purposes. Some of the veins from the eye pass down 
 through the base of the nose. In a recent case one of these veins 
 was plugged by a piece of paraffin in injections as above stated, 
 and the result was total blindness in a few hours. 
 
 SECOND SIGHT. — Some elderly people regain their vision 
 by what is called second sight. This is an abnormal condition of 
 the lens of the eye, in which it swells and gains magnifying power. 
 In some cases second sight is permanent and a great comfort, but 
 usually it is followed by slowly failing vision, until, if the person 
 lives long enough, there is blindness. 
 
 WHAT TO DO WITH AN INFLAMED EYE. 
 
 NATURE OF INFLAMMATION.— There are three kinds 
 of eye inflammations : Severe accident, disease, and mechanical 
 irritation due to the presence of some foreign particle. In the 
 first two cases the party should get to a doctor without the slight- 
 est delay. In the third case he should be recommended to go to 
 a doctor, but if he will not, ordinary human feeling demands that 
 we do something. Suppose there is lime in the eye, wash the eye 
 
76 
 
 THE TRIAL CASE AND HOW TO USE IT. 
 
 with a solution of vinegar in water, a teaspoonful to a cup of 
 water, or olive oil may be used, whichever can be had the first. 
 In case of burns by acids, use lime water from the druggist or 
 milk is just as good. In severe cases the doctor should have 
 been sent for whether the patient agrees or not, for the injuries 
 are apt to be very serious ; and this applies with especial force 
 to pieces of metal which have sunk into the surface of the eye. 
 
 DUST OR SAXD OR CINDER IX THE EYE.— This is a 
 very common occurrence, and every one should know what to do 
 to help the sufferer. As a matter of fact, dust is getting into the 
 eyes all the time, but tears and winking keep working it out. 
 
 Fig. 25. — Removing the Cinder. 
 
 Unconsciously we rub our eyes a great many times every day 
 to get rid of this dust, which gathers, moistened by the natural 
 tears of the eye, at the inner canthus. When, however, something 
 <iharp gets into the eye, a cinder, for instance, it is apt to catch 
 
SOME USEFUL INFORMATION. 77 
 
 cither on the under surface of the cycHd, usually the upper one, 
 or the cornea itself. The old woman's way to get rid of it is 
 to pull out the upper lid, and suddenly insert her tongue into 
 the cavity. Not a very pleasant method, but often very effective. 
 Another way is to run the loop of a horsehair in and draw it 
 across the ball of the eye. This is dangerous, as the eye is apt 
 to be infected. Some druggists sell, or used to sell, what is called 
 "eye-stones," little flat, smooth stones about the size of the scale 
 of a fish, which would be inserted under the upper lid, and which 
 by their movements from place to place, because of the continual 
 turning of the eyeball, would carry out the obstruction. Some- 
 times when the druggist would be out of eyestones he would fur- 
 
 FiG. 26. — A Special Tool for Everting the Eyelid. 
 
 nish a small seed for the purpose. Here again there is danger 
 of infection. Still another way is to pull out the lid and blow 
 into the eye. The best way to proceed, however, is as follows: 
 Bring the patient near a bright light ; but if the examiner's eyes 
 are presbyopic, and he cannot see well at a close range, say 
 6 inches, he should put on a pair of spectacles which will permit 
 him to do so, or else use a jeweler's loupe ; pull out the lower lid 
 and see if the irritating particle is there ; sometimes it is not, as the 
 patient himself will have removed it by the rubbing. Now evert 
 the upper eyelid, stick a hairpin in a cork, catch with the fingers of 
 one hand the edge of the upper lid ; touch the center of the lid 
 with the curve of the hairpin of the cork, and turn the eyelid 
 
78 THE TRIAL CASE AND HOW TO USE IT. 
 
 inside out. The cinder or other matter, if not already out, will 
 be seen at once, and can be removed with the tip of a clean hand- 
 kerchief or a tuft of absorbent cotton. Remember that the irri- 
 tation will cause the eye to be painful for some time, even when 
 the cinder has been removed ; also that with all your care and 
 searching the particle may be so small that you cannot find it ; or it 
 may be so imbedded that you cannot remove it; in either case try 
 to get the patient to go to the doctor for a healing collyrium. He 
 may not take your advice, but at least you have done your duty. 
 
 HANDLING LENSES.— Lenses should never be touched 
 by the fingers, as this soils them, which in turn may lead to errors 
 in the subjective tests. They should be kept clean by the use of 
 a fresh cloth each day, and should be removed from the trial case 
 and returned thereto by the handles only. 
 
 t- 
 
APPENDIX 
 
 MEASUREMENTS OP THE EYE {Jaeger). 
 
 Anterior-posterior diameter 24.3 mm. 
 
 Horizontal diameter 23.6 mm. 
 
 Vertical diameter 23.4 mm. 
 
 Diameter of cornea 12 mm. 
 
 Average thickness of cornea 1 mm. 
 
 Average diameter of pupil 4 mm. 
 
 Average diameter of optic nerve through sclerotic 1.5 mm. 
 
 Thickness of crystalline lens 3.7 mm. 
 
 Diameter of crystalline lens 10.3 mm. 
 
 XoTE. — A millimeter (mm.) is very close to 1-25 inch. 
 
 APPROXIMATE PERCENTAGES OF VISUAL CONDITIONS IN 
 
 DARK ROOM. 
 
 Per cent. 
 
 Emmetropia 4 
 
 Hyperopia 30 
 
 Myopia 4 
 
 Simple hyperopic astigmatism 10 
 
 Simple myopic astigmatism 2 
 
 Compound hyperopic astigmatism 45 
 
 Compound myopic astigmatism 3 
 
 Mixed astigmatism ., 2 
 
 100 
 
 TEST TYPES FROM PRINTERS' FONTS {Jaeger). 
 
 No. 1 — Diamond. No. 8 — Pica. 
 
 No. 2— Pearl. No. 9 — Two-line Brevier. 
 
 No. 3— Nonpareil. No. 10 — Two-line Long Primer. 
 
 No. 4— Minion. No. 11 — Two-line Pica. 
 
 No. 5 — Brevier. No. 12 — Three-line Pica. 
 
 No. 6— Long Primer. No. 13 — Four-line Pica. 
 
 No. 7— Small Pica. No. 14— Five-line Pica. 
 
 TEST TYPES (Snellen.) 
 
 200 ft. 3^ in. square. 40 ft. ^ in. square. 
 
 160 ft. 3 in. square. 30 ft. 9-16 in. square. 
 
 120 ft. 2% in. square. 20 ft. ^ in. square. 
 
 100 ft. 1^ in. square. 15 ft. 9-32 in. square. 
 
 80 ft. VA in. square. 10 ft. 3-16 in. square. 
 
 60 ft. lii in. square. 7^ ft. 9-64 in. square. 
 
RECORD OF CASES. 
 
 Xame 
 
 Address 
 
 Date 
 
 HISTORY. 
 
 Difficulty in seeing far ? 
 
 Difficulty in seeing near ? 
 
 Headaches ? 
 
 Eye-tire ? 
 
 Winking ? 
 
 Flow of tears ? 
 
 Photophobia ? 
 
 Sore eyes in morning ? 
 
 Diplopia ? 
 
 Special symptoms ? 
 
 R. E. Finding : 
 
 L. E. Finding : 
 
 R. E. Prescription for distance • 
 
 L. E. Prescription for distance 
 
 R. E. Prescription for near inches 
 
 L. E. Prescription for near inches 
 
 Note. — The above is a record of the case kept by the optom- 
 etrist for future reference. It is distinct from the prescription 
 order sent to the shop to be filled. 
 
14 DAY USE 
 
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