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CORNELL 
 
 UNIVERSITY 
 
 LIBRARY 
 
Cornell University Library 
 RE 81.C58 
 
 The functional examination of the eye 
 
 3 1924 012 164 400 
 
Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924012164400 
 
THE F UNCTIONAL 
 EXAMINATION OF THE EXE. 
 
 BY 
 
 John Herbert Claiborne, Jr., M. D., 
 
 Adjunct Professor of Ophthalmology, N. Y. Polyclinic ; Instructor of Ophthal- 
 mology in the College of Physicians and Surgeons, N. Y.; Assistant 
 Surgeon to the New Amsterdam Eye and Ear Hospital, N. Y. ; 
 Formerly Attending Surgeon, North Western Dispensary, 
 Eye, •' Ear and Throat Department ; Formerly 
 Clinical. Assistant to the Manhattan Eye 
 and Ear Hospital. 
 
 Author of " Theory and Practice of the Ophthalmoscope." 
 
 WITH TWENTY-ONE ILLUSTRATIONS 
 
 PHILADELPHIA: 
 
 THE EDWARDS & DOCKER CO. 
 
 1895 
 
COPYRIGHT, 1895 
 BY THE EDWARDS & DOCKER CO. 
 
TO 
 
 Dr. EMIL GRUENING 
 
 THIS BOOK IS DEDICATED IN GRATEFUL RECOLLECTION OF 
 HIS EXCELLENT TEACHING 
 
PREFACE 
 
 A philosopher has said that the task of an author 
 is either to teach that which is not known or to recom- 
 mend known truths by his manner of adorning them. 
 
 The author presents this book to the medical pro- 
 fession in the hope that he has put the known facts of 
 a dry subject in a pleasing form. 
 
INTRODUCTION. 
 
 ""THE importance of the functional examination in the 
 determination of the refractive condition of the eye, 
 and in the determination of the necessity for wearing 
 glasses, cannot be over-estimated. For, whatever value 
 may lie in keratoscopy, the ophthalmoscope, and the oph- 
 thalmometer, the fact remains that, in almost all cases, the 
 functional examination is the crucial test. Moreover, the 
 widespread conceit which exists that the fitting of glasses is 
 an easy matter and lies within the intellectual capacity of 
 most any one, warrants the publication of a monograph on 
 this subject. 
 
 It is, indeed, difficult for any student to read the 
 meagre descriptions of this examination that are found in 
 text-books and retire with even a clear theoretical under- 
 standing of the subject. It is the purpose of the author to 
 make the subject clear beyond peradventure for those who 
 shall read these pages. It is his purpose, in short, to pre- 
 sent it in such a way that a student may follow the lines 
 laid down and perform the examination with scientific and 
 mechanical accuracy without further instruction. 
 
 A fair success in teaching the subject for a number of 
 years has led him to believe that he has won the right of 
 presenting it. The ventilation of the subject of refraction, 
 while it may be tedious, he believes to be essential for those 
 who know little of the subject, or for those who have for- 
 
gotten what they once knew. The author desires to call 
 particular attention to the chapter on Presbyopia. To 
 judge from the frequency with which glasses are prescribed 
 for this condition by totally ignorant people, one might 
 imagine it to be a very simple affair. As a matter of fact, 
 it is the most difficult problem in refraction, and a thorough 
 knowledge of it implies a thorough knowledge of all the 
 anomalies of refraction. 
 
 The author also desires to call attention to the graphic 
 formula or cross system, by which he indicates the refrac- 
 tive condition of the two principal meridians of the eye. 
 He has reason to believe that by the use of this system he 
 has succeeded in making students more readily understand 
 the optical results of the combination of spherical with 
 cylindrical glasses. 
 
 He has deemed it pertinent to add a chapter on the 
 use of mydriatics, since, upon their use, the success in 
 prescribing glasses in some cases largely depends. If a 
 somewhat colloquial style has been adopted in the prepara- 
 tion of this monograph, the author would say that it has 
 not been unintentional. He believes that the best way to 
 catch and hold the attention of a student is to avoid a 
 didactic style and stilted phrases. The book is a result of 
 a course of lectures delivered for a number of years at the 
 New York Polyclinic, and more particularly of a course in 
 practical instruction given by the author in the College of 
 Physicians and Surgeons, New York. 
 
CONTENTS 
 
 CHAPTER I 
 The Faculty of Vision ... . . 9 
 
 CHAPTER II 
 The Method of Conducting the Examination . .17 
 
 CHAPTER III 
 Descriptions of Prisms, Lenses and the Trial Case . .20 
 
 CHAPTER IV 
 The Refraction of the Eye . . . . . 30 
 
 CHAPTER V 
 Application of the Test Card to the Errors of Refraction . . 38 
 
 CHAPTER VI 
 Astigmatism ... . 48 
 
 CHAPTER VII 
 Cases of Astigmatism . . . . , ... 59 
 
 CHAPTER VIII 
 Presbyopia .... 67 
 
 CHAPTER IX 
 Mydriatics ... .82 
 
 Jaeger's Test Types . . 87 
 
 SnehEns Test Types . . . . . 91 
 
CHAPTER I. 
 
 THE FACULTY OF VISION. 
 
 The faculty of vision is the physiological function of 
 the eye. It is needless almost for me to tell you that this 
 faculty does not, strictly speaking, lie within the eye. It 
 lies, in fact, in the brain, and the most recent researches in 
 the physiology of vision place the seat of this function in 
 the cuneus of the occipital lobe of the cerebrum. The 
 retina itself, then, has absolutely no power of perceiving 
 the light that falls upon it. In what way the retina is in- 
 fluenced by light, what the change in its elements is 
 when light falls upon it, has never been fully explained. 
 It seems certain, however, that some change is wrought in 
 it, and that this impression is conveyed through the nerve 
 fibres of the optic nerve upward to the centre I have men- 
 tioned, and that there it is interpreted as light. You 
 remember very well, I am sure, that the optic nerve itself, 
 is incapable of receiving this impression, and you remem- 
 ber the familiar experiment in physiology by which you 
 may find the " blind spot " in your eye. This blind spot 
 corresponds to the entrance of the optic nerve, or the optic 
 disc, as it is called. At the disc there are only optic nerve 
 fibres, the outer layers of the retina being entirely absent. 
 There is another spot of peculiar interest in the background 
 of the eye, and that is the macula lutea or Yellow Spot of 
 Sommering. This is the spot of most distinct vision in the 
 retina, and may be called the seeing spot as opposed to the 
 2 (9) 
 
IO CLAIBORNE, 
 
 blind spot. You know that there are ten layers of the retina, 
 but as we come to the edge of the yellow spot, all the lay- 
 ers cease except that of the rods and cones, and that when 
 we reach the fovea centralis or central pit, nothing but the 
 cones remain. This pit is the point of most distinct vis- 
 ion, and the light that falls into it is appreciated or seen 
 most clearly by the visual centre in the cuneus. From 
 this pit outward the acuteness of vision diminishes until 
 we reach the confines of the retina, the ora serrata, where 
 the visual acuity is least. Inasmuch as there are only 
 cones in the macula, and their number diminishes as we 
 progress outward from the fovea, it is not an unreasonable 
 assumption that the cones are the element in the retina in 
 which that wondrous change is created that is interpreted 
 by the cuneus as light. This, at least, is the dictum of the 
 physiologists. It is consistent with these facts that there 
 are found some birds whose retinae consist entirely of 
 cones and that they are possessed of wonderful power of 
 vision. This amounts to their retinae being composed of 
 a number of yellow spots. 
 
 Outside of the yellow spot in man the rods predomi- 
 nate over the cones, but in birds the cones, as a rule, pre- 
 dominate. In some nocturnal birds, eminently the owl, 
 only rods exist. 
 
 Vision may be divided into four kinds : Central, Peri- 
 pheric, Distant and Near. 
 
 We have already dealt with central vision when we 
 pointed out the faculty or function of the macula lutea. 
 We have referred indirectly to the peripheric vision, when 
 we said that the acuteness of vision diminished from the 
 macula outward. The peripheric vision was doubtless 
 given to animals primarily for the purpose of self-protec- 
 tion, and for the acquisition of prey. If you wish an illus- 
 
THF, FACULTY OF VISION. 1 1 
 
 tration of the value of peripheric vision, roll up in scroll 
 form two sheets of music, and holding one in front of each 
 eye, endeavor to cross some crowded thoroughfare. You 
 would find that your field of vision would be restricted to 
 the very small circle in front of each eye, and you would 
 not progress far before you would be in imminent danger. 
 
 It is through the medium of peripheric vision that 
 many arts can be practiced. It is through the medium of 
 peripheric vision that we see many of the beauties of 
 nature, for the world would indeed be but a small one were 
 we able to see only those things whose images fall within 
 the circle of the macula lutea. It is the peripheric vision 
 which enables the individuals in an orchestra to see the 
 baton of the leader beating time, while they keep their 
 central vision upon the sheet of music before them. It is 
 the peripheric vision which enables a pianist to see the 
 movements of his fingers as they pass over the keyboard, 
 while his central vision is cast upon the notes. 
 
 The distant vision is the faculty of the eye to recog- 
 nize objects at a distance, and the near vision is the faculty 
 of recognizing objects near. What these two terms, " dis- 
 tance " and " near " specially mean will be developed later. 
 We shall proceed now to deal with the distant and central 
 vision, leave the peripheric altogether, and shall take up 
 the consideration of the near vision in the last lecture on 
 refraction. 
 
 There are few people who see well in the distance who 
 are not guilty of conceit about it, and it is not an unusual 
 thing to see a number of people comparing their vision by 
 looking at some distant object, such as a sign. It is ob- 
 vious to you that however satisfactory this may be to them, 
 it is not in any sense scientific, and that we must settle 
 upon some degree of vision as that which is normal and 
 
12 
 
 CLAIBORNE, 
 
 physiological, in order that we may be able to determine 
 when the function is within and when without the limits 
 of proper sight. Vision is a function which is more nearly 
 even in man than any other function of the body. There 
 is a certain power of vision which is the birthright of all 
 men. There is the widest difference in the faculty of hear- 
 ing in man, and no standard has been absolutely set down 
 as normal. How much more true is this of taste and smell 
 and feeling? Yet we can make a standard in the vision, 
 and say that man must have vision equal to that or fall 
 below the standard. 
 
 It is in a high degree probable that rays of light from 
 two different sources or points must fall upon different 
 cones in order to be seen as two things or objects ; in other 
 words, if rays from different objects were to fall upon one 
 cone, the objects would appear as one. Now the smallest 
 visual angle that can be perceived at the macula corre- 
 sponds to i'. So that our two objects must be separated 
 by an interval of as much as or more than i' in order to 
 be seen as two. If they are separated by an interval less 
 than i', they will appear as one. 
 
 The visual angle is the angle included between the 
 two lines drawn from the opposite sides of an object and 
 passing through the nodal point ; see figure i. CD. is an 
 object, and the angle formed by it with reference to the 
 eye is included between the lines Cc. and Dd. which meet 
 at the nodal point N, and the angle C.N.D. is the angle 
 under which the object CD. is seen. 
 
 With the view of establishing some standard test by 
 which the vision of all eyes can be measured, cards have 
 been constructed upon which the letters of the alphabet 
 are printed. We English-speaking people use the ordinary 
 English letters of course, and these are serviceable for 
 
THE FACULTY OF VISION. 1 3 
 
 almost all cases. Nevertheless, in clinical work it becomes 
 sometimes necessary to have German characters at hand, be- 
 cause the middle class of Germans do not all recognize the 
 
 Fig. i. 
 
 English letters. A card equally good for all is that on which 
 figures are printed. For whatever may be the status of a 
 person's learning in the matter of letters, there are a few 
 people who know anything at all, who do not know the 
 meaning of figures. The Arabic figures will probably be 
 recognized by all the patients with whom you will come in 
 contact. There is also a test card on which pot-hooks are 
 printed. This seems to me to be of no value. It requires 
 more knowledge to describe a pot-hook accurately than it 
 does to recognize a letter or a figure. By way of using a 
 universal system some one has suggested and had printed 
 on the test card the hearts, diamonds, spades and clubs of 
 playing cards. I have never seen anyone who has failed 
 to recognize these. 
 
 By regarding the test card presented you will see that 
 the letters diminish in size gradually from the top to the 
 bottom of the card, and if you will look still more care- 
 fully, you will notice that over each line are inscribed cer- 
 tain Roman figures ; these figures indicate the distance at 
 which the line over which they are written should be read 
 by an eye possessed of the normal acuteness or acuity of 
 
14 CLAIBORNE, 
 
 vision. The Roman figures indicate feet in this card. 
 There are other cards in which the distance is indicated in 
 metres. Now to those of us who have been accustomed to 
 measure distance all our lives in feet and inches and lines, 
 metres mean very little until we have translated them into 
 feet and inches. At school you used to jump so many feet, 
 not so many metres. It is immaterial, however, whether 
 you use metres or feet, as you will see in a few minutes. 
 The cards usually employed are those of Snellen, and let- 
 ters are constructed upon the principle of the visual angle 
 which is formed at the nodal point by the letters when sit- 
 uated at the distance indicated by the Roman figures over 
 each line. 
 
 It has been stated that the objects must be separated 
 by an angle of i' in order to be seen as two. Hence, the 
 smallest retinal image which can be perceived at the mac- 
 ula corresponds to an angle of i' and each letter of the test 
 card " is so made that when at its proper distance, each 
 part of it is separated from the other by an interval equal 
 to not less than the arc subtending an angle of i' at the 
 nodal point," while the whole letter subtends an angle of 
 
 5'- 
 
 Fig. 2. 
 
 The letter L, for example, subtends an angle of 5' at 
 the nodal point at the distance of 6 metres (the equivalent 
 of our 20 feet). 
 
THE FACULTY OF VISION. 1 5 
 
 The letter A subtends an angle of 5' at 60 m. distance, 
 or 200 feet on our card. 
 
 It is clearly then a matter of no concern to us whether 
 our patient recognizes the letter L, at twenty feet or A at 
 200 feet. Each letter subtends at its respective distance 
 the proper angle viz., 5' at the proper point, — the nodal 
 point, and the conditions for the normal acuity of vision, so 
 far as the angle is concerned, are fulfilled. But the brain 
 must have the faculty of recognizing the letter. The 
 angle would be formed, if the open eye of a dead man 
 were placed in the track of rays emanating from the let- 
 ters, but, of course, they would not be seen. L,earn, there- 
 fore, immediately the difference between the optical condi- 
 tion and the function of the organ. 
 
 Although it may be the birthright of all men to be 
 able to appreciate the angle of 5', there may be those who 
 have been cheated of it. In plain words, there are those 
 who are not able to recognize the letter L, at 20 feet, nor 
 the letter A at 200 feet. Such people are said to have less 
 than the normal acuity of vision. If you will cast your 
 eye down the card we use you will observe that there are 
 lines for 200 feet, 100 feet, 70 feet, 50, 40, 30 and 20 feet. 
 So you will immediately see that it is unnecessary for 
 us to place our card at 200 feet or any great distance. We 
 may place it at 20 feet, as this card is placed, or we may 
 place it at 15 or 10 feet. If the 20 line is read at 20 feet, or 
 the 15 line at 15 feet, the 10 at 10 feet, we know that the 
 patient has the normal acuity of vision because his brain 
 has the power of knowing an angle of 5 minutes. Hence, 
 the acuity can be reduced to a formula, and that formula 
 amounts to the simple Rule of Three. 
 
 Suppose a man can read the 20 line at 20 feet, the pro- 
 portion is this : 
 
1 6 CLAIBORNE, 
 
 His vision ; Normal vision = 20:20 and this, you see, 
 is reducible to the fraction -f-jj-. Hence we would say 
 V = f$, and as the numerator and denominator of this 
 fraction are equal, it is equal to the integer 1, which is per- 
 fection. 
 
 But suppose a man cannot read the 20 foot line at the 
 distance of 20 feet, and can only read the 40 foot line at 
 this distance, the proportion would be : 
 
 His vision ; Normal vision = 20:40 
 and this is equal to f {}- or ^ of the normal vision. In like 
 manner we would record -^^ when a man can only read 
 the 200 line at 20 feet, and his acuity of vision wonld be 
 ^ of the normal. The meaning then of f$, 3^-, •§-$, f-g- 
 is clear. 
 
 Sometimes you meet people who can read further 
 down the card than the 20 foot line at 20 feet. For exam- 
 ple, a man may read the 10 foot line at 20 feet. Such a 
 man would be said to have V=f-£ or twice the normal vis- 
 ion. 
 
 From all these facts we may draw this simple formula 
 that V=5 in which d, the numerator, equals the distance 
 of the patient from the card, and D, the denominator, 
 equals the figuring over the line read. 
 
CHAPTER II. 
 
 THE METHOD OF CONDUCTING THE EXAMINATION. 
 
 It now becomes necessary for you to know how this 
 examination is conducted. This is a very important point, 
 and it is the simplest. 
 
 In the first place adopt a routine. Hang or place the 
 test card in a good light and place the chair of the patient 
 preferably at the distance of 20 feet. The reason of this 
 will be apparent in the next lecture. Let the light be be- 
 hind the patient if possible, at any rate, to the side. 
 
 Examine the right eye first. The left eye must be 
 covered, and this may be done in several ways. You your- 
 self may hold a card in front of it, but you soon will get 
 tired ; or the patient may hold a card in front of it, but 
 he will get tired. It is best to put on the patient a pair of 
 spectacle frames for testing the eyes, such as you will find 
 in the test case, and slip into the left side of the frame the 
 opaque metal disc you will find in the case. In this way 
 both yourself and the patient are relieved from work. This 
 is a decided advantage in nervous or hysterical patients. 
 Now tell the patient to read the card from above down- 
 ward carefully. You might specify from left to right, for 
 many stupid people will read a letter on each line in a ver- 
 tical series. I have even known some who attempted to 
 pronounce words which they supposed the letters are 
 intended to spell. When the lowest line possible has been 
 read record it mentally or otherwise, preferably on piece of 
 3 (17) 
 
1 8 CLAIBORNE, 
 
 paper, and indicate that it is the vision of the right eye. 
 Then uncover the left eye and cover the right one with the 
 disc. Tell the patient now to read with the left eye as far 
 as possible. Then record that as the vision of the left eye. 
 This may be done in several ways. You may write it out 
 in full if you wish, but the formula is more economical. 
 
 You may write R.E.V., which means right eye vision, 
 or R.V., or R. You may use the L,atin abbreviations, if 
 you wish, O.D.V., which means oculi dextri visio; in like 
 manner you may write L.E.V., L.V., or I,., or oculi sinistri 
 visio, for the vision of the left eye, for example : 
 
 O.D.V.=f#; 
 O.S.V.=||; 
 
 Always use the equality marks, the periods after the ab- 
 breviations, and the semicolon after the fraction. The 
 semicolon indicates that something is to follow, and what 
 that is you will find out in the next lecture. 
 
 Patients are apt to close the covered eye. Advise 
 them to keep it open ; it is more comfortable to do so, and 
 there is certainly no necessity of closing it when the opaque 
 disc is used. By no means allow the patient to close the 
 eye by pressing with the hand. If this is done, the vision 
 of that eye is obscured for some seconds, on account of the 
 temporary anaemia produced in the retinal vessels by the 
 pressure. If the patient cannot read the first letter on the 
 card at the distance at which he sits, bring the card nearer, 
 or place him nearer the card. It is better for you to take 
 the card and gradually approach the patient and mark the 
 point at which he first sees the initial letter. When you 
 have found this point there is no necessity of coming 
 nearer. A man who cannot read the first letter at 20 feet 
 
THE METHOD OF CONDUCTING THE EXAMINATION. 19 
 
 may be able to read it at 16 feet, if so, record his vision as 
 ■2^, by application of the rule as directed. It is clearly 
 unnecessary to bring the card nearer than 16 feet if he can 
 read the first letter at that distance. 
 
 Suppose a patient can read only the first letter at 1 foot 
 his vision is of course, ^-J-g-. If he can read it only at 6 inches, 
 his vision is -^--g- inches by the rule. This, however, is an 
 extremely vulgar fraction, and I would suggest that you 
 simply write the fact and not the formula. Now the terms 
 "fingers " and " 200," are equivalent, and when a surgeon 
 writes that a patient counts his fingers at 1 foot, he means T5T 
 by the card. The fingers are often used near-by, instead 
 of the card. If the patient cannot count the fingers, the 
 hand is moved upward and downward, outward and inward 
 in front of the face. If the movements are correctly seen, 
 it is stated that he sees "movements of the hand." If he 
 is able only to recognize light from dark, or can recognize 
 different degrees of luminosity, it is stated that he has 
 " quantitative perception of light." Take care in making 
 this test with the hands that the source of light is behind 
 the patient. If the patient cannot tell the difference be- 
 tween day and night, his vision may be said to be O, i. e., 
 he has no perception of light. In plain English you may 
 state that he is stone blind. 
 
CHAPTER III. 
 
 DESCRIPTION OF PRISMS, LENSES, AND THE TRIAL-CASE. 
 
 There are two kinds of lenses used in correcting the 
 errors of refraction — spherical and cylindrical ; these may 
 be convex or concave. Before passing to the consideration 
 of their properties, it is necessary to refer to the primary 
 law of refraction of light and to the behaviour of rays of 
 light that are incident to prisms, for upon the comprehen- 
 sion of these things depends the comprehension of spheri- 
 cal and cylindrical lenses. 
 
 Fig. 3. 
 
 Rays of light in passing from a less dense into a denser 
 medium are refracted toward a perpendicular drawn to the 
 surface of the medium at the point of entrance ; in passing 
 from a denser to a less dense, they are refracted away from 
 a perpendicular drawn to the surface of the medium at the 
 
 (20) 
 
PRISMS, LENSES, AND TRIAL-CASE. 21 
 
 point of emergence. If the rays be at right angles to the 
 surface separating the two media, they are not refracted at 
 all. 
 
 At B the ray A B is refracted toward the perpendicular 
 PP. At C the ray B D is refracted away from the perpen- 
 dicular P P. The ray H K falling at a right angle to the 
 surface of the medium, is not refracted. 
 
 In Fig. 3, the sides of the refracting medium are paral- 
 lel, but in the case of a prism the surfaces are not parallel, 
 and a ray can therefore be perpendicular to one surface 
 only at a time. A ray that falls on a prism is refracted, 
 and the deviation must be toward the base. 
 
 Fig. 4. 
 
 The ray D M falling upon a prism, is bent in the di- 
 rection M N ; at N it is again bent, so that an observer, 
 catching the ray at E, would receive it as if it came from K. 
 
 Spherical convex and concave lenses may be regarded 
 as being composed of prisms ; the former with their bases, 
 the latter with their apices, opposed. Since rays in passing 
 through a prism are refracted towards its base, we can 
 readily comprehend the fact that convex lenses cause con- 
 vergence, and concave lenses divergence of rays. 
 
 A line which passes through the centre of a lens (opti- 
 cal centre) at right angles to the surfaces of the lens, is 
 
22 
 
 called the principal axis. 
 is not refracted. 
 
 CLAIBORNE, 
 
 A ray passing through this axis 
 
 Fig. 5. 
 
 The ray B strikes the lens L at a right angle to its 
 surface, and pursues a straight course to the point H. The 
 ray A strikes the lens L obliquely at D, and is refracted 
 
 Fig. 6. 
 
 toward a perpendicular to the surface of the lens at that 
 point, as shown by the dotted line M K. On leaving the 
 lens at O, the ray is refracted away from the perpendicular 
 N O, and meets the central ray B at the point H. The 
 ray C in like manner meets the other rays at H. 
 
 Parallel rays then passing through a biconvex lens, 
 are rendered convergent. 
 
PRISMS, LENSES, AND TRIAE-CASE 
 
 23 
 
 The ray B strikes the lens L, at right angle, and is not 
 refracted. The ray A strikes the lens L, obliquely at D, 
 and is refracted toward the perpendicular, G H. On emerg- 
 
 Fig. 7. 
 
 ing from the lens at K, it is bent away from the perpen- 
 dicular O P in the direction K M. The like takes place 
 with the ray C. 
 
 Parallel rays then passing through a bi-concave lens 
 are rendered divergent. 
 
 All rays that do not pass through the principal axis 
 are refracted. Those rays that pass through the optical 
 centre, but not through the principal axis, are termed 
 secondary rays. 
 
 Fig. 8. 
 
 They do undergo refraction, but in thin lenses it is so 
 slight that they are assumed to pass in a straight line. 
 
24 CLAIBORNE, 
 
 Parallel rays passing through a convex lens (L,) are 
 brought to a focus (A) at a certain fixed distance from the 
 optical centre of the lens. Such a point is called the 
 principal focus of the lens, and the distance of this point 
 from the optical centre of the lens is called the focal dis- 
 tance of the lens. 
 
 Fig. 9. 
 
 If parallel rays, passing through a concave lens be 
 rendered divergent, the focus must be a virtual, negative 
 one, situated on the same side of the lens as the object from 
 which the rays proceed. If the divergent rays in Fig. 10 
 below, be continued backward, they will meet at F, the 
 principal focus. 
 
 Fig. 10. 
 
 Spherical lenses may be plano-convex (Fig. 11, 1), that 
 is, having one surface plane and the other convex ; double 
 convex (Fig. 11, 2) having both surfaces convex with the 
 
PRISMS, LENSES, AND TRIAL-CASE. 25 
 
 same radius of curvature to both ; converging concavo-con- 
 vex (Fig. 11, 3) having one surface concave and the other 
 convex, with the predominance of the latter, the so-called' 
 positive meniscus; plano-concave (Fig. 11, 4) double or bi- 
 concave (Fig. 11, 5); diverging concavo-convex (Fig. 11, 6)1 
 with predominance of the concavity, the negative meniscus.. 
 
 123 45 
 
 Fig. 11. 
 
 Cylindrical glasses are segments of cylinders. If we 
 describe a circle on the outer side of an upright solid glass 
 cylinder, the portion included within the circle will repre- 
 sent the surface of a convex cylindrical glass. The trans- 
 verse diameter will have the greater radius of curvature,. 
 the vertical meridian which corresponds to the axis of the 
 cylinder will be plane. 
 
 If we describe a circle on the inner side of an upright 
 hollow glass cylinder, the portion included within the cir- 
 cle will represent the surface of a concave cylindrical glass. 
 The transverse diameter will have the greater radius of 
 curvature, the vertical, which corresponds to the axis of 
 the cylinder, will be plane. 
 
 Such glasses, therefore, refract only those rays which 
 are at right angles to their axis. 
 
 Cylindrical glasses are usually made planoconvex and 
 plano-concave, and parallel rays passing through them at 
 
26 CLAIBORNE, 
 
 right angles to the axis are rendered convergent or di- 
 vergent respectively. 
 
 The axes of cylindrical glasses are often indicated by 
 ground lines, one on either side of the lens or by the glass 
 being ground rough on either side, so that the edges of the 
 ground portion are parallel with the axis. 
 
 There are two systems of numbering lenses, one is the 
 inch system and the other the metric system. For the 
 former the convex lens, which brings parallel rays of light 
 to a focus one inch from its optical centre, is taken as the 
 standard for convex, spherical, and cylindrical glasses. 
 Such a glass is called a convex No. i. The convex lens 
 which brings parallel rays of light to a focus at two inches 
 from its optical centre is called a convex No. 2, and so on. 
 The strength of a convex number two is obviously one-half 
 that of a number one, and the strength of a number three 
 obviously one-third that of a number one. Hence the 
 strength of lenses is inversely as their focal distances, and 
 the strength is expressed in the form of a vulgar fraction, 
 1 ill A. i ptr 
 
 ¥> "3") 4i 5' T5T' TEf> CLL- 
 
 The concave lens which gives to parallel rays such a 
 divergence that, if prolonged backward, they will meet one 
 inch from the optical centre of the lens, is taken as the 
 standard for concave, spherical and cylindrical lenses. 
 Such a lens is called a concave number one. A concave 
 number two lens would give parallel rays such a divergence 
 that, if prolonged backward, they would meet two inches 
 from the optical centre of the lens. The strength of the 
 latter is obviously one-half that of the former. Convex 
 glasses are writen with the algebraic plus sign before them: 
 + i> +T5") +Tir> etc - Concave glasses are written with the 
 algebraic minus sign before them: — x \, — j^-, — ^, etc. 
 The plus and minus sign obtain also in recording convex 
 
PRISMS, LENSES, AND TRIAL-CASE. 2J 
 
 and concave cylindrical glasses. The standard or unit of 
 the metric system is a lens of one metre focal distance ; 
 this is called a dioptry. 
 
 In some respects the dioptric system is preferable. It 
 is certainly more commonly employed. The use of the 
 vulgar fractions gave rise to much trouble in the handling 
 of the common denominators. Moreover, the English and 
 French inch differ slightly in length. In the metric sys- 
 tem then we deal with integers and decimal fractions. D. 
 is the abbreviation for dioptry. Thus + 1 D. + 2 D. — 3 
 D., etc. In fractions we write thus: +1.5 D. — 2.25 D. 
 + 3-75, +-25 D. +.50 D. 
 
 This simplifies matters a good deal. 
 
 It is necessary for yon to know how to reduce the 
 inch system to the dioptric system and the reverse. The 
 English metre is 39+ inches, the French 37. For the 
 sake of convenience we regard 39+ as 40 and 37 as 36. 
 Of course, you understand that the metre is a fixed dis- 
 tance , it is the inch of France and England that differs. 
 The English inch is shorter than the French, for it takes 
 39+ English inches and 37 French inches to make the 
 metre. 
 
 Let us accept -£$ as the equivalent of 1 D. 
 1 D.=^ 
 
 ,T) — 2 — 1 
 1 D — 3 — 1 
 
 4 D.=A=i- 
 .50 D.=- s - B -X-3r=7-y. 
 
 •75 u -— TS" X 4— TT¥ — Tg- 
 .25 D. =-g-g- X T = T¥T- 
 
28 
 
 CLAIBORNE, 
 
 Then 
 
 1 . 
 
 1.50 D.=^L+ 
 1.25 D.=^V+xi 
 i-75 D-=W+ 
 
 44 
 1 . 
 
 48" 
 
 -3 1 
 
 -T2— "2T- 
 
 — 5 — 1 _|_. 
 
 — 144 — HI - 
 
 — 7 - _ 1 
 "144 20" 
 
 - 1 
 
 To get the value of the dioptres in the inch system, 
 multiply ^g- or Jg- by the number of dioptries. 
 
 The reduction of the inch system to the dioptry is 
 equally simple : 
 
 -5TX36 -g-g- 
 
 1 
 
 XT 
 
 iD. 
 
 X36=4f=2 D. 
 ^X 3 6=ff=3D. 
 
 X 3 6=ff=. 5 oD. 
 
 1 
 
 xi4X36= T 3 A=-25l>. 
 ^X 3 6=^- 
 
 2-4 
 
 X36= 
 
 "4 8 
 - 36 
 "24 
 
 =■75 D. 
 = 1.5 D. 
 
 To reduce the inch system to dioptres, multiply the 
 numerator of the vulgar fraction by 36 or 40. 
 
 THEO. MUNDORFF, 
 OPTICIAN. 
 
 N£W YORK. 
 
 ; ■■ 
 
 Fig. 12. 
 
PRISMS, LENSES, AND TRIAL-CASE. 29 
 
 Fortunately, our test cases are so arranged that you 
 are not under the necessity of making this reduction. It 
 is done for you and recorded under your eyes. 
 
 The test case (see Fig. 12) contains convex and con- 
 cave and cylindrical glasses ; on the left are the concave 
 glasses, on the right the convex. In the centre are the 
 cylinders. The concave glasses are usually rimmed with 
 brass, the convex with nickel. The same thing applies to 
 the concave and convex cylinders. There are two of each 
 set, and between each row is recorded the number of each 
 glass in inches and dioptries, so that you can write either 
 you choose. The smallest number, .25 D., is usually 
 placed at the bottom of the column, nearest to you. There 
 are not as many cylinders as there are spherical glasses. 
 
 There are usually two pairs of spectacle frames in the 
 case, with an opaque disc for insertion in the frame to 
 cover one eye while the other is under examination. 
 
 There are also prismatic glasses in the test case, but 
 you do not concern yourself with them in the functional 
 examination. 
 
CHAPTER IV. 
 
 THE REFRACTION OF THE EYE. 
 
 The eye-ball may be considered an imperfect sphere, 
 composed externally of the sclera of and the cornea. The 
 cornea is a segment, in rough terms, of a smaller sphere, 
 and is inserted in the anterior aspect of the sclera. It is 
 the window through which the rays of light pass into the 
 interior of the eye. 
 
 Within the eye are found, from before backward, the 
 aqueous humor, the crystalline lens and the vitreous hu- 
 
 Fig. 13. 
 
 mor. At the posterior pole lies the retina, spread out 
 upon the choroid, which latter, in its turn, is spread out 
 on the sclera. The eye is indeed a photographic camera, 
 and may be called a camera obscura in view of the dark 
 pigment of the choroidal coat. This choroidal coat is in- 
 
 (3o) 
 
THE REFRACTION OF THE EYE. 
 
 3 r 
 
 tended to absorb the rays of light, and keep them from 
 being reflected about within the eye. Albinos do not 
 possess this pigment, hence they are dazzled by light. 
 
 There are three kinds of eyes : 
 
 i. Emmetropic eyes ; 
 
 2. Hypermetropic eyes or hyperopic eyes ; 
 
 3. Myopic eyes. 
 
 The three conditions are called emmetropia, hyperme- 
 tropia or hyperopia, myopia. The emmetropic eye is the 
 natural eye, and is about -^ of an inch in length — 23 mm., 
 if you wish it in the fractions of a metre. The other two 
 eyes differ only in that one is longer and the other shorter 
 
 Fig. 14. 
 
 than the emmetropic eye. The hypermetropic or hyper- 
 opic eye is shorter than y 9 -^ of an inch, and the myopic eye 
 longer than ^ of an inch. 
 
32 CLAIBORNE, 
 
 A represents the emmetropic eye, B the hyperopic, and 
 C the myopic eye. 
 
 The names can hardly be said to be well-chosen, as 
 you will soon see. 
 
 The first, emmetropia, is derived from the Greek, 
 meaning within the measure of vision. The second, hyper- 
 metropia or hyperopia, mean respectively over the -measure 
 of vision or over-vision, while the third is a distinct anomaly, 
 meaning — well, it is difficult to say what. The fact is, the 
 word myopia is derived from the Greek word (nuetv, to 
 close the eyes, and &4>, the eye. Myopes, when they do not 
 use their proper correcting glasses, squeeze the lids together 
 for the purpose of seeing better, and this habit has given 
 them the name of myope, i. e., one who sees with the eyes 
 half closed. You have all doubtless observed this in 
 myopes. In like manner, emmetropic persons are called 
 emmetropes, and there is no equivalent in the English 
 language for this term — we are condemned to the Greek. 
 Hyperopic people are called hyperopes or hypermetropes ; 
 but for the terms hyperopia and myopia, English equiva- 
 lents exist. Hyperopia is far or long sight, and myopia is 
 short or near sight. Observe, now, the curious antithesis 
 which has worked itself out — the short eye, the hyperopic 
 eye, is the long- or far-sighted eye ; and the long eye, the 
 myopic eye, is the short- or near-sighted eye. There is 
 another term for myopia, a very good term, indeed, and for 
 this reason it is never used, viz. : brachymetropia, which is 
 a literal translation into Greek of "short sight." 
 
 It becomes necessary, now, to consider these three eyes 
 from an optical standpoint. In order to do that, allow me a 
 moment's digression. When rays of light start from the same 
 luminous point, they are necessarily divergent, and they 
 continue to be so until they have traversed the distance of 
 
THE REFRACTION OF THE EYE. 33 
 
 20 feet. At this distance and beyond it, they are prac- 
 tically parallel. They are, indeed, quite as parallel as 
 those that arrive from infinity, and the rays therefore that 
 come to us from the card situated on the wall 20 feet away, 
 have the same optical value as those that arrive from a 
 star or planet in the firmament. The distance of 20 feet, 
 then, is considered infinite distance in ophthalmology, 
 and it is ordinarily referred to as distance. Anything nearer 
 than 20 feet, is referred to as being near. 
 
 An emmetropic eye may be described as an eye which, 
 in a state of rest, focuses parallel rays of light upon the 
 macula lutea. (See A, Fig. 14.) The parallel rays of light 
 from a distant source are focused upon the retina by virtue 
 of the refractive power of the media without an effort on 
 the part of the eye. A hyperopic eye is an eye which, in a 
 state of rest, causes parallel rays of light to be focused be- 
 hind the macula lutea. It is hardly necessary for me to 
 say to you that no focus is formed behind the eye since the 
 rays do not pierce the coats ; but, since the eye is shorter 
 than it should be, the rays fall upon the retina in the act 
 of convergence before they have formed a focus. See B, 
 Fig. 14. A myopic eye is an eye which, in a state of rest, 
 focuses parallel rays of light in the vitreous humor, i. e., in 
 front of the macula lutea, so that the rays of light which 
 form a focus in the vitreous humor again diverge and fall 
 upon the retina in a condition of divergence. See C, Fig. 
 
 14- 
 
 An emmetropic person will therefore see distant ob- 
 jects because a focus is formed on the macula ; and this act 
 is accompanied by no effort on the part of the possessor of 
 this eye. It is not improbable that some of the pleasure 
 derived from regarding distant landscapes, apart from the 
 pleasing effect of the hues and tone of distance, is due to 
 
34 CLAIBORNE, 
 
 the rest which the eye enjoys under these circumstances. 
 Such an eye, looking into distance, is as much a mechani- 
 cal instrument as the camera of a photographer. 
 
 Let us now turn our attention to the hyperopic eye. 
 The rays do not form a focus on the retina, as you can see ; 
 such an eye, therefore, cannot see distant objects well. 
 Instead of the points that make up a focus, circles of diffusion 
 are formed, and for every point there is a circle. An im- 
 perfect, enlarged, and blurred image is formed on the re- 
 tina, and the shorter the eye, the larger, more blurred and 
 more imperfect the image. You are surprised to know 
 that a far-sighted eye cannot see far ! From the cut it is 
 clear that it cannot see well in the distance, but it is a 
 fact that it does see distant objects well. Just here it 
 is necessary to digress once more. You are surely ac- 
 quainted with the ciliary muscle ; if you will refer once 
 more to Fig. 13, you will see it just behind the root of 
 the iris. This muscle runs round the eye, and depend- 
 ing from it is a ligament, called the ciliary ligament, one 
 layer of which is attached to the anterior, and the other 
 to the posterior, surface of the lens. The lens is elastic 
 and resilient, and will readily swell if pressure be taken 
 from it. Now this lens and muscle is in a condition of 
 perfect repose when the emmetropic eye is in a state of 
 rest, i. e., is looking at distant objects, but when the gaze is 
 turned upon near objects, a change takes place in this ap- 
 paratus. The rays coming from near objects are not paral- 
 lel, but are divergent, as you know, and the emmetropic 
 eye in a state of rest can focus only parallel rays on the 
 retina ; hence, this rest must be abandoned if that eye has 
 to see near objects. The brain gives the cue to the centres 
 of the third nerve that the time has come for action, and 
 tells them how much nerve force must be sent to the mus- 
 
THE REFRACTION OF THE EYE. 35 
 
 cle of accomodation to accomplish the purpose of clear vis- 
 ion. The ring-shaped muscle then acts, and, like all mus- 
 cles, it shortens its origin upon its insertion. As that is 
 done, the tension upon the anterior surface of the lens is 
 relieved and the lens springs forward, thereby increasing 
 its antero-posterior diameter and increasing its power of 
 refraction. In this way the eye accommodates itself for 
 
 Fig. 15. 
 
 different distances inside of 20 feet, and the most beautiful 
 thing about the function is that the brain always measures 
 the distance accurately, and sends just the force necessary 
 to do the work and no more. The act of accommodation be- 
 longs properly to vision within 20 feet. But we have seen 
 that the unfortunate hyperope cannot see distant objects 
 well on account of the shortness of his ball. The brain 
 searching around for a means of forming a good focus, 
 turns to the accommodation, and finds that, by the use of 
 this function, a good focus can be formed, and its desire for 
 clear, distant vision be satisfied. This is an iniquitous use 
 of the muscle of accommodation, but it is persisted in. The 
 hyperope then does see clearly in the distance, but he does 
 so at the expense of a muscular action that is intended by 
 nature only for the act of near vision. Whenever a law of 
 nature is broken, retribution is inevitable, and the rupture 
 of this law constitutes no exception. The hyperope pays 
 
36 CLAIBORNE, 
 
 for his clear vision in headache, eyeache, nausea, vomiting, 
 tumbling gait, and many other symptoms which are char- 
 acterized as those of asthenopia or weak eyes. The hyper- 
 opic errors are by far the greatest cause of asthenopia in 
 the errors of refraction. 
 
 I withdraw, then, the statement that the hyperope 
 does not see well in the distance. 
 
 By referring to C, Fig. 14, you will perceive that a 
 myopic eye cannot possibly see distant objects well, for the 
 parallel rays are focused in the vitreous humor, and, hav- 
 ing formed a focus, again diverge, so that they arrive at 
 the retina in a condition of divergence. Circles of diffusion 
 are formed on the retina instead of points, and for every 
 point a circle is formed. The image of the distant objects, 
 therefore, is blurred and enlarged. There is no remedy 
 for this condition within the eye. Suppose the eye en- 
 deavors to remedy the defect by the act of accommodation. 
 The refractive power of the eye will be increased, and so 
 far from the eye seeing better, it will see worse, for the 
 focus will be formed still further forward in the vitreous 
 humor, and the circles of diffusion will be proportionately 
 larger. The trust of the myope lies in the art of man. 
 Pain is not so frequently caused by myopia as it is by hy- 
 peropia, and the reason is clear. The myopic eye has a 
 dreamy look, in other words, a look which is an attribute 
 of beauty. Myopic eyes often appear large, and this has, 
 from immemorial time, been regarded as an attribute of 
 beauty. The expression "ox-eyed," as applied to Juno, is 
 familiar to many of you. This dreamy look has been 
 termed the " myopic stare." There can be little doubt 
 that myopia, to some extent, influences the mental quali- 
 ties when it develops in early life. A boy who cannot see 
 well in the distance is little likely to engage in field sports, 
 
THE REFRACTION OF THE EYE. S7 
 
 for not only would he be unsuccessful, but he would also 
 be in danger of injury. Consequently he would be inclined 
 to be a book-worm and studious, if he has brains and the 
 proper disposition. If naturally stupid, he is apt to become 
 a drone. The future of many a person could have been 
 altered, if their refractive error had been corrected in 
 youth. The world in which a myope lives is a narrow 
 one, and the more myopic he is, the narrower it is. His 
 powers of observation are limited, and his knowledge of the 
 wide world corresponds. 
 
CHAPTER V. 
 
 APPLICATION OF THE TEST CARD TO THE ERRORS OF 
 REFRACTION. 
 
 It becomes necessary now for us to apply the test card, 
 and what we have learned about the acuity of vision to the 
 refraction of the eye. Let us take up each condition in 
 its turn. The term emmetropia we have seen means wtili- 
 in the measure of vision. Any eye, therefore, you would 
 naturally assume, that has vision within the normal meas- 
 ure would be emmetropic. This is not true. You must 
 learn for good that the term emmetropia refers by consent 
 to the refraction of the eye and not to the function. So 
 try to forget the etymological meaning of emmetropia. An 
 emmetropic eye, we have seen, focuses parallel rays of light 
 upon the retina without an effort of the accommodation. 
 A man may be dead and have emmetropia or his optic 
 nerve may be atrophic, so that he cannot tell light from 
 darkness, and yet be emmetropic. Conversely, because a 
 man has ff vision, it is not a necessary conclusion that he 
 is emmetropic. 
 
 Hypermetropia means beyond themeasure of vision, and 
 you would infer from this that any man who can see more 
 than ff is hyperopic. This also is not true. An emme- 
 trope sometimes has the exceptional vision of ff- or f-2-. On 
 the other hand, hyperopes naturally see farther than em- 
 metropes, for their eyes are capable of recognizing a smaller 
 visual angle than emmetropes. Yet a hyperope whose fun- 
 dus and media are normal may not be able to see as much 
 
 (38) 
 
ERRORS OF REFRACTION. 39 
 
 as |$. He may not have had that amount of acuity of vis- 
 ion by nature and there may be other reasons also. For ex- 
 ample, his muscle of accommodation may have been par- 
 alyzed by atropine, or as a sequella of diphtheria or syphilis. 
 Weakness from prolonged fever may interfere with his ac- 
 commodation, or what is more natural, he may not be able 
 to overcome the error through age. In any of these cases, 
 a hyperope will not be able to see ■§-§•, hence the term would 
 appear to be an incorrect one. 
 
 A myope cannot see well in the distance, and hence, 
 cannot see §-{}-. A man, however, who does not see |-§- need 
 not be myopic, since we have just seen that he may be em- 
 metropic with function diminished from disturbance with 
 the perceptive apparatus or the media ; a hyperope too, may 
 have less than f $ vision, as we have seen. So that vision 
 less than ■§■$■ means nothing at all with reference to the re- 
 fraction of an eye. 
 
 Let us sum up : 
 
 If a person reads f$ on the card, i. e., has normal vis- 
 ion, you have learnt one negative fact, namely, that he 
 cannot possibly be near-sighted. There remain two other 
 conditions of refraction, emmetropia and hyperopia ; he 
 must possess one or the other of these. 
 
 If a person reads less than f -§-, say f$-, you have learnt 
 nothing whatsoever about his refractive condition. For he 
 may be emmetropic with some disturbance in the fundus 
 or media, or he may not have his birthright of |-g- vision ; 
 he may be hyperopic with his accommodation weakened or 
 eliminated ; or he may be myopic with an imperfect image 
 on his retina by reason of his elongated eyeball. 
 
 L,et us now make a practical demonstration of a few 
 cases. 
 
40 CLAIBORNE, 
 
 This patient whom I now present to you I have taken 
 at random from among those on our benches. I shall ask 
 him no questions, but will proceed to take the vision first 
 of his right eye, and for that purpose I place this spectacle 
 frame on his face and cover the left eye with the metal 
 disc. He read |^- as you see. Now I shall take the vision 
 of his left eye ; that also is ■§-§-. What have we learned 
 about this man ? In the first place, he has normal acuity 
 of vision, his eye is capable of appreciating an angle of 5' 
 accurate^. So much for his function. But what have we 
 learned about his refraction ? Why this, that he cannot 
 possibly be near-sighted, for he sees well at a distance. 
 There are now only two other conditions of refraction left 
 for us to consider, namely, hyperopia and ernmetropia. To 
 decide between these two, we must have recourse to our 
 box of test glasses. I now pick out the weakest of the 
 convex glasses, a +.25 D. or y^ in the inch system, and 
 place it before the right eye. He tells me, as you can hear, 
 that he does not see so well through that glass as without 
 it. The conclusion from this is inevitable ; the man can- 
 not be far-sighted, for if he had been, he would have been 
 only too glad to have relaxed his accommodation and 
 allowed me to represent it by my glass. He must, there- 
 fore, possess the only remaining condition of refraction, and 
 that is ernmetropia. The other eye gives the same result, 
 as you see. I shall now ask the man what he complains of. 
 He says " nothing whatever," and tells us that he brought 
 his boy for treatment. He is not a patient. When the 
 glass was put in front of his eye the parallel rays coming 
 to him from distance were focused in front of his retina, so 
 that he was rendered artificially near-sighted. Hence, as 
 an emmetrope he saw worse than before, since he had cir- 
 cles and not points on his macula. 
 
ERRORS OF REFRACTION. 4 1 
 
 Let us take another patient. This boy complains of 
 pain over his brows and headache in the occiput when he 
 reads at school and when he studies at night. 
 
 Let us take his vision. With his right eye he sees •§-#, 
 and also with his left eye. You have now learnt one thing 
 about his refraction, namely, that he cannot be near-sighted. 
 So that two conditions remain for us to consider, hyperopia 
 and emmetropia. This boy is apparently in the same con- 
 dition as the man we have just examined, save that he has 
 pain in his eyes and head on reading. Let us now place 
 the weakest convex lens in front of his right eye, the .25 D. 
 which I pick out of the case ; I now ask him to read the 
 20 line and he does it, as you see, easily. He also tells us 
 that he sees it just as well. This boy has accepted a con- 
 vex lens, and in this respect differs from his father 
 whom we have just examined. What is the conclusion? 
 He cannot be emmetropic like his father, for if he were, he 
 would not see so well with as without the glass, for circles 
 of diffusion instead of points would be formed on his ret- 
 ina. There is only one other possibility for us to consider 
 and that is hyperopia. By exclusion then, the boy has 
 hyperopia. When the convex glass is put in front of his 
 eye he relaxes his accommodation to the extent of the value 
 of the convex glass and allows me to represent his effort 
 by my lens. He has just as good a focus as before and is 
 saved work. Am I content to stop here ? By no means. 
 He may have still more hyperopia. Hence I now place 
 the next strongest glass +.50 D. in front of his eye, and he 
 tells me that is just as good, if not better, and, as you see, 
 he still reads f-J. This boy then has as much as .50 D of 
 hyperopia. I am not yet satisfied. I go further and find 
 that he accepts -f .75 D. and reads |~|. He says also that 
 it gives him a feeling of rest. I go still further and place 
 
42 CLAIBORNE, 
 
 -f- i D. in the frame. He shakes his head and says he does 
 not see quite so well. He may call off the letters for he 
 has learned them by heart by this time, but he is intelli- 
 gent enough to know that he does not see them so well. 
 What have we accomplished here. We have measured the 
 total amount of this boy's manifest hypermetropia, and 
 that amount is .75 D. We continued to put glasses in 
 front of his eye till he saw worse. That means that we 
 formed a focus in front of his retina in the vitreous humor 
 so that the focus on his retina or macula was imperfect. 
 Hence the image of the letters was imperfect. 
 
 There is such a thing as an obstreperous muscle of 
 accommodation. A muscle that will not relax its tension 
 in hyperopia, but so far as you are concerned at present, a 
 person who will not accept a convex lens, must be considered 
 to be not far-sighted. 
 
 Let us draw our conclusion now from the study of this 
 case. A person who sees f$ cannot be near-sighted, and 
 must be either hyperopic or emmetropic. If he sees equally 
 well with a convex glass he cannot possibly be emmetropic, 
 hence he must be hyperopic and the strongest convex glass 
 through which he sees equally as well as without it, is the 
 measure of his hyperopia. 
 
 We lay aside the class of cases in which the vision is 
 as much as f$ and take up those in which it is less. If a 
 patient reads less than f-g-, you have learned absolutely 
 nothing about his refraction, and I hope you have not for- 
 got the reasons for this statement. I repeat them. A per- 
 son who reads less than f$ may be emmetropic with some 
 change in the fundus or media, or as a bare possibility, may 
 not have the birthright of normal power of perception ; 
 he may be hyperopic with his accommodation limited or 
 
ERRORS OF REFRACTION. 43 
 
 eliminated ; finally he may be myopic with an imperfect 
 focus due to too great length of his eyeball. 
 
 I shall now pick out some cases illustrating these con- 
 ditions. Here is an old man who can barely see in each 
 eye as much as -^/o i ne has opacities in his lenses — has 
 commencing cataract. Here is a middle-aged man who 
 sees still less than 2% ; he has partial atrophy of the optic 
 nerve. Here is a little girl with dilated pupils, who has a 
 high degree of hyperopia. She sees -^fa in each eye be- 
 cause her muscle of accommodation is paralyzed, and she 
 has an imperfect focus in consequence. This is an old 
 man who reads f f , who is also hyperopic. No mydriatic 
 has been put into his eyes, but he has an imperfect focus 
 because he cannot use his muscle of accommodation. His 
 muscular strength is going fast. 
 
 This woman with the prominent eyes is near-sighted 
 and sees -fg- in each eye. She too has an imperfect focus 
 because the rays meet in her vitreous chamber and fall on 
 her retina in divergence. 
 
 The cause of the imperfect vision in the cases just 
 shown, I have discovered by the use of the ophthalmoscope. 
 But you must learn to settle on the cause by the functional 
 method. Here is a case to which we will apply this 
 method solely. The patient reads y 2 ^ in each eye as you 
 can see. Following the invariable rule, I place a plus 
 .50 D. in front of his right eye. He says he sees worse. 
 He cannot be hyperopic — he must be either emmetropic 
 with disturbance in the media or fundus, or myopic. I now 
 place a concave glass in front of the same eye and he tells 
 me he can see no further — no better. He says the letters 
 look a little sharper and smaller, that is all. The cause of 
 his poor vision is not near-sight either. He must have 
 
44 CLAIBORNE, 
 
 some disturbance in his media or fundus, and the great 
 probability is that he is emmetropic. 
 
 This patient reads |-| with each eye. The weakest con- 
 vex glass makes him see worse. We exclude hyperopia. 
 The weakest concave glass makes him see better. He must 
 be near-sighted ; he now reads f-g- with difficulty but he sees 
 better. Shall we stop here ? By no means. We increase 
 the strength of the glass. He now sees |-g- with — .75 D.; 
 with — 1 D. he sees -|$. Are we content ? By all means 
 we should be. We wish no more than perfection, and that 
 is expressed in |^. 
 
 You perceive that the concave glass I placed in front 
 of his eyes causes the rays to enter into his eye in the 
 condition of divergence so that the focus that was first 
 formed in the vitreous humor is then formed on the retina, 
 and the circles of diffusion are supplanted by points. 
 Hence, the retina has a perfect image, and as the function 
 is unimpaired he sees f$. You understand too that the 
 first glass that causes -§-§■ vision is the measure of the myo- 
 pia, for I might continue to use stronger glasses than is 
 necessary and the patient still see ■§-§-, since he would use 
 his accommodation to overcome the excessive divergence 
 of the rays. This would be equivalent to making him 
 hyperopia We do not wish to do that, we merely wish to 
 render him emmetropic. Of course, we cannot always 
 give f-£ with the proper correction, so that we may formu- 
 late our conclusions in myopia in this wise : 
 
 If a person sees better with a concave glass he is myo- 
 pic, and the weakest concave glass with which he sees -|$, 
 or gets the best possible vision, is the measure of his myo- 
 pia. 
 
 There is here too such a thing as a spasm of the ac- 
 commodation, so that an emmetropic person may appear 
 
ERRORS OF REFRACTION. 45 
 
 myopic, but so far as you are concerned in the functional 
 method, the above conclusion is sound and good. 
 
 I^et us now sum up in as few words as possible the 
 propositions contained in what has been said at such great 
 length. 
 
 If a person reads |~£, one thing has been learned in 
 regard to his refraction — he cannot be near-sighted ; he 
 may be emmetropic or hyperopic. If he sees worse with 
 the weakest convex lens in the case, he cannot be hyperopic, 
 hence, he must be emmetropic. If he sees equally as well 
 through the weakest convex lens, he cannot be emmetropic 
 hence, must be hyperopic, and the strongest convex glass 
 through which he sees equally as well or better is the 
 measure of his hyperopia. 
 
 Any one who sees equally as well or better through a 
 convex glass must be hyperopic. 
 
 If a person reads less than -f|-, nothing has been learned 
 in regard to the refraction — he may be emmetropic with 
 changes in media or fundus or he may not be possessed of 
 the proper acuity of vision naturally ; he may be hypero- 
 pic with the function of accommodation eliminated or im- 
 paired, whereby an imperfect image is formed on the 
 retina ; he may be myopic whereby an imperfect image is 
 formed on the retina. If he sees worse through the weak- 
 est convex glass he cannot be hyperopic. If he sees better 
 through the weakest convex glass he is hyperopic, and the 
 strongest convex glass through which he sees best is the 
 measure of his hyperopia. If he sees worse through the 
 weakest convex glass and better through the weakest con- 
 cave, he is myopic, and the weakest concave glass through 
 which he sees best is the measure of his myopia. 
 
 If he sees worse through the weakest convex glass, 
 and no better through the weakest concave, he is, in all 
 
46 CLAIBORNE, 
 
 probability, emmetropic, with disturbance either in the 
 media or fundus. 
 
 Cases and Formulae. 
 
 Allow me to insist that you adopt a regular method of 
 recording your results. You remember how I said the 
 simple statement of vision was recorded. L,et us record 
 now the cases I have given you of E., H. and M. 
 
 Our first patient had this vision : 
 
 R.E.V.=f£; 
 L.E.V.=f| ; 
 
 We found this patient to be emmetropic, so we simply write 
 after the statement of the vision, E. thus : 
 
 R.E.V.=fi; E. 
 L.E.V.=||; E. 
 
 Our next patient was hyperopic to the extent of .75 D., 
 and his vision was f| in each eye. We record his case 
 thus : 
 
 R.E.V.=f|; hm. .75D. 
 L,E.V.=fi ; hm. .75 D. 
 
 Hm., means manifest hyperopia. Another patient 
 with hyperopia of 2 D. was unable to read f$. We record 
 his case thus : 
 
 R.E.V.=f|; f£w. + 2 D. 
 L,.E. V.=fl; Hw. + 2D. 
 
 His hyperopia is not said to be manifest since he failed 
 to read f$. 
 
 Our case of myopia is recorded in like manner : 
 
ERRORS OF REFRACTION. 42 
 
 R.E.V.=flf; f|w.- 3 D. 
 Iv.E.V.=f|; f£w.- 3 D. 
 
 The w. stands for with, and you observe that the two- 
 statements of vision are placed side by side for easy com- 
 parison, i. e., the vision before correction and the vision 
 after correction. 
 
 Do not fail to adopt this method of recording your 
 results. It is the plainest and simplest. There are many 
 irregular ways of doing it which are clear to an expert, but 
 nothing can be better than an unequivocally plain state- 
 ment. 
 
CHAPTER VI. 
 
 ASTIGMATISM. 
 
 We come now to discuss the matter of astigmatism. 
 This subject is ordinarily regarded by students as extremely 
 difficult to comprehend. Permit me to say that the diffi- 
 culties lie on the surface and in the imagination. If you 
 have followed me so far in the description of emmetropia, 
 hypermetropia and myopia, and in the correction of the 
 latter two, you will find no difficulty in following me in 
 the exposition of astigmatism and its correction. 
 
 Astigmatism is the refractive condition of the eye in 
 which a point cannot be recognized as such. It is seen as 
 a line instead. The word is derived like so many terms in 
 ophthalmology, from the Greek a privative — signifying 
 not and sri-pm a point — not a point. 
 
 Let me state as the initial proposition in astigmatism, 
 that there are but two meridians to the cornea, one being 
 given, the other is at a right angle. So that if you accept 
 90 as the first, 180° is the other. If one meridian be 
 45°, the other is 135 , or if one be 75°, the other is 165 , 
 etc. Remember the errors we have dealt with heretofore 
 have been spherical errors, i. e., they have been errors of 
 refraction that have been common to the two meridians of 
 the eye. 
 
 We may refer to astigmatism also as a meridian error, 
 since it belongs to one or the other meridian. When an eye 
 is emmetropic both meridians of the cornea have the 
 
 (48) 
 
ASTIGMATISM. 49 
 
 same radius of curvature, and the eye from before back- 
 wards in each meridian is T 9 T of an inch long. When an 
 eye is spherically hypermetropic, each meridian has the 
 same radius of curvature, but the length of the ball in each 
 meridian is less than -^ of an inch. When an eye is 
 spherically myopic each meridian has the same radius of 
 curvature, but the length of the ball in each meridian is 
 more than ^ of an inch. 
 
 When an eye is astigmatic, one meridian differs from 
 the other in radius of curvature and in length from before 
 backward. 
 
 We usually refer to the radius of curvature of the cor- 
 nea when we speak of astigmatism, though there is such a 
 thing as an astigmatism due to a prolongation of the eye- 
 ball at its posterior pole, as there probably is an astigmatism 
 due to a badly shaped crystalline lens. L,et us, however, 
 keep our minds upon the cornea as the seat of astigmatism. 
 
 It will be very easy for you now to call off for me the 
 various kinds of astigmatism. 
 
 i. Let us suppose a case in which the vertical meridian 
 of the eye has the radius of curvature of emmetropia, and 
 the horizontal meridian has the radius of curvature of 
 hypermetropia ; in other words, a cornea which in its ver- 
 tical meridian is normally curved and in its horizontal 
 meridian is curved too little, i.e., is slightly flattened. The 
 condition is called 
 
 Simple hyperopic astigmatism. 
 
 Fig. 16. 
 
5o 
 
 CLAIBORNE, 
 
 2. Let us suppose another case in which the horizon- 
 tal meridian has the radius of curvature of emmetropia and 
 the vertical meridian has the radius of curvature of myopia. 
 In other words, an eye whose horizontal meridian is nor- 
 mally curved and whose vertical meridian is too sharply 
 curved. The condition is called 
 
 Simple myopic astigmatism. 
 
 Fig. 17. 
 
 3. There is an eye, the vertical meridian of which is 
 curved too little, and the horizontal meridian of which is 
 curved still less. It is too flat in both meridians, and one, 
 the horizontal, is flatter than the other, the vertical. Both 
 meridians have the hypermetropic length from before back- 
 wards, but one is more hypermetropic than the other. 
 The condition is called 
 
 Compound hyperopic astigmatism. 
 
 Fig. 18. 
 
ASTIGMATISM. 5 1 
 
 4. There is an eye, the horizontal meridian of which 
 is curved too much, and the vertical meridian of which is 
 curved still more. Both meridians have the myopic curve 
 and length from before backwards, but one is more myopic 
 than the other. The condition is called 
 
 Compound myopic astigmatism. 
 
 Fig. 19. 
 
 5. There is an eye, the horizontal meridian of which 
 is less sharply curved, and the vertical meridian of which 
 is more sharply curved than it ought to be. There is 
 hypermetropia in the horizontal meridian and myopia in 
 the vertical meridian. The condition is called 
 
 Mixed astigmatism. 
 
 Fig. 20. 
 
 6. Occasionally the cornea of an eye may have scat- 
 tered over it small opacities from old inflammation or from 
 coal or foreign bodies which have lodged there. This con- 
 dition is known as 
 
52 CLAIBORNE, 
 
 Irregular corneal astigmatism. 
 
 Occasionally the lens is badly made, so that it differs 
 in many places in refractive power. This is known as 
 
 Irregular lenticular astigmatism. 
 
 Irregular astigmatism, either corneal or lenticular, 
 cannot be corrected by glasses or any other device. 
 
 You will now see that when once you have learned 
 simple myopic and simple hyperopic astigmatism, you have 
 learned all the forms of regular astigmatism. And you have 
 already become convinced, I am sure, that what I said is 
 true, namely, that astigmatism is the refractive conditions, 
 E., H. and M., applied in combination to the two merid- 
 ians of the eye. 
 
 L,et us now once more sum up the various forms. 
 
 I. Regular astigatism. 
 
 i. Simple hyperopic astigmatism. 
 
 2. Simple myopic astigmatism. 
 
 3. Compound hyperopic astigmatism. 
 
 4. Compound myopic astigmatism. 
 
 5. Mixed astigmatism. 
 
 II. Irregular astigmatism. 
 
 (a) corneal. 
 
 (b) lenticular. 
 
 We will now take up the consideration of astigmatism 
 from the standpoint of the behavior of the rays of light in 
 each case. This necessitates a few preliminary remarks. 
 From every luminous object rays of light proceed into 
 space in every possible direction. From the planet Jupi- 
 ter, for example, as it revolves in space, rays proceed in 
 
ASTIGMATISM. 53 
 
 all conceivable directions. From a point made by chalk 
 on a blackboard, rays proceed in all directions that lie 
 anterior to the plane of the board. They clearly cannot 
 pass backward owing to the imperviousness of the board 
 to light. But so far as the eye is concerned there are 
 only two sets of rays, — one being given, the other lies at 
 a right angle to it. If I hold up this pencil in front of 
 you in a vertical position, you see it by virtue of the two 
 meridians of the cornea, the vertical and horizontal. If I 
 hold it at an angle of 45 ° to the horizon, you see it by vir- 
 tue of the meridian which is 45 and of that which is 135 . 
 If I hold it at the angle of 75 , you see it by virtue of the 
 meridians of 75 and 165 . 
 
 Let me now hold the pencil vertical. From every 
 luminous point on this pencil there proceed a set of verti- 
 cal rays and a set of horizontal rays. The horizontal rays 
 I indicate by the index and middle fingers between which 
 I stick the pencil in the vertical position. These horizon- 
 tal rays pass into your eye through the horizontal meridian, 
 and are focused on your retina as a point. From the next 
 luminous points above and below the first other horizontal 
 rays proceed and pass through other planes of the horizon- 
 tal meridian. Arriving at the retina they also form points, 
 the one below and the other above the first point, so that 
 there are now on your retinae 3 points arranged in a verti- 
 cal series, which is a line. The same thing takes place 
 with reference to all the other luminous points on the pen- 
 cil, and the result is that the vertical position of the pencil 
 is indicated on your retinae by a vertical line which con- 
 sists of luminous points arranged in a vertical series. Sup- 
 pose I turn the pencil to the horizontal position. From 
 each luminous point on the pencil there proceeds a set of 
 vertical rays and a set of horizontal rays. The vertical 
 
54 CLAIBORNE, 
 
 rays I now indicate by the index and middle fingers between 
 which the pencil is held horizontally. These vertical rays 
 pass into the eye through the vertical meridian and are 
 formed as points on the retina. From the next luminous 
 points on the right and left other vertical rays proceed and 
 passing into the eye through other planes of the vertical 
 meridian are focused in a horizontal series. So that there 
 are now on your retinae 3 points arranged in a horizontal 
 series, which is a line. The same thing takes place with 
 reference to all the other luminous points, and the result 
 is that the horizontal position of the pencil is indicated on 
 your retinae by a horizontal line which consists of a series 
 of points arranged in a horizontal series. 
 
 The vertical position of the pencil then, is indicated 
 by the horizontal rays that pass through the various planes 
 of the horizontal meridian, and the horizontal position of 
 the pencil is indicated by the vertical rays that pass through 
 the various planes of the vertical meridian. In each posi- 
 tion, however, both sets of rays are focused on the retina at 
 the same time, so that the totality of the marks of the pen- 
 cil is recognized, and it is distinguished from some other 
 thing. Mark, however, that the image of a vertical object 
 on the retina is vertical, and the image of a horizontal object 
 on the retina is horizontal. Bear in mind also that there 
 are many planes to each meridian. 
 
 1. Simple hyperopic astigmatism, see fig. 16. 
 
 In this case the rays of one meridian are brought to a 
 point on the retina ; those of the other meridian are brought 
 to a focus behind the retina. 
 
 2. Simple myopic astigmatism, see fig. 17. 
 
 In this case one set of rays are focused in front of the 
 retina, the other on the retina. 
 
 3. Compound hyperopic astigmatism, see fig. 18. 
 
ASTIGMATISM. 55 
 
 In this case both sets of rays are focused behind the 
 retina, one set being focused further behind it than the 
 other. 
 
 4. Compound myopic astigmatism, see fig. 19. 
 
 Both sets are focused in front of the retina, one set be- 
 ing focused further in front than the other. 
 
 5. Mixed astigmatism, see fig. 20. 
 
 One set is focused in front of the retina, the other be- 
 hind it. 
 
 We proceed now to the consideration of the correction 
 of astigmatism. Before doing so, however, allow me to 
 review what has been said with reference to cylindrical 
 glasses. 
 
 Inasmuch as the error astigmatism, is an error of a 
 meridian, it follows that the glass which corrects it must 
 be a glass that refracts light in one meridian. Cylindrical 
 glasses are used for this purpose. Cylindrical glasses 
 reflect only those rays which are at a right angle to the 
 axis. The axis is the plane surface which does not refract. 
 If I hold a convex cylinder with its axis vertical, it is 
 clear that only the horizontal rays are refracted ; the ver- 
 tical rays are unaffected, since they pass through a plane 
 surface. If now, I turn the cylinder and make its axis 
 horizontal, the vertical rays alone are refracted. The same 
 thing is true of a concave cylinder. 
 
 Now a spherical convex glass is a representation of 
 the human eye, and there are only two meridians to it as 
 there are to the eye ; one being given, the other is at a right 
 angle. So that a convex spherical glass is composed of 
 two cylinders with their axes at a right angle. If I can 
 take two convex cylinders and place their axes at a 
 angle and form a spherical focus, I have proved this point. 
 Let us make this experiment : I take a convex cylinder of 
 
56 CLAIBORNE, 
 
 6 D. and hold it with its axis vertical ; the horizontal rays 
 from our candle pass through the convex surface of the 
 cylinder and form points in a vertical series, making a line 
 of light. I turn it round at a right angle and hold the axis 
 horizontal. The vertical rays now passing through the 
 convex plane of the cylinders form points in a horizontal 
 series and a horizontal line of light is seen. I take another 
 cylinder of equal strength and place their axes at a right 
 angle. This gives a convex surface horizontally and a 
 convex surface vertically, so that both sets of rays are re- 
 fracted. The result is, a perfect focus of the candle is 
 formed. This is a typical illustration of the eye. When 
 there is no astigmatism, the two meridians of the eye are 
 equal in their refractive power and a perfect focus is formed. 
 Suppose now I use a cylinder of 6 D. and couple that with 
 a cylinder of 5 D., immediately an imperfect focus is formed 
 on the blackboard, and you have before you the illustration 
 of an astigmatic eye. 
 
 What I have said about convex cylinders applies to 
 concave cylinders, with this exception, that no focus is 
 formed by concave cylinders crossed, nor can any line of 
 light be seen when the cylinders are used separately. 
 
 Let me impress this point upon you indelibly. The 
 spherical eye is the equivalent of a spherical convex glass 
 both of whose meridians are equal in radius of curvature 
 and refractive power. If one meridian of the eye differs 
 from the other in radius of curvature, there is astigmatism. 
 
 Let us now apply the cylinder to the various forms of 
 astigmatism. 
 
 I. Regular astigmatism. 
 
 a. Simple hyperopic astigmatism. 
 In a very large majority of cases the erring meridian 
 in this form is the horizontal. The vertical meridian has 
 
ASTIGMATISM. 5J 
 
 the normal emmetropic curve, but the horizontal is flat- 
 tened. It becomes necessary for us to so place the cylin- 
 der as that the refractive power of the horizontal meridian 
 is increased. 
 
 Remember now that cylinders refract those rays that 
 are at a right angle to the axis. We choose a convex 
 cylinder, of course, since the error is hyperopic, and we 
 place the axis vertical, thereby throwing the convex sur- 
 face of the cylinder in the horizontal meridian in order to 
 make up the deficiency there. 
 
 b. Simple myopic astigmatism. 
 
 In a very large majority of cases the erring meridian 
 in this form is the vertical. The horizontal meridian has 
 the normal curvature of emmetropia, while the vertical is 
 too sharply curved. The cylinder must be so placed as 
 that the refractive power of the vertical meridian be 
 diminished. A concave cylinder must be used and the 
 axis be placed horizontal in order to throw the concave 
 surface of the cylinder vertical, to diminish the refraction 
 in the vertical meridian. 
 
 c. Compound hyperopic astigmatism. 
 
 So far as the cylinder is concerned, the same rule ap- 
 plies to these cases as to simple hyperopic astigmatism. 
 The cylinder has to be coupled with a spherical convex 
 lens, and the axis of the cylinder, as a rule, is vertical. 
 For the horizontal meridian is less curved than the verti- 
 cal, and both are less curved than they should be. 
 
 d. Compound myopic astigmatism. 
 
 Both meridians are curved too sharply, and the verti- 
 cal more sharply than the horizontal. So that the cylinder 
 has to be coupled with a spherical concave glass, and the 
 axis of the cylinder, as a rule, is horizontal. 
 
 e. Mixed astigmatism. 
 
58 CLAIBORNE, 
 
 One meridian has the curvature of myopia and the 
 other that of hyperopia. 
 
 Following out the rule in myopic astigmatism and in 
 hyperopic astigmatism, for you remember that mixed as- 
 tigmatism is a mixture of the two, the axis of the concave 
 cylinder lies horizontal and that of the convex cylinder 
 vertical. So that the cylinders are crossed at a right angle. 
 It must be clear to you that neither cylinder interferes 
 with the refraction of the other. For the rays that have 
 passed through the horizontal refracting surface of the con- 
 vex cylinder pass through the plane surface of the concave 
 cylinder, and the diverging rays that have passed through 
 the vertical refracting surface of the concave cylinder pass 
 through the plane surface of the convex cylinder. Neither 
 cylinder, therefore, interferes with the other. There are 
 other ways of writing this combination, which will be 
 shown later. 
 
 When the axes are as indicated above, namely, when 
 the axis of the convex cylinder is vertical and that of the 
 concave horizontal, the astigmatism is called astigmatism 
 with the rule. When the reverse is the case, it is called 
 astigmatism against the rule. 
 
 II. Irregular astigmatism. 
 
 There is no correction for this condition. 
 
CHAPTER VII. 
 
 CASES OF ASTIGMATISM. 
 
 i. Simple hyperopic astigmatism. 
 
 A young woman, of delicate health and slight phy- 
 sique, who makes her living with her needle, complains 
 that for several months her head has ached, particularly 
 when she works or reads. The headache often reaches far 
 into the night. She is unable to take much exercise, 
 owing to her employment. 
 
 O. D. V.=M— ; 
 O. S. V.=fi-; 
 
 The errors she makes in reading the card are charac- 
 teristic of astigmatism. She misses two or three letters in 
 the 30 foot line, and scarcely gets one right in the 20 foot 
 line. We suspect astigmatism from the start. But we 
 first place +.50 D. S. before her eye. She states that 
 makes it no better — brings out some letters that were un- 
 clear, but obscures others ; — .50 D. makes her see worse. 
 We now take +.50 D. cylinder and hold it, axis vertical, 
 the usual position in As. H. She immediately sees better 
 and expresses herself as pleased with the glass. But she is 
 not yet able to read the 20 foot line perfectly. We try the 
 next glass, +.75 D. cylinder, axis again vertical, and she 
 reads the 20 foot line perfectly. Let us try the 1 D. cylin- 
 der now. She states that blurs the 20 foot line. We have 
 
 (59) 
 
60 CLAIBORNE, 
 
 corrected her error, and it is +-75 D- cylinder axis 90 . 
 The same is found for her other eye. 
 
 We now proceed to write the result in a formula : 
 
 R. E. V.=M— ; H W. + .75 D. c. ax. 90°. 
 E. E. V.=fS— ; U W. + .75 D. c. ax. 90°. 
 
 We prescribe : 
 
 R +.75 D. c. ax. 90 . 
 
 This method of recording is intelligible beyond per- 
 adventure. 
 
 2. Simple myopic astigmatism. 
 
 This case is a student of the college, one of your num- 
 ber. He complains of his eyes blurring after using them 
 for any length of time at reading. Has some headache. 
 Eyes occasionally water. Cannot see the black-board and 
 cuts well in the lecture-room. His eyes have the general 
 look of being strained. 
 
 R. E. V.= 
 
 20 
 
 "40 
 
 E. E. V. 
 
 -~5T) > 
 
 He also misses a letter or two before he arrives at the 
 40 foot line. We suspect astigmatism from that fact. 
 Following the rule, we place +.50 D. S. in front of his 
 eye. He sees worse. We place — .50 D. S. in front of it ; 
 he sees some letters better, but others worse. We try 
 + .50 D. c. ax. 90 ; he sees worse still. We try — .50 D. 
 c. ax. 180 and he immediately sees better. We are not 
 content, for he has not yet reached -§-§-. We continue using 
 concave cylinders, axis 180 , till we arrive at — 1.25 D. 
 With that he reads |-g- clearly. We are content, and leave 
 well enough alone. We find he requires — 1.75 D. c. ax. 
 180° to read |-g- in the left eye. 
 
CASES OF ASTIGMATISM. 6l 
 
 We record the result thus : 
 
 R.E.V.=H- 
 
 ■ 14 w 
 
 — 1.25 D. c. ax. 180 
 
 E. e.v.=h-; 
 
 2 0,,, 
 
 — 1.75 D. c. ax. 180 
 
 The glass is prescribed thus : 
 
 R R. E. — 1.25 D. c. ax. 180 . 
 L. E. — 1.75 D. c. ax. 180 . 
 
 The optician attends to the rest. 
 
 3. Compound hyperopic astigmatism. 
 
 This patient is a young mechanic, who uses his eyes 
 for near work constantly. You can see he is pale and not 
 over-strong looking. He has had periodic headaches from 
 childhood. During these attacks he becomes nauseated, 
 throws up, has to go to bed and stay in a dark room for a 
 day or two. Then he goes to work again until another 
 attack. He is 28 years old. 
 
 R. E. V.=M— ; 
 E.E. V.=f|-; 
 
 With +-5° D. S. he sees equally as well as without the 
 glass. He must be, to some extent, spherically hyperopic. 
 We increase the strength of the convex spherical glass till 
 we reach +2. D. He sees equally as well with this. 
 + 2.5 D. makes him see worse, so that we retreat to + 2 D., 
 with which he saw |-j}- — ; i. e., quite as well as he saw with- 
 out any glass. He must have 2 D. of spherical hyperme- 
 tropia. But he does not yet see -§-§-, and our duty is to en- 
 able him to do that. We couple a convex cylinder +.50 
 D. with the + 2 D., and, holding that combination, with 
 the axis of the cylinder vertical before his right eye, we 
 find he immediately reads further. We increase the 
 
62 CLAIBORNE, 
 
 strength of the cylinder till we arrive at i D., when he 
 reads f-g- without an error. 
 
 We find the same condition in the left eye. We record 
 the result thus : 
 
 O. D. V.=f#— ! H w. + 2 D. S. C + 1 D - c - ax - 9°°- 
 O. S. V.=H|— ; || w. + 2 D. S. C + 1 D - c - ax - 9°°- 
 
 We may prescribe the glass thus : 
 
 R + 2 D. S. C + i D. c. ax. 90°. 
 
 The optician knows from the formula that both eyes 
 have the same correction. If the two eyes differed, we 
 would write the prescription for them separately. 
 
 4. Compound myopic astigmatism. 
 
 This patient does not complain of very much headache 
 or pain. He simply does not see well for reading or dis- 
 tance, and, saving his presence, you see his eyes have a 
 far-away look and his whole countenance is apathetic. 
 
 O. D.V.=f£— ; 
 O. S. V.=*a 
 
 Convex glasses make his vision worse. Concave 
 glasses immediately improve it. We find that — 2 D. is 
 the weakest concave spherical glass with which the best 
 vision is attained, but f •§■ has not yet been reached. We 
 now couple concave cylinders with the concave spherical 
 and we find that with — 1*50 D. cylinder, together with 
 the — 2 D. S., the vision in each eye is |-g, so that we write: 
 
 R. E. V.=U— ; U w - — 2 D - s - C — !-5 D - c - ax - l8o °- 
 L. E. V.=fg — ; f| w. — 2 D. S. C — 1.50 D. c. ax. 180 . 
 
 We prescribe thus : 
 
 — 2 D. S. C — 1.50 D. c. ax. 180 . 
 
CASES OF ASTIGMATISM. 63 
 
 5. Mixed astigmatism. 
 
 This patient complains of constant, moderate head- 
 ache, weariness of the eyes, the desire to close them to get 
 rest, and the inability to see well near or in the distance. 
 
 R. E.V.=fi-; 
 L. E.V.=f|-; 
 
 We try first convex spherical glasses which fail to 
 give any better vision. The same result attends the trial 
 of concave spherical glasses. We next place a convex 
 cylinder, .50 D., axis vertical, in front of his eye. He im- 
 mediately sees better, and we continue to use stronger cyl- 
 inders. With + 1 D. cylinder he sees all the 40 foot line 
 and makes one mistake only in the 30 foot line. With 
 + 1.25 D. cylinder he fails to see as well. We decide that 
 he has, at least, As. H., and as we have excluded spherical 
 hypermetropia, we turn to mixed astigmatism, as the 
 possible explanation of his want of proper vision. We now 
 couple — .50 D. c. ax. 180 with the +1 D. c. ax. 90 , and 
 immediately he says he sees better. We continue to in- 
 crease the strength of the concave cylinder till we arrive 
 at — 1 D. He now reads the 20 foot line perfectly, and 
 expresses himself as satisfied. We conclude our patient 
 has mixed astigmatism, and that it is with the rule, i. e., the 
 axis of the convex glass is vertical and that of the concave 
 horizontal. 
 
 The same result is obtained in the left eye. 
 
 It is recorded thus : 
 
 R. E. V.=f#— ; fjw.+ iD.c. ax. 90 C — 1 D. c. ax. 180 . 
 L. E. V.=J#— ; f| w.+ 1 D. c. ax. 90 3 — 1 D. c. ax. 180 . 
 
 There are three ways of writing this glass for the op- 
 tician. First we may write it as it stands with the cylin- 
 der crossed : 
 
64 CLAIBORNE, 
 
 + i D. c. ax. 90 3 — 1 D. c. ax. 180 . 
 
 Secondly, we may correct the As. H. by a spherical 
 convex glass of 1 D. This will obviously double the error 
 in the myopic meridian, so that we may also write it thus : 
 
 + 1 D. S. C — 2 D. c. ax. 180°. 
 
 Thirdly, we may correct the myopia by a spherical 
 glass, and that will obviously double the error in hyperopic 
 meridian, so that we may also write the prescription thus : 
 
 — 1 D. s. ^ + 2 D. c. ax. 90 . 
 
 Any one of these writings is correct. I would sug- 
 gest, however, that you write it as you find the glasses in 
 your hands, namely, with the cylinders crossed, and let the 
 optician grind it his own way. 
 
 And now a word about the axis of astigmatism. I 
 have spoken so far only of those cases of astigmatism in 
 which the axis was 90 or 180 . It has, doubtless, oc- 
 curred to you that the axis might lie at other points than 
 these. It is possible for the axis of astigmatism to lie at 
 any point in the circle of 360 . There are, however, be- 
 yond a question, " positions of preference." In a paper in 
 the N. Y. Medical Journal, June 25 and July 2, 1892, en- 
 titled " The Axis of Astigmatism," I propounded the prop- 
 osition that the axis of astigmatism does not occur at hap- 
 hazard ; that there are positions of preference in hyperopic 
 and myopic astigmatism, and in their combinations. 
 
 Our spectacle frames, as you can see (Fig. 12), do not 
 possess entire circles, but half circles. Sometimes the half 
 circle is below, sometimes above, so that we number only 
 180 for each half circle. Now you may indicate the po- 
 sition of the axis of the glass in two ways, either by writ- 
 ing out the axis of the glass, such as 75 , 105 , 135 , etc., 
 
CASES OF ASTIGMATISM. 
 
 65 
 
 or by saying that the axis lies toward the nose or temple 
 so many degrees, such as 20 or 15 or 45 ° ; but you should 
 take care to observe that the upper end of the axis is to- 
 ward the nose or temple, for it must be plain to you that 
 if the upper end of the axis is 45" toward the nose, the 
 lower end must be 45 ° toward the temple. For my part, 
 I always write the number of degrees without referring to 
 nose or temple, and I think it much the best way. Inas- 
 much as we use semi-circles in the frames, either above or 
 below, the figures are invariable. Observe the two spec- 
 tacle frames, one above the other, Fig. 12. 
 
 In addition to the test-card, we sometimes use a figure 
 called Snellen's Sun-rise, or a clock-face with lines radiat- 
 ing toward the various hours, such as in Fig. 21. 
 
 Fig. 21. 
 
 If astigmatism be present in a case, the various lines 
 do not have the same degree of distinctness. Some are 
 gray, while others are clear, or both are grayish, and some 
 more gray or clear than others. If the cylinder or cylin- 
 ders are properly applied, the lines appear equally clear. 
 
66 CLAIBORNE, 
 
 I think these figures of value only in very slight de- 
 grees of astigmatism, such as that of .25 D. or .50 D. For 
 greater errors the letters are sufficient, and, as a matter of 
 fact, Snellen's Sun-rise or the clock-face is rarely used. 
 
CHAPTER VIII. 
 
 PRESBYOPIA. 
 
 The first thing I wish you to learn in regard to the 
 condition known as as presbyopia is that it is not an error 
 of refraction. It is no error at all. It is a normal physio- 
 logical condition to which every one comes if he lives long 
 enough. The derivation of the word gives a clear insight 
 into its meaning — itpia^ an old man, and "><P, eye — the eye 
 of an old man. And that is exactly what presbyopia is. 
 But we must remember that it is his vision for near ob- 
 jects. It has nothing to do with his distant vision, strictly 
 speaking. I promised you in the first lecture that I would 
 take up the consideration of near central vision in this 
 lecture, and I now proceed to do so. 
 
 Refer once more to the description of the act of accom- 
 modation. 
 
 You remember that the accommodative apparatus con- 
 sisted of the lens, the muscle, and the ligament of Zinn. I 
 said that the legitimate function of the accommodative 
 apparatus was the adjusting of the refraction of the eye for 
 different distances within 20 feet. I wish to lay particular 
 stress upon that fact. That is why the act is called accom- 
 modation. It is accommodation of the pronounced sort to 
 the possessor of an eye, and it enables the eye to accommo- 
 date itself for different distances. 
 
 The emmetropic eye you know is focused in a state of 
 rest for parallel rays. If rays are divergent it is clear that 
 
 (67) 
 
68 CLAIBORNE, 
 
 there must be an increased refractive power in the eye in 
 order that they may be focused upon the retina accurately. 
 This power lies in the accommodative apparatus. When 
 an object is brought nearer than 20 feet to a person, his 
 brain judges the distance and sends to the muscle of 
 accommodation a stimulus which causes it to contract. In 
 contracting it relieves the pressure made on the anterior 
 surface of the lens by the anterior layer of the ligament of 
 Zinn, and the lens, by virtue of its elasticity, springs for- 
 ward, increasing its convexity and its antero-posterior 
 diameter. The beautiful part of this act lies in this, that 
 the muscle contracts just enough to form the focus accu- 
 rately. In other words, when a man wishes to see an object 
 10 feet or 10 inches away, he focuses for the distance of 10 
 feet or 10 inches, and not for a less or greater distance. 
 This faculty of accommodation has its limitations. It is 
 greatest in early childhood. And this has been taken ad- 
 vantage of by tapestry manufacturers in Europe to set 
 children to work, straining their eyes at a very early age. 
 Owing to the fact that children are able to see smaller ob- 
 jects than grown people, they are enabled to use finer nee- 
 dles and do finer work. It has been estimated that the 
 accommodation has reached its acme by ten years of age, 
 and that thereafter it gradually decreases with advancing 
 years till a certain age, when the condition of presbyopia 
 is said to be present. Presbyopia then, is a condition in 
 which there is a diminution in the power of the accommo- 
 dative act in vision for near objects. This diminution is 
 due partly to imperfect muscular action and to a loss of 
 resiliency in the crystalline lens. When this has set in, a 
 man may be said to have arrived at the acme of his years 
 and strength. The road lies for him thereafter down-hill. 
 The age of presbyopia in males lies somewhere between 
 
PRESBYOPIA. 69 
 
 40-45. It supervenes a little earlier in women. This must 
 vary in a measure with a man's manner of life and employ- 
 ment. One who has lived an out-of-door life, free from 
 impure air, who has kept regular hours, avoided excesses 
 of all kinds, and who has not abused his eyes for reading 
 and study or work, must retain the power of accommoda- 
 tion longer than one whose life has not been modelled 0.1 
 these lines. It would be an interesting thing to know 
 when presbyopia supervenes, as an average, in a race of 
 savages. 
 
 I have spoken of presbyopia with reference to any ob- 
 ject that is nearer than 20 feet. But as a practical matter 
 we treat of presbyopia with reference to reading. 
 
 In order that we may have a standard for this exami- 
 nation, as we had a standard for the distance examination, 
 we take the various kinds of type that are used in printing 
 books. They have been arranged in order, starting with 
 the smallest and running to the largest. The card is 
 known as Jaeger's Test Types, and we speak of a person's 
 ability to read Jaeger No. 1 or Jaeger No. 2, etc. Jaeger 
 No. 1, the diamond type, is taken as the standard. A nor- 
 mal adult should be able to read Jaeger No. 1 at 8 or 9 
 inches. Let us accept 8 inches. If he is unable to read it 
 at this distance, but has to push the card further away, we 
 say he lacks accommodation, in other words, he is presby- 
 opic. 
 
 The nearest point at which a person can read Jaeger 
 No. 1 is called the punctum proximum or near point. We 
 may say that an adult's power of accommodation is the 
 value of a plus 8 inch lens or 5 D., since he can read Jaeger 
 No. 1 at eight inches. Conversely, we may say that a man 
 has lost his entire power of accommodation when he has 
 lost 5 D. 
 
•JO CLAIBORNE, 
 
 A table has been constructed showing how much ac- 
 commodation is lost by the emmetropic eye at various ages : 
 40 — o D. 
 
 45- 1 D- 
 
 50— 2 D. 
 
 55- 3 D- 
 
 60— 4D. 
 
 65— 4-75 D. 
 
 70— 5-5 D - 
 
 You see, then, that a man may be said to have lest his 
 entire accommodation between the ages of 65—70, for at 70 
 he has lost 5.5 D., or more than the value of 'an 8 inch 
 convex lens. But remember, we speak of his ability to 
 read. He has not lost all his accommodation, and he prob- 
 ably never entirely loses it all. 
 
 The correction of presbyopia becomes an easy matter 
 — to restore to a man that which he has lost. We must 
 consider presbyopia with reference to E., M., H. and astig- 
 matism. The list which has just been shown has been 
 constructed for the emmetropic eye. And allow me just 
 here to lay down for you this unalterable law, that every 
 eye has to be restored to the condition of emmetropia be- 
 fore the proper presbyopic glass can be prescribed for it. 
 The preceding examination which has been made clear to 
 you, I hope, must be employed invariably before the exam- 
 ination for presbyopia. Let us take up a few cases. 
 
 Case 1. — Emmetropia and Presbyopia. 
 
 A gentlemen, of 45, complains that for the last 6 
 months his eyes have annoyed him in reading — particu- 
 larly at night. They feel sandy ; he has a slight headache 
 after prolonged reading. He has arrived at the age of 
 
PRESBYOPIA. 71 
 
 presbyopia, but before attempting to give him a glass, we 
 discover the condition of his refraction. He reads f$ in 
 each eye and refuses the weakest convex glass. We find 
 him to be emmetropic. We have plain sailing before us 
 now. The list tell us that an emmetrope at 45 requires 
 + 1 D. to bring his p.p. to 8 inches, or that he has lost + 1 
 D. of his accommodation. We restore to him what he has 
 lost, and he reads, therefore, with his usual former com- 
 fort. If he lives long enough, he will take each correction 
 for the succeeding years, as it is outlined in the list. 
 
 Case 2. — Hyperopia and Presbyopia. 
 
 This gentleman is 45 years of age. He has had more 
 or less trouble with his eyes since boyhood, when he was 
 subject to occasional headaches. For some time reading 
 has been painful to his eyes, and it begins to dawn on him 
 that he is getting old. He comes to find out whether it is 
 true. By questioning him we find that he has been a 
 student all his life. We proceed to carry out the distance 
 examination first. We find that he reads f -§■ with much 
 difficulty and apparent strain. We also find that he accepts 
 -f 1 D. in each eye as the strongest possible glass. The 
 man is hyperopic, and his age is that of presbyopia. If we 
 are to give him a reading glass, we must certainly correct 
 his hyperopia. We place + 1 D in front of each eye, and 
 give him Jaeger's test types to read. He reads it with dif- 
 ficulty, as you see, at about 12 inches. He is presbyopic 
 as well as hyperopic. We now add + 1 D to the + 1 D of 
 his hyperopia. This makes + 2 D and we give him that 
 glass. He reads Jaeger No. 1 now at 8 inches, and he can 
 carry the book with ease out to 12 or 14 inches, so that we 
 are content. We have given him a good range of accom- 
 
72 CLAIBORNE, 
 
 modation, the distance between 8 and 14 inches, which is, 
 6 inches. So that you learn this fact from this case : the 
 hyperopia must be added to the presbyopia. 
 
 H+Pr.=Total correction. 
 
 As he waxes in years, he will have to add the presby- 
 opia for each age to the hyperopia which he has ; at the 
 age of 50 he will require 3 D. ; at 55, 4 D., etc. 
 
 Case 3. — Myopia and Presbyopia. 
 
 Here is a patient whom I have selected from the clinic 
 at large. He tells me he has arrived at the age of 46. I 
 have asked him no questions, but inasmuch as he is 46, we 
 may find a case of presbyopia. 
 
 He states that he has no difficulty in reading at all, 
 although he is 46. He says he does not see very well in 
 the distance ; he thinks he is short-sighted. His vision in 
 each eye is less than normal, and we find that — 1 D. is the 
 weakest glass with which he reads f$. He is myopic to 
 the extent of 1 D. 
 
 He is 46 years of age and by rights, if he were emme- 
 tropic, would accept -fiD. for reading. He does not need 
 a convex glass to read with, because he has the value of 
 + 1 D. in the length of his eyeball. So that when he 
 comes to read, he simply lifts his distance glasses to his 
 brow or takes them off entirely. 
 
 Let us now give him the Jaeger Test Type. He reads 
 Jaeger No. 1 at 8 inches with each, and has a good range 
 of accommodation. Let us now put on his correction for 
 distance, namely, — 1 D. He is now emmetropic, and we 
 give him Jaeger No. 1 to read once more. He is unable to 
 do it at 8 inches. He reads it with difficulty at 10 to 14 
 
PRESBYOPIA. 73 
 
 inches. If we add to his distance correction, the correction 
 for the presbyopia of an emmetropia, i. e., +i D., the re- 
 sult is o, for — i D and + 1 D. cancel each other. 
 
 If this man lives to the age of 50, he will require our 
 help, for at 50 years an emmetrope requires + 2 D., and as. 
 our patient has a myopia of 1 D only, he will require the 
 difference between +2 D and — 1 D., which is +1 D. At 
 55 he will require +3 D — 1 D=2 D., etc. A man who 
 has a myopia of 2 D will not require our services at 45 nor 
 at 50. He will simply lift his distance glasses in order to 
 read, but when he is 55 he will require help, and the glass 
 he will need will be the difference between +3 D., an em- 
 metrope's loss at 55, and — 2 D., his myopia. He will then 
 require +iD. This method may be carried out in any 
 case of myopia and presbyopia combined. 
 
 When myopia and presbyopia occur in a case, subtract 
 the myopia from the amount of presbyopia that would exist 
 in a case of emmetropia of the age of the myope. 
 
 Pr. — M : = Correction. 
 
 When a man has a myopia of as much as 3 D,= which 
 is ^2, or 4 D= which is-|-, he probably never will require 
 a plus glass at all for reading, for his far point lies at 12 or 
 8 inches, and he can read with great comfort at either 
 point, because he does not need his accommodation at all. 
 But suppose a man has a myopia of ^-, he will find it diffi- 
 cult to converge his visual lines for so short a distance. 
 We must throw his far point further out. He has a myo- 
 pia of 6 inches, i. e., his far point lies at 6 inches in front 
 of his eye. We must throw that far point out to 12 inches, 
 let us say for comfort. We give him — ^ in order to do 
 so, for — £ — iV = — tz- A man with a myopia of — |- 
 may not care to read at the distance of 8 inches. Let us 
 
74 CLAIBORNE, 
 
 throw his far point out to 12 inches also. We give him a 
 i- for l 3- = J- 
 
 •> 4 lul 8 12 2 -t • 
 
 Astigmatism and Presbyopia. 
 
 I will say in the beginning, for your comfort, that 
 presbyopes rarely require or wish to have their astigmatism 
 corrected when it is slight in degree. High degrees must, 
 however, be noticed. 
 Case I. Simple hyperopic astigmatism and presbyopia. 
 
 We find that this patient has worn this glass for years. 
 
 + 1 D c. ax. 90 . 
 
 If you will allow me to employ a system of crosses this 
 matter can be made more graphically clear : 
 
 .H 
 
 The E lies in the vertical meridian and the H in the 
 horizontal. 
 
 In other words, this glass has rendered him emmetro- 
 pic. Since he is now emmetropic we will apply the rule 
 as before for emmetropes. He is 45 years old, and is, 
 therefore, at the presbyopic age. At this age our list tells 
 us a man has lost + 1 D. When we give him the test card 
 to read he has to hold it out at a considerable distance, 
 even while he has on his distance glasses. We now place 
 over his spectacles our trial frames with +iD in it and 
 give him the card. He says that is better and more com- 
 fortable for his eyes. We have added + 1 D to his astig- 
 
PRESBYOPIA. 75 
 
 matic correction, and that has to be ground as a compound 
 lens by the optician. We prescribe for him thus : 
 
 R + 1 D s. ^ + 1 D. c. ax. 90 . 
 
 Case 2. Simple myopic astigmatism and presbyopia. 
 
 Our patient has always worn — 1 D. c. ax. 180 . 
 The graphic formula for the astigmatism is this is : 
 
 M 
 
 He is 45 years old, and commences to feel the need of help 
 in reading. If he takes off his distance glasses he is astig- 
 matic, and since he is 45 years old, let us place + 1 D. s. 
 over his distance glasses. We then have this combination : 
 
 + 1 D. s. 3 — 1 D. c. ax. 180 . 
 
 This doubtless appears to you to be a curious combi- 
 nation. Let us see what it really amounts to. The — 1 
 D. c. ax. 180 neutralizes the +1 D. s. in the vertical me- 
 ridian, so that the covex spherical practically becomes a 
 convex cylinder with its refracting surface horizontal. 
 Now, as the patient is myopic naturally, to the extent of 
 1 D. in the vertical meridian, the combination really 
 amounts to giving him an artificial myopia of 1 D horizon- 
 tally. So that he has a myopia of 1 D. in each meridian, 
 and as he is 45 years of age, he is in the position of a 
 spherical myope of 1 D. The demands of his age have 
 been satisfied. We may write this glass much more sim- 
 ply, thus : 
 
76 CLAIBORNE, 
 
 -+-1 D. c. ax. 90 . 
 
 For this glass gives him -fiD. s. in his horizontal 
 meridian and this with his natural myopia of 1 D. vertical, 
 puts him practically in possession of + 1 D- spherical. 
 
 You may write the glass either way. The optician 
 will select his own way of grinding it. 
 
 Case 3. Compound hyperopic astigmatism and presbyopia. 
 
 In compound hyperopic astigmatism coupled with 
 presbyopia, the presbyopic correction is simply to be added 
 to the compound glass. This, of course, merely increases 
 the spherical glass, the strength of the cylinder remaining 
 the same. 
 
 Graphic formula for compound hyperopic astigma- 
 tism : 
 
 H 
 
 HH 
 
 Case 4. Compound myopic astigmatism and presbyopia. 
 
 In this condition, the cylinder may be considered con- 
 stant, and the simple myopia must be subtracted from the 
 presbyopia. 
 
 Let us take a case of this, for it is more complicated 
 than the preceding. 
 
 A man of 50 wears for distance, 
 
 — 1 D. s. 3 — 1 D. c. ax. 180 . 
 The graphic formula for this condition of refraction is : 
 
PRESBYOPIA. 77 
 
 MM 
 
 -M 
 
 This combination renders him emmetropic. He is 50 
 years of age, and, as an emmetrope at that age requires 
 + 2 D, we add + 2 D to the above formula : 
 
 — 1 D. s. 3 +2 D. s. ^ — 1 D. c. ax. 180 . 
 
 The result is 
 
 + 1D.S.C-1 D- c. ax. 180 . 
 
 Now a man with compound myopia 
 
 — 1 D. s. C — 1 D - c - ax - I 8o°. 
 
 has a myopia of 2 D. in the vertical meridian and 1 D. in 
 the horizontal. As he is 50 years old, he requires 2 D. in 
 each meridian according to the list, so that we prescribe : 
 
 + 1 D. c. ax. 90 . 
 This gives him 2 D. of myopia in the horizontal and verti- 
 cal meridians, and his demands are satisfied ; e. g., graphi- 
 cally : 
 
 MM 
 
 MM 
 
 You have doubtless observed that we have corrected a 
 case of simple myopic astigmatism, see case 2, and one of 
 
78 CLAIBORNE; 
 
 compound myopic astigmatism, with the same glass. The 
 explanation lies in the spherical myopia of the latter case, 
 and in the difference between the ages of the patient. 
 
 L,et us take the case of a man of 45, with the correction, 
 
 — 1 D. s. 3—1 D. c. ax. 180 . 
 
 He has a compound error, and we only need to correct 
 the simple myopic astigmatism ; we thus leave him with 
 1 D. of myopia in each meridian, which is enough for him 
 to read with. We give such a case, 
 
 — 1 D. c. ax. 180 . 
 
 M 
 
 M 
 
 Case 5. Mixed astigmatism and presbyopia. 
 A patient of 50 years has worn this correction, 
 + 2 D. c. ax. 90 3 — 2 D. c. ax. 180°. 
 
 MM 
 
 -HH 
 
 This renders him emmetropic. If we put on his spec- 
 tacles and ask him to read, he is unable to do so. We 
 place + 2 D s. over his spectacles and he reads with ease. 
 
PRESBYOPIA. 79 
 
 From our studies in mixed astigmatism you remember 
 that there are 3 ways of writing the above formula : first, 
 the way it is written above in crossed cylinders, secondly, 
 
 + 2 D. s. 3 — 4 D. c. ax. 180 
 
 or thirdly, 
 
 — 2 D. s. 2 +4 D. c, ax. 90 . 
 
 Now if to either of the last two we add + 2 D, the 
 presbyopic correction for a man of 50 years, we write : 
 
 + 4 D. s. 3 — 4 D. c. ax. 180 or 
 
 + 2 D. s. 3 — 2 D. s. 3 + 4 D. c. ax. 90 . 
 
 This latter formula is equal to 
 
 +4 D. c. ax. 90 . 
 
 But the great probability is that the optician prefers 
 to grind the second formula, i. e., a concave cylinder of 
 4 D. on a spherical plus glass of 4 D. Under either cir- 
 cumstance, the resultant value is 
 
 +4 D. c. ax. 90 . 
 
 The vertical meridian now has its natural myopia of 
 2 D., and the hypermetropia of 2 D of the horizontal merid- 
 ian has not only been corrected, but 2 D. more added to it. 
 Hence, each meridian has 2 D., and the demands of the 
 patient's age have been satisfied. 
 
 Although it is apparently easy to correct presbyopia, 
 the fact is that failure is more common in its correction 
 than in errors of refraction. The cause lies in this that 
 presbyopia is a matter of function. The muscle of accom- 
 
80 CLAIBORNE, 
 
 modation has not always the same innervation. This dif- 
 fers with time and circumstance. In youth there is a regu- 
 lar tone to the muscle as a rule, but such is not the case in 
 presbyopia. A patient who is satisfied with one correction 
 one day, will return the next and complain that the glasses 
 are unsatisfactory. This is particularly the case with 
 females. They are not able to analyze their sensations as 
 accurately as men. 
 
 And now, a few words of common sense about the cor- 
 rection of presbyopia. 
 
 Do not stick to any iron-clad rule in giving a glass. 
 Sometimes a stronger and sometimes a weaker glass than 
 apparently the correct one, is accepted. 
 
 I have stated that every adult, not presbyopic, ought 
 to be able to read Jaeger No. i at 8 inches. It is not im- 
 probable that the great majority of adults can do this for a 
 few seconds, but there are very few that can keep it up 
 longer than a minute or two. Most people read at the dis- 
 tance of i o or 12 inches, and books are usually printed in 
 type of the size of Jaeger No. 4 or 5, at least ; more fre- 
 quently in type of the size of Nos. 6 or 7. So that the test 
 when made with Jaeger No. 1 is a test of supreme capacity, 
 not of ordinary working power. Try always to give your 
 patient as long a " range of accommodation " as possible, 
 that is, to give a glass that gives the greatest possible dis- 
 tance between the nearest point and the farthest point of 
 distinct vision. 
 
 After you have made your estimate of what the patient 
 ought to accept, try that glass, and then the glasses on 
 either side of it, that is, weaker and stronger glasses, and 
 ask the patient this question, which do you prefer ? If you 
 satisfy your patient you are correct. If you do not satisfy 
 him you need not be wrong, for there are some people who 
 
PRESBYOPIA. 8 1 
 
 cannot be made to say that they are satisfied, and, more- 
 over, the case may be complicated. Do not try to force a 
 glass upon a person because your science tells you it is the 
 correct glass. Common sense should be your guide as 
 much as science. 
 
CHAPTER IX. 
 
 MYDRIATICS. 
 
 Mydriatics are used for the purpose of paralyzing the 
 accommodation with a view to discovering the true condi- 
 tion of the refraction. In hypermetropia and myopia there 
 is probably a tonic contraction of the ciliary muscle which 
 is not altogether lost till advanced age. There is also an 
 excessive contraction of the ciliary muscle which is known 
 as spasm of the accommodation, and renders emmetropes 
 myopic, hypermetropes less hyperopic, and myopes more 
 myopic. The action of the mydriatic by eliminating the 
 action of the muscle, enables us to judge of the true refrac- 
 tive power of the eye. 
 
 Spasm occurs in cases in which the eyes have been 
 strained by excessive use, either for distance or near, but 
 more frequently for the latter, and is evidenced in the func- 
 tional examination by alternate or irregular clearness and 
 dimness of the letters and by the contradictory or uncer- 
 tain answers of the patient when glasses are put before the 
 eye. Headache almost invariably accompanies this condi- 
 tion whatever may be the refractive state. 
 
 The two agents for paralyzing the accommodation are 
 homatropine hydrobromate and atropine sulphate. 
 
 Homatropine hydrobromate is a derivative of atropine 
 and its effects are more transient than those of atropine 
 sulphate. The length of the duration of either depends, in 
 a measure, on the strength of the solution. Homatropine 
 
 (82) 
 
MYDRIATICS. 83 
 
 is made into a 1%, 2% or 3% solution; that is, roughly- 
 speaking, 5 grains, 10 grains or 15 grains to the ounce. 
 For my part, I never use a greater strength than a 2 <f 
 solution. The 3 <f c solution causes the eye to be red and 
 congested if rapidly instilled. The redness, however, dis- 
 appears after a short while. 
 
 The frequency of the instillations is a matter of some 
 importance. In adults six or eight instillations of one or 
 two drops each may be used. But in children it is well to 
 be more careful, although I can record no case of toxic 
 symptoms among them from the use of homatropine. L,et 
 the solutions be made up with a few grains of boric acid to 
 keep them sweet. And do not prescribe a large amount 
 when you prescribe it for home use. A one drachm solution 
 is quite sufficient. For the drug is one of the most costly 
 that exist. L,et us write the formula for a two per cent, 
 solution for office use : 
 
 B Homatropinae hydrobromat. grs. x. 
 Acidi borici grs. x. 
 
 Aquae dist. Si. 
 
 Sig. 2 f solution of Homatropine hydrobromate. 
 
 The effect of this solution lasts about 24 hours, and 
 the maximum effect on the accommodation is 3 or 4 hours 
 after the first instillation. It is not necessary, however, to 
 wait for the maximum effect. When you find that the 
 patient cannot read any of the type on either of the first 
 two pages of the Jaeger Test, you may consider the accom- 
 modation fairly well eliminated. In cases in which the 
 symptoms are not grave and the asthenopia is not compli- 
 cated with other reflex symptoms, homatropine is satisfac- 
 tory. In those cases, however, in which there are symp- 
 toms simulating some grave nervous disturbance, or in 
 
84 CLAIBORNE, 
 
 which the headaches and eye-pains are extraordinarly 
 severe, and particularly in the case of children with strabis- 
 mus, atropine sulphate is preferable. The paralysis of the 
 accommodation is more complete and lasting from this 
 drug. Its duration is, on an average, a week — sometimes 
 it is two weeks. I never use a stronger than a i % solution 
 for children. Care must be taken to watch for the point of 
 toleration. Some children can stand an astonishing amount 
 of atropine, and some exhibit toxic symptoms after one or 
 two instillations. It is always well to caution the parents 
 in regard to the possible effects, in order that they may not 
 persist in the use of the drug after the appearance of toxic 
 symptoms, and that they may not be frightened. An ordi- 
 nary child can stand one drop in each eye 3 times a day. 
 It is rare that toxic effects are seen in adults when atropine 
 is used for the paralysis of the accommodation. A two per 
 cent, solution is most satisfactory for this purpose. 
 
 R Atropinse sulphat. grs. x. 
 
 Acidi borici grs. xv. 
 
 Aquse dist. Si. 
 
 Sig. 2 % solution of atropine sulphate. 
 
 Atropine may be kept in the eyes of children for 
 months without the slightest evil result to the ultimate 
 power of the accommodation. This is not the case in 
 adults and old people. 
 
 It undoubtedly impairs the accommodation in both, 
 and in old people particularly, when used for any length of 
 time. The effect of both of these drugs is accelerated by 
 combination with cocaine hydrochlorate in a 4 fo solution. 
 For office work a mixture of cocaine and homatropine may 
 be kept. 
 
Homatropinae hydrobromat. 
 
 grs. v. 
 
 Cocainee hydrochlor. 
 
 grs. x. 
 
 Acidi borici 
 
 grs. v. 
 
 Aquae dist. 
 
 5r. 
 
 85 
 
 Sig. 1 fc Sol. of cocaine and homatropine. 
 
 The all important point to be settled is when the 
 glasses should be prescribed — before the mydriatic, during 
 its effect, or afterward. There is little doubt amongst 
 authority that mydriatics were formerly more frequently 
 prescribed than was necessary. More respect is now paid 
 to the tonic contraction of the ciliary muscle than in the 
 past. It is rare indeed that a hyperope in youth, even after 
 the use of the mydriatic, shows the entire amount of his 
 error. And it is not improbable that a myope possesses 
 and retains a certain amount of tonic contraction of his 
 ring muscle, thereby apparently increasing his myopia. 
 Judgment and experience alone can direct you in the select- 
 ion of cases in which mydriatics should be used. It is safe 
 to say, however, that they are rarely, if ever, necessary 
 after the age of forty. They may be used, broadly speak- 
 ing, in youth, and when cases possess the symptoms of ob- 
 scure nervous complaint ; also, when the prescription of 
 glasses, without their use, has failed to relieve the astheno- 
 pia. I do not see how any intelligent surgeon can pre- 
 scribe glasses during the effect of the mydriatic, except in 
 one class of cases, and that class is children, who have a 
 high degree of hypermetropia and strabismus. In such 
 cases, the total correction may be given while the eye is 
 under the maximum effect of the drug, and the mydriatic 
 may then be allowed to wear off gradually. If a child is 
 very young, it will wear the glasses which were first given. 
 If it is old enough to analyze its sensations, the glass, in 
 
86 CLAIBORNE, 
 
 all probability, will have to be changed to one that is 
 weaker after the mydriatic has disappeared. I do not rec- 
 ognize any other class in which the total correction, under 
 a mydriatic, should be given. The examination should be 
 made before the use of the mydriatic, during the height of 
 its effect, and immediately after the effect has entirely worn 
 off. If homatropine is used, three examinations are neces- 
 sary for an intelligent knowledge of the refractive condi- 
 tion of the eye ; if atropine sulphate is used, at least three 
 examinations, probably more. Under all circumstances, 
 the final examination should be made immediately after 
 the mydriatic effects disappear. This is indicated, of course, 
 by the patient's ability to read Jaeger No. i at the normal 
 distance, if he be under the age of presbyopia. During the 
 time the eyes are under examination, the patient should 
 strictly abstain from their use for near work. The tempta- 
 tion for patients to use their eyes, particularly when the 
 effect of the mydriatic has just worn off, is very great. 
 This inclination should be resisted, for sometimes the eyes 
 will relapse into the original condition of spasm, and the 
 examination will have to be made again. 
 
87 
 
 No. 1. — Brilliant. 
 
 The place of our retreat wn s little neighborhood, consisting of fur men, who tilled their own grounds, and were equal atrnngem to opulence and povovlj. 
 
 As they had il ..... .1 nil the conveniences of life within themselves, the; seldom visited tonne or cities in <■ 1. of euperBultiea. It emote from polite, ther 
 
 ■still retained the primaeval simplicity of manners; and frugal by habit, they scarce knew that temperance was a virtue, They wrought with cheerfulness on 
 ■days of labor, but observed festivals sw intervals of idlunoHfl and pleasure. They kept up the Christmas carol, sent trae-love knots on Valentino morning, ate 
 pancakes on Shrove-tide, showed their wit an the first of April, and religiously cracked nuts on Mlahoalmas-eve. Being apprised of our approach, the whole 
 neighborhood came out to meet their minister, dressed in their One clothes, and preceded by a pip* and tabor; A feast also was provided for our reception, at 
 
 No. 2.— Pearl. 
 
 The place of our retreat was a little neighborhood, consisting of farmers, who tilled their own grounds, and were 
 equal strangers to opulence and poverty. As they had almost all the conveniences of life within themselves, they 
 seldom visited towns or cities in search of superfluities. Remote from polite, they still retained the primaeval 
 simplicity of manners ; and frugal by habit, they scarce knew that temperance was a virtue. They wrought with 
 cheerfulness on days of labor, but observed festivals as intervals of idleness and pleasure. They kept up the 
 Christmas carol, sent true-love knots on Valentine morning, ate pancakes on Shrove-tide, showed their wit on the 
 
 No, 3. — NonparieL 
 
 The place of our retreat was a little neighborhood, consisting of farmers, who tilled their own 
 grounds, and were equal strangers to opulence and poverty As they had almost all the con- 
 veniences of life within themselves, they seldom visited towns or cites in search of superflu- 
 ities. Remote from polite, they still retained the primaeval simplicity of manners ; and 
 frugal by habit, they scarce knew that temperance was a virtue. They wrought with cheer- 
 fulness on days of labor, but observed festivals as intervals of idleness and pleasure. They 
 
 No. 4. — Minion. 
 
 The place of our retreat was a little neighborhood, consisting of farmers, who tilled 
 their own grounds and were equal strangers to opulence and poverty. As they had 
 almost all the conveniences of life within themselves, they seldom visited towns or 
 cities in search of superfluities. Remote from polite, they still retained the primaeval 
 simplicity of manners; and frugal by habit, they scarce knew that temperance was .1 
 virtue. They wrought with cheerfulness on days of labor, but observed festivals as 
 
 / 
 
88 
 
 No. 5. — Bourgeois. 
 
 The place of our retreat was a little neighborhood, consisting of farm- 
 ers, who tilled their own grounds, and were equal strangers to opul- 
 ence and poverty. As they had almost all the conveniences of life 
 within themselves, they seldom visited towns or cities in search of 
 
 No. 6. — Long Primer. 
 
 The place of our retreat was a little neighborhood, consisting of 
 farmers, who tilled their own grounds, and were equal strangers to 
 opulence and poverty. As they had almost all the conveniences of 
 life within themselves, they seldom visited towns or cities in search 
 
 No. 7. — Small Pica. 
 
 The place of our retreat was a little neighborhood, consist- 
 ing of farmers, who tilled their own grounds, and were equal 
 strangers to opulence and poverty. As they had almost all 
 the conveniences of life within themselves, they seldom 
 
 No. 8 — Pica. 
 
 The place of our retreat was a little neighborhood, con- 
 sisting of farmers, who tilled their own grounds, and 
 were equal strangers to opulence and poverty. As 
 they had almost all the conveniences of life within 
 
8 9 
 
 No. 9. — English. 
 
 The place of our retreat was a little neighbor- 
 hood, consisting of farmers, who tilled their own 
 grounds, and were equal strangers to opulence 
 and poverty. As they had almost all the con- 
 
 No. 10. — Great Primer. 
 
 The place of our retreat was a little 
 neighborhood, consisting of farmers,who 
 tilled their own grounds, and were equal 
 strangers to opulence and poverty. As 
 
 No. 11. — Two-line Small Pica. 
 
 The place of our retreat was a 
 little neighborhood, consisting 
 of farmers, who tilled their own 
 grounds, and were equal stran- 
 
90 
 
 Kb. 12.— Two-lint English. 
 
 The place of our retreat 
 was a little neighbor- 
 hood, consisting* of far- 
 mers, who tilled their 
 
 Xo. IS.— Tico-linf Gnat Prin 
 
 The place of our 
 retreat was a little 
 neighborhood, 
 consisting of far- 
 
9 T 
 
 SNELLEN'S TEST TYPES. 
 
 cc. 
 
92 
 
 C. 
 
 
93 
 
 LXX. 
 
 l^-— i 
 
 H ! 
 
94 
 
 XL. 
 
XXX. 
 
 95 
 
 XX. 
 
96 
 
 XV. 
 
 U A C E 
 
 x. 
 
 V Z B D F