1' 
 
 - 
 
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^5 CORNELL UNIVERSITY 
 
 (^5 6 THE 
 
 Movant B^tprtnar^ fCtbrartf 
 
 SlCi "fic FOUNDED BY 
 
 ROSWELL P. FLOWER 
 
 for the use of the 
 
 N. Y. State Veterinary College 
 
 1897 
 
EXTRACTUM PANCREATIS. 
 
 (FAIRCHILD.) 
 
 Is a pure dry product from the pancreatic gland, in the form of a light 
 yellow powder. 
 
 We are happy to announce that we have made steady progress in 
 the manufacture of the pancreatic ferments, and, as the result of per- 
 sistent efforts our Extractum Pancreatis is now markedly improved in 
 refinement and activity. 
 
 It contains all the digestive ferments of the Pancreas, vi^.. 
 
 TR y/'5/^— Which converts albumens (of Milk, Beef, etc.) into Pep- 
 tone, in either neutral, alkaline or slightly acid media. 
 
 DIASTASE — Which converts starches into dextrines and sugar. 
 
 THE EMULSIVE FERMENT— EssenMsX to assimilation of fats 
 and oils. 
 
 THE MILK-CURDLING FERMENT. 
 
 "The pancreatic secretion is the most energetic and general in its 
 action of all the digestive juices. It unites in itself the action of the 
 saliva and the gastric juices, besides having properties of its own." — 
 T. Lauder Brunton. 
 
 Extractum Pancreatis is, therefore, the most important and widely 
 useful remedy in the treatment of Dyspepsia, and its practical value has 
 been amply established by years of trial and clinical experience. By its 
 use, also, the preparation oj peptonised or artificially digested food for the- 
 sick is rendered entirely practicable and successful. The value of such a-- 
 resource is so obvious that it requires no enlargement here. 
 
 Extractcm Pancreatis is usually prescribed in three to fiVe graini 
 doses, in capsule, pill or tablet, alone or combined with other remedies- 
 (bismuth, charcoal, soda, etc.) at the discretion of the physician. 
 
 The Extractum Pancreatis is supplied in ounce vials; also preparedl 
 
 in the form of Tablets and in Peptonizing Tubes. 
 
 Fairchild Bros. & Foster, 
 
 82 AND 84 FULTON ST., NEW YORK. 
 
WW B Cornell University 
 
 i!ill j h) Library 
 
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 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924104224658 
 
CORNELL UNIVERSITY LIBRARY 
 
 3 1924 104 224 658 
 
 THE 
 
 THEORY AND PRACTICE 
 
 OF THE 
 
 OPHTHALMOSCOPE. 
 
 A HAND-BOOK FOR STUDENTS. 
 
 JOHN HERBERT CLAIBORNE, Jr., M. D 
 
 Instructor in Opkthal?nology in the Neiv York Polyclinic: Clinical 
 Assistant in the Vanderbilt Clinic {^Department of Ophthalmol- 
 ogy); Attending Surgeon to the North-Western Dispen- 
 sary^ Eye, Ear nnd Throat Department; formerly 
 Clinical Assistant to the Manhattan Eye 
 and Ear Hospii-al, New York, 
 
 1888. 
 GEORGE S. DAVIS, 
 
 DETROIT, MICH. 
 
Copyrighted by 
 GEORGE S. DAVIS. 
 
 iS8S. 
 
TO MY FATHER, 
 
 DR. JOHN HERBERT CLAIBORNE, 
 
 OP VIRGINIA, 
 
 THIS MANUAL IS AFFECTIONATELY 
 
 DEDICATED. 
 
PREFACE. 
 
 In presenting this brochure to the medical profession, 
 the author has not hoped to establish a claim for originality. 
 The lines are cast in familiar places. His object has been to 
 present in a clear and brief manner the main facts in ophthal- 
 moscopy and the method of using the ophthalmoscope. 
 
 While a reasonable degree of success in teaching the use 
 of the instrument has led him to formulate his ideas in writing, 
 it is not without a certain amount of fear that he subjects his 
 first essay to public criticism. 
 
TABLE OF OONTEIsTTS. 
 
 CHAPTER I. 
 
 PAGE. 
 
 The Law of the Refraction of Light — Behavior of Rays of 
 Light in Passing Through a Prism — The Composi- 
 tion of Convex and Concave Lenses — The Principal 
 Axis of Lenses — Behavior of Rays of Light Passing 
 Through Convex and Concave Lenses — " Secondary 
 Rays " — The ' ' Principal Focus " of Convex and Con- 
 cave Lenses — The Varieties of Spherical Lenses — 
 Cylindrical Glasses — Their Refraction — Their Axes, 
 and Hovsr Marked 3-11 
 
 CHAPTER n. 
 
 The Strength of Convex and Concave Lenses, and How 
 Recorded — Tabulated Statement of Size and Position 
 of Images Formed by Convex and Concave Lenses — 
 Formula for Finding Distance of Image from Lens 
 in Convex and Concave Lenses — Reflection — State- 
 ment of Law — Reflection from Plane Surface — Re- 
 flection from Concave Surface — Reflection from Con- , 
 vex Surface 1 1-19 
 
 CHAPTER III. 
 
 Optic Axis — Visual Axis — Nodal Point — Emmetropia — 
 Ametropia — Hypermetropia — Myopia — The Angle 
 "a" — Astigmatism — The Perception of a Line — The 
 Near Point — The Far Point — Illustration of Far Point 
 and Near Point — How Rays of Light Emerge from 
 Eyes — Anisometropia (Heterometropia) 19-28 
 
X 
 
 CHAPTER IV. 
 
 PAGE. 
 
 Description and Cut of the Ophthalmoscope 28-30 
 
 CHAPTER V. 
 
 Table of the Methods of Using the Ophthalmoscope — The 
 Transmitted or Reflected Illumination — The Oblique 
 Illumination — The Recognition of Opacities in the 
 Media of the Eye, and the Location of Them 30-37 
 
 CHAPTER VI. 
 
 The Indirect Method — The Manner of Employing It — The 
 Point in the Eye to be Sought in the Employment of 
 this Method — The Recognition of Emmetropia; of 
 Simple Hypermetropia; of Simple Hypermetropic 
 Astigmatism; of Compound Hypermetropic Astig- 
 matism — The Recognition of Simple Myopia; of 
 Simple Myopic Astigmatism; of Compound Myopic 
 Astigmatism; of Mixed Astigmatism — The Meaning 
 of the Increase and Decrease in the Size of the Disc 
 as the Objective is Withdrawn — The Explanation of 
 These Phenomena. , 37-46 
 
 CHAPTER VII. 
 
 The Direct Method — The Manner of Employing It — The 
 Minute Examination of the Vitreous Body — The Re- 
 cognition of Emmetropia, of Simple Hypermetropia, 
 Simple Myopia — The Measuring of the Degree of 
 Myopia and Hypermetropia — The Recognition and 
 Measurement of Simple Hypermetropic Astigmatism; 
 of Compound Hypermetropic Astigmatism ; of Simple 
 Myopic Astigmatism; of Compound Myopic Astig- 
 matism; of Mixed Astigmatism — The Measurement 
 
XI 
 
 PAGE. 
 
 of the Depth of Excavations and the Extent of the 
 Prolongation Forward of Tumors in the Fundus — 
 General Characteristics of the Appearance of the 
 Fundus in E., H. and M 46-58 
 
 CHAPTER VIII. 
 
 The Vessel Test— The Recognition of E., H. and M. by 
 Means of It — The Appearance of the Fundus-reflex 
 in High Degrees of Ametropia — The Recognition- of 
 Irregular Lenticular and Corneal Astigmatism by the 
 Vessel Test— The Shadow Test or Retinoscopy. . . .58-74 
 
 CHAPTER IX. 
 The Selection of Mydriatics 74-77 
 
INTRODUCTION. 
 
 The object of this introduction is to say a 'few 
 words to those who propose to read this manual care- 
 fully. The selection of the matter preliminary to the 
 " Methods of using the Ophthalmoscope," has not been 
 unattended with difificulty. The difficulties have been 
 to avoid in the first place exuberance, in the second 
 too great conciseness. The author has found in teach- 
 ing that a correct understanding of those facts in op- 
 tics which are set forth in the first three chapters, is 
 absolutely necessary to the scientific use of the oph- 
 thalmoscope. It might be supposed that most 
 students are acquainted with these elementary prin- 
 ciples; it has been the author's fortune to teach many 
 who evidently knew nothing of them. It will be ob- 
 served that repetition characterizes this manual. It 
 has been intentional. There is no more certain 
 method of producing an impression. It is hoped that 
 clearness has not been sacrificed to brevity. The 
 methods of using the instrument have been divided 
 somewhat differently from others. It will be observed 
 that four headings are employed. Retinoscopy and 
 the "Vessel Test has been put under the first method, 
 the reflected. Most teachers suggest the oblique il- 
 lumination as the first method. By this method the 
 physical condition alone of the cornea, aqueous 
 humour, lens, and anterior portions of the vitreous 
 
humour are recognized. By the Reflected method, 
 not only is this information obtained, but the Vessel 
 Test and Shadow Test may be employed at the same 
 time, and a definite idea be gotten of the quality and 
 the approximate quantity of the refraction. Surely 
 that method of procedure is most to be commended 
 which enables one to obtain the greatest amount of in- 
 formation in the shortest time and with the least effort. 
 To those who would follow the teachings of this man- 
 ual, it is earnestly suggested that the following 
 sequence in examination be observed: 
 
 I St. The Reflected Illumination, (a) Vessel Test, 
 (i>) Shadow Test or Retinoscopy. 2nd. Oblique Il- 
 lumination. 3rd. The Indirect Method. 4th. The 
 Direct Method. It is the author's desire to call 
 especial attention to the chapter on Retinoscopy. 
 This method is too little used in this country. As a 
 qualitative and as an approximately quantitative 
 method of estimating the refraction of an eye it is in 
 the highest degree to be commended. The quantita- 
 tive determination of errors of refraction by this 
 method with the aid of the trial case, the author has 
 employed only in the class of cases referred to in the 
 Chapter on this subject. The disinclination on the 
 part of some ophthalmologists in this country to use 
 this method at all can only be attributed to over-con- 
 servatism. Although it is not properly in the scope 
 of this manual as proclaimed by the title, it has been 
 deemed wise to add a chapter on Mydriatics. The 
 
— 3 — 
 following authorities have been consulted in the 
 preparation of this monograph: Landolt.^Schweigger, 
 Soelberg Wells, Juler, Swanzy, Nettleship, Hartridge, 
 Morton and others. 
 
 In conclusion the author wishes- to express his 
 thanks to Dr. John Dunn, for the valuable criticisms 
 and suggestions made during the preparation of the 
 following pages. J. H. C. Jr. 
 
CHAPTER I. 
 
 On a correct knowledge of the laws of optics de- 
 pends the comprehension of the facts of ophthalmos- 
 copy. For practical purposes, it is only necessary to 
 speak of the behavior of rays of light that pass through 
 prisms, spherically concave and convex glasses, and 
 through cylindrical glasses, as well as that of rays in- 
 cident to and reflected from concave, convex and 
 plane surfaces. 
 
 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 en- 
 trance; in passing from a denser to a less dense are 
 refracted from a perpendicular drawn to the surface of 
 the medium at the point of emergence. If the rays 
 be at right angles to the surface separating the two 
 media, they are not refracted at all. (Fig. i.) 
 
 At B, the ray of A B is refracted toward the per- 
 pendicular P P. 
 
 At C, the ray of B D is refracted from the per- 
 pendicular P P. 
 
 The ray H K falling at a right angle to the sur- 
 face of the medium, is not refracted. 
 
 In Fig. I, the sides of the refracting medium are 
 parallel, but in the case of a prism the surfaces are not 
 
— 5 — 
 parallel and a ray can therefore be perpendicular to 
 only one surface at a time. Any ray that falls on a 
 
 Fig. I. 
 
 prism must be refracted and the deviation must be to- 
 ward the base. 
 
 Fig. 2. 
 
 The ray D M falling upon a prism is bent in the 
 direction M. N.; at N it is again bent so that an ob- 
 
— 6 — 
 
 server catching the ray at E, would receive it as if it 
 came from K. Let it be observed that the relative 
 direction of the rays is unaltered. 
 
 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 com- 
 prehend the fact that convex 
 lenses cause convergence, and 
 concave lenses divergence of 
 rays. 
 
 Fig. 3. 
 
 A line which passes through the centre of a lens 
 (optical centre) at right angles to the surfaces of the 
 lens, is called the principal axis. A ray passing through 
 this axis is not refracted. 
 
 Fig. 4. 
 
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 toward a perpendicular to the surface of 
 the lens at that point, as shown by the dotted lines 
 MK. On leaving the lens at O the ray is refracted 
 away from the perpendicular NO 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. 
 
 Fig. 5. 
 
 The ray B strikes the lens L at a right angle and 
 is not refracted. The ray A strikes the lens L 
 obliquely at D and is refracted towards the perpen- 
 dicular, G H. On emerging from the lens at K it is 
 bent away from the perpendicular 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. 
 
— 8 — 
 
 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. 
 They do undergo refrac- 
 tion, but in thin lenses it 
 is so slight that they are 
 assumed to pass in a straight 
 
 line. 
 
 Fig. 6. 
 
 Parallel rays passing through a convex lense (L) 
 are brought to a focus (A) at a certain fixed distance 
 from the optical centre of the lens. Such a point is 
 
 Fig. 7. 
 
 called the principal focus of the lens, and the distance 
 of this point from the optical centre of the lens is 
 called the focal distance of the lens. 
 
 If parallel rays, passing through a concave lens 
 be rendered divergent, the focus must be a virtual. 
 
— 9 — 
 negative one, situated on the same side of the lens as 
 the object from which the rays proceed. If the 
 divergent rays in Fig. 8 below, be continued back- 
 ward, they will meet at F. the principal focus. 
 
 Fig. 8. 
 
 Spherical lenses may be plano-convex (Fig. 9, i), 
 that is, having one surface plane and the other convex; 
 double convex (Fig. 9, 2), having both surfaces 
 convex with the same radius of curvature to both; 
 converging concavo-convex (Fig. 9, 3), having one 
 surface concave and the other convex, with the pre- 
 dominance of the latter, the so-called positive meniscus j 
 plano-concave (Fig. 9, 4), double or bi-concave (Fig. 
 8, 5); diverging concavo-convex (Fig. 8, 6), with pre- 
 dominance of the concavity, the negative meniscus. 
 
 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 represent the surface of a convex cylindrical 
 glass. The transverse diameter will have the greatest 
 
radius of curvature, the vertical meridian which cor- 
 responds to the axis of the cylinder will be plane. 
 
 Fig. 9. 
 
 If we describe a circle on the inner side of an 
 upright hollow glass cylinder, the portion included 
 within the circle will represent the surface of a con- 
 cave cylindrical glass. The transverse diameter will 
 have the greatest 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 plano-con- 
 vex and plano-concave, and parallel rays passing 
 through them at right angles to their axis are rendered 
 convergent or divergent respectively. 
 
 The axis 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. 
 
CHAPTER 11. 
 
 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 cylin- 
 drical glasses. Such a lens is called a convex number 
 one. Having a standard, we may proceed to others; 
 a convex lens which unites parallel rays at two inches 
 from its optical centre is termed a convex number 
 two, and so on. The strength of lenses is inversely as their 
 focal distances. The strength of a convex number two 
 is obviously one-half as great as that of a convex 
 number one. 
 
 The strength of lenses is expressed in the form 
 of a vulgar fraction, \, \, ■^^, and so on. 
 
 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 glasses. 
 
 Such a lens is called a concave number one. A 
 concave number two would give parallel rays such a 
 divergence that if prolonged backward, they would 
 iheet two inches from the optical centre of the lens. 
 The strength of the latter is obviously one-half that 
 of the former. 
 
 Convex glasses that are written with the algebraic 
 plus sign before them: + ^, + -i-^, + ■g'^, etc.; con- 
 cave glasses with the algebraic minus sign before 
 them: — i, — i^j, — -gV, etc. 
 
In this country glasses are usually recorded in 
 the form of vulgar fractions; in England and on the 
 continent the French system of dioptrics or dioptries* 
 is commonly used. One dioptry is the equivalent of 
 ^ or jijf, accordingly as the French or English inch is 
 taken as the standard. 
 
 When written in dioptries, the numbering of 
 glasses is done in integers and decimal fractions: 
 + A = I + D, — A = - i-S D, + gV = + 0.5 D, 
 — i = — S D, etc. 
 
 The tabulated statement of the following facts is 
 deemed pertinent: 
 
 I. Parallel rays passing through a convex lens 
 are brought to a focus at a certain distance from the 
 optical centre of the lens. The point at which they 
 unite is termed the Principal Focus of the lens. The 
 image is inverted and smaller than the object 
 from which the rays proceeded. (Fig. 10.) 
 
 The candle A B is presumably placed at infinite 
 distance; the rays from it proceed to the lens parallel. 
 
 * The choice between the words dioptry and dioptric may 
 be left to the taste of the reader. Quite an animated discus- 
 sion has taken place in the New York medical journals in re- 
 gard to this point between Dr. Swann M. Burnett, of Washing- 
 ton, D. C, and the late Dr. Loring, of New York. Perhaps Dr. 
 Knapp has suggested the most plausible means of settling the 
 difficulty — by referring the matter to the Queen, whose language 
 we speak. 
 
— 13 — 
 
 b a is the real inverted diminished image of the ob- 
 ject A B, and is situated at, the Principal Focus of the 
 lens. 
 
 Fig. 10. 
 
 2. If the rays proceed from an object situated at 
 twice the focal distance of the lens, the image will be 
 formed at twice the focal length behind the lens, and 
 will be of the same size as the object. 
 
 3. If the object be situated at the focal distance 
 (principal focus) of the lens, they will emerge from 
 the lens parallel, no image will therefore be formed. 
 
 4. If the rays proceed from an object situated 
 within the focal distance of the lens, they will emerge 
 from the lens divergently. The image will be virtual 
 and will appear to an observer's' eye, placed in the 
 track of the emerging rays, upright and larger than 
 the object. (Fig. 11.) 
 
 The candle A B is situated within the focus F. 
 The rays from the candle A B pass through the lens 
 and ■ emerge divergently. Some of these divergent 
 rays are caught by the eye E, and are received as if 
 
— 14 — 
 
 they came from a b. The image a b is larger than 
 the object A B, and is upright. 
 
 Fig II. 
 
 In concave glasses the image is on the same side 
 of the lens as the object (virtual) is upright and 
 smaller than the object. 
 
 Fig. 12. 
 
 Rays coming from the candle A. B. pass through 
 the concave lens C and emerge divergently. These 
 divergent rays, to an observer who looks- at A. B. 
 through the lens, have the appearance of coming from 
 a. b. 
 
— IS — 
 While a real image may be thrown upon a screen, 
 a ptrtual one can only be seen by looking through the 
 lens. 
 
 The distance of the image from the lens in con- 
 vex glasses may be found by the following formula: 
 _i_ _i I 
 
 X b a 
 where 
 
 X = the distance of the image from the lens. 
 
 b = the focal length of the lens. 
 
 a = the distance of the object from the lens. 
 
 1. Suppose rays from an object at infinite distance 
 (parallel rays) pass through a 2 inch convex lens: to find x, 
 the distance of the image from the lens. 
 
 X 1 I T 1 I . , 
 
 — = — = — ..x = 2 inches. 
 
 X 2 00 2 O 2 
 
 2. Suppose rays coming from an object at four inches, 
 pass through a two inch convex lens ; to find x. 
 
 — == = — .". x = 4 inches. 
 
 X 2 4 4 
 
 3. Suppose rays coming from an object at two inches, 
 pass through a two inch convex lens ; to find x. 
 
 — = = o.'. x = — = 00 = infinity. 
 
 X 2 2 O ■' 
 
 5. The distance of the image from the lens in 
 concave glasses may be found by the formula: 
 
 X b ^ a ' b ~ a 
 
 with the same valuations as in the formula for convex 
 glasses. 
 
i6 — 
 
 Reflection. Rays of light incident to a polished 
 surface are chiefly reflected. 
 
 The angles of incidence and reflection are always 
 equal. 
 
 Fig. 13. 
 
 A B is the ray incident to the surface CD. BE 
 is the reflected ray. The perpendicular P B divides 
 the angle ABE into two equal parts. The angle A 
 B P is then equal to the angle P B E. 
 
 In reflection from a plane mirror, the image is 
 projected behind the mirror, is upright, of the same 
 size as the object, and at the same distance from the 
 mirror as the object. (Fig. 14.) 
 
 The image of the candle Cis projected behind the 
 mirror M at C, a distance behind the mirror equal to 
 the distance of the candle in front of it. The eye E 
 receives the rays from the candle C as if they came 
 from C 
 
 Parallel rays falling upon a concave mirror are 
 reflected as convergent rays; these convergent rays 
 form a focus on the axis of the mirror at a point i^ 
 (Fig. 15), which is called the principal focus. If the 
 
— 17 — 
 
 source of illumination be placed at F, the rays will be 
 
 'reflected parallel. If the source of illumination be 
 
 placed at a, the rays will be focussed at A; if it be 
 
 / Fig. 14. 
 
 placed at A, they will unite at a; these two points are 
 the conjugate foci oi the mirror. C is the "centre of 
 concavity " of the mirror; if the source of the illumina- 
 tion be placed at C, the rays will be focussed at C; 
 the object and image will then be at the same point. 
 If a person look at his face in a concave mirror 
 at a certain distance beyond the principal focus, his 
 features will appear reversed and diminished; at the 
 principal focus they will disappear; within the principal 
 focus, they will appear upright and enlarged. 
 
— i8 — 
 
 Parallel rays falling upon a convex mirror are re- 
 liected as divergent rays; hence they never come to a- 
 focus. If the rays thus rendered divergent be pro- 
 
 FiG. 15. 
 
 longed backward, they will meet at a point F (Fig. 16) 
 on the other side of the mirror, the principal focus. 
 The image is here virtual. 
 
 Fig. i5 
 
— 19 — 
 
 If a person look at his face in a convex mirror, 
 his features will appear diminished and upright; the 
 nearer he approches, the larger they become, while 
 they still remain upright. 
 
CHAPTER III. 
 
 optic Axis. — The optic axis is coincident with a • 
 line drawn through the centre or apex of the cornea 
 backward, impinging on the retina at a point situated 
 slightly to the inner side of the macula lutea. 
 
 Fig. 17. 
 
 The optic axis is represented in Fig. 1 7 by £he 
 line O A. 
 
 Visual Axis. — The visual axis is coincident with 
 a line drawn from the point of fixation (object looked 
 at) to the fovea centralis in the macula lutea. The 
 line V M in Fig. 17 represents the visual axis. 
 
 Nodal Point. — The nodal point is the point of 
 intersection of the optic and visual axis. 
 
 It is situated in the crystalline lens, just in front 
 of its posterior surface. 
 
 In Fig. 17, N is the nodal point, where the lines 
 O A and V M intersect. 
 
 Emmetropia ('er, within, pLBxpov, measure, ''03^, 
 
21 
 
 eye), is that condition of the refraction of the eye in 
 which, when the muscle of accommodation is in a state 
 of rest, parallel rays of light are brought to a focus at 
 the macula lutea. The symbol is E. 
 
 Ametropia {'a, privative, fie'rpov, ''wip) is a gen- 
 eral term, signifying that an eye is not emmetropic. 
 Symbol A. 
 
 Hypermetropia (v'nep, over, beyond, juirpov, 
 "(a>p) is that state of refraction in which, when the ac- 
 commodative muscle is in a condition of rest, parallel 
 rays of light are brought to a focus behind the retina 
 (macula lutea). Symbol H. 
 
 * Myopia {fxvEiv, to close, "a>^) is that state of 
 refraction in which, parallel rays of light are f ocussed in 
 front of the retina (macula lutea), Symbol M. (Fig. i8.) 
 
 A, Emmetropic eye, £, Hypermetropic eye, 
 C, Myopic eye. 
 
 The name Myopia is taken from the fact that near- 
 sighted people often close their eyes slightly in order 
 to lessen the size of the " circles of diffusion " on 
 the retina, thereby gaining a more distinct image of 
 the objects. 
 
 Astigmatism ('«, privative, ffriyjxa, a point) is 
 the condition in which the refraction of the different 
 meridians varies in the same eye. 
 
 * In E, the visual axis, at the cornea lies to the inner side 
 and slightly above the optic axis, forming with it an angle (the 
 " angle a, " Fig. 17) of about 5°. In H the angle a is greater 
 than in E. In M it is smaller, or, at times the visual and optic 
 axes are coincident, or, the "angle a " may even be negative. 
 
One meridian may be emmetropic, the other 
 myopic or hypermetropic — simple myopic astigmatism, 
 symbol As. M. or simple hypermetropic astigmatism. 
 As. H. 
 
 Fig. i8. 
 
 Both meridians may be myopic, one more so 
 than the other, compound myopic astigmatism As. M. 
 + M. ; both may be hypermetropic, one more so than 
 the other, compound hypermetropic astigmatism. As. 
 H. + H. 
 
 One meridian may be myopic and the other 
 hypermetropic, mixed astigmatism. 
 
The symbol As. H. M. is used for this condition 
 when the H. is predominant, the symbol ^s. M. H, 
 when the M. is predominant. Lastly there may be 
 irregular astigmatism which is usually due to irregu- 
 larities ol the cornea from injuries, inflammations, etc., 
 or, it may have its seat, according to some, in the lens. 
 
 Perception of a line. — A line may be considered 
 as composed of an indefinite number of points, ar- 
 ranged longitudinally from which rays proceed in all 
 directions. In order to see a line distinctly, it is 
 necessary that the rays which emerge from the points 
 in planes at right angles to the long axis of the line, be 
 focussed in corresponding planes on, the retina. 
 
 A vertical line is seen through the horizontal 
 meridian of the eye. The horizontal rays proceeding 
 from each point that helps to make the vertical line, 
 pass through the horizontal medium of the eye and 
 are focussed as a point on the retina. Such points 
 being arranged in a vertical series, the vertical line is 
 reproduced.^ A horizontal line is seen through the 
 vertical meridian of the eye. The vertical rays that 
 proceed from the points which go to make up the 
 horizontal line, pass through the vertical meridian and 
 are focussed as points in a horizontal series on the 
 retina. The horizontal line is thus reproduced. If, in 
 any meridian rays are not focussed on the retina, as 
 in As. H. or As. M., " circles of ■ diffusion " will be 
 formed instead of points. The line from which such 
 rays proceed will then be seen indistinctly. 
 
— 24 — 
 
 The Near Point (Punctum Proximum) is the 
 nearest point of distinct vision, /. e. the nearest point 
 for which the eye can accommodate itself. Symbol, P.P. 
 
 It is nearest in childhood and recedes as age ad- 
 vances, on account of the loss of resiliency in the lens 
 and the diminution of the power of the accommoda- 
 tive muscle (Presbyopia). 
 
 The Far Point (Punctum Remotissimum) is the 
 "furthest point of distinct vision." It is constant for 
 a given condition of refraction. Symbol P. R. In 
 order to comprehend fully the significance of the Far 
 Point, the following considerations are necessary. 
 Bearing in mind the definitions of E. H. and M., and 
 the tabulated statements given on page 12, we can 
 "readily understand how rays of light emerge from 
 eyes. Parallel rays are brought to a focus upon the 
 retina (macula lutea of emmetropic eyes); if the lumin- 
 ous point be situated on the retina of such an eye 
 rays from it would emerge parallel. Conferre 3, 
 page 13. 
 
 Fig. 19. 
 The bundles of rays A C and B D emerge from 
 
— 25 — 
 the eye parallel; the image of the retina is therefore 
 not formed at all. 
 
 The furthest point of distinct vision for an em- 
 metropic eye lies, theoretically at infinity. Parallel 
 rays are brought to a focus behind the retina of a 
 hypermetropic eye. If the luminous point be situated 
 on the retina, rays from it will emerge from the eye 
 divergently. Conferre 4, page 13. 
 
 Fig. 20. 
 
 The rays from the points A and B emerge from 
 the eye in two sets of diverging rays which have the 
 appearance of coming from the points a and b, situat- 
 ed behind the retina. The greater the divergence of 
 the emerging rays the nearer to the retina (more 
 properly the nodal point) , will they meet, when pro- 
 longed backward. The points a and b represent the 
 Far Point of a hypermetropic eye. The greater the 
 hypermetropia, then, the nearer will the far point be 
 to the nodal point. The image formed is erect. 
 
 Parallel rays of light are brought to a focus in front 
 
— 26 — 
 
 of the retina of a myopic eye; rays from a luminous point 
 situated on a retina of such an eye will emerge from 
 the eye convergently. Conferre 2, page 13. 
 
 Fig. 21. 
 
 The rays from the points A and B emerge as two 
 sets of converging rays; those from the point A uniting 
 at a, those from the point B uniting at b. The image 
 of the retina is therefore formed at a finite distance in 
 front of the eye and is inverted. The points a and b 
 represent the far point of a myopic eye. The greater 
 the myopia then the nearer is the far point to the eye 
 (the nodal point). 
 
 To sum up: 
 
 jRays emerge from emmetropic eyes parallel, from 
 hypermetropic eyes divergently, from myopic eyes con- 
 vergently. 
 
 Practically, we have to do with the far point only 
 in myopia. 
 
 Myopic people cannot see distinctly beyond their 
 far point; erametropes can see distinctly objects at 
 twenty feet (practically infinity, since rays coming 
 
— 27 — 
 
 from objects at twenty feet are practically parallel); 
 hyperopes also, with the power of accomodation un- 
 diminished, can see distinctly at twenty feet and theo- 
 retically should see better at greater distances than 
 emmetropes. The t^rms far point z.nA near point are 
 used in reference to binocular 'and single vision. 
 
 Anisometropia in the general acceptation of the 
 term is the condition in which the fraction of the two 
 eyes is different in any manner. 
 
 From the etymology of the word, we are inclined 
 to agree with Dr. Noyes, of New York, who thinks 
 that this term should be used only when the two eyes 
 have the same quality of refraction and differ only in 
 degree, i. e., both having H. or M., with more H. or 
 M. in one than in the other. 
 
 Instead of the term anisometropia, to signify that 
 the refraction of the two eyes is simply different, we 
 would suggest the word, Heterometropia* 
 
 *'ETSpoi, in composition signifies "other," "different;" 
 this word seems to us to exactly express the meaning intended. 
 Instead of anisometropia, Dr. Noyes has suggested the word 
 Antimetropia, the Greek prefix 'auri (against), signifies in com- 
 position, *'' opposition," not oppositeness. 
 
CHAPTER IV. 
 
 The ophthalmoscope consists of a plane or a con- 
 cave mirror (when concave, usually of nine inches 
 focal distance), embedded in a metal plate. By means 
 of this mirror, the rays of light are reflected from the 
 source of illumination into the eye. The mirror is 
 pierced centrally by an aperture through which the 
 observer looks. Behind the mirror are arranged 
 glasses, convex and concave, which can be thrown 
 over the aperture by a ratchet. The whole is mounted 
 upon a handle. Two biconvex lenses are usually 
 placed in the case; they may have a focal distance of 
 2, 2^ or 3 inches. 
 
 The rotating glasses should preferably be cov- 
 ered, in order to protect them from injury or dust. 
 The mirror may be either tilting or stationary — here 
 personal preference would seem to be the guide. The 
 tilting mirror is made in the shape of a parallelogram; 
 the area of illumination in the fundus, of course, cor- 
 responds to the shape of the mirror. The stationary 
 mirror is usually round, at times is in the shape of a 
 parallelogram, or a circle with a section lopped 
 off laterally. The convex glasses are arranged on one 
 side of the aperture, the concave on the other. The 
 numbering of the former is usually in white, that of 
 the latter in red. Under each glass the value in inches 
 and dioptrics is placed. In some instruments -^ is 
 
— 29 — 
 
 taken as the value of i D., in others -^. An ophthal- 
 moscope that contains lo or 12 spherical glasses on 
 either side of the aperture furnishes sufficient means 
 for correct diagnosis. 
 
 The accompanying cut shows the "Polyclinic 
 
 Fig. 22. 
 
— 3° — 
 Opthalmoscope," * which we are accustomed to use. 
 We would suggest to the beginner the propriety of 
 obtaining as simple an instrument as possible, within 
 the limitations set above. We have, not infrequently- 
 seen a student thoroughly discouraged by the inability 
 to manage a complicated instrument. 
 
 The older instruments, Liebreich's for instance, 
 are not advisable. 
 
 * This instrument may be obtained of Mr. Ernest Gold- 
 bacher, g8 Fulton street, N. Y. 
 
CHAPTER V. 
 
 We divide the methods of examination with the 
 ophthalmoscope as follows: 
 
 I. Transmitted or Reflected Method, Physical Condi- 
 tion of the Refractive Media. 
 
 r 
 
 (a) Vessel Test. 
 
 (b) Shadow Test or Retiaoscopy. 
 
 Condition of the 
 
 (a) Qualitative 
 and approxi- 
 mately quan- 
 
 refraction oi-l titative. 
 the eye. (b) Quantita- 
 
 tive and 
 (. qualitative. 
 
 2. Oblique Illumination, Inspection of the conjunctiva 
 cornea, aqueous humour, iris, the lens and the anterior por- 
 tions of the vitreous humour. 
 
 3. Indirect Method. — Qualitative and ap- f 
 proximately quantitative determination of the I Condition of 
 refraction. { the fundus 
 
 4. Direct Method. — Qualitative and quan- I oculi. 
 titative determination of the refraction. I 
 
 THE TRANSMITTED OR REFLECTED METHOD. 
 
 In this examination the patient is seated or stands; 
 the source of illumination is on the side corresponding 
 to the eye under examination, in the same plane as the 
 eye and just far enough back for the face to be thrown 
 into the shade. Seated or standing at a certain dis- 
 tance, usually from 12 to 18 inches, the observer 
 places the ophthalmoscope to either eye and, looking 
 through the aperture, casts the rays gathered from the 
 source of illumination into the patient's eye. If the 
 media be clear a more or less reddish reflex is ob- 
 
— 32 — 
 served, corresponding to the size of the pupil. The 
 light being kept upon the pupil, the patient is told to 
 look in all possible directions. 
 
 The Vessel Test and Shadow Test, which we 
 nave made subdivisions of the Transmitted Method, 
 we will treat in chapter VIII. 
 
 THE OBLIQUE ILLUMINATION. 
 
 The source of illumination is on the side corre- 
 sponding to the eye under examination, in the same 
 plane as the eye and slightly in front of it. The rays 
 of light are concentrated upon the eye by means of 
 one of the biconvex lenses (preferably the strongest), 
 contained in the instrument case. The patient is 
 niade to look in all possible directions. 
 
 The vision of the observer may be materially 
 aided by the use of a convex lens held between his 
 eye and that of the patient, so that it may act as a 
 magnifying glass. This lens may be held in the dis- 
 engaged hand or one may use a pair of strong convex 
 eye glasses. By means of this method the conjunc- 
 tivas the cornea, aqueous humour, the lens with its 
 capsules, and the anterior portions of the vitreous 
 humour may be carefully inspected. Artificial illum- 
 ination is preferable, though at times reflected sun- 
 light may suffice. The direct rays of the sun should, 
 of course, never be concentrated on the eye. 
 ^ By means of the first two general methods we 
 convince ourselves of the condition of the media 
 
— 33 — 
 namely, commencing from before backwards, the 
 cornea, the aqueous humour, the lens with its capsules 
 (anterior and posterior), and the vitreous body — at least 
 to the extent of the area of the pupil. Now if there 
 be in any of the media within this area, an opacity, it 
 will stand out in the field of the pupil as a dark spot 
 on the reddish background when the reflected method 
 is employed. Let us suppose that on throwing in the 
 light by this method, we discover the presence of an 
 opacity. We proceed to locate it. 
 
 We exclude the cornea and aqueous humour first 
 by means of the oblique illumination, we can also, by 
 this means, as stated, explore the lens and the an- 
 terior portions of the vitreous body, but for this pur- 
 pose it is generally necessary to have the pu{)il dilated. 
 Suppose we have excluded the cornea and aqueous 
 humour and" have located the opacity in the lens. 
 We must decide whether it be on the anterior capsule, 
 the posterior capsule, or, if in the lens substance, in 
 what portion. 
 
 In order to settle this point let us regard the eye- 
 ball as a sphere, with an anterior pole, a posterior 
 pole and an equator. Within this sphere is placed 
 the lens which may also be considered as a sphere, 
 with two poles (anterior and posterior), and an equa- 
 tor. The lens is fixed in the ball anterior to its equa- 
 tor. Whenever the ball moves the lens moves with 
 it and any point situated on the anterior surface of 
 the lens will move with a corresponding point situated 
 
 4 ' 
 
— 34 — 
 on the anterior surface of the ball; any point on the 
 posterior surface of the lens will move with any corre- 
 sponding point on the posterior surface of the ball. 
 
 Having hypothetically located the opacity in the 
 lens, suppose we find by the reflected method that it 
 moves upward when the eye is, rolled upward, down- 
 ward, when the eye is rolled downward (/. e. moves 
 with the eye), we conclude that the opacity lies anter- 
 ior to the lenticular equator. 
 
 Suppose the opacity moves downward when the 
 eye is rolled upward, and upward when the eye is 
 rolled downward (/. e., against the movements of the 
 ball), we conclude that it must be posterior to the 
 lenticular equator. 
 
 Having in this manner decided that the opacity 
 is anterior or posterior to the lenticular equator, we 
 next proceed to locate it either in the capsule or in the 
 cortical substance. The opacities which occur on the 
 capsules have, as a rule, appearances quite character- 
 istic, and a knowledge of these together with the al- 
 ternate employment of the oblique and reflected 
 methods enables us quite definitely to decide their 
 location. 
 
 The opacities occurring on the capsules are usu- 
 ally anterior and posterior polar cataracts. Anterior 
 polar cataract appears generally as a white spot (by the 
 oblique method), or a dark spot (by the reflected 
 method); or, it may, by the oblique illumination, ap- 
 pear as a whitish pyramid projecting somewhat into 
 
— 35 — 
 the anterior chamber; by the reflected light this latter 
 form would appear as a more or less dark square. 
 Of course there may be other opacities on the an- 
 terior capsule. Posterior polar cataract is generally 
 star-shaped. 
 
 Suppose the hypothetical opacity moves "with the 
 eye; and suppose we have excluded the cornea, 
 aqueous humor and anterior capsule by the oblique 
 illumination, the opacity must then be in the anterior 
 cortical substance by exclusion. A star-shaped opacity 
 in the lens that is seen to move against the movements 
 of the ball may be diagnosed as posterior polar catar- 
 act. 
 
 If there be an opacity in the optical centre of the 
 lens, the so-called axial cataract, there is practically no 
 movement of the opacity when the eye is rolled in the 
 various directions. The points of opacification in 
 progressive lenticular cataract may be found in any or 
 all parts of the lens-substance. 
 
 To sum up: If an opacity moves regularly with 
 the ball, it is either in the cornea or lens, the oblique 
 illumination will exclude the cornea; it may be located 
 in the lens in the way shown above. 
 
 If an opacity moves in a direction opposite to 
 that of the ball, it cannot be in the cornea and is prob- 
 ably in the lens, posterior to its equator.* 
 
 Another medium remains for our consideration, the 
 
 *A fixed opacity of any description in the vitreous body 
 would constitute an exception to the last clause. 
 
_ 36 — 
 
 vitreous humour. If we have discovered an opacity 
 in the media, and the cornea, aqueous humor and lens 
 have been excluded, as its locality, we decide that it must 
 be in the vitreous humour. Opacities in the later 
 usually float; they sweep about in the field of the 
 pupil irregularly, when the ball is moved about. They 
 may have many shapes, may also be fixed, diffuse or 
 circumscribed and may differ in degree of opaqueness. 
 It must be borne in mind that cholesterine 
 particles occur in the vitreous humour. They do not 
 appear dark, but on the contrary, as bright, highly re- 
 fracting particles that dance about at will when the 
 eye is moved. Opacities in the vitreous humour 
 are usually detected by the transmitted method; 
 though when far forward, they may be recognized by 
 the oblique illumination. 
 
CHAPTER VI. 
 
 THE INDIRECT METHOD. 
 
 This method enables us to recognize the quality 
 of the refraction present in an eye, to measure the 
 quantity approximately and to examine the condition 
 of the fundus. The rays of light are reflected into 
 the patient's eye; as they emerge from it they are 
 caught on a biconvex lens, held immediately in front 
 and are focussed in the air between the observer and 
 the patient. 
 
 Fig. 23. • 
 
 The rays coming from A, pass through the bi- 
 convex lens, C, and are focussed at a. The rays 
 coming from B are focussed at b. The rays coming 
 from A and B form then inverted images of A and B 
 in the air. 
 
 The image of the fundus is therefore inverted 
 and the landmarks are found in positions opposite to 
 those they are found to occupy in the anatomical ex- 
 amination. 
 
- 38 - 
 
 The light should be placed on the side cor- 
 responding to the eye examined, in the same plane as 
 the eye and just far enough behind the patient's head 
 to throw the face into the dark. 
 
 The patient should be directed to look over the 
 shoulder of the observer, which is diagonal to the eye 
 under examination, i. e., over his right shoulder 
 for the right eye, over his left shoulder for the left 
 eye. This insures relaxation of the accommodation 
 and a certain degree of dilatation of the pupil; in 
 addition, it brings the optic disc more nearly into a 
 direct line with the pupil, since, in the anatomical 
 position of the parts, the optic disc is slightly to the 
 inner side of the median line. Stress should be laid 
 on making the patient look over the shoulder, and not 
 at it or the ear. We prefer to stand while the patient 
 sits, but for beginners it is perhaps best for both ob- 
 server and patient to be seated. At a distance of i8 
 to 20 inches (arm's length), the observer, looking 
 , through the aperture of the ophthalmoscope, throws 
 the light into the eye; having a good reflex, with the 
 biconvex lens held between his thumb and index 
 finger, and his little or ring finger supported on the 
 forehead of the patient, he brings down the lens into 
 the track of the rays as they emerge from the patient's 
 eye. The lens should not be brought down until the 
 reflejc is observed. When it is lost, the objective 
 should be lifted until it is found again. 
 
 The strict observance of this rule will save a 
 
— 39 — 
 
 world of trouble. Classically, when examining the 
 right eye of a patient, the observer should use his left 
 eye and hand for the instrument, and should hold the 
 objective in his disengaged r^ght. For examining the 
 left eye, the opposite should be done. The majority 
 of surgeons do not observe this rule, but use the right 
 eye and hand always for, the ophthalmoscope. If the 
 upper lid of the patient should droop, as in ptosis, or 
 when he is wearied, it may be lifted by the ring finger, 
 while the little finger is propped against the forehead. 
 
 Theoretically, the objective should be hpld at 
 right angles to the optic axis of the eye. If this is 
 done, however, the reflexes on the anterior and pos- 
 terior substance of the lens, coming together, will dis- 
 turb the vision. The lens may be slightly tilted in 
 order to place an undisturbed space between the two 
 reflexes. (Loring). 
 
 After some experience one becomes able to ignore 
 these reflexes. The beginner usually sees best in this 
 examination, if he be emmetropic, through the aper- 
 ture; when, however, he has acquired the power and 
 habit of relaxing his accommodation, he will find that 
 if a convex glass be turned on behind the aperture, 
 it will improve the vision by magnifying the serial im- 
 age. This method of examination is certainly more 
 difficult to learn than the Direct. It is nevertheless 
 indispensable in the proper examination of the eye. 
 It does away with the unpleasantness often experi- 
 enced in the examination of dispensary patients by 
 
— 4° — 
 
 the direct method. It can be done rapidly, and in 
 many cases, as in high degrees of ametropia (par- 
 ticularly myopia), where the fundus can be seen only 
 indistinctly by the direct method, supplants the latter. 
 
 In regard to the strength of the objective to be 
 used we would say that either one of those contained 
 in the case may be employed; for beginners, the 
 weaker is better, since the image appears larger when 
 seen through this. 
 
 The disc is the point to be looked for. The 
 macula lutea cannot be seen as a rule. 
 
 In emmetropia the disc appears round and of a 
 certain size. As the objective is moved towards and 
 away from the eye, the size and shape of the disc re- 
 mains constant. The optic disc may not be round 
 even in E, for, it may be misshaped anatomically. 
 Under such circumstances, however, it would retain 
 the same shape when the objective is withdrawn. 
 
 Since rays emerge from emmetropic eyes parallel, 
 the image formed will always be at the same distance 
 from the lens and since the " relative sizes of image 
 and objective are as their distances from the lens " 
 (Morton), the size of the image will remain constant 
 when the objective is withdrawn. 
 
 Fig. 24 represents an emmetropic eye from which 
 the rays of light emerge parallel; the focus is formed 
 at the same distance from the lens, at whatever dis- 
 tance the latter is held from the eye. 
 
 In simple hypermetropia, the disc appears larger 
 
— 41 — 
 than in E, but diminishes in size in all meridians 
 equally as the objective is withdrawn. Rapid and 
 marked diminution indicate a high degree of H, slight 
 diminution, a low degree. 
 
 Fn;. 24. 
 
 As the rays emerge from the hypermetropic eye, 
 they have the characteristic of rays that come from 
 objects nearer than infinity, namely, divergence ; since 
 the size of the image in convex lenses is smaller the 
 further the object is removed from the lens (within 
 20 feet), the image of the disc in the indirect method 
 appears smaller in E. than it does in H. ; conversely it 
 appears larger in H. than in E. 
 
 In simple hypermetropic astigmatism the disc dimin- 
 ishes in one meridian as the objective is removed, but 
 remains constant in the other. The astigmatism is in 
 the meridian that decreases. ' The axis of the correct- 
 ing glass would lie at right angles to this. 
 
 In compound hypermetropic astigmatism the disc 
 diminishes in all meridians but more in one than in 
 the opposite; that meridian is more hypermetropic, i. e., 
 astigmatic, in which there is the greater decrease. 
 
— 42 — 
 
 In simple myopia the disc appears smaller than in 
 E., but increases in all meridians equally as the ob- 
 jective is withdrawn. 
 
 Rapid and marked increase indicates a high de- 
 gree of M, slight increase, a low degree. 
 
 Since rays issue from myopic eyes convergently, 
 in passing through a convex lens they will be focussed 
 more rapidly, that is nearer to the lens, than parallel 
 rays would be. The image of the disc is therefore 
 smaller in M than in E. 
 
 In simple myopic astigmatism the disc increases in 
 one meridian as the objective is withdrawn, while it 
 remains constant in the opposite. The astigmatism is 
 in the meridian that increases. The axis of the cor- 
 recting glass would be at right angles to this. 
 
 In compound myopic astigmatism the disc increases 
 in all meridians, but more in one than in the opposite; 
 that meridian is more myopic, /. e. astigmatic, in which 
 there is the greater increase. 
 
 In mixed astigmatism one meridian decreases 
 while the other increases. There is present As. H.M. or 
 As.M.H., accordingly as the H. or the M. predominates. 
 In correction, the convex cylinder would have its axis 
 at right angles to the meridiah in which there was de- 
 crease on withdrawing the lens; the concave 
 cylinder would have its axis at right angles to the 
 meridian in which there was increase; in other words, 
 the axis of the convex cylinder would lie parallel with 
 the myopic meridian, that of the concave cylinder, 
 parallel with the hypermetropic meridian. 
 
— 43 — 
 
 The simple presence of astigmatism may be 
 recognized by oblongness of the disc when the object- 
 ive is held before the eye without being moved. It 
 has been stated what the change in the shape of the 
 disc signifies when the objective is withdrawn. 
 
 We have alfeady demonstrated that the disc re- 
 mains constant in E when the objective is withdrawn. 
 
 An explanation of the cause of increase in M and 
 of decrease in H when the objective is withdrawn, 
 will not be amiss. 
 
 Fig. 25. 
 
 Fig. 25 represents a hypermetropic eye. The 
 rays proceeding from A and B pass out of the eye di- 
 vergently; they are focussed by the lens C, held in 
 front of the eye at a fi. 
 
 Fig. 26 represents the sarrle eye with the same 
 lens held at a greater distance from the far point, a-b, 
 situated behind the eye; the focus is here formed at a yS 
 which is nearer to the lens than in the preceding 
 figure. The formula previously given for finding the 
 
— 44 — 
 distance of the image from convex lenses will serve us 
 here. 
 
 Fig. 26. 
 
 Suppose our objective has a focal distance of two 
 inches and it is held four inches in front of the far 
 point of a hypermetropic eye, in the track of the 
 diverging rays. What is the distance of the image 
 from the lens ? 
 
 i_i i- = — • X— + inches. 
 
 X 2 4 4 ■ 
 
 Suppose the objective be removed to the distance 
 of 8 inches from the far point. To find X : 
 
 2- = ± — J- = l. • X-— 2?^ inches. 
 X 2 8 8 • • 3 
 
 " The ratio of the distance of the image from the 
 lens as compared with that of the object from the lens" 
 is less in the second case (2| : 8) than in the first (4:4)- 
 In hypermetropia, then, the disc diminishes as the 
 objective is withdrawn. 
 
 Fig. 27 represents a.myopic eye from which the 
 rays A and B emerge convergently, forming an inverted 
 
— 45 — 
 aerial image at a /3 the far point. This latter we 
 must now regard as the object. It is of this object that 
 we obtain a final image b a, by means of the bi-convex 
 lens C. 
 
 Fig. 27. 
 
 Since the image and object are on the same side 
 of the lens, the formula for finding the distance of the 
 image from concave lenses, will serve us here: 
 
 X b T^ a 
 
 Suppose our objective is a 2 inch lens and we 
 hold it 8 inches from the far point, in the track of the 
 convergent rays; what is the distance of the image from 
 the lens? 
 
 = ^ + ^-i.-. X 
 
 T^ inches. 
 
 Suppose now we carry the objective further from 
 the eye and hold it 4 inches from the far point. To 
 vfind X 
 
 A = i + 2-_i- • X— iJ^ inches. 
 X 2 4 4 ■ ■ '^ 
 
 "The ratio or the distance of the jmage from the 
 
— 46 - 
 
 lens as compared with that of the object from the lens " 
 is greater in the second case (i|-:4) than in the first 
 
 (If- 8) 
 
 In myopia, then, the image increases as the objec- 
 tive is withdrawn from the eye. 
 
 ■ ,( 
 
CHAPTER VII. 
 
 THE DIRECT METHOD. 
 
 By this method we are enabled to determine the 
 quality and quantity of the refraction present in an 
 eye and to examine the condition of the fundus. The 
 patient and surgeon may be seated or standing ac- 
 cording to circumstances or preference.' The light 
 should be on the side, corresponding to the eye under 
 examination, in the same plane as the eye and just far 
 enough back to throw the face into the shade. It is 
 often advantageous, especially in the case of children, 
 to steady the head with the disengaged hand. 
 
 The surgeon should be slightly to that side of the 
 patient which corresponds to the eye under examina- 
 tion. The patient should look straight out into dis- 
 tance or slightly towards the opposite side, in order to 
 relax the accomodation, dilate the pupil and bring the " 
 disc into a line with the later. The surgeon places 
 the ophthalmoscope to his eye — corresponding to the 
 eye under examination, and, looking through the 
 aperture, throws the light into the patient's eye. It is 
 best to commence this examination -at a distance of 
 lo or 12 inches. Having the red reflex distinctly, the 
 observer approaches as near as possible, still keeping 
 the light in the pupil and preserving the red reflex. 
 The moment this is lost, it should be regained, before 
 attempting to proceed further. The usual distance at 
 
_ 48 — 
 
 which the fundus is viewed in this examination is one 
 or two inches. In order to render the chances of ac- 
 commodating on the part of the surgeon and patient, 
 least, it is well for both to become as comfortable as 
 possible in their positions before commencing the ex- 
 amination. We have often observed, particularly in 
 our own case, that one frequently falls short of the 
 exact diagnosis, when in an uncomfortable position. 
 
 For the examination of the right eye, then, the 
 observer should close his right eye, hold the instru- 
 ment in his right hand and sit or stand slightly to the 
 right of the patient. In examining the left eye, the 
 opposite should be done. The index-finger should 
 always be placed upon the ratchet or wheel so that 
 the glasses may be turned on without taking the in- 
 strument from the eye. For our part, we prefer to 
 stand, but, at times, it is far better to sit, as in the 
 case of children or when it is desired to make a draw- 
 ing of the fundus. 
 
 This method of examination may be used with 
 great advantage for the minuter examinations of the 
 vitreous body, lens or even cornea, by turning on strong 
 convex lenses over the aperture. 
 
 In order to obtain an absolutely correct knowledge 
 of condition of the refraction, neither the patient nor 
 the observer should accommodate, and in addition, the 
 latter should be emmetropic or rendered so, if ame- 
 tropic. 
 
 As a practical matter we cannot eliminate accom- 
 
— 49 — 
 modation entirely either on the part of the surgeon or 
 patient. If there be no doubt that the patient is ac- 
 commodating strenuously, this element of error should 
 be eliminated by a mydriatic. Continuous practice is 
 the only means by which the muscle of accommodation 
 can be gotten under the control of the will. 
 
 • If the observer, being emmetropic or rendered so, 
 looks through the aperture of the instrument and sees 
 the fundus distinctly, the patient is either hyperme- 
 tropic or emmetropic, the weakest convex -(-(-) glass 
 should now be turned on; if the fundus does, not ap- 
 •pear as distinct as without the glass, the patient is 
 emmetropic; if the fundus appears equally as distinct 
 as through the aperture, the patient is hypermetropic 
 and the strongest convex glass through which the 
 fundus is seen distinctly, minus the distance between 
 the patient's and the observer's eye is the measure of 
 the hypermetropia manifest by the ophthalmoscope. 
 From the above it may be concluded that if the 
 fundus is seen distinctly by an emmetropic observer 
 looking through the aperture, myopia is out of the 
 question. 
 
 If an emmetropic observer cannot see the fundus 
 distinctly, there is probably myopia. 
 
 There may be hypermetropia, in which case -the 
 observer either cannot overcome the divergence of the 
 rays of light as they emerge from the patient's eye or 
 will not overcome it; in other words, intentionally 
 relaxes his accommodation. 
 
— 5° — 
 
 (It is possible also for the observer or the patient, 
 separately or together, to so accommodate, that the 
 fundus is rendered indistinct. This last possibility, 
 we will lay aside for the sake of clearness.) 
 
 If the w'eakest convex glass render the vision 
 more indistinct, while the weakest concave glass ren- 
 ders it more distinct, there is myopia, and the weakest 
 concave through which the details of the fundus are 
 seen distinctly //«j-, the distance between the surgeon's 
 and the patient's eye is the measure of the myopia 
 present. 
 
 Fig. 28. 
 
 Fig. 28 represents two emmetropic eyes in a state 
 of rest; the rays from a emerge from the eye parallel, 
 and passing into the opposite eye, are focussed at b. 
 A clear image of a is then formed on the retina of 
 the observing eye at b. A convex glass interposed in 
 the track of the parallel rays would obviously bring 
 the rays to a focus before they reached the retina of 
 the observing eye. 
 
 Fig. 29 represents two eyes, an emmetropic E 
 and a hypermetropic H. Rays coming from a in the 
 
— 51 — 
 hypermetrppic eye H, emerge divergently, as if they 
 came from'R, the far point. The convex lens L ren- 
 ders them parallel, so that they are brought to a focus 
 at b, situated on the retina of the emmetropic eye E. 
 If the lens were not interposed, and the emmetropic 
 
 Fig. 2g. 
 
 eye E remained in a state of rest, the focus would be 
 formed behind the retina of the latter eye. The con- 
 vex lens must be y«j^ strong enough to render the diver- 
 gent rays parallel. If it be too weak to do this, the 
 entering rays will still be divergent, and the observing 
 eye would either see indistinctly or would have to use 
 the muscle of accommodation to obtain distinct vision. 
 The strongest convex glass, then, with which the fun- 
 dus is seen distinctly is the measure of the H in a 
 given case. 
 
 Fig. 30 represents two eyes, an emmetropic E 
 and a myopic M. Rays coming from a in the myopic 
 eye M emerging convergently, woujd come to a focus 
 at R, the far point, if the eye E were not interposed 
 The concave lens L gives the convergent rays exact 
 
_ 52 — 
 
 parallelism, so that they are focussed at b on the retina 
 of the emmetropic eye. 
 
 Fig. 30. 
 
 If the lens L be too weak to give the convergent 
 rays parallelism, the observing eye will still see the 
 fundus of the myopic eye indistinctly, for the entering 
 rays, being still convergent, will be focussed in front 
 of the retina. If the lens L be so strong as to give 
 the convergent rays divergence, the fundus of the ob- 
 served eye will be seen indistinctly, if the accommo- 
 dation of the observing eye be relaxed, for then the 
 focus would be formed behind the latter's retina; it 
 may be seen distinctly, however, if the observer use 
 the requisite amount of accommodation. The weakest 
 concave glass, then, with which the fundus is seen dis- 
 tinctly is the measure of the M'm.z. given case. 
 
 We have spoken thus far of simple or spherical 
 error; we come on now to the consideration of astig- 
 matism. 
 
 In the following the surgeon is assumed to be 
 emmetropic (See "Perception of a Line," p. 23.) 
 
— 53 — 
 
 SIMPLE HYPERMETROPIC ASTIGMATISM. 
 
 If the vessels of the vertical meridian, let us say, 
 are seen distinctly through the weakest convex glass, 
 while the horizontal vessels are rendered indistinct, by 
 it, there is AS. H. in the horizontal meridian. The axis 
 of the correcting glass would lie vertically. 
 
 COMPOUND HYPERMETROPIC ASTIGMATISM. 
 
 If the vessels of the vertical meridian can be seen 
 
 distinctly through a convex glass of a certain strength, 
 
 while those of the opposite meridian, the horizontal, 
 
 can be seen through a stronger ^convex glass, there is 
 
 'as. H., + H. 
 
 The excess of error is at right angles to the hori- 
 zontal meridian, i.e., in the vertical meridian. The 
 axis of the correcting cylinder would lie horizontally. 
 
 SIMPLE MYOPIC ASTIGMATISM. 
 
 If the vertical vessel can be seen distinctly through 
 the aperture, while the horizontal vessel can be seen 
 distinctly only through a concave glass, there is myopia 
 in the vertical meridian. In order to exclude hyper- 
 trophia in the horizontal meridian, it would be neces- 
 sary to turn on the weakest convex glass; if this 
 renders the vertical vessels less distinct, there is em- 
 metropia in the horizontal meridian. The case would 
 then be oiie of AS. M. in the vertical meridian. 
 
 The axis of the correcting cylinder would lie hori- 
 zontally. 
 
— 54 — 
 
 COMPOUND MYOPIC ASTIGMATISM. 
 
 If the horizontal vessels can be seen distinctly 
 only through a concave glass of a certain strength, 
 while the vertical vessels can be seen distinctly only 
 through a stronger concave glass, there is AS. M. -|- M., 
 The excess of error lies in the horizontal meridian. 
 The axis of the correcting cylinder would lie verti- 
 cally. 
 
 MIXED ASTIGMATISM. 
 
 If the vessel of the vertical meridian can be seen 
 distinctly only through a concave glass, while those of 
 the horizontal can be seen distinctly through a convex 
 glass, there is AS.M.H., or AS.H.M., accordingly as the 
 M.' or the H. predominates. 
 
 The axis of the concave cylinder would lie verti- 
 cally; that of the convex cylinder, horizontally. 
 
 The measurment of the degree of astigmatism is 
 subject to the same rules as the measurment of spheri- 
 cal errors. 
 
 It will be observed, by reading the foregoing, that 
 the axis of the correcting cylinder should always bt laid 
 parallel with that meridian, which is found to be astig- 
 matic by the Direct Method. 
 
 At times it is necessary to measure the refraction 
 of the eye at various points on the fundus, as for ex- 
 ample, in the measurement of the depth of an excava- 
 tion of the disc or of the extent to which a tumour pro- 
 jects into the vitreous humour. In the case of an 
 
— 55 — 
 excavation of the disc the measurement of the edge 
 should first be taken, then that of the bottom. In the 
 case of a tumour, the refraction at its apex or forward 
 limit should be estimated; then the refraction at its 
 base. The difference between the two measurements 
 would give us, in the first case, the depth of the ex- 
 cavation, in the second, the extent of the projection 
 of the tumour. 
 
 In E. the details of the fundus are bright, dis- 
 tinct and magnified. 
 
 In H. one is struck by the fact that the details 
 of the fundus stand out with remarkable brilliancy 
 and distinctness (if accommodation be used sufficient- 
 ly) ; the disc and vessels are sharply and clearly cut 
 and appear smaller, than in the emmetropic eye; they 
 seem to be removed to a distance backward; in fact,' 
 one gets the impression of looking through a concave 
 glass. The area of the field seen is smaller than in E. 
 These features are often enough for an expert to base 
 the diagnosis upon, or at least are enough to war- 
 rant a reasonable suspicion of the refractive con- 
 dition present. 
 
 In M. the fundus appears indistinct, nor can any 
 effort of accommodation on the part of the emmetropib 
 observer render it less indistinct. When the disc and 
 vessels can be made out, they appear much larger that, 
 in E. The area of the field seen is greater than in H. 
 The field of vision in all cases, however, depends 
 primarily upon the size of the pupil of the person un- 
 der examination. 
 
-56- 
 
 We have spoken in the foregoing of the distance 
 between the eye of the surgeon and that of the pa- 
 tient. We should more strictly speak of the distance 
 between the " nodal points " of the two eyes. In M. 
 we have stated that this distance is added to, in H. sub- 
 tracted from the measure found at the distance of the 
 observer. 
 
 If the eye under observation be hypermetropic 
 the rays will emerge from it divergently, vid. Fig. 20. 
 An emmetropic eye in a state of rest cannot focus such 
 rays on its retina. Hence by means of a convex lens 
 the divergent rays must be rendered parallel. 
 
 Suppose the H. in a given case equals \. The 
 far point of such an eye lies 8 inches behind its nodal 
 point. If the glass could be placed at the nodal point 
 of thW observed eye a + ^ would render the divergent 
 rays parallel. If the measurement be made two inches 
 in front of the nodal point, the distance from the far 
 point would be (8 -|- 2 =10) 10 inches, and it would, 
 require a plus ^ to render the divergent rays parallel ; 
 10 — 2 ^ 8 ^ -J^ strength.* Hence the refraction of 
 a hypermetropic equals the strongest convex glass 
 through which the fundus is seen distinctly minus the 
 distance of the correcting glass from the nodal point 
 of the observed eye. , 
 
 If the eye under observation be myopic, rays will 
 
 *The addition and subtraction must be made in integers, 
 since the fraction is only the expression of the strength. 
 
— 57 — 
 emerge from it convergently, vide Fig. 21. An emme- 
 tropic eye receiving these rays will not be able to 
 focus them upon its retina, since such an eye in a 
 state of rest is f ocussed for parallel rays only. Hence 
 by means of a concave lens the convergent rays must 
 be rendered parallel. Suppose the observed eye is 
 myopic to the extent of ^. The far point of such an 
 eye lies at the distance of 6 inches in front of the 
 nodal point. If the surgeon could place the correcting 
 glass at the nodal point of the observed eye, a minus 
 ^ would render the convergent rays parallell. But 
 this is practically impossible. Two inches is the usual 
 distance at which the measurement is taken. This 
 would place the surgeon two inches nearer the far 
 point of the observed eye, z. e. 4 inches from it, 
 (6 — 2=4) and a ^ would be required to render the 
 rays at this point parallel; 4-]- 2=6=^ strength. 
 Hence the refraction of a myopic eye equals the weak-^ 
 est concave glass through the fundus is seen distinctly 
 plus the distance of the correcting glass from the 
 nodal point of the observed eye. 
 
CHAPTER VIII. 
 
 THE VESSEL TEST— THE SHADOW TEST. 
 
 The Vessel Test, it will be remembered, together 
 with the Shadow Test, Retinoscopy, we have includ- 
 ed under the head of the Reflected Method. 
 
 By means of the Vessel Test we are able to tell 
 the quality of the refraction in a given case; approxi- 
 mately, also, the quantity. The light should be so 
 placed that the face of the patient is thrown into the 
 dark. 
 
 The surgeon should sit or stand at a distance 
 usually, of i6 or i8 inches. Looking through the 
 aperture of the instrument he throw's the light into 
 the patient's eye. 
 
 If emmetropia be present, while the reflex is 
 bright, the vessels of the fundus will not be seen. A 
 glance at fig. 31 will explain this. The rays from the 
 two points, m and n situated on the retina, emerge 
 from the eye parallel, but since the two bundles of 
 rays cross each other on their way out, they finally 
 diverge so widely, that an eye placed at A receives 
 none of them. 
 
 Now it must be borne in mind that such bundles 
 of rays proceed from all points on the fundus, so that 
 though many rays are received, not enough are caught 
 to make a distinctiimage. In H, the vessel can be 
 
— 59 — 
 seen. If the surgeon move his head, holding the 
 mirror stationary before his eye, and the vessels be 
 found to move with his head, H, is present. 
 
 Fig. 31. 
 
 In M. also the vessels can be seen. 
 
 If the surgeon move his head and the vessels be- 
 seen to move in a direction opposite to that of his head, 
 M. is present. 
 
 If the case be one of a very high degree of ame- 
 ti^opia, the vessels are not seen at the usual distance 
 and the reflex appears indistinct and dim. This en- 
 ables us to make an approximate estimation of the de- 
 gree of A present in a given case. 
 
 If it be a case of a high decree of H, the rays 
 diverge so rapidly on emerging from the eye, that at 
 the usual distance, only ^ few are caught by the ob- 
 server's eye. 
 
 If it be a case of a high degree of M., the rays 
 
— 6o — 
 
 converge so rapidly on emerging that a focus is found 
 very near the patient's eye; from this point the rays 
 diverge with such rapidity that practically the same 
 thing takes place as in a high degree of H. 
 
 Let it be remembered that the image seen in 
 myopia is an aerial and inverted one (when the sur- 
 geon is beyond the far point) ; that in hypermetropia 
 it is upright and apparently behind the eye. 
 
 If the surgeon get within the far point of a my- 
 opic eye, the vessels will not be seen distinctly, if the 
 observer be emmetropic, unless he use a concave 
 glass. 
 
 Very slight degrees of A can not be detected by 
 this means of examination with the usual ophthalmos- 
 copic mirrpr. 
 
 It is taught by some that simple, compound and 
 mixed astigmatism may be diagnosed by the vessel 
 test. We deem this practicable only for the most con- 
 summate experts. 
 
 Irregular lenticular astigmatism may be recog- 
 nized by the vessel test. 
 
 "Instead of the vessels moving regularly and 
 evenly, they move slowly across the centre of the 
 pupil, but rapidly and irregularly toward the peri- 
 phery, giving the appearance of rotating bent spokes 
 of a wheel." , 
 
 • In irregular corneal astigmatism, the characteristic 
 facets appear darker than the surrounding normal 
 cornea, owing to the fact that their refraction is dif- 
 
— 6i — 
 
 ferent from that of the latter. This last form of 
 irregular astigmatism may also be easily recognized 
 by the oblique illumination. 
 
 THE SHADOW TEST OR RETINOSCOPY. 
 
 This method has been erroneously termed kerato- 
 scopy. 
 
 As a qualitative and quantitative method of deter- 
 mining the condition of the refraction of the eye, it is 
 of undoubted value. 
 
 Its adoption has been slow upon the European 
 continent and especially in this country, while in Eng- 
 land it is popular and universal. 
 
 The following well-known and simple experiment 
 will enable us to understand the behavior of the deter- 
 mining elements in retinoscopy, viz.: light and 
 shadow. 
 
 If rays of light be reflected from a concave mirror 
 upon a screen placed beyond its focus, they will ar- 
 rive at the screen in divergence. 
 
 Fig. 32. 
 
— 62 — 
 
 A convex lens may now be interposed in the track 
 of these divergent rays and a perfectly distinct image 
 of the source of the illumination may be formed on the 
 screen, e, fig. 32. 
 
 The image will be upright, since the rays have 
 been focussed twice, once in the air at the focal point 
 of the concave mirror, as an inverted image, a second 
 time on the screen, as the reverse of the inverted, 
 namely, an upright image. When the lens is held 
 so as to make the image perfectly distinct, the illum- 
 ination will be brightest and there will be around the 
 image a sharply defined dense shadow whose edge 
 will more nearly approach a straight line. If now the 
 lense be moved either towards or from the screen or 
 the screen towards or from the lens, the image will 
 not be distinct, the illumination will appear less bright, 
 the shadow less dense and its edge more curvilinear, 
 since " circles of diffusion " will be formed upon the 
 screen, d. f. (fig. 32). 
 
 If now the mirror be turned on its vertical axis, 
 to the right or the left, or upon its horizontal axis, 
 from above downward or the reverse, it will be seen 
 that the light and shadow move against the mirror. 
 The movement of the light and shadow will be the 
 same in whatever direction the mirror be tilted. The 
 media of the eye are represented in the above by the 
 lens, the retina by the screen. In fig. 32, e represents 
 the retina of an emmetropic, d that of a hypermetropic, 
 /, that of a myopic eye. 
 
- 63 - 
 
 We speak of the movement of the shadow; we 
 should speak more properly simply of that of the 
 light, since the shadow is an absence of the light. . 
 
 As custom and want have sanctioned " shadow," 
 we will use it in the following. 
 
 The light is placed over the patient's head and 
 far enough back to throw the face into the shade. 
 The patient is directed to look over that shoulder of 
 the surgeon which is diagonal to the eye under ex- 
 amination. If the patient be under the influence of 
 tropine, we may get the refraction at the macula 
 lutea, by making the patient look into our face. When 
 atropine has not been employed, we can not hope to 
 get the refraction at the macula, and must content 
 ourselves with taking it at the disc. The reasons for 
 making the patient look over the shoulder have been 
 sufficiently explained. 
 
 The surgeon sits or stands at a distance of about 
 48 inches, and uses a concave mirror, generally, of 
 nine inches focal distance. 
 
 If the A be of a very high degree, the surgeon 
 must be nearer than the regular distance, 48 inches, in 
 order to see the movement of the shadow distinctly. 
 
 The light is thrown into the patient's eye, and the 
 the mirror is rotated in all directions, vertically, hori- 
 zontally, obliquely. 
 
 As the ophthalmoscope is tilted, a shadow is ob- 
 served to creep from under the iris at the periphery pf 
 the pupillary field, and to pursue a definite course in 
 the latter. 
 
- 64 — 
 
 The movement of this shadow, as compared with 
 the movement of the mirror, furnishes the means of 
 determining the refraction. 
 
 If the shadow move against the. mirror, there may 
 be hypermetropia, emmetropia, or a low degree of 
 myopia. 
 
 If the shadow move with the mirror, there is 
 myopia. 
 
 We have seen in the experiment with our screen 
 and candle that the direction of the shadow is always 
 against the movement of the mirror, whether the screen 
 be held at e, d, or f (Fig. 32). Now as e is situated at 
 the principal focus of the lens, rays coming from this 
 point will pass through the lens and emerge parallel; 
 as d is situated within the principal focus, rays coming 
 from this point will emerge from the lens divergently; 
 as/ is situated beyond the principal focus, rays com- 
 ing from this point will emerge from the lens con- 
 vergently, but their convergence will be so slight that 
 they will unite behind the eye of the observer who is 
 presumably at the distance of 48 inches. These rays 
 are practically the same as divergent or parallel rays 
 since the observer is within their focus. The move- 
 ment of the shadow is the same then in H, E, and M, 
 which is less than ^. If now the myopia be so great 
 that the focus (far point) lies between the surgeon and 
 the patient; the movement of the shadow will be re- 
 versed, /. e. it will move with the mirror. 
 
 In myopia three images are formed when retinos- 
 
- 6s - 
 
 copy is used; first the inverted image of the light 
 formed at the focus of the concave mirrdr, then the 
 upright image in the eye, and finally the inverted 
 image again, in the air. 
 
 We have spoken thus far of H. and M. in general 
 terms. It is necessary, however to " differentiate " 
 simple or spherical errors from meridional errors, 
 and in case of astigmatism to " differentiate " the 
 various kinds. 
 
 We have already shown that in E. the illumina- 
 tion is brightest, the shadow is densest, and that the 
 latter's edge most nearly approaches a straight line; 
 that in ametropia, the illumination is dim, the shadow 
 less dense and the latter's edge is curvilinear in direct 
 proportion to the degree of ametropia. 
 
 There is still another determining element, the 
 rapidity with which the shadows move. 
 
 In emmetropia, the far point lies at infinity; in 
 myopia, at a finite distance in front of the eye; in 
 hypermetropia, at a finite distance behind the eye. 
 
 The higher the degree of H or M, the nearer is 
 the far point to the nodal point. 
 
 Fig. 33 represents a myopic eye. Let a line be 
 drawn from A, a luminous point on the retina, through 
 the nodal point B to C. 
 
 Since the eye is myopic, an inverted image of 
 A. is formed somewhere on this line, let us say at C. 
 The higher the degree of M., the nearer will the image 
 (far point) be to the nodal point. Let us assume, 
 
 6y 
 
— 66 — 
 
 then, that there is another far point at D. When the 
 mirror is tilted from M to M', C and D move through 
 arcs' of circles; D moves to d and C to c, each moves 
 through its respective arc in the same time; since C's 
 
 Fig. 33. 
 
 arc is greater than D's, C must move the faster — con- 
 versely, D moves more slowly than C. 
 
 Fig. 34. 
 
 Fig 34 represents a hypermetropic eye. The 
 image is situated behind it. We assume, as above, the 
 presence of two far points, one at C, the other at D. 
 
— 67 - 
 
 When the mirror M is moved to M', C moves to c 
 and D to d; each moves through its respective arc in 
 the same time; since C's arc is greater than D's, C 
 must move the faster. In each case D has been 
 nearer to the nodal point than C. The slower the 
 movement of the shadow, then, the greater the degree 
 of the ametropia. Since the far point of an emme- 
 tropic eye lies at infinity, the shadow moves with the 
 greatest degree of rapidity in E. 
 
 The characteristic appearance in this latter condi- 
 tion has been described by one writer as "irregular 
 play of light and shadow." 
 
 In teaching we describe the movement of the 
 shadow in E. as a flitting movement. 
 
 If the shadow move with equal rapidity in all 
 meridians, there is simple myopia, hypermetropia, or, 
 emmetropia. 
 
 The significance of the direction of the shadow 
 has been given. The " differentiation" between H., E. 
 or a low degree of M. will be given presently. In astig- 
 matism the same general rules obtain. If, for instance, 
 the shadow move with the mirror in the vertical 
 meridian, there is M in this meridian; if it move in the 
 , opposite direction in the horizontal meridian, there 
 may be in this H., E., or a low degree of M. If the 
 shadow move with the mirror in each meridian, but 
 more slowly in one, with greater curvature of its edge, 
 and with less illumination than in the other, there is 
 compound myopic astigmatism and the astigmatism is 
 
— 68 — 
 
 in that meridian along which the shadow moves more 
 slowly, with less illumination and with greater curva- 
 ture of its edge. 
 
 If the shadow move against the mirror in each 
 meridian, but with greater curvature of its edge, less 
 illumination and more! slowly in one than in the other 
 there is probably coiiipound hypermetropic astigmat- 
 ism. 
 
 There is certaihly H. in the meridian along which 
 the shadow moves more slowly but there may in the 
 other H., E., or a low degree of M., as we have shown. 
 
 If the shadoikr move against the mirror in one 
 meridian and with it in the opposite, we certainly 
 have M. in one and perhaps H. in the other /. e. mixed 
 astigmatism. But we must exclude E. and a low de- 
 gree of M. from that meridian along which the shad- 
 ows move against the mirror, before we can make an 
 absolutely certain diagnosis. A little experience will 
 enable anyone to recognize the characteristic flit of 
 emmetropia. As a practical matter, then, when we 
 see a shadow that has not this flit but rather a well 
 defined movement against the mirror, we may con- 
 clude in favor of H. 
 
 If the astigmatism be vertical or horizontal, the 
 shadow of the vertical meridian will be seen when 
 the mirror is rotated on its horizontal axis, the 
 the shadow of the horizontal meridian will be seen 
 when the mirror is rotatated on its vertical axis. 
 
 If the astigmatism be oblique, the shadow will 
 
- 69 - 
 
 always be oblique, it matters not in what direction 
 the mirror is tilted. A glance at Fig. 35 will ex- 
 plain this: 
 
 Fig. 35. 
 
 Let us place obliquely behind the circle, which 
 represents the pupil, an oval piece of card, to re- 
 present the light or shadow on the retina. If we 
 move the card across the circle in the direction OD, 
 it will have the appearance of moving in the direc- 
 tion OC, which is at right angles to its edge. The 
 oblique edge of the shadow is due to the shape of 
 the image on the retina and not to the direction 
 of the movements of the mirror. 
 
 We come now to the differentiation between H, E, 
 and low degrees of M when the shadow moves against 
 the mirror. For this purpose the patient should put 
 on a spectacle frame. If -|-.s D (^^) placed in the 
 spectacle frame before the patient's eye, reverse the 
 shadow, /. e., make it move with the mirror, there is a 
 low degree of M present. To illustrate, suppose the 
 patient is -^ myopic, if the observer stand at the dis- 
 
— 70 — 
 
 tance of 48 inches, the far point of the patient's eye is 
 32 inches behind his head (80 — 48 = 32). If + -^ 
 be added to the degree of the patient's myopia, the far 
 point is brought to 40 inches from the latter's ' eye. 
 The observer standing at the distance of 48 inches, 
 sees the movement of M. 
 
 But suppose that -j- ^ does not reverse the 
 shadow, that it still moves against the mirror; under 
 these conditions we assume that there is no myopia, or 
 if present, that it is so insignificant as to require no 
 correction. 
 
 We next proceed to the exclusion of either H or E. 
 If -f- tD {^) placed before the patient's eye reverse 
 the shadow, emmetropia is present. 
 
 It is evident that .sD {■^) will not reverse the 
 shadow, if E be present, since this glass will render 
 an emmetropic eye artificially myopic to the extent of 
 only ^; the far point under such a condition would 
 be behind the observer's head, li -\- -^ he added to 
 an emmetropic eye, its far point would lie at 40 inches, 
 since the eye is rendered this much artificially myopic. 
 Under such a condition the surgeon being at a dis- 
 tance of 48 inches would observe the movement of M. 
 
 It is evident then that, if neither .5D nor iD re- 
 verse the shadow, H must be present. 
 
 In making an approximately quantitative deter- 
 mination of the refraction of a given case we may 
 sum up: 
 
 The less brilliant the illumination, the slower the 
 
— 7' — 
 movement of the shadow and the more curvilinear 
 (" crescentic ") its edge, the higher the degree of A. 
 
 In astigmatism, that meridian is astigmatic along 
 which the shadow moves. 
 
 For the exact quantitative determination of the 
 refraction, the spectacle frame, placed on the patient, 
 should again be used. 
 
 In myopia the weakest concave glass which reverses 
 the movement of the shadow is practically the 
 measure. 
 
 But we have shown that with .5 D of M, the 
 shadow will move against the mirror; for the sake of 
 greater accuracy then, — .5 D should be added to the 
 first glass which reverses the shadow in m. 
 
 In hypermetropia, practically, the' strongest con- 
 vex glass with which the shadow still shows the move- 
 ment of II., g\ve.& the measure. If, however, we add 
 glasses till the movement is reversed, we should sub- 
 tract / Z>. from the first glass that reverses the move- 
 ment. The reason of this will be clear, if the preced-" 
 ing differentiation be borne in mind. 
 
 In correcting astigmatism the axis of the cylinder 
 must be placed at right angles to the meridian along which 
 the shadow moves. 
 
 In correcting A S.H. + H. or AS. M. + M, the 
 meridian of less error should be first corrected by an 
 appropriate spherical glass, the other meridian after- 
 wards by the appropriate cylindrical glass. 
 
 In correcting mixed astigmatism, two cylinders 
 
— 72 — 
 
 may be used with their axes at right angles to each 
 other, or one meridian may be corrected with a spheri- 
 cal glass; this would obviously increase the error in 
 the opposite meridian, which might then be corrected 
 by the appropriate cylinder, as in the functional ex- 
 amination. 
 
 If a plane mirror be used, the movements of the 
 shadow will be reversed, that is, it will move with the 
 mirror in H., against it in M., while the other signs re- 
 main unaltered. 
 
 In the determination of the refraction of the eye 
 with the ophthalmoscope, it must be remembered that 
 accommodation on the part of the patient will cause 
 incorrect results to be obtained. An emmetropic eye ' 
 may appear myopic, a myopic, more myopic; a hyper- 
 metropic eye may accomodate so as to appear just 
 emmetropic, or may appear to a high degree myopic. 
 Thoroughly accurrate results cannot be obtained un- 
 less the accommodation be eliminated. 
 
 In the direct method, the accommodation of the 
 surgeon also comes into play, and if he be young, it is 
 quite improbable that he entirely relaxes it. 
 
 In retinoscopy, the stimulation to accommodation, 
 both on the part of patient and surgeon, is least; the 
 patient looks into the distance and fixes no object; 
 the surgeon is at a considerable distance from the pa- 
 tient, and has to look only through the aperture of 
 the instrument, no convex or concave glasses are 
 placed before his eye, and accommodation on his part 
 
— 73 — 
 will not mark the results. It seems to us that this 
 much is enough to commend retinoscopy. Moreover, 
 in a certain class of patients, young children, ignorant 
 and foolish people, and idiots, from whom one can get 
 no answer at all, or, at best, an uncertain one, in, the 
 functional examination, retinoscopy is, in our opinion, 
 of peculiar advantage; indeed, preferable to the direct 
 method. 
 
 We are not unaware that many American surgeons, 
 of the highest repute, depreciate this method of exam- 
 ination. The late Dr. Loring, of New York, who, per- 
 haps, wrote the best book in English on the refraction 
 of the eye, states that the method has never proved of 
 any value in his hands. The majority of the glasses 
 prescribed at Moorfield's Hospital, London, are de- 
 termined by retinoscopy. That the method is not 
 difificult to learn has been attested by the rapidity with 
 which students, working at our clinic, in the New 
 York Polyclinic, have acquired it, learning it far more 
 rapidly than either the direct or indirect method. 
 
 We do not hold that it or any other single method 
 of examination should be employed to the exclusion of 
 others, but we do hold that it is preferable in many 
 cases and of advantage in all. 
 
CHAPTER IX. 
 
 MYDRIATICS. 
 
 At times the pupils are so small that even in the 
 dark room sufficient light is not admitted to get a clear 
 or satisfactory view of the fundus. At times, also, it is 
 necessary to eliminate the accommodation, as we have 
 seen. For simply dilating the pupil without reference 
 to paralyzing the accommodation, a 2-per-cent. or 
 4-per-cent solution of cocaine hydrochlorate is highly 
 to be recommended. Formerly, gelatine discs of 
 homatropine were much used, or a weak solution of 
 the same agent. Although the effects of this drug 
 last but 12 to 24 hours, it is not now to be considered 
 for the simple purpose of dilating the pupil. In the 
 dark room, cocaine hydrochlorate (4-per-cent. solu- 
 tion) will dilate some pupils almost ad maximum, 
 while the effect upon the accoihmodation is so slight 
 that it demands no consideration. The effect upon 
 the pupil passes off in a few hours. 
 
 For the sake of paralyzing the accommodation 
 and dilating the pupil, the sulphate of atropia has for 
 a long while been the agent far excellence. Repeated 
 instillations of a one (grs. v to | i) or two (grs. x to 
 J i) per cent, solution will effectually attain this end. 
 Weaker solutions we have found inadequate. With 
 this drug the " point of toleration " is easily reached, 
 especially in the case of children; this should be borne 
 carefully in mind. 
 
— 75 — 
 Among mydriatics duboisine should be mentioned. 
 This drug paralyzes the accommodation and dilates 
 the pupil ad maximum. It is mOre rapid in attack 
 than atropine and its effects pass off more quickly. 
 It was first used in ophthalmology a number of years ago 
 particularly for the purpose of paralyzing the accom- 
 modation with reference to gaining an accurate knowl- 
 edge of the refraction. It was soon laid aside, how- 
 ever, for the sulphate of atropia, which is now almost 
 universally used for the above purpose. We have 
 used a mixture of duboisine and cocaine for the same 
 purpose with excellent results, in the following pro- 
 portions: 
 
 Duboisini, grs. iiss. 
 Cocaini hydrochlor. , grs. xxx. 
 Acidi borici, grs. xv. 
 Aquae destill. , § j. 
 
 Duboisine was laid aside chiefly on account of 
 certain cerebral symptoms which were observed under 
 its use at the hands of several experimenters. Up to 
 the present time, we have used the above solution for 
 the purpose of dilating the pupil and paralyzing the 
 accommodation not less that 150 times; no unpleasant 
 symptom has been found to follow its use. The 
 quantity employed has never been more than five 
 drops in each eye. In test experiments made with 
 this solution in emmetropic eyes, it has been found 
 that the accommodation was entirely paralyzed in from 
 one-half to one hour; the effects on both the pupil 
 
- 76 - 
 
 and accommodation entirely disappear by the evening 
 of the second day or the morning of the third after its 
 instillation. 
 
 By the use of this formula the final examination 
 can be made in three days. 
 
 The amount of time saved in this way is of great 
 value to those engaged in the active pursuits of life. 
 We have settled to our own satisfaction, by observing 
 a large number of cases, that the eyeball tension is 
 diminished by the instillation of this solution. This in 
 itself is an advantage over atropine which, if instilled 
 for a number of days, may cause increase of tension. 
 Moreover it has never been necessary to make more 
 than two examinations under the influence of this 
 mixture. 
 
 The examination following the second day's in- 
 stillation has always been satisfactory as attested by 
 the accompanying ophthalmoscopic examinations. 
 We deem this solution superior to duboisine alone, 
 or to atropine sulphate alone, or to the latter in com- 
 bination with cocaine. We have noticed that eyes 
 treated with this solution more nearly accept the 
 total correction of their errors than those treated 
 with atropine. The hydrobromate of homatropine in 
 I per cent, or 2 per cent, solution is said to com- 
 pletely paralyze the accommodation. 
 
 It is very expensive and not commonly found 
 in the shops. 
 
 Daturine and hyoscyamine, although they par- 
 
— 77 — 
 alyze the accommodation and dilate the pupil ad 
 maximum are not in vogue for these purposes m 
 ophthalmology. ^ 
 
ELIXIR NATIVE COCA 
 
 (LORINI.) 
 
 An Elixir of Bolivian Coca Leaves (Erythroxylon Coca) Prepared 
 
 Exclusively for Parke, Davis & Co in the Locality Where 
 
 They are Grown, from Leaves Freshly Gathered. 
 
 Each flaidouiice represents 60 grains fresh natire coca leayes. 
 
 Tliis elixir of Coca leaves, prepared in the native habitat\of the drug differs 
 from all other preparations of coca in containing all the original constituents of 
 the native leaves. It has now become well-known that coca-leaves suffer very 
 extensive changes in transportation, and that there are no means by which these 
 can be prevented. That the loss begins as soon as the leaves have been collected 
 is shown by the fact that the Indians themselves refuse to accept the leaves after 
 they have been dried for a few weeks. (Coca at HoTne, by Dr. H. H. Ensby, Thera- 
 peutic Gazette, March, 1888, p. Ids'. 
 
 Experience has shown that from cocaine, the only appreciable constituent of 
 of exported leaves, the characteristic effects of coca-chewing cannot be obtained 
 in any degree. Obviously, these effects are to be obtained only by the use of a 
 preparation of the recent leaves. This elixir, made for us from carefully selected 
 leaves immediately after they are collected, represents their full strength, and 
 possesses the stimulating and supporting powers of the native drug. Representing 
 only 2 oz. of dried leaves to the pound, each fluidounce contains only about 1-4 
 gr. of cocaine, so that its continued use is free from the objectionable features of 
 that drug. 
 
 Trials that have been made with this preparation by leading practitioners, and 
 its extensive use in Bolivia, fully warrant us in recommending it in the following 
 conditions: 
 
 1 . In exhaustion due to excessive physical or mental strain, or resulting from 
 disease. 
 
 2 In pneumonia and Jdndred diseases involving difScult respiration. 
 
 3. In dyspepsia, either gastric or intestinal, of the atonic type. 
 
 The dose is a fluidounce and should be taken immediately after eating. 
 
 PAEKE, DAYIS & CO., 
 
 Manufacturing Chemists, 
 
 NEW YORK: 
 
 OfSces, 60 Maiden Lane. DFTROIT MICHIGAN 
 
 Warehouse and Shipping Depot, 21 LibertySt. "c-lKUll, lviiv,niurAiM. 
 
 Crude Drug Warehouse, 218 Pearl St. 
 
Si|e 'S^pkki}^' geisiii-e %lbt^t^. 
 
 PRICE i PAPER, 25 CTS. PER COPY, $2.50 PER SET ; CLOTH, 50 GTS. PER COPY, 
 $5.00 PER SET, 
 
 SERIES I. 
 
 Inhalers. Inhalations and Inhalants. 
 By Beverley Robinson, M. D. 
 
 The Use of Electricity in the Rennoval of 
 Sup.erfluous Hair and the Treatment of 
 Various Facral Blemishes. 
 By Geo. Henry Fox, M. D. 
 
 New Medications. 
 
 By Dujardin-Beaumetz, M. D. 
 
 The Modern Treatment ofEar Diseases. 
 By Samuel Sexton, M. D. 
 
 Spinal Irritation. 
 
 By William A. Hammond, M. D. 
 
 The Modern Treatment of Eczema. 
 By Henry G. PifiEard, M. D. 
 
 Antiseptic Midwifery. 
 
 By Henry J. Gamgues, M. D. 
 On the Determination of the Necessity for 
 Weanncr Glasses. _ 
 
 By DTB. St. John Roosa, M. D. 
 
 The Physiological, Pathological and Ther- 
 apeutic Effects of Compressed Air. 
 By Andrew H. Smith, M. D. 
 
 GranularLidsandContagiousOphthalmia. 
 
 By W. F. Mittendorf, M. D. 
 Practical Bacteriology, 
 
 By Thomas E. Saiterthwaite, M . D. 
 Pregnancy, Parturition and the Puerperal 
 State and their Complications. 
 
 By Paul F. MundS, M. D. 
 
 SERIES II. 
 
 The Piagnosisand Treatment of Haemor- 
 rhoids, _ 
 
 By Chas. B. Kelsey, M. D. 
 
 Diseasesof the Heart. Vol.1. 
 
 By Dujardm-Beaumetz, M. D. 
 
 Diseases of the Heart, Vol. II. 
 By Du]ardin-Beaumetz, M. D. 
 
 The Modern Treatment of Diarrhoea and 
 Dysentery* _ 
 
 'By A.'b. Palmer, M. D. 
 
 Intestinal Diseases of Children. 
 By A. Jacobi, M. D. 
 
 The Modern Treatment of Headaches. 
 By Allan McLane Hamilton, M. D. 
 
 The Modern Treatment of Pleurisy and 
 Pneumonia. 
 
 By G. M. Garland, M. D. 
 How to Use the Laryngoscope, 
 
 By an Eminent Laryngologist. 
 Diseasesof the Male Urethra. 
 
 By Kessenden N. Otis, M. D. 
 The Disorders of Menstruation. 
 
 By Edward W. Jenlis, M. D. 
 The Infectious Diseases, In 2 vols. 
 
 By Karl Liebermeister. 
 
 SERIES III. 
 
 Abdominal Surgery* 
 
 By Hal C. Wyman, M. D. Ready. 
 Diseases of the Liver. 
 
 ByDujardin-Beaumetz, M.D. Ready. 
 Hysteria and Epilepsy. 
 
 By J. Leonard Coming, M. D. Aug. 
 
 Diseases of the Kidney, _ 
 
 By Dujardin-Beaumetz, M. D, Sept. 
 
 The Theory and Practice of the Ophthal- 
 moscope. 
 
 By J. Herbert Claiborne, Jr., M. D. 
 September. 
 Modern Treatment of Bright's Disease. 
 By Alfred L. Loomis, M. D. 
 October. 
 
 Clinical Lectures on Certain Diseases of 
 Nervous System. 
 By Prof. J. M. Charcot, M. D. 
 October. 
 The Radical Cure of Hernia. 
 
 By Henry O. Marcy, A. M., M. D., 
 L. L. D. November. 
 
 The Treatment of Diseases of the Blad- 
 der, Prostate and Urethra. 
 
 By H. O. Walker, M. D. Nov. 
 Dyspepsia. 
 
 By Frank Woodbury, M. D. Jan. '89. 
 The Treatment of the Morphia Habit. 
 By Erlenmeyer. December. 
 Translated by J. B. Mattison, M.D. 
 
 GEORGE S. DAVIS. 
 PUBLISHER, 
 
 S". O. Bosk ■4'7'0. XDetroit, Iiw<Elc2a.. 
 
-J. J^