THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES TEXT-BOOK OF BY EDWAKD G. LOKING, M. D. PART I. THE NOEMAL EYE, DETERMINATION OF EEFEACTION, DISEASES OF THE MEDIA, PHYSIOLOGICAL OPTICS, AND THEOEY OF THE OPHTHALMOSCOPE. NEW YOEK: D. APPLETON AND COMPANY, 1, 3, AND 5 BOND STREET. 1886. COPYRIGHT, 1885, BY D. APPLETON AND COMPANY. CONTENTS. CHAPTER I. PAGE Remarks on the ophthalmoscope. Examination by daylight. Examination of the eye by artificial light 1-7 CHAPTER H. Examination with the ophthalmoscope. Method of examination. Examination by the inverted image. Examination by the upright image 8^20 CHAPTER III. The anatomy of the fundus of the normal eye 21-43 CHAPTER IV. The fundus of the normal eye as seen with the ophthalmoscope. Anomalies 43-105 CHAPTER V. Determination of the optical condition of the eye with the oph- thalmoscope. Refraction. Astigmatism. Refraction accord- ing to the standard of the inch. Directions in case the observ- er is ametropic. Determination of the refraction of an eye by the mirror alone, and by means of the inverted image. Astigmatism with the mirror alone. Astigmatism with the inverted image. Amount of enlargement produced by up- right image 106-145 iv CONTENTS. CHAPTER VI. PAGE Examination of the media of the eye. Oblique illumination. The aqueous humor. The iris. The lens. Opacities of the lens. Examination of the media by the ophthalmoscope. The iris. The lens. Vitreous humor, and fundus of the eye. Differ- ential diagnosis of troubles in the media. Entozoa . . . 146-194 APPENDIX. General principles of the ophthalmoscope. Physiological optics. Theory of the ophthalmoscope. The metric system. Oph- thalmoscopes. Adjuncts to the ophthalmoscope . . . 195-259 TEXT-BOOK OF OPHTHALMOSCOPY. CHAPTER I. REMARKS ON THE OPHTHALMOSCOPE. IN the whole history of medicine there is no more beautiful epi- sode than the invention of the ophthalmoscope, and physiology has few greater triumphs. With it it is like walking into Nature's labo- ratory and " seeing the Infinite in action," since by its means we are enabled to look upon the only nerve in the whole body which can ever lie open to our inspection under physiological conditions, and to follow in a transparent membrane an isolated circulation from its en- trance into the eye through the arteries to its exit in the veins. We are further enabled to watch and study daily, or even hourly, morbid processes in each and every phase, from simple hyperaemia to absolute stasis, and from passive O3dema to the most violent inflammation ; while oftentimes through its agency also we get the first intimation of disease in remote and seemingly unconnected organs, so as to read, as if in a book, " the written troubles of the brain," the heart, the spleen, the kidneys, and the spine. It is little wonder, then, that the adept learns to look upon the ophthalmoscope as one of the most beautiful in theory, the most per- fect in practice, and the most far-reaching in results, of any of the in- struments known to medical science, or that he should be brought to consider the invention of Helmholtz as the most potent factor in bringing the art of ophthalmology to the highest plane of medical diagnosis and treatment.* Nor is it surprising that even the student, once entered upon its investigation, finds the study of the instrument as fascinating as it can be made profound. It is to enable him to prosecute such studies with greater ease and with more expedition than if left to himself, that the following pages are written. * Virchow, " Trans. Internat. Congress," London, 1881. 1 2 TEXT-BOOK OF OPHTHALMOSCOPY. That the ophthalmoscope has become a necessity in the detection of disease is now universally admitted. Physicians, therefore, at the present time are much more interested in the facts which the mirror reveals than in the principles upon which it depends. To understand, however, the practical working of the instrument and the full extent of its application, the few fundamental laws upon which it depends must be thoroughly understood. For such as are not already ac- quainted with them, these laws, briefly and simply stated, will be found in the Appendix at the end of the volume. In making an ophthalmoscopic examination three principal things are to be considered : 1. The instrument and the illumination used. 2. The optical condition of the observer's eye. 3. The optical and physical condition of the eye to be observed. The great aim in an ophthalmoscope should be largeness of field of view, with suitable and sufficient illumination. These require- ments seem to be fulfilled best in the general shape and construction of what is known as Liebreich's small ophthalmoscope, which consists of the concave mirror with a central aperture attached to a short, straight handle. The mirror is usually about seven inches focal length, with a clip at the back for the necessary correcting-glasses. Unfortunately, these instruments as made abroad, though cheap, are comparatively worthless, from the mirrors not being true, and from the annoying reflections arising from the edges of the perforation and back-plate of the mirror. For lightness, freedom from reflections, and durability, there are no superior instruments to those now made in New York, notably by Messrs. Hunter and Meyrowitz, whose instru- ments in the way of workmanship and optical accuracy are unsur- passed. Almost every ophthalmologist has taken a hand in perfect- ing or at least altering the instrument, and from the first I have, per- haps, done more than my share. To mention all the modifications now known and in use would make a book of itself, and I must refer those who are curious as to the evolution of this beautiful instrument to the current literature of the day. My advice to the student is in the beginning to get the best instrument of its kind, not necessarily the most complex and the highest priced, assuring him that it makes no difference whatever whose instrument he uses, provided it is com- prehensive enough to suit his wants, and that he learns how to use it with judgment and skill. Beginning with the simpler ones, he can pass to those which are more complex, should occasion require. In the Appendix will be found a description of some of the forms sug- REMARKS ON THE OPHTHALMOSCOPE. 3 gested by the writer, not because they are in any way better than others, but simply because he is better acquainted with their quali- ties, good and bad. Of his rather voluminous contributions in this line, only those are mentioned which have stood the test of time and proved their usefulness. The Illumination. The great convenience attending the use of gas, and its universal adoption as a source of light in this country, would give to its use for the purposes of ophthalmoscopy a decided preference, even if it did not possess the most suitable quality of light. As, however, there can be but little objection to it even on this score, all that need be considered is the shape in which it shall be employed. The best form for an ophthalmoscopic lamp is that made after the English pattern, consisting of two parallel tubes with such an arrange- ment of joints as to give a wide extent of vertical and lateral move- ments.* From their somewhat elaborate construction they are per- haps better fitted for institutions and the offices of specialists than for those of the general practitioner. A form of lamp which an- swers every purpose in an admirable way is the common drop-light, with a flexible tube and Argand burner fitted to a stand with a slid- ing-bracket, by which the height of the light can be regulated at will. Kerosene gives an admirable light, especially some of the purer qualities ; but, if used, the old-fashioned lamp, where the flame is a broad one, is better than the German student-lamp, where the flame, though very brilliant and white, is so narrow that the circle of disper- sion on the retina is very much drawn out in a vertical and reduced in a lateral direction. To the fastidious, some improvement in all these sources of illumination can be obtained by the use of a light- blue chimney or a screen of blue glass placed before the lamp. Any lamp, however, which gives a good light may be used, and its position, if the flame be of the larger kind, should be a little behind and a little to one side of the patient's head, and about on a line with the eye to be observed. It should, however, be as close to the head as is comfortable, so that the angle of the incident and reflected light should be as small as possible, so as to prevent a too great rotation of the ophthalmoscope on its vertical axis. When, however, the flame of the lamp is small and the inverted image is used, as, for example, a candle-flame at the bedside, this should then be placed between the patient and the observer, and nearer to the latter than the former. The lateral distance should be about the same as in an ordinary examination. In this way we get a * These lamps, which carry an Argand burner, can be had from the firm of Mitchell & Vance, New York. 4 TEXT-BOOK OF OPHTHALMOSCOPY. larger and brighter circle of dispersion, and use to the best advantage the little light at our disposal. In regard to the quantity of light given by different mirrors, of course those which are silvered produce a greater illumination than those which are not ; and those which are concave, greater than those which are plane. Each kind of mirror has its advantages, and it would be better theoretically to use different mirrors, embracing also different degrees of curvature for different kinds of work. This is, however, so inconvenient as to render it practically impossible ; still, a word must be said as to the great and positive advantage in some cases of what is known as Helrnholtz's or the weak-light mir- ror, which consists of three parallel plates of thin plane glass.* No mirror gives a more beautiful illumination than this when all the con- ditions for its use are favorable, such as a sufficiently dilated pupil and clearness of the media ; for by its subdued light slight changes in the fundus of the eye, and even slight variation in shade of color especially, as will be seen later, in the optic nerve are made mani- fest ; changes which under a brighter illumination are lost in an excess of light. As would naturally be inferred, this mirror is of great advantage where there is a marked dread of light on the part of the patient. It is not, however, serviceable for general work, as it can not be used for the inverted image, while some of its virtue can be obtained, in great part at least, with the " strong-light " mirrors by reducing the quan- tity of light coming from the source of illumination. Simple concave mirrors of such a strength as are ordinarily used in ophthalmoscopy throw upon the eye a converging cone of light, the base of which is equal to the surface of the mirror, though, of course, as we bring the mirror more closely to the eye only those rays which are reflected from its central portions will enter the pupil. The shorter the focus the greater is the condensation of the light ; but experience as well as theory shows that only mirrors of moder- ately short focal lengths are suitable for ophthalmoscopy. As a rule, the mirror should not have a focus shorter than seven nor longer than ten inches. EXAMINATION BY DAYLIGHT. This consists simply in substituting natural for artificial illumi- nation, and can be accomplished by having a small slit cut in the shutter. Its only advantage is that we see the fundus more nearly under its natural color, as the reflection from the bottom of the eye is free from * See description in Appendix, p. 230. KEMARKS OX THE OPHTHALMOSCOPE. 5 the yellow it receives from either oil or gas. When thus seen, its color varies from a pure red to a delicate reddish-pink. The method is, however, inconvenient in its application, and, as artificial light be- comes from force of habit our natural criterion, the method is really of little practical use. It is, however, in those very rare cases of re- tinitis from leucaemia, of decided advantage, as under dispersed day- light the fundus maintains the characteristic orange-color, while the normal eye loses all trace of it. To obtain the best results, the pupil of the eye should be dilated, and the only light admitted to the room should be through the narrow aperture which serves as the source of illumination. I have, however, often obtained a perfectly clear view of the fundus when the pupil was dilated, by placing the patient with his back to the window. EXAMINATION OF THE EYE BY ARTIFICIAL LIGHT. Oblique Illumination. The first step toward an ophthalmoscopic examination of the fundus of the eye should be the consideration of the condition of the interposing media the cornea, aqueous humor, lens, and vitreous body. This is a most important step, and as a precautionary measure should never be omitted, for disturbances in any of these bodies, although so slight as to readily escape observation, may nevertheless have a considerable effect on the character and clearness of the image, and any want of attention to this particular may lead the practitioner not only into error but even into disgrace. The habit of picking up an ophthalmoscope and making straight for the optic disk is fatal to exact ophthalmoscopy, and many a " slight effusion or oedema into the retina " has in other and more careful hands resolved itself into a dif- fuse opacity of the vitreous, the lens, or even the cornea and that too, not only in the hands of a beginner, but also in those of an adept. One of the principal ways of ascertaining the condition of the me- dia is by means of a 'condensing lens. This method of examination is called that by oblique illumination, because a cone of light is thrown by the lens upon and obliquely through the anterior parts of the eye. The manner in which the lenses are used will be understood readily from the drawing, Fig. 1. The light should be placed at a little distance from the head of the patient a foot, more or less and on the same side as the eye to be examined, and at about the same height, but in a somewhat more ad- vanced plane. Any convex lens of a moderately short focal length may be used, the ordinary two-and-a-half -inch glass of the ophthalmoscope answer- 6 TEXT-BOOK OF OFHTHALMOSCOPY. ing every purpose. The lens should be held between the light and the eye, at a little less than its focal length. A converging cone of light is thus thrown upon and into the eye, and this should be made to play about by slight lateral displacements of the glass, so that the -- FIG. 1. illumination may reach successively different parts of the surface of the cornea. When a general survey of this is to be made for the pur- pose of detecting any change, and of contrasting such a change with the surrounding tissue in a general way, the lens should be held nearer to the eye, so that the surface of the cornea may cut the cone of light thrown upon it some way from its apex. The circle of illu- mination is in this way increased, though the light is at the same time less condensed. If a small and isolated portion of the surface is to be carefully examined, as, for example, the seat of a minute foreign body, then the lens should be gradually withdrawn till this comes just within its focus, so as to obtain the greatest amount of illumination. The cornea, aqueous humor, iris, and lens should in turn be care- fully observed, and the examination should be further helped by caus- ing the patient to move his eyes in various directions ; for oftentimes a sudden turn of the eye will bring to view a delicate and comet-like opacity which would otherwise have escaped detection. The first lens can be supplemented by a second, as seen in the drawing. This is placed immediately in front of the observed eye, and in the path of the rays coming to the observer. This second EEMAKKS ON THE OPHTHALMOSCOPE. 7 glass acts simply as a magnifier, and as such should be held at about the focal distance of the glass from the cornea. Simple as all this appears, it nevertheless requires a good deal of skill and experience to reap the full benefits of the method of exami- nation by oblique illumination, and especially in regard to the troubles of the lens and deeper structures. To do this thoroughly, the pupil should be dilated by atropine. In such cases it is often advantageous to have the lamp placed directly above and a little in front of the pa- tient's head, which should then be thrown slightly back. The observer should then stand a little to one side, so as not to interfere with the light entering the eye, but still be hi the track of the returning rays. By this means the angles of incidence and reflection are made a little larger, and a better view is obtained. The conditions of the posterior capsule and anterior portions of the vitreous can be, and often are, advantageously examined by this method ; but, from the difficulty of the illumination, most observers prefer, rather than to waste time and run the risk of overlooking minute disturbances in these deeper parts, to use the direct light from the ophthalmoscope. Still, lateral illumination has advantages of its own, even for these parts, especially when the disturbances are of a diffused nature, and it should never be neglected. CHAPTER II. EXAMINATION WITH THE OPHTHALMOSCOPE. YEKY little, I had almost said nothing, can be learned of the technical working of the ophthalmoscope from a book. The neces- sary skill must be acquired in the presence of the subject, and with the instrument in the hand. That ophthalmoscopy in its widest sense is a very difficult art must certainly be admitted. But it has always struck me that its difficul- ties have been exaggerated, so far as its practical working is concerned, by the abstruse manner in which its principles have been inculcated. In this way a sort of dread of the instrument has been created in the minds of many practitioners in whose hands, with a trifling effort in overcoming a few technicalities, it might have been a source of in- creased knowledge to themselves and of absolute advantage to their patients. The greatest good to the greatest number is, or ought to be, as much the watchword of medicine as it is of politics ; and I sincerely hope that the time is not distant when the ophthalmoscope will be in the hands of every thoughtful and observant physician, to be used by him just as the microscope now is, without affectation, as a means for the detection of disease. It would be a sorry day for the sick and suffering if every physi- cian who used the microscope had to be a Yirchow, or who used the ophthalmoscope a Helmholtz. The ability to add and subtract vulgar fractions is all the mathematical knowledge which is required to put the ordinary physician, clinically speaking, on a par with the pro- foundest mathematician, and, now that the metric system has been adopted, one can dispense with even this small amount of knowledge. Strictly speaking, before looking into the condition of another's eye, the observer should have a knowledge of the visual power and refraction of his own eye, and should possess the ability of correcting any defects should they exist. Some methods of examination require this, others do not ; at least where the error of refraction is still within moderate limits, as, for example, in the examination by the " inverted EXAMINATION WITH THE OPHTHALMOSCOPE. 9 method." It is, however, absolutely necessary when the "upright method " is employed, and more will be said on the matter under that heading. The first step in the examination of an eye with the ophthalmo- scope is to illuminate the eye in a suitable manner. One of the greatest obstacles to this with inexperienced observers, and one which, more than any other, has discouraged the general practitioner at the very outset from pursuing his studies, has arisen from the fact that his first essays have been made with subjects where the pupil has been undilated. A good deal of prejudice exists in the minds of many writers against the use of atropine, especially when, after many years of ex- perience, they themselves have become emancipated from its use. It certainly must be admitted that it is an inconvenience to the patient for the time being, but the duration of this inconvenience can be so shortened that it is not to be weighed against the positive advantage gained by a thorough and minute examination. Delicate changes often escape detection, even in the hands of skilful observers ; and, when this is the case, it is usually from two causes : either the in- verted image alone is used, and thus a sufficient enlargement is not obtained, or the examination is made through an undilated pupil. Thus, even if the upright image has been used, the examination often proves fruitless from the fact that the observer, from a natural dread of subjecting his patient to the annoying effect of atropine, has failed to get anything like an adequate view of those parts of the eye in which these changes are apt to occur ; that is to say, of the peripheri- cal parts of the lens, and of the region of the macula lutea. For the purposes of an ophthalmoscopic investigation it is only necessary to employ the drug in the mildest possible form, so as to limit its action to a single day. By far the best way of using it seems to me to be by the gelatine wafers * or disks prepared by Savory & Moore, of London. These disks come of three degrees of strength, each disk containing 20 ^ 00 , ?0 ft o0 , and TO oVirfF f a gr am of atropia. One of the first, or even one of the second strength, placed in the cul-de-sac of the conjunctiva, is sufficient to dilate the pupil fully, unless unnatural irritation is present, in the course of an hour or two. Even if it fails to do this completely, it produces a partial dilata- tion, and with it a rigidity of the iris, which is usually all that is needed. If these wafers can not be procured, then a very weak solu- * The officinal name of these wafers is "Ophthalmic Gelatine Di^ks atropized. Savory & Moore, 143 Bond Street, London." They can also be had of Caswell, Hazard & Co., New York City. 10 TEXT-BOOK OF OPHTHALMOSCOPY. tion, gr. j of the neutral sulphate of atropia to aqua des. iij, may be employed, or a drop of a two-per-cent solution of the hydrochlorate of cocaine, which produces usually a sufficient but temporary dilation of the pupil. As skill in the use of the instrument increases, the necessity for the use of atropine will become less and less, until it is finally reserved for rare occasions. I never hesitate, however, to use a wafer when trouble either in the periphery of the lens or at the macula lutea is suspected. It should, however, be stated that in the minds of some of the profession a belief exists that the use of atropine has a tendency to bring on an acute attack of glaucoma in eyes which are predisposed that way. Luckily the part affected, limited as it chiefly is ophthal- moscopically to the optic nerve, is the part of the eye most readily seen and studied with an undilated pupil. METHOD OF EXAMINATION WITH THE OPHTHALMOSCOPE. Simple Illumination of the Fundus. The patient should be placed in a darkened room, with his back to a well -burning lamp with- out any shade or globe. This should be on the same side and on about the same level as the eye to be observed. It should, however, be placed a little behind the head, say five or six inches, and some- what removed from it laterally. The observer's seat should be a little higher than the patient's, and he should sit not directly in front of the latter, but to one side, so that his chair should come, not in front of the patient's chair, but by the side of it. This gives plenty of room for movements, both on the part of the observed and the ob- server, and avoids the necessity of the latter being compelled, when he wishes to approach closely to the eye examined, to be directly in the face of the patient. The observer's eye should be about eighteen or twenty inches from that of the patient, who should be made to di- rect his gaze in front of him, and, if the right eye is to be examined, a little to the left, and if the left, a little toward the right. Light is now thrown from the ophthalmoscope directly upon the observed eye, and the observer, looking through the hole of the mir- ror and in the direction of the reflected rays, sees the pupil glow. This glow is nothing but the reflection of light from some portion of the fundus which has become illuminated through the pupillary space. We, therefore, speak of the presence or absence of the " reflex " of the fundus, according as the pupil shines or does not shine. The illumination of the pupil, or, more properly speaking, of the fundus, having been obtained, when the patient is looking straight EXAMINATION WITH THE OPHTHALMOSCOPE. H ahead he should be made to change the direction of his gaze by look- ing up and down and to the right and left, first slowly and then quickly, the observer all the time covering the eye with the light cast from the mirror, thus keeping the pupillary space constantly brilliant. In this way different portions of the eye are successively illuminated. The mirror should also be gently rotated from side to side on its vertical axis by a slight movement of the wrist, so as to get the advan- tage of the alternate play of light and shade, oftentimes in itself an all-important factor in the detection of disease. This done, the observer should learn to move his own head back and forth, directly toward and then away from the patient. By this means he is often able to detect the presence of membranes, growths, and separations of the retina, and their probable antero-posterior posi- tion. He should also move his head from right to left, and vice versa, keeping the pupil of the observed eye always brilliant. All these various movements should be practiced over and over again, first with an enlarged and then with an undilated pupil, till the ability to " get the reflex " in all possible positions and movements of the eye is acquired with ease and precision. Having illuminated the back of the eye, the next step is to resolve this indefinite glow into a definite picture or image. It will have al- ready been noticed by the attentive observer, however inexperienced, that whereas we usually get with the illumination from the mirror alone merely a diffuse brilliancy in the pupillary space, we do, never- theless, with some eyes obtain a distinct image of a small portion of the f undus, as, for example, a limited section of a retinal vessel or a small segment of the optic nerve. This is due to some error in the refraction of the eye observed, and is present notably in myopic eyes, and the more so the greater the degree of myopia. If the eye be myopic, an inverted and aerial image will be formed in front of the observed eye, and at a distance equal to the degree of the myopia present. It is this aerial image which the observer sees, and not a part of the fundus itself. On the other hand, if the eye observed is hypermetropic, the observer gets a direct view of a small part of the fundus itself seen through the patient's pupil. To tell whether the image in any case is in verted or erect, the observer has simply to move his head. If the image is inverted, and the eye ob- served consequently myopic, the image will appear to move in a con- trary direction to the movement of either the observer's or patient's head. If the image is upright, and the eye consequently is hyperme- tropic, then it will seem to move in the same direction. The optical reasons for the formation of these images with myopic and hyperme- 12 TEXT-BOOK OF OPHTHALMOSCOPY. tropic, as well as occasionally with emmetropic eyes, their compara- tive enlargement and extent of the fundus seen, are discussed in the chapter on the theory of the ophthalmoscope. EXAMINATION 13 Y THE INVESTED IMAGE. The view of the fundus seen as just described with the mirror alone, even if it could be always obtained, would be entirely too re- stricted to ba of any clinical value ; and another means of producing an image, and at the same time of enlarging the field of view, would be an absolute necessity. One way of obtaining this object is by sup- plementing the use of the mirror with that of a convex lens. This is held by the observer before the eye of the patient, and directly in the path of the returning rays, as shown in the drawing (Fig. 2). FIG. 2. A lens so held not only increases the circle of illumination on the retina, but intercepts the rays leaving the fundus, which are by its means brought to a focus, and thus an aerial image is formed between the glass and the observer's eye, as is fully explained in another place ; moreover, a great number of peripheric rays which would have passed outside of the observer's line of vision are brought directly into it by having their direction changed by the lens, and thus the field of view is enlarged, this enlargement depending, as we shall see later, on the strength of the glass used. The most conspicuous portion of the fundus, and one which serves as an objective point for the examination, is the optic disk. To bring this opposite the pupil of the eye to be observed, and in the observ- EXAMINATION WITH THE OPHTHALMOSCOPE. 13 er's Hue of vision, the patient must be directed to look a little inward, that is, toward the nasal side of his field of view. "When the nerve is opposite the pupil, the observer will at once become aware of the fact by the peculiarly white reflex filling the pupillary space. For the purpose of bringing the nerve-entrance easily into view, and at the same time of furnishing to the patient a definite object to look at, it is a common expedient with many observers to hold the instrument not in a vertical direction, with the handle downward, as shown in the drawing, but to place this horizontally outward, across the patient's field of view, and then to elevate the little finger, at which he is told to direct his view ; or the patient may be told to look at the right ear of the surgeon if it be the right eye, or the left ear if it be the left eye, which is under examination. The white reflex from the disk having been obtained, the object- glass should be brought into position, as shown in the drawing (Fig. 2), directly in front of the pupil, and in the path of the returning rays. The glass should be held between the thumb and forefinger, and the observer should place his little finger of the same hand on the patient's forehead, for the purposes of a rest. The observer should then practice until he acquires a perfect facility in moving the glass backward and forward in the line of vision for the purpose of focusing. The glass should not be held in a plane exactly at right angles to the visual axis, but should be turned a little on its vertical axis, so as to lie obliquely across this line. By this manoauvre the images of the lamp formed by the anterior and poste- rior surfaces of the glass are separated from each other, and a space in the centre of the field is obtained free from these annoying reflexions. This to-and-fro movement of the glass having been acquired, the observer should then learn to move the glass back and forth directly across the visual line, and upward and downward. The image is in this way displaced from side to side, and a parallax is obtained be- tween objects occupying different planes in the eye. One can thus form an estimate of differences in level formed by projections and excavations, as, for example, that of the nerve in glaucoma. The explanation of this effect may be illustrated as follows (Fig. 3) : Let L be a convex lens, o its optical centre, and the line a o a' its principal axis. Let a and b be two points on this line behind the lens, and at a distance greater than its focal length. The images of a and b will be formed at a given distance in front of the lens and on its principal axis, say at a' and b'. If, now, the lens be moved into the position shown by the dotted line, then o, the optic centre, passes to o'. The image of a will then be formed at ", and that of b at b'' '. By 14 TEXT-BOOK OF OPHTHALMOSCOPE the displacement of the lens the image of 5 makes a greater excursion than that of , and will lie farther from the line a o a'. The nearer one of the objects is to the lens, the greater the displacement it under- goes. We can thus make some anterior point either move dispro- portionately to, or even pass over, a posterior one, and thus learn that FIG. 3. the former must lie in front of the latter. In this way the edge of an excavated optic nerve can be made to pass over the lamina cribrosa and shut out portions of the vessels lying in its plane, and from the degree in which this takes place we can form an estimate of the depth of the cavity. Though this method is of considerable use in detecting the exist- ence of inequalities in the bottom of the eye while taking a general and rapid survey of the fundus, it is, however, vastly inferior to the upright image for the purposes of ascertaining their exact amount, as is explained in the chapter of "Determination of the Errors of Refraction." The rule laid down in the books, in making an examination by this method, is to hold the object-glass at a distance in front of the eye equal to its focal length. Practically it is better to make this dis- tance a little greater. This is done to sink the image of the iris, for by gradually withdrawing the glass from a close proximity to the eye outward the pupillary space becomes larger and larger, till the rim of the iris passes out of the observer's field of view, and the only rays which can then enter the observer's eye are those coming through the pupil from the fundus itself. The stronger the object-glass the larger will be the extent of the fundus seen at one time, but the smaller will its individual details appear, and vice versa ; the weaker the glass the smaller the tield, but the greater the enlargement of its component parts. It is, therefore, always an advantage, sometimes a necessity, to make use of glasses of EXAMINATION- WITH THE OPHTHALMOSCOPE. 15 different strengths. Thus we often find it serviceable when we wish to make a general inspection of the f undus, and thus learn the rela- tions of morbid changes to definite and recognized landmarks, to use a comparatively strong glass, such as a two or, less advantageously, a two-and-a-half -inch lens ; but, when we wish to examine a certain spot under an increased enlargement and more in detail, we employ a weaker number, say a three, four, or even a five-inch lens. Some observers strike a mean, and use a two-and-a-half or even a three-inch lens for all work. The writer feels sure that he has been able to observe changes in a comparatively satisfactory manner, which would otherwise have re- mained undetected, by sometimes using a one-and-a-half-inch lens. The advantages of so strong a glass are particularly well shown in cases where the pupil is abnormally small, reduced as it sometimes is to a pin-point, or where this is bound down by adhesions, and the pu- pillary space is the seat of minute deposits or thin membranes, which are, however, still permeable to strongly condensed light. So, too, with troubles in the lens which partly occlude the pupil, or those in the vitreous, or in fact in any case where we wish to see through a narrow opening where a large field is desired and a suitable illumina- tion is difficult to obtain. As the observer gains skill in the use of the instrument, the aerial image formed by the first glass, which we have spoken of as the object-glass, may be magnified by placing a convex lens behind the ophthalmoscope, which then acts the part of an eye-piece. In mak- ing use of this glass the observer should endeavor to relax his accom- modation as fully as he can, so as to use the strongest glass practica- ble, and thus get as great a magnifying power as possible. To facili- tate this, the observer may resort to the same expedient as is used with the microscope, namely, to keep both eyes open and to exclude one from the visual act by keeping the visual axes parallel as when look- ing at a distance ; moreover, this glass, besides its magnifying power, is often a relief to the eye by removing the strain from the accommo- dation. This applies particularly when the observer is hypermetropic, in which case the glass may be an absolute necessity, especially when the error of refraction is of a high degree. It must be used, of course, where the observer is presbyopic in any but the most moderate degree, or where from any cause there is a limited range of accom- modation. When either of the above conditions is present, even a myope of a low degree may require a weak eye-piece. An observer who is myopic to a moderate degree, say from J% to $ (2 to 4 D.), sees the inverted image under peculiar advantages, as his eye is 16 TEXT-BOOK OF OPHTHALMOSCOPY. adapted to receive the rays coming from the aerial image without any eye-piece behind the mirror, and with little or no effort at accommo- dation. The myopia may, however, be so great as to necessitate the use of a concave glass, so as to make vision distinct for the distance at which the image lies. Suppose the observer is myopic , then his farthest point of distinct vision lies at live inches before his eye, and, provided he occupies the usual position, the image is at ten to twelve inches from his eye. and his far point must be carried out to this dis- tance, ^ iV rV tf D. 3.5 = 3.5 D.), which will be the glass that such an observer requires. He could, however, by moving his head forward, lessen the distance between his eye and the image till he saw this clearly. It is sometimes extremely difficult, if not impossible, when the eye under observation is very myopic, say above (12 D.), to get a satisfactory view of the f undus with the upright image, because the correcting-glass must be so strong that it necessarily consumes a great deal of light. Liebreich's * method of obtaining the same degree of enlargement as that of the upright image by means of the inverted, while preserv- ing the clearness and brilliancy of the latter, is as useful as it is in- genious. Suppose the eye is myopic ^ (12 D.), then the aerial image formed by the lenticular system of the eye itself will be three inches in front of the eye. This image will, of course, be inverted and con-' siderably enlarged. A lens of a low power, % (9 D.) or even (7 D.), is now held in front of this image, and at about four or five inches in front of the eye. So used, it acts like any magnifier; but, as the image is considerably within the focal length of the glass, its magni- fying power is much limited. Still, this is sufficient to so enlarge the area of the pupil that the image of the iris passes out of sight and the field of view is enlarged. The writer has found it advantageous to use a second weak convex glass behind the mirror, say -J- y 1 ^ or -f- T? (^i ^0 3 D.). As the object-glass- one of the common magnifiers sold in the shops has a diameter of two and a half inches, it is broad enough to throw into the eye a large quantity of light, and the result- ing picture is therefore not only very large but very brilliant, and perfectly well defined. Each observer can readily find for himself, by a few trials, what combination is best adapted for his own eye ; those unable to relax their accommodation find it easier to use a weaker glass, say + -fa (1.5 D.) behind the mirror. The optic disk and its immediate neighborhood having been suffi- ciently examined, the other parts of the fundus should be brought * Graefe's "Archiv," 7. Ab., 11, p. 130. EXAMINATION WITH THE OPHTHALMOSCOPE. 17 successively into view by making the patient look up and down and to the right and left, first to a moderate degree and then to his utmost capacity, according as the equator, or the parts toward the ora serrata, are to be inspected. The region of the yellow spot is brought into view by the patient looking directly at the hole in the mirror. When he does this, however, the corneal reflex comes exactly over his pupil, and thus obscures or obliterates the image of the fundus. The pupil must be dilated to get a satisfactory view of this part of the fundus, except in case of the young. The difficulty is further increased by the light falling directly on the most sensitive part of the retina, and to the stimulation of which the iris most readily responds. Some- thing can be done toward avoiding these difficulties by making the patient look, not at the centre of the mirror, but at its edge, or even a little more to his temporal side. In this way, by a little patience and skilful manipulation, one can see round the corneal reflex, and thus bring the part into a comparatively fair view. The examination of the region of the macula lutea by the inverted image, even at the best and with a dilated pupil, is very inferior, as a rule, to that with the upright image. It is, however, sometimes in- dispensable, as, for example, when there are changes and opacities in the different media which it requires a very strong light to overcome. This is especially the case in commencing cataract where the nucleus of the lens has become opaque, with more or less diffuse opacity in the cortical substance. Changes at the yellow spot can often be detected in this manner, when by the upright image nothing can be seen. It is usually assumed that the examination by the inverted is easier and more convenient than that by the upright image. It has been certainly, until lately at least, much more frequently used than the latter, and by some, as it never should be, exclusively. The one is, or should be, the necessary supplement of the other, and both should be employed in every case, and the final preference of the one over the other should depend on the nature of the trouble then under investi- gation. In regard to the comparative difficulties of the two methods, it has always appeared to me that there was but little choice between them. It may often be easier and it certainly is when the pupil is small or bound down to get a picture of the fundus by the indirect than by the direct method. But to use either so as to bring out its full capabilities requires a certain though very limited amount of optical knowledge. This once acquired, the upright is, to my mind, the easier of the two, as the manipulation of the instrument is sim- pler. No one, however, can be a good or even passable ophthalmos- copist who can not make use of both. 18 TEXT-BOOK OF OPHTHALMOSCOPY. If the illumination of the eye by oblique light is the first step in an ophthalmoscopic examination, the second should be that by the inverted image. With it a general survey of the fundus is obtained, and, from the extent of the field seen, the entire seat of the disease may be taken in at once and contrasted with the surrounding and healthy tissue. So, too, from the comprehensiveness of the view, the relations of changes to certain fixed objective points, such as the optic disk, the macula lutea, the equator of the eye, and the neighbor- hood of the ora serrata, are readily determined. Peculiarities of shade and color are sometimes for the same reason made more manifest than with the upright image. That the inverted image is often indis- pensable where, from any cause, an increased illumination is desired, has already been pointed out. EXAMINATION BY THE UPRIGHT IMAGE. If the ophthalmoscope was one of the most brilliant inventions ever known to medical science, it was certainly, also, one of the most complete, for the very method first proposed by Helmholtz still re- mains by far the most beautiful, comprehensive, and truthful of all the means yet in our possession for the exploration of the bottom of the eye. As a knowledge of this method is absolutely necessary for the determination of the optical condition of the eye, a few words as to the manner in which it should be performed in general may be of service to the reader before proceeding to the more difficult task of determining in a given case the nature and exact degree of refraction. The position of the patient and examiner is not without impor- tance. The observer should sit well to the side of the patient, and on the side, of course, of the eye to be examined. If the right eye is to be examined, the patient should be directed to look slightly toward the right ; if the left eye, then toward the left. In fact, the directions are exactly opposite to those given for the inverted image, and just the contrary to what are usually laid down in the books. This position in the examination throws the optic axis away from the median line, places the optic nerve just opposite the pupil, and allows the observer to approach very near the observed eye without bending too much over the person examined. The observer must learn to use either eye and either hand as occa- sion may require, so as to be able to examine the patient's right eye with his right, and the left with his left, holding the ophthalmoscope in the right or left hand, as the case may be. EXAMINATION" WITH THE OPHTHALMOSCOPE. 19 As the examination by the upright image consists, as shown in the drawing (Fig. 4), of looking directly through the pupil to the fimdus beyond, the observer should bring his own eye as closely to the ob- served eye as is possible ; for, when obliged to look through a nar- FIG. 4. row opening, the nearer we bring our eye to the edges of the aper- ture, the wider will be the field of view of what lies beyond. Also, as a matter of course, the larger the pupil, the easier the inspection and the greater the extent of fundus seen. For this reason the first attempt of the observer should be with a dilated pupil. For an observer to see the details of the fundus clearly with the upright image, some knowledge of the optical condition of his own eye is necessary, as well as that of the eye to be observed, and any existing fault should be corrected by the proper neutralizing glass. The inexperienced observer, even if emmetropic and able to relax his accommodation perfectly for distant objects, is usually a little, sometimes a good deal, myopic for the ophthalmoscope. This comes from the fact that he is unable to adjust his eye for parallel rays when looking into an eye which he knows to be only a short distance from him. He instinctively accommodates and transforms his eye for the time being from an emmetropic to a myopic eye. This must be cor- rected by a suitable concave glass behind the mirror. It is better for the beginner not to waste too much time in trying to correct his myopia, either natural or acquired, too exactly ; but to 20 TEXT-BOOK OF OPHTHALMOSCOPY. take such a glass as will enable him to see the fundus with ease and distinctness, and, this having been attained, the observer will gradually learn to discard the use of too strong a glass by gradually substituting for it a weaker one. The weaker the concave glass, consistent with perfectly clear vision, the better. If, on the other hand, the observer is hypermetropic, and can so relax his accommodation as to be able to use a convex glass, this should be as strong as possible, so that he may see with as little strain on his accommodation and get as large an image as can be secured. The general directions for the movements of the patient's eye, up and down, to the right and left, are of course the same as with the in- verted image, only it must be borne in mind that the positions of the objects are really as they appear, and not, as with the inverted image, reversed. The macula lutea is found by following a line directly out- ward from a little below the centre of the optic nerve, and for a dis- tance from its edge of a little over two of its diameters. CHAPTER III. THE ANATOMY OF THE FUNDUS OF THE NORMAL EYE. NOWHERE, except perhaps with the microscope, is the difference between mere sight on the one hand and observation on the other so clearly exemplified as in the use of the ophthalmoscope. It is easy enough after the requisite practice to see with the instrument ; but to appreciate properly what is seen, and especially to differentiate between slight variations, whether of health or disease, requires not only a per- fect perception of the picture as a whole, but an intimate and exact observation and analysis of each and every constituent of the part under consideration. To appreciate every detail of the picture, and to give to each its due significance, necessitates therefore an intimate acquaintance with the anatomical elements of the part and their relationship with and dependence upon each other ; and I earnestly recommend to those who wish to acquire the art of ophthalmoscopy, so as to use it with ease and surety, to become as conversant as their opportunities will permit, not only with the grosser anatomical construction, but also with the essential details of the minute anatomy of the parts which contribute either directly or indirectly to what is seen with the mirror. As the works by which this would be accomplished are often inaccessible to the student and practitioner, I have thought it advisable to preface what I shall have to say in regard to the ophthalmoscopic picture of the normal eye by a short account of the principal anatomical factors out of which the picture is developed. The optic nerve, in its passage through the orbit, is invested by two sheaths, an " inner " and " outer sheath." The outer sheath, since it is continuous with the dura mater, if not a part of it, is called the dural sheath, while the inner, being derived from the pia mater, is called the pial sheath. The entire space between these two sheaths that is to say, between the dural and pial sheath is called the inter- vaginal or subvaginal space, but it is important to notice here that this space taken as a whole is divided longitudinally by another sheath, the arachnoidal sheath, which is shown in the drawing by the letter (a). 22 TEXT-BOOK OF OPHTHALMOSCOPY. This subdivides the intervaginal space into two spaces. The space lying between the outer, or dural sheath, and the arachnoidal sheath (a) is called the subdural space, and is continuous with the subdural or arachnoidal space of the cranium. This space, as will be seen from FIG. 5. Section through the optic-nerve entrance. (From Henle, modified by Schwalbe.) r, retina ; cA, choroid ; scZ, sclera ; will be only four inches ; con- sequently, it will require a concave to render the rays parallel at two inches from the eye, while it only required | at the nodal point. If the glass ( -ff= -iV-4 i- The hypermetropia in the observed eye is, therefore^ for an emme- tropic observer always equal to the glass used, minus the distance of the glass from the nodal point of the examined eye. As the accommodation is equivalent to a convex glass of different focal lengths, it is evident that the observer may substitute his own accommodation for the glass, provided he knows just how much he is using, and how far his nodal point is from that of the examined eye. For example, if the observer sees an eye distinctly, while he is conscious that he is accommodating for ten inches, he knows that the H in the observed eye must be equal to T ^- minus the distance be- tween the nodal points of his own and the observed eye. If this is two inches, then H = -fa _ 2 = . The ability to judge of refraction by the degree of tension required of the accommodation can only, of course, be brought into play in one condition that is, where the observed eye is hypermetropic, and REFRACTION ACCORDING TO THE STANDARD OF THE INCH. 127 even here it is rather a tour de force than an essential advantage. We can all of us, by a little practice, get an approximate idea as to the amount of hypermetropia in a given case by the amount of ten- sion required of our accommodation in getting a clear view of the fundus, but very few, even with any amount of practice, ever approxi- mate that precision which can be obtained with infinitely less trouble by means of glasses. As in the above cases the rays of light passing through the hole of the mirror are parallel, and will continue so if uninterrupted to infinity, it makes no difference in the result whether the observer's eye is close against the instrument or a little removed from it. The only calculation necessary is the distance between the glass and nodal point of the examined eye. The above directions, which are sufficient for an emmetropic ob- server whose eye is in a state of rest to determine any condition of refraction, may be summed up in this general rule : The ametropia in a given case is equal to the glass used plus the distance between it and the nodal point if the eye examined be myopic, minus the distance if it be hypermetropic. If, however, the observer is so unfortunate as to be ametropic, then the simplest way for him is to reduce his eye to a condition of emmetropia that is to say, to that condition of refraction that paral- lel rays unite on his retina, considering that portion of the accommo- dation which can not be relaxed as part and parcel of the refraction. If the ametropic observer does this, then of course the preceding directions will be all that he will have to bear in mind. Should he not wish, however, to pursue this course, he will find a little later the methods which he must follow. The following tables show the amount of decrease and increase in the length of the optical axis in various degrees of hypermetropia and myopia, according to the old system : H TABLE III. equals a shortening of 3.97 mm. H ^ equals a shortening of 0.85 mm. i a 2.9 " " TV M 0.74 " x (4 2.3 ' iV U 0.65 i a 1.89 ' TV U 0.58 1 u 1.6 ' inr u 0.52 | M 1.4 sV u 0.45 * u 1.25 nV tt 0.35 i u 1.12 M 0.26 -iV u 1. Iv (i 0.21 A U 0.92 -Iff u 0.18 128 TEXT-BOOK OF OPHTHALMOSCOPY. TABLE IY. increase of 8.6 mm. M -fa equals an increase of 0.97 ran ' 4.81 TT 0.82 i 3.34 TV 0.71 2.56 TV 0.63 * 2.07 -ZT5 0.56 4 1.97 Jl 0.46 1 1.5 sV 0.37 1.31 f u 0.27 1.17 50 0.22 1.06 1 It 0.20 M \ equals an " i " i 7 TV It should be remembered that these tables are calculated for the actual degree of ametropia present, and not for the glass used in cor- recting it. The observer must consequently make the proper addition or subtraction according as the glass is positive or negative, and ac- cording to the distance at which it is placed from the nodal point. This varies with different observers from about an inch to two or even three inches from the nodal point. If, for example, the ob- server sees the bottom of a hypermetropic eye with -J- , and the distance of his eye from the nodal point is two inches, then the real hypermetropia is not |-, but _ 3 = J-, and it is for the latter degree that the observer must consult the table for the true amount of shortening of the axis. So, too, with the negative glass, except that the distance between the glass and the nodal point must be added. If the observer uses -|- two inches distant, then the real M is -J- + 2 = -fa. As the dis- tance from the anterior surface of the cornea to the nodal point is only a little over a quarter of an inch, the observer may, for all practical purposes, make his calculations as between his own and the observed eye. The formula used in the construction of the table given in the text is that used by Helmholtz.* This is h 4 =f\ F%. In this equation ^ signifies the distance of the object from the first focal point when the object lies in front of it ; Z 2 is the distance of the image of the object behind the second focal point. F^ F 2 are the two principal focal lengths. Tf Tf From Z t Z 2 = f\ F z we get directly ^ , As the value of l lt f'l the distance of the object, is given, and JF\ and F z are already estab- lished values, we can at once calculate that of 1 2 . In case, however, the object lies behind the first focal point, l { will * " Handbuch der physiolog. Optik," p. 64. REFRACTION ACCORDING TO THE STANDARD OF THE INCH. 129 lie in front of the second point, and then both ^ and 1 2 have a nega- tive significance. The practical application of the formula is as follows: Suppose M% exists, what is the increased length of the antero-posterior axis ? The far point of such an eye, calculated from the first nodal point, is two inches or 54.2 mm. But as Z l5 the distance of the object, is not calculated from the first nodal point but from the anterior focal point, which is 19.875 mm. in front of it, l t therefore equals 54.2 19.875 = 34.3 mm. "We have then the following values : l v = 34.3 mm. ; f\ = 14.858 ; F 2 = 19.875. Substituting these values in the equation I, = ^ we get h , 14.858 X 19.875 295.3 l * = -3473- = 34. : The increase of the antero-posterior axis in J/ equals 8.6 mm., as seen by the table. Supposing on the other hand II = ^ is present. Z x is negative and lies two inches behind the second nodal point, which, in its turn, is 20.3 mm. behind the first focal point ; ^ therefore equals 54.2 -4- 20.3 = 74.5 mm. F^ F% as before equals 295.3 mm. Therefore 295 3 Z 2 = ~7fTfC = ~ 3-97 mm. Thus a hypermetropia of ^ corresponds to a decrease of the antero-posterior axis of 3.97 mm. DIRECTIONS TO BE OBSERVED IN CASE THE OBSERVER IS AMETEOPIC. The observer being myopic. PROPOSITION I. For a myope to examine an emmetropic eye. It is very evident that, as the rays which leave an emmetropic eye are parallel, the myopic observer, provided he can relax his accom- modation, will simply have to use the glass behind the mirror which neutralizes his myopia that is to say, which brings parallel rays to a focus on his retina. If a concave ^ does this, then -- will be the glass employed, and whenever he sees an eye distinctly with this glass, he knows that the rays which leave it must be parallel, and consequently it must be emmetropic. But it may happen that the myopic observer, like the emmetropic, can not relax his accommodation while using the ophthalmoscope. This will make him just so much more myopic, and instead of using, say, , which fully neutralizes his myopia, he will with the ophthal- moscope have to use, in order to bring parallel rays to a focus on his retina, % or . Under these conditions his eye is equivalent to a 130 TEXT-BOOK OF OPHTHALMOSCOPY. myope's of or , whose accommodation is entirely relaxed. The observer will then know that when the eye under examination is seen clearly with this glass it must be emmetropic. As the rays leaving the emmetropic eye will always strike upon the glass used as parallel, it is evident that the distance between the two eyes need not be here taken into account, and that, consequently, the observer may be one or more inches from the observed eye, as he pleases. PROPOSITION II. For a myope to determine the degree of myopia in the observed eye. If the observer does not wish to wear a correct- ing-glass, which is often inconvenient and clumsy, the simplest way for him is to proceed with the examination just as an emmetrope would, and find by trial with what glass he sees the fundus most dis- tinctly, his accommodation being, of course, relaxed, and then to take into account the amount of his error in refraction ; saying, for exam- ple, a myope of finds that he sees the fundus of the examined eye with concave ^, what is the amount of M present ? The observer knows that a part of this glass \ is employed in neutralizing his own myopia, consequently, to get the true glass through which the fundus would be seen independent of his error of refrac- tion, he must subtract this ^ from % used, ^ -^ = ^. Now, assum- ing the distance to be two inches, we have ^ + 2 = J-. The amount of myopia in the examined eye is, therefore, equal to , and a myope of % will have to use at two inches in order to see the fundus clearly. From this it will be seen that the myope of even a medium degree will have to use very strong glasses to see the fundus of an eye which is only moderately myopic. PROPOSITION III. For a myopic eye to determine the degree of hypermetropia in a given case. Let A represent a hypermetropic eye FIG. 54. of $ ; rays coining from the fundus of such an eye will diverge as if they came from a point eight inches behind the nodal point at a'. If REFRACTION ACCORDING TO THE STANDARD OF THE INCH. 131 now a myope of ^ (B) place his eye two inches in front of the ob- served eye, then the rays which enter his eye will diverge as if they came from a point ten inches in front of his nodal point, that is to say, his far point, and, as his eye is just adapted for such rays, they will come to a focus on his retina, and he will get a clear view of the f undus without the use of any glass (Fig. 54). If the observer's eye is at four inches from the observed eye, then the rays which enter his eye will diverge as if they came from a point twelve inches in front of his nodal point, and the observer will only have to be myopic ^ to bring such rays to a focus. The hypennetropia in the observed eye is then always greater than the observer's myopia by as much as the observer's eye is distant from the observed. In the above case H -^ _ 2 = -|-. II = ^ _ 4 = fa. If the hypermetropia in the observed eye is greater than the ob- server's myopia (the distance between the two eyes being taken into consideration), it is evident that the rays will emerge so divergent that they will no longer meet upon the observer's retina, but behind it. In order to bring such rays to a focus, he must make himself so much more myopic. This he does by a convex glass which he finds by trial just as an emmetrope would. For example, a myope of T 1 finds that he needs a convex -^ to see the f undus distinctly. If he adds this glass he is no longer myopic ^ but T^ + iV = i- Now we have just found that the H equaled the M minus the distance, and as the M ' fa we get H = % _ 2 = ^. The observer in this case may use his A instead of a lens, provid- ing he can estimate the amount. If, however, the hypermetropia in the observed eye is less than the myopia of the observer (the distance between the eyes being taken into account), it is evident that the rays emerging from the eye will be so little divergent that the stronger myopia of the observer will cause them to meet in front of his retina. The observer must make himself less myopic in order to bring such rays to a focus on his retina; this he does by means of a concave glass. For example, a myope of fa can only see the fundus in a given case with -fe, what is the H of the observed eye ? By placing the concave glass before his eye, he has reduced his myopia so that he has no longer M = -J-, but fa T *g- = fa. As we have previously found that H M minus the distance, we have H = fa _ 2 = %. The observer being hypermetropic. PROPOSITION IY. For a hypermetropic observer to see an em~ metropic eye. Inasmuch as the rays leaving an emmetropic eye are 132 TEXT-BOOK OF OPHTHALMOSCOPY. parallel, the observer, in order to bring such rays to a focus on his retina, will simply have to neutralize his manifest hypermetropia. If he is H -fa, then he will simply have to place a convex fa behind the mirror. He may find, however, that with the ophthalmoscope he does not relax his accommodation. His hypermetropia, consequently, will be re- duced by just the amount of accommodation which he is using. And he may find that instead of using say a convex of -fa, which fully neutralizes his manifest II, he will, with the ophthalmoscope, require only -^ to bring parallel rays to a focus. Under these conditions his eye is in fact equal to a hypermetrope's of ^-, who can entirely relax his accommodation, and the observer will then know that an eye seen distinctly through this glass must be emmetropic. It may happen in this way that a person, who is slightly hypermetropic for the distance, becomes for the ophthalmoscope emmetropic, and so has to use no glass. For example, a hypermetrope of -fa may find, on account of his inability to relax his accommodation, that in order to see an em- metropic eye he needs a concave g^. The amount of accommodation which he uses would then only be -fa, and many inexperienced ob- servers use fa. In this case the observer is virtually myopic, and must proceed as such. The observer may of course use his accommodation in all cases instead of a convex glass, that is to say, the lens in his own eye instead of one behind the mirror. He would, however, in this case have to know just what amount of tension of his ciliary muscle corresponds to a given glass. PKOPOSITION V. For a hypermetropic observer to determine the amount of myopia in the observed eye. Let A be myopic \ (Fig. 55) ; rays of light coming from a will meet eight inches in front of A's nodal point at a'. If B, who is hypermetropic -J-, places his eye two inches from A, then rays from A would meet, if uninterrupted, at a point just six inches behind I?s nodal point. Now, as B's eye being hypermetropic ^ is adapted for such rays, they will be brought to a focus on the retina. Consequently A's myopia must be equal to REFRACTION ACCORDING TO THE STANDARD OF THE INCH. 133 hypermetropia plus the distance, J/=^ +2 =|-. From this it follows that a hypermetrope of a certain degree can see the fundus of a myope of a certain degree without any glass. If, however, the myopia of the observed eye is greater than the observer's hypermetropia, it is evident that the rays emerging from the eye examined will be so convergent that they will meet in front of the observer's retina ; to bring them to a focus he must make him- self more hypermetropic. This he does by means of a concave glass, which he finds just as an emmetrope does by trial. For example, a hypermetrope of -fa finds that he, with his accommodation relaxed, sees the fundus distinctly in a given case with concave -^, what is the myopia in the observed eye ? By putting the concave -^ before his eye, the observer has made himself just so much more hypermetropic. He is consequently no longer hypermetropic one eighteenth, but -fa -f- ^ = ^. Now, as the myopia in the observed eye is equal to the observer's hypermetropia, plus the distance, we get M = ^ + 2 = |-. If, however, the myopia in the observed eye is less than the ob- server's hypermetropia (the distance between the two eyes also taken into consideration), rays emerging from the observed eye will not be convergent enough to meet on the retina, but behind it. To make such rays meet on his retina he must make himself less hyperme- tropic. This he does by a convex glass which he finds by trial. For example, a hypermetrope of ^ sees in a given case with a convex -fa, what is the degree of myopia present in the examined eye? By adding the convex y 1 ^ to his eye, the observer has reduced his hyper- metropia, making himself no longer hypermetropic ^, but -^ fa = fa. Now, as the myopia equals the hypermetropia plus the distance, we get M = fa + 2 = jjJjj-. Thus we see that a hypermetrope may, accord- ing to circumstances, in estimating myopia, use no glass at all, or a convex, or a concave one. PROPOSITION VI. For a hypermetropic observer to estimate the amount of hypermetropia in the examined eye. The best way in this case is for the observer to find by trial with what glass he sees the fundus most distinctly, and then to take his own error of refraction into consideration. For example, a hypermetrope of fa sees the ex- amined eye with convex -^, what is the hypermetropia present ? The observer knows that a part of this, equal to one eighteenth, is em- ployed in neutralizing his hypermetropia ; consequently, to get at the true glass which would be used independently of his error in refrac- tion, he must subtract this fa. | fa = fa. As the observer has thus 134: TEXT-BOOK OF OPHTHALMOSCOPY. neutralized his hypermetropia, lie is virtually emmetropic, and knows that the H present must be equal to the glass used minus the distance. & = T5-2= ITT- THE DETERMINATION OF THE REFRACTION OB' AN EYE BY THE MIRKOR ALONE, AND BY MEANS OF THE INVERTED IMAGE. It has been already shown how, with a myopic eye, we get with the mirror alone an inverted aerial image of a small portion of the fun- dus, an image which is situated in front of the eye, and at the distance of its far point. With a hypermetropic eye, on the contrary, we get a virtual and erect image behind the eye, and at a distance equal to the degree of the hypermetropia. If, then, we could only tell in a given case whether the image which we see is inverted or upright, then we should know at once whether the eye examined was myopic or hypermetropic. There are various ways of ascertaining this : (1.) Both the image and the field of view are larger (except in very extreme degrees) in myopia than in hypermetropia. (2.) In myopia the image moves in a sense contrary to that of the observer's head, and the more so the farther it is in front of the ob- served eye. In hypermetropia it moves with the head of the observer, and the excursion is less. (3.) The observer, as a rule, can tell whether he is accommodating for an image which lies in front of the eye examined, or behind it, the difference in the position of the images even in high degrees of the two kinds of ametropia being considerable. Suppose, in this connection, the observer is emmetropic, and that his near point lies in six inches. He can then accommodate for an object at that distance, but no nearer. In a given case in putting up the mirror he gets an image which, on his gradually approaching his head and exerting in a corresponding degree an increased tension on his accommodation, remains distinct up to a certain point, when sud- denly it begins to grow a little indistinct. Withdrawing his head a trifle till the image is clearly defined again, the observer know r s that the image must lie six inches in front of his own eye. And, if the distance between this and the observed eye is greater than six inches, the image must then lie in front of the eye examined, which is con- sequently myopic. But, on the other hand, supposing the image does not grow indis- tinct at all till the observer gets close up to the observed eye say two inches from it he then knows that the image can not lie in front of REFRACTION ACCORDING TO THE STANDARD OF THE INCH. 135 the observed eye, which is only two inches distant, for if it did it would be so blurred as not to be recognizable, being so far within the limits of his accommodation. The image must lie behind the eye, which must be consequently hypermetropic. The nature of the refraction having been ascertained in this way, it remains to determine its degree. The application of the mirror in this manner and for this purpose is at the best but limited, as it is only in cases of high degrees of ametropia that it is of any service at all, and only in cases of great myopia where its advantages outweigh its difficulties and give it a practical importance. Theoretically it would, of course, be just as applicable to // as M, the only difficulty being the telling just how far behind the observed eye the virtual image of a small segment of the f undus really is. The difficulty is, however, so great, either by means of the accommodation or with glasses, that it is hardly worth while attempting it, especially when with the upright image the fundus of a hypermetropic eye is so readily and distinctly seen an advantage which does not obtain from the very construction of the eye in myopia of high degrees, the illumination of which, for many reasons, is difficult and insufficient. It is thereof ore to the illustration of this latter condition alone that our examples will be applied. We will begin, for the sake of simplicity, by supposing that the observer is himself myopic, for example, -. His far point would then lie at eight inches, and any object at a greater distance than this would appear indistinct. Such an observer in a given case gets an image with the mirror alone, and at the ordinary distance say sixteen inches an image which, though recognizable as to its general outlines, is not sharply defined. Approaching the eye till the definition becomes perfect, and stopping the moment it does so, the observer knows that the image must lie at his far point, or eight inches in front of him. The observed eye is still, however, twelve inches from him ; conse- quently the image must lie four inches in front of it, and the myopia be equal to ^. Suppose, however, the distance between the two eyes had been ten instead of twelve inches, then the distance of the image in front of the observed eye would have been 10 8 = 2 inches, and the myopia would have been equal to . Again, suppose the observer had been myopic ^, and the distance between the eyes was ten inches, then the place of image would have been 10 6 = 4, and M = . The observer has then only to know his own myopia and the distance between the two eyes, and to subtract the former from the latter, to know the amount of M in the observed eye. If, however, the observer is not myopic naturally, he can make 136 TEXT-BOOK OF OPIITIIALMOSCOPY. himself so very readily by putting a convex glass behind the mirror. If he be emmetropic and can fully relax his accommodation, and uses -|--g-, his far-point will then lie at eight inches, as in the former case, and he now proceeds in precisely the same way as if he were naturally myopic, and in the manner just related. If he can not fully relax his accommodation, then allowance must be made for this. If, for exam- ple, he involuntarily uses what is equal to -\- -fa, then he is already myopic -fa, and will have to add the difference between that and -|-. | fa = T ^-, and with this glass he will be in precisely the same con- dition as a myope of % or an emmetrope with -|- -|-, who can relax his accommodation entirely. If, on the other hand, the observer is hyper- metropic, he must first neutralize this. If, for example, he has 11= -fa, he will, in order to make himself equal to a myope of , have to use I -f- fa = ^, and so on. In all these cases requiring the addition of a convex lens the ob- server might have used his accommodation instead of the glass, pro- vided he had such a control over it as to be able to estimate precisely what amount he was using. It may even happen that the observer's myopia is so great that he will be forced to use a concave glass in order to bring his far-point to six or eight inches. It is better to do this when the M is greater than , as the difficulty increases when the observer has to approach closer than this to the image. If he has J^f= %, then he will need to carry his far-point out to eight inches, J -|- = . DETERMINATION OF ASTIGMATISM WITH THE MIRROR ALONE. Many years ago, Mr. Bowman * pointed out the fact that he had been led to the detection of regular astigmatism and the directions of the chief meridians by the use of the mirror of the ophthalmoscope in the way which he had previously suggested for conical cornea. The mirror is to be held at about two feet from the eye, and its inclination rapidly varied so as to throw the light on the eye at small angles to the perpendicular, and from opposite sides, in successive meridians. The area of the pupil then exhibits a somewhat linear shadow in some meridians rather than in others. Little or no effect occurs, however, from moderate or even from comparatively well-marked deviations from the normal curvature. Mr. Couper, in 1872,f dilated somewhat upon this method, and proposed the use of a special mirror of thirty inches focal length, with which the eye is illuminated from a distance of some three or four * See " Refraction and Accommodation," Donders, p. 490, 1864. t "Fourth International Congress Report," London, 1872, p. 109. ASTIGMATISM WITH THE MIRROR ALONE. 137 feet. In this way Mr. Couper asserts that very low degrees of astig- matism can be detected, and the directions of the principal meridians ascertained. There are many objections, theoretical as well as practi- cal, to this method in the author's mind, and in his hands it has not proved either " easy or expeditious." Mr. Couper himself admits that it is not very well adapted to several of the commonly occurring forms of astigmatism, and it would hardly seem advisable to take the trouble of procuring a special and uncommon form of mirror for so limited a sphere of action, especially when not only the presence and kind, but even the degree of. every form of astigmatism can be accu- rately and easily measured with the ordinary mirror by the use of the upright image in the manner already explained in the foregoing pages. Since Mr. Bowman's article, others have taken the matter up and produced many and voluminous essays upon the subject of deter- mination of refraction with the mirror alone under the titles of " Keratoscopy," " Pupiloscopy," and " Retinoscopy." It still re- mains, however, in my opinion, the most difficult and least satisfactory of any of the methods of determining the refraction of an eye, and contributes nothing which can not be more easily and more expedi- tiously performed by the upright image. I would refer the curious, however, and those fond of optical problems for their own sake, to papers on the subject by Cuignet, u Keratoscopie," "Recueil d'Ophth.," 1873, p. 14; ibid., 1874, p. 316 ; ibid., 1877, p. 59 ; ibid., June, 1880. Mengin, " Eecueil d'Ophth.," April, 1878. Litton Forbes, "On Keratoscopy," "Royal Ophth. Hosp. Reports," vol. x., part i., p. 62, 1880. Morton, " Re- fraction of the Eye," London, 1881. Charnley, "Royal London Ophth. Hosp. Reports," vol. x., part iii., p. 344, 1882. Landolt, " Traite Complet d'Ophthalmologie," vol. iii., part i., p. 265, 1883 ; and others. DETERMINATION OF THE REFRACTION BY MEANS OF THE INVERTED IMAGE. Since the nearer an image is formed behind a lens the smaller it will be, it follows that the inverted image with a myopic eye, from which the rays already emerge as convergent, must be smaller than with an emmetropic eye when the same lens is used with each, and is held at or within its focal length from the eye. On the other hand, the image will be larger with a hypermetropic than with a normal eye under the same conditions. In this way we can often tell by the size of the image alone whether an error in refraction is present, and what its character is ; 138 TEXT-BOOK OF OPHTHALMOSCOPY. but only in a general way, and only when the defect is of a marked degree. We are able, moreover, to supplement the evidence gained in this manner by slight to-and-fro movements of the lens. "With a myopic eye, the size of the image, for example, of the disk, increases as we draw the lens away from the observed eye. With hypermetropia, on the contrary, it decreases as the lens recedes. In emmetropia the image remains the same for all distances of the lens.* Various appliances have from time to time been brought out for the purpose of ascertaining the exact position and size of the inverted image formed through the objective glass in different degrees of ame- tropia, with the aim of determining thereby its exact degree. Thus, Hasner produced an ophthalmoscope with sliding tubes and a gradu- ated scale on the principle of some of the optometers ; Coccius, an ocular composed of two lenses, also in a sliding tube ; Colsmann, a plano-convex lens, with a scale engraved transversely on the plane surface, by which the size of the image could be numerically meas- ured and some idea of the degree of refraction estimated. But all these, together with other devices, even the most recent, would seem to be either useless or inexpedient. The observer can, however, if he thinks it of sufficient importance, gain some insight not only into the kind of ametropia present, but also, approximately at least, as to its degree. To do this he has only to reduce all eyes to a greater or less degree of myopia by putting before them a convex lens of a constant strength, and then proceed to estimate the place of the image precisely as if the observed eye were really myopic. Let -|- -- be either held close before the eye, or, better still, placed in the spectacle-frame of the test-case. Rays leaving an emmetropic eye are parallel, and consequently such rays, after passing through the lens, will come to a focus at six inches in front of the glass where the image would lie. Rays from a myopic eye would strike the glass as already conver- gent, and the image would then be inside of the focal distance, and to a degree corresponding to the amount of the M. On the other hand, the image would lie with the hypermetropic eye farther from the glass than its principal focus, and the farther the greater the degree of II. In a given case the observer sees the image distinctly, while his A is perfectly relaxed through -j- \. The image must then be six inches in front of him. The distance between his and the observed eye or rather between his eye and the glass is twelve inches ; the image of the observed eye must be then six inches in front of the glass, or at its * Giraud Teuton, " Annales cTOculistique," September, 1869, p. 95. REFRACTION BY MEANS OF THE INVERTED IMAGE. 139 principal focus. To produce an image at this place the rays must leave the observed eye as parallel ; consequently, the observed eye must be emmetropic. In a second case the observer, through -f- ^-, sees the image while he is only nine inches from the glass ; consequently, the image must be only three inches in front of the observed eye, consider- ably within its principal focus. To produce an image in this place, the rays leaving the eye must have been convergent ; consequently, the observed eye is myopic, and the M = ^ $ = ^. Again, the observer sees the image clearly when the distance be- tween his eye and the glass is sixteen inches. The image must be therefore ten inches in front of the observed eye, and beyond the principal focus. The rays coming from the observed eye must have been divergent, and the eye hypermetropic. If = $ T V = -^. The distance between the glass and the nodal point has been neglected, as the method, at the best, has no sufficient claim to ex- actness. Its range of usefulness is indeed very limited ; still, it may often be of advantage to those who use the inverted image, and that only. THE DETERMINATION OF ASTIGMATISM BY MEANS OF THE INVESTED IMAGE. From what has already been said in connection with astigmatism, as observed by the upright image, it will be remembered that, when this irregularity of refraction is present, we see in the direct method the disk elongated in the meridian of greatest curvature, because, the lenticular system being stronger in that direction, the magnifying power is greater. With the inverted image we see the disk elongated in. the opposite direction, that is, in the direction of the weakest meridian, because, the image being formed behind the lens, it is less reduced in that meridian than the others. Thus, as Knapp and Schweigger showed by the alternate use of the upright and inverted image, we can not only detect the presence of astigmatism, but also the direction of its principal meridians. This, however, only holds good, as will be explained a little later, when the glass is held at a distance less than its focal length from the eye observed. It was in accordance with this restriction that Javal * pointed out the fact that it was not necessary to have recourse to the alternate use of both methods, but that the same interchange in the form of the disk could be effected with the inverted image alone, with the great advan- tage of keeping a continuous picture of the disk before the eye of the * "Etudes Ophth.," Wecker; tome ii., fasc. 2, p. 836, 1867. 140 TEXT-BOOK OF OPHTHALMOSCOPY. observer a picture which gradually changed its form, through all the phases of an oval with its longest diameter in one direction, to a circle, and then to an oval again, with its longest diameter in the opposite direction. The change is brought about by simply varying the dis- tance of the object-glass from the observed eye within the limits set by the image of the disk becoming smaller than the pupillary space, either from too close an advancement toward or too great a separation of the lens from the eye. Giraud Teulon * has amplified this idea of Javal's in a most ex- tended and elaborate mathematical discussion, with a clearness of style and a wealth of formula as varied as it is vast. To this essay, which is beyond the scope and character of the present work, the mathe- matical reader is referred for particulars. To such as are not, the following resume, condensed from the original so far as its ophthal- moscopic bearing is concerned, will be of service as well as interest : (1.) In the emmetropic eye, when the accommodation is relaxed, the image of the optic disk remains identically the same in character, and of the same size for every distance of the lens. (2.) In an eye which is regularly ametropic the image decreases (77) or increases (J/) with the distance of the lens. It always pre- serves, however, its original form, remaining circular if the disk is circular, and oval if it is oval. (3.) In an astigmatic eye the recession of the lens causes a varia- tion not only in the dimensions but also in the form of the image itself, i. e., of the disk. If the image be oval, with its long axis in a certain direction, when the lens is a short distance from the eye, it becomes exactly circular when this distance equals the focal length of the lens. At a greater distance, however, the direction of the long axis of the oval changes, becoming perpendicular to its former direction. Thus nothing is easier than to determine whether an eye is or is not astigmatic. Any positive lens which is suitable to produce an inverted image of all the diameters of the optic disk will solve the problem and indicate at the same time the direction of the principal meridians, and will, moreover, with a little care on the part of the observer, point out the nature of the defect ; thus : When the lens is close to the eye, the long diameter of the oval belongs to the meridian of the least refraction. From this position of the lens to one which is equal to its focal length from the eye,f when the image is exactly circular, the different diameters of the image have * " Ann. d'Oculistiqnes," Sept. et Oct., p. 95, 1869. t Plus the distance of the anterior focus, about one half inch. ASTIGMATISM BY MEANS OF THE INVERTED IMAGE. either increased or decreased. Those which have increased indicate myopic, those which have decreased hypermetropic meridians. If the two principal meridians have decreased or increased at once, that which has done so most rapidly belongs to the most ame- tropic meridian. This shows compound astigmatism general M or H, with increased $f or If in one meridian. Beyond the distance at which the image is exactly circular the con- ditions are reversed and become the same as in the upright image that is, the long diameter of the oval is in the meridian of the great- est curvature. The principle contained in the above may perhaps be more tersely expressed as follows : If the long diameter of the oval contracts when the lens is moved from the eye so as to become equal to the short, and thus make a cir- cle, then the astigmatism is due to //. If, on the contrary, the short diameter expands so as to become equal, at the focal distance of the lens, to the long, and thus make a circle, then it is due to myopia. If all the diameters contract but one contracts more than the rest then general If is present with II increased in one meridian. If all increase but one more than the rest then M is present with M increased in one principal meridian. The astigmatism is compound. If one diameter expands and one contracts, then both J/" and H are present, and the astigmatism is mixed. We see from this that astigmatism may be detected in two stages in the passage of the lens : first, when it is moved from a point close to the eye to a distance equal to its focal length ; secondly, from this point outward to a distance limited to the contracting field of view by which the image of the disk is rapidly shut out by that of the iris. It is in this last stage from the focal distance outward that the effect is most pronounced, as a rule. It is, however, better to make the lens move through the entire course. Great care must be taken not to rotate the lens at all, but to maintain it as exactly as possible in a plane perpendicular to its line of motion. So sensitive is this test that Javal declares that 1 D or less can be detected by it. Thus this method should never be omitted in making the preliminary examination with the inverted image, for, by a few passes back and forth with the lens, we can determine not only the existence of ametropia, but also its nature, and moreover gain an ap- proximate idea as to its degree. To determine this latter, however, with any exactness, it is far better as well as simpler to go at once to the upright image, which, in the comprehensiveness and delicacy of the test mentioned in the TEXT-BOOK OF OPHTHALMOSCOPY. light-streak of the vessels, amply fulfils all requirements either theo- retical or practical. By this means the determination of astigmatism of any form or degree becomes almost as simple as that of regular refraction. THE AMOUNT OF ENLARGEMENT PRODUCED BY THE UPRIGHT IMAGE. Looking through the lenticular system of the eye at an object be- yond say the optic nerve is precisely like looking through any lens of an equivalent power. The object thus seen appears enlarged, and the question is to determine, in case of the eye, how great this enlarge- ment is. Since the relative dimensions of the images of the same object on the retina are to each other as the respective distances of the object in front of the eye, that is in front of the nodal point, all that is needed to determine the comparative size of the image on the retina is to know the distances at which the object is seen. If, for example, a given object is at eight inches from our nodal point it will produce an image on our retina of a certain size. If moved to two inches and it is assumed that through the accommodation the object remains clear then the size of the image of the object at two inches will be, to that when it is at eight, as 8 : 2 = 4. The image in the last case will be four times as large. The result would have been precisely the same if, instead of our accommodation, we had used -j- placed close against the eye, and we had neglected the distance between the glass and our nodal point. To get, therefore, the magnifying power of any glass when the object viewed is at its focal length, we have simply to divide some distance taken as a standard by the focal length of the lens used. A distance of eight inches has been agreed upon. The magnifying power, therefore, of a two-inch lens = f = 4 ; of a one-inch lens f = 8 ; of one-half-inch lens = 16, and so on. Now, the focal length of the lenticular system of the eye has been calculated to be equal to 6.7" Paris lines that is to say, the distance from the nodal point of the eye to the retina is 6.7 lines. The mag- s'' 96'" nifying power of such a lens is consequently -7^ or ' ^ = 14. The fundus of an emmetropic eye is therefore seen under an enlarge- ment of 14 diameters. Moreover, when we look through a magnifying-glass placed close to our eye at an object, say, at its focal length, we do not see the object itself but its virtual image, and this image becomes, for the time being, a denned picture, which the observer can project to AMOUNT OF ENLARGEMENT BY UPRIGHT IMAGE. any distance, finite or infinite, that he pleases. The greater the dis- tance to which the image is projected, the greater the space which it appears to cover just as a small scotoma in one's eye may appear, when projected upon a piece of white paper held near the eye, to cover only a small circumference, but yet seem, when projected against the neighboring wall, to occupy a large extent of surface. This is due, of course, merely to the increased opening of the visual angle. This may be illustrated in a very simple way by imitating the con- dition of a normal eye. Set, for example, a one-inch lens so that it shall be just one inch from a piece of card on which some object as a picture of the fundus, for instance has been drawn. This is a rough but sufficiently exact imitation of the eye.* If we now place the model of the eye close to our own eye, we see an enlarged image of the picture beyond, which, by keeping the other eye open, can be projected to any distance we see fit. So, too, with the real eye as well as with the model, the optic nerve being thrown up against the oppo- site wall, and to all appearances covering a wide extent of surface. If we vary the experiment a little and draw, instead of the fundus, a square, each side of which is a determined length, say one line, and then rule a sheet of paper with squares of the same dimensions, we can then have ocular proof of the amount of enlargement. To do this we have simply to hold the model as close to our eye as possible, and then to hold the sheet of paper previously ruled into squares at ex- actly eight inches, since this distance is taken for the standard. If, now, the experiment is correctly performed, and the different measure- ments are likewise correct, we shall see, by keeping both eyes open, that the single square seen by one eye, and projected against the paper seen by the other, covers eight squares in each direction. Thus, the square seen with the glass forms on the retina the same size image as eight squares do without the glass. The magnifying power of the glass, therefore, is eight-fold. By moving the paper away from us, we see that the single square seen through the glass covers always an increasing, while if toward us a decreasing, number of squares. We have seen that with the emmetropic eye the enlargement is 14J times, and it remains to be seen how this is influenced by a con- dition of ametropia. * I might say here that a very convenient representation of the emmetropio eye can be had ready-made, in what is known in the shops as a cotton or linen counter. This consists of a small upright bit of brass, in which is set an inch Jens of about half an inch in diameter. This upright is connected with a second upright by a short horizontal bottom-piece which is just the focal length of the glass. To the second upright can be attached a bit of card with the picture of the fundus of the eye drawn upon it. TEXT-BOOK OF OPHTHALMOSCOPY. Let Iffa or 12 D, be present, due to the shortening of the antero- posterior axis. A convex $ (12 D], placed close against the cornea the distance between the nodal points being neglected will, for all practical purposes, reduce the eye to a condition of emmetropia, as rays leaving it would be parallel ; yet the lenticular power, at the focal distance of which is the retina in each case, is very different from that of the naturally ernmetropic eye, for, whereas in the latter it is equal to 6.7 lines, in the reduced hypermetropic eye it is greater by the lens which we have added, and equals ^, f , -f- , or, reducing this last to lines, -g* T -j- fa = -fa. AVe have, consequently, as the enlarge- ment, 8", or 96'", divided' by 5.6'". f.f = 174 times - It would have been the same had If been latent and corrected by the accommodation. Suppose M , or 12 J), is present, caused by lengthening of the axis. It would require (12 D) close to the cornea to make the rays leave the eye as parallel. The lenticular system, at the focal dis- tance of which the retina is, would then be equal to fa,,, -fa,,, = -J^. 06 111 gV2T 11 '2- If in any case it could possibly happen that with a normal length of axis there was a faulty condition of refractive power an increase on the one hand producing J/, and on the other a decrease causing H then the lens which restored the balance would simply reduce the eye to an emmetropic eye, and we should have the same enlargement as in the normal eye. Now, although all this is exceedingly simple in theory, it is by no means so when we come to apply it in a practical manner and to the wants of the ophthalmoscope ; for the correcting-glass can not be ap- plied directly against the cornea, neither can the distance between the nodal points be neglected. Kor can we assume, as we have done, that the anatomical conditions are the same in all eyes to such a degree that the component parts of the fundus as, for example, the optic disk and vessels are invariably the same size. Indeed, we are certain that here, as elsewhere in the body, they vary to a considerable amount. This would be naturally expected, and would be in accordance with the fact that considerable variations occur in the size of the image in eyes which are known to be emmetropic. Mauthner is inclined to believe that this difference in size of the image in a normal eye may be due to a difference in the length of the antero-posterior axis, which is counterbalanced by a corresponding increase or decrease in the refracting apparatus of the eye, by which the rays still issue as parallel. Thus, we might have a longer axis with a weaker, or a shorter axis with a stronger lenticular power. The AMOUNT OF ENLARGEMENT BY UPRIGHT IMAGE. 145 eye would in each case be emmetropic, but the enlargement would be greater in the latter than in the former case, and in proportion to the degree of shortening. Mauthner has calculated that while the enlargement in II = \ (12 D) is 17 times, the glass being considered an integral part of the eye, it is in the same degree of H corrected by -j- 3i, half an inch from the nodal point, but 15^ times; and again, if corrected by-j-J one inch in front of the nodal point it is only 13 times. From a series of mathematical deductions, the same author arrives at the following general conclusions : When an anomaly in refraction is corrected by the proper glass one inch from the nodal point, we obtain with M always a greater, and with H always a less, enlarge- ment than with emmetropia, while with the inverted image the en- largement is less with M and greater with // than with E. The examination of a myopic eye with a concave glass, which is necessarily stronger than the degree of the myopia, since the glass can not be placed at the nodal point, is on the principle of the Galilean telescope, in which the lenticular system of the eye is the object-glass, and the lens behind the mirror the eye-piece. In such a combination the stronger the eye-piece the greater the magnifying power, but the farther the eye-piece must be from the eye. If, for example, we have a myopia of ^-, the fundus can \>e seen, A. being relaxed either through - at one inch, or \ at two, or i at four inches from the nodal point of the observed eye. In each case the fundus will be seen under an increasing enlargement, but at the same time with a rapidly decreasing field of view. Stammeshaus, taking advantage of this principle, proposed to re- duce such eyes as were not naturally myopic to that condition by con- vex glasses, and then to view the fundus through concave glasses of different strengths and increasing distances in front of the eye, accord- ing to the amount of enlargement desired. This method, which had already been tried in this country several years before the suggestion of Stammeshaus appeared in print, possesses theoretical rather than any practical merits, in which indeed it is signally wanting, not only on account of the great reduction of the field, but also from distortion of the image and from annoying reflections which arise from both sur- faces of the interposed convex glass. When, however, the myopia is natural, and the pupil fully dilated with atropine, the method may be occasionally used with advantage, though even here it is better to go at once to the inverted image, using a weak object-lens in the manner suggested by Liebreich, and already described in the chapter on the use of the inverted image. 10 CHAPTER VI. EXAMINATION OF THE MEDIA OF THE EYE. THERE are two principal methods of examination of the media : (1.) Oblique illumination. (2.) The ophthalmoscope. The former should never be omitted as a preliminary step to the latter, even where there is apparently no reason to suspect that there is any trouble in the media, for I have been so often the subject of mor- tification myself, and seen it so many times in others, that I can not refrain from again warning those who would use the ophthalmoscope successfully never to neglect this important factor in the detection of disease, especially before speaking of " diffuse opacity or oedema of the retina," or " want of definition in the outlines of the optic disk." OBLIQUE ILLUMINATION. THE CORNEA. The normal cornea, as a rule, even in adult life, has the appearance in ordinary diffused light, whether natural or artificial, of being a perfectly clear and transparent membrane. When, how- ever, condensed light is thrown upon it at an angle, as, for example, by oblique illumination, a delicate, smoke-like haze can be detected, which, though always present, even in infancy, becomes more and more pronounced as life progresses, until, in extreme old age or pre- mature decay, this haziness is sometimes so dense as to lead to the sus- picion that it is due to a pathological and not a physiological condition. This opalescent appearance, whether in old or young eyes, is due to the laminated structure of the cornea and the mesh-like manner in which its component parts are arranged ; for, although the substance proper of the cornea can not be said in any very strict sense to be arranged in regular layers, still its tissue, together with the corneal epithelium, Bowman's membrane, the membrane of Descemet, and the endothelium, is sufficiently stratified to present a number of surfaces at different levels, from which, taken as a whole, enough light is reflected to produce the slight want of transparency expressed in the delicate haze just alluded to ; and especially is this true when the angle of incidence and reflection is of a considerable degree. EXAMINATION OF THE MEDIA OF THE EYE. 147 The amount of this haze varies very much with different individu- als even of the same age. Thus, in children, or even in young adults, especially in those who seem to have some scrofulous taint, I have often noticed an unnatural pellucidness of the cornea, which gave an un- wonted brilliancy and glassy expression to the eye ; while, in others of the same age, the cornea, when subjected to oblique light, showed all that want of transparency corresponding to a much later time of life. By throwing the light obliquely from the side into the eye, we illuminate the surface of the iris and the anterior capsule, which re- flect the light thrown upon them back to our own eye. Thus, we detect the shape and position of even the minutest speck in the other- wise clear substance of the cornea, by the contrast produced between it and the surrounding tissue, by transmitted light, while at the same time, from that portion of the light which is reflected from their an- terior surfaces, we see the opacities themselves in their true color and form, or what very nearly approaches it. Even when the pupil is thoroughly dilated by atropine, sufficient light is reflected from the anterior capsule and body of the lens and deeper portions of the eye to get the effect of contrast between the opacities and surrounding clear tissue quite as well, and, I have sometimes thought, better marked than with an nndilated pupil ; and especially is this true with the minutest spots in keratitis punctata and slight disturbances in or upon the membrane of Descemet. The entire surface of the cornea must, of course, be gone over with the eye in its various positions. Yery different from the delicate, smoke-like haze seen in the healthy eye, and which seems to lie beneath the polished surface of the cornea, is the coarse, dull reflex of a diffuse character which is seen by oblique illumination in some forms of superficial corneal dis- ease, and which is due to a lack of transparency and roughness of the epithelial layer. In such cases a part, usually the lower half, or even the whole surface of the cornea, has a dead, lack-lustre look, which is often noticeable even in ordinary daylight, but which under concen- trated light becomes strongly, sometimes intensely, marked, so that the surface of the cornea, either in part or whole, has the appearance of ground glass. This may vary in its color from a pure gray to a yellowish-brown, or even a rosy tint, especially near the corneal mar- gin, as if this latter appearance was borrowed from the presence of some vessels too minute to be seen as such. In rare instances, I have also seen what had the appearance of interstitial haemorrhage, so deep and close was the injection. In one case the entire cornea was a blood- red mass, as if the bleeding had occurred into the very substance of the membrane, the epithelial layer retaining its polish. 148 TEXT-BOOK OF OPHTHALMOSCOPY. So, too, the proper substance of the cornea may be the seat of a diffuse opacity, or want of translucency, which, though of pathological origin, may be so slight as to be distinguished with difficulty from a physiological condition, and which requires oblique illumination for its detection. When, however, the opacity is sufficient to produce any marked effect upon vision, and lies in the outer portions of the mem- brane, it is usually to be recognized in ordinary daylight, and then presents no difficulty of diagnosis to the naked eye. This, however, is not the case when the trouble lies in the inner layers of the cornea, or in the membrane of Descemet. Here oblique illumination plays a most important role and renders a most useful service. "With it the minute spots due to inflammation of the mem- brane of Descemet (Descemitis), or serous iritis, or choroiditis, come out boldly into view, when under examination by diffused light nothing abnormal could be detected. So, too, slight abrasions of the surface, minute specks, or deposits from foreign bodies, or the foreign bodies themselves, are brought distinctly into view. It is sometimes a little difficult even for a trained observer to tell the precise level which opacities in the cornea occupy, though experi- ence in a little while usually enables him to form a pretty accurate estimate of their position, so much so that I think it hardly necessary to go into an elaborate explanation of the method of examining the cornea for this purpose under water, especially as I have never done it myself or ever seen it done. Still, it is well enough to know that it can be done, and that the instrument by which it is accomplished is called an orthoscope, of which there are various patterns, such as those of Czermak, Coccius, and Arlt.* THE AQUEOUS HUMOR. The entire cornea having been thoroughly examined, the observer should pass next to a consideration of the anterior chamber and its contents. The aqueous humor, which in a state of health is a per- fectly transparent fluid, is often disturbed to a greater or less degree by the presence of minute particles, which are for the time held in suspension in it, and which make themselves manifest, under oblique illumination, by a more or less diffuse cloudiness of the anterior cham- ber. These diffused disturbances in the aqueous, whether of a puru- lent or sanguineous nature, offer but little trouble in their detection and need but little comment, except to call attention to the fact that it sometimes requires a little care to determine whether the opacity in * " Zander," Carter's Translation, p. 62. EXAMINATION OF THE MEDIA OF THE EYE. 149 question is really in the anterior chamber itself or in the inner layers of the cornea. Still less need be said of the aggregate masses of pus, or blood, or other detritus so often found at the lower borders of the anterior chamber, and which can be plainly seen with the naked eye, but which can be rendered a little more conspicuous by means of con- densed light, and seen to much better advantage with it than with the ophthalmoscope. As a great rarity, fine filamentous bands have been seen to stretch across from the apex of a pyramidal cataract w r hich projects from the anterior surface of the lens to the inner surface of the cornea oppo- site ; moreover, very minute, thread-like synechise, suggestive of a former and long-past perforation of the cornea, or at least of con- tact of the iris with its inner surface, are sometimes brought to light in this manner. Precisely the same thing may occur after small per- forated wounds, or even after the performance of an iridectomy, where the cut edge of the pupillary border of the iris has laid for a shorter or longer time against the inner surface of the cornea. While on the subject of the aqueous humor, it may be well to remind the reader that occasionally it is the abode of that species of entozoa known as filaria. These animals have been seen by several observers, among them Macnamara, who says there is no possibility of mistaking the appearance of entozoa of this kind in the anterior chamber, as the creature may be distinctly seen moving about in the aqueous. From Dr. Barkan's case in " Knapp's Archiv," the detec- tion would seem not such an easy matter, as it was not until a portion of the animal was examined under the microscope that a diagnosis was confirmed. THE IRIS. By means of light thrown obliquely into the eye, the anterior sur- face of the iris can be thoroughly illuminated, and can then be seen under considerable enlargement if a second lens is used in the manner already pointed out (page 6). By this method the grosser appear- ances of the membrane can be studied both in health and disease. With oblique illumination, also, the presence of small cysts, tumors, and other irregularities of its surface, such as condylomata, can be seen and watched in their course of growth and decline. The em- bossed, roughened, and, at the same time, velvety appearance of the entire surface of the iris due to iritis, and more yet to irido-choroidi- tis, comes out strongly marked under the influence of condensed light, and even increased vascularity of the membrane with a little care can generally be ascertained. In rare cases the iris may be the seat of 150 TEXT-BOOK OF OPHTIIALMOSCOPY. minute crystals of cholesterine, which then glitter like points of dia- mond dust under oblique illumination. I have seen a case in which the entire iris was studded with minute particles, giving to the mem- brane the appearance as if made of gold sealing-wax. The minute, as well as the larger, adhesions of the pupillary bor- ders of the iris to the capsule of the lens, their extent, form, and color, can be observed to the fullest advantage by this method of illumina- tion. So, too, exudations upon the surface of the lens, the remains of capsule after an operation for cataract, or the membranes which so often stretch themselves across from the pillars of an iridectomy, or the thread-like remains of the pupillary membrane. Yery deli- cate membranes, even where no operation has been performed, some- times form over the pupil, and I have known these web-like forma- tions to be so delicate as not to interfere in some cases, in any ap- preciable degree, with the clearness of the picture of the fundus as seen with the direct light from the ophthalmoscope, while in others the interference is so slight as to express itself only by a delicate want of definition of the entire fundus, the exact cause of which it is ex- ceedingly puzzling, if not impossible, to ascertain without the aid of oblique illumination. As a modification of the method of examining the iris by oblique illumination, Liebreich* proposed that the cone of condensed light should be thrown not directly upon the surface of the iris, but obliquely through the pupil and behind the membrane, so that this latter should be seen by transmitted light, or that reflected for the more posterior portions of the fundus. It is, however, only in albi- notic eyes, or where the iris itself is destitute of pigment, or very atrophic, that the method yields any satisfactory results. The same objection is applicable to Becker's method of throw- ing a cone of light upon the eye from a common ophthalmoscopic mirror in such a way that only one half of the cornea is illuminated, while the remainder of the light falls upon the sclera. In this way one half of the cornea and the deeper parts of the eye are in the shade, and only slightly illuminated by direct light in comparison with that which is reflected from the back of the eye, that is, by transmitted lightf THE LENS. Although the lens is apparently a perfectly transparent body when viewed by diffuse light, nevertheless, like the cornea, when subjected to condensed light thrown upon it from an angle, it betrays its want * Graefe's " Archiv," Vol. I., Ab. i., p. 353. t " Wiener medicinische Jahrbucher," 1863, p. 162. EXAMINATION OF THE MEDIA OF THE EYE. 151 of transparency by a delicate network of fine striae, which, cross the anterior portions of the lens and form radiating lines which consti- tute, as Mr. Tweedy * has expressed it, a visible stellation of the nor- mal lens. These lines are exceedingly fine and difficult to perceive except under the most favorable circumstances. ' A much more tangible appearance, and one which can always be obtained, is the delicate and smoke-like cloudiness following the pas- sage of the rays into the substance of the lens. This is due partly to the fact that the anterior capsule has a greater index of refraction than the aqueous humor, but more particularly to the anatomical arrangement of the fibres of the lens itself. From the multiplicity of these fibres, and from the fact that they are laid, as they are, one over the other, sufficient light is reflected to produce the delicate haze in question. This mist-like opacity exists as a physiological condition, to a greater or less degree, in all lenses. Barely perceptible in early youth, it grows more and more pronounced with progressing years, till oftentimes in old age it becomes, through some chemical or physi- cal change in the fibres, so dense as to suggest unmistakable evidence of the presence of cataract, or, if of a greenish or yellowish hue, the existence of glaucoma. Fortunately this apparent want of transpar- ency in the majority of cases vanishes under the ophthalmoscope, and with it the doubt in the observer's mind whether the turbidity is due to a pathological or physiological condition ; for, as a rule, when the reflex in the field of the pupil is perfectly clear and free from inter- ruptions, and the details of the fundus come out sharply, little fear need be entertained as to trouble in the lens. Care, therefore, should be taken not to pronounce too positively as to the presence of disease, from any peculiarity in the color of the reflex from the eye, either under daylight or from oblique illumination, as a physiological reflex may, from age or other circumstances, vary in its density and color from a delicate steel-like gray to a yellowish or reddish-brown. Still, there are cases, especially in young and middle-aged people, or those who have grown prematurely old, in which the utmost care is neces- sary to make a differential diagnosis, or to say whether a somewhat too pronounced haziness seen under oblique illumination is or is not an abnormal condition of the media. These are the cases which test most thoroughly the skill and acumen of even a practised observer, and the inexperienced must be doubly on their guard. Luckily, diffuse opacity of the lens, without one or more well- defined imperfections, be they never so small, is very rare. The state * " Royal London Opbth. Hosp. Reports," vol. viii, Pt. 1, p. 24. 152 TEXT-BOOK OF OPHTIIALMOSCOPY. of vision often helps us to a diagnosis, for this is very seldom reduced in itself, or the cause of complaint on the part of the patient, when the want of transparency is due to physiological conditions, perhaps from the fact that it conies, especially in elderly people, so slowly as not to have excited comment. When the diffuse haziness is the result of a pathological process, vision is usually reduced, and the loss, as a rule, easily detected by the patient; even when it happens in one eye, though the reverse may take place, and the trouble escape notice for a long time, and then only by accident be brought to light. Before the invention of the ophthalmoscope, and the more ex- tended use of oblique illumination, great reliance was placed on what is known in the older works as the catoptric test. In later times this has gradually fallen into disuse, until among the more modern observ- ers it is rarely, if ever, employed. This is regretted, as it should be, by some writers, especially by Mauthner, who loudly and not unpoetic- ally sings its praises. But I must confess that, with the exception of determining, in the most beautiful and, at the same time, most irrefu- table manner, the presence or non-presence of the lens itself, this method has not given in my own hands as satisfactory results, either as to the existence or position of lenticular opacity, as have the other more simple methods now in common use, that is, by oblique illumi- nation and the ophthalmoscope. Still, I have introduced a descrip- tion of this test here, as it is claimed that it lends its most important service in the very conditions now under consideration, that is, diffuse opacity of the lens. The principles which govern this test and its application are briefly stated as follows : The anterior surface of the lens curves outward, so as to present a convex surface to exterior objects. As the surface is highly polished, and the index of refraction higher than that of the aqueous humor, it has all the properties of a convex mirror, and will produce a reflec- tion of an object placed in front of it. The image of such object will be upright and reduced. It is a little difficult to see this image, as it lies directly behind that from the surface of the cornea ; it suffers, moreover, in contrast with the latter, being much less brilliant, since the difference between the index of refraction of the cornea and the air is much greater than that between the lens and the aqueous humor. The posterior capsule of the lens, on the other hand, backed by the vitreous, presents a concave surface to objects placed in front of it, and, as these latter must always be at a greater distance from the reflecting surface than the length of its radius of curvature, the images of the objects will be reversed as well as reduced. In this way the EXAMINATION OF THE MEDIA OF THE EYE. 153 reflection from the posterior can readily be told from that of the ante- rior surface of the lens. It can also be easily distinguished from that of the cornea, since it is not only reversed and paler, but also is at a distance from it. Moreover, the two images move, when the object is moved, in opposite directions to each other. The best method of viewing these images is to place the object used at one side of the eye examined, and for the observer to stand upon the other. The best object for this test, and the one which gives on the whole the most conspicuous images, is the classical one of a lighted candle. This should be held as close to the eye as possible, though, as be- fore said, to one side, while the observer stands upon the opposite side. In this way we get the largest possible image and the brightest illumination, since the angle of incidence and reflection are as large as circumstances will allow. If the candle now be held below the eye (the patient being seated, while the observer stands), the corneal image, which is upright, is formed near the lower border of the membrane, while that from the posterior capsule is reversed and stands considerably above the former, since the line of direction, passing from the candle through the cor- neal image, will impinge, if continued, at the upper part of the poste- rior capsule. If the candle is now carried upward, the corneal image rises, while that from the posterior capsule sinks. If the former passes to the right, the latter goes to the left, and so on. In this manner the image may be made to cover, by slight successive move- ments, the entire surface of the capsule. If, now, there is a disturbance in the body of the lens anterior to its posterior surface, that part of the image which would be formed by the posterior surface, were the rays not cut oif by the opacity lying in front, is wanting. The image of the candle-flame is then either obscured or entirely interrupted, according to the density of the opacity. If, on the other hand, the opacity lies behind the reflecting surface, that is, the posterior capsule, it has no effect either on the continuity or brilliancy of the image. The opacity must lie, there- fore, in the vitreous body. Now as to the diffuse opacity of the lens. " When the sun," says Mauthner, with a pardonable enthusiasm in comparing greater with lesser things, " sets or rises in a murky atmosphere, his at other times golden face has a rosy and occasionally even lurid tinge, from the fact that the red rays survive the quenching effect of a troubled medium better than the others, and therefore pass through it in greater quan- tities. For precisely the same reason the image of the posterior cap- 154 TEXT-BOOK OF OPHTHALMOSCOPY. sule, in case of a diffuse disturbance in the lens, has a rosy or even blood-red appearance, while that of the anterior capsule is not af- fected." * So, too, in cases of mild hyalitis, where there was a delicate, yel- lowish-gray reflex from the fundus, the writer has been able to ex- clude all participation of the lens by the perfect brilliancy offered in the reflexes of the anterior and posterior capsules, as shown by the catoptric test. OPACITIES OF THE LENS. Passing from the examination of the diffuse disturbances of the lens to those of a defined character, we enter the field where oblique illumination has its happiest exemplification, for in no other way do these lenticular imperfections come out so strongly in their true form, color, and position, as by this method when properly applied. All lenticular opacities whether of the capsule, anterior or pos- terior, or of the substance of the lens, cortical or nuclear show them- selves under oblique illumination as interruptions, of greater or less extent and density, in what under normal conditions is a uniformly clear field of pupil. When the opacity is in the capsule it is called an anterior or posterior capsular cataract, according as it is in the anterior or posterior portion of the investing membrane. If the dis- turbance is in the outer layers of the lenticular substance it is called a cortical, if in the inner a nuclear, cataract. All these varieties may exist alone or be combined with each other. In the latter case the cataract is said to be mixed. It is certainly not worth while to weary my readers with a de- tailed description of all the multitudinous shapes which the opacities included under the name of cataract, either stationary or progressive, may assume. Still, there are several varieties which possess such uni- form and characteristic features as to have a distinctive name, and as such merit a short description. Anterior Capsular Cataract. This usually appears under lateral illumination as a sharply defined spot in the centre of the capsule ; it may, however, be more or less irregular in shape, and vary consid- erably in size as well as position. So, too, with the posterior capsular cataract. Pyramidal Cataract. This consists of a whitish mass in the pu- pillary space, the apex of which projects, to a greater or less degree, from the centre of the anterior capsule into the anterior chamber, while its base extends backward into the substance of the lens. * "Lebrbucb der Ophtb.," Mauthner, p. 149. EXAMINATION OF THE MEDIA OF THE EYE. 155 Mautlmer * mentions having seen in several cases a modification of this form of cataract, which consisted of a double pyramid with a common base at the anterior capsule. The apex of one extended into the anterior chamber, that of the other backward toward the centre of the lens. In one case he saw two pyramidal cataracts in the game lens. The same author mentions the fact that sometimes, by oblique illumination, the anterior capsule may be seen to lie in radiating folds in the neighborhood of the pyramid. Zonular Cataract. This is a disturbance of the lens, in which the outer layers of cortical substance remain clear, as does the centre or nucleus of the lens, while the intermediate portion is affected. Thus, the nucleus is inclosed by a more or less dense and cloudy en- velope or zone, which is usually of a uniform thickness, and through which with the ophthalmoscope we get more or less distinctly a reflex from the fundus. Zonular cataract, instead of consisting of a single zone, may be composed of two (Graefe, Sichel), or even three concentric layers, which are opaque, and which are separated from each other by inter- mediate layers of clear substance. The zonular, like other forms of cataract, may be either simple or mixed ; when the latter it is usually progressive. In this respect it may be well to mention that Graefe observes that the cataractous proc- ess remains stationary so long as the cortical substance preserves its transparency ; but, if this becomes the seat of diffuse or punctate opacities, it may be looked upon as a sure sign that the process is pro- gressing. Spindle-shaped Cataract. Under this title a curious and very rare form of lenticular disturbance is described by several authors (von Ammon, Pilz, Miiller, Becker). From the centre of the anterior capsule in Becker's case, a bluish- white opacity extended, gradually increasing in size, toward the cen- tre of the lens. Here it inclosed the nucleus in a globular-like envel- ope, and then gradually decreased in size till its apex was inserted into the posterior capsule. Though not always so regular in its out- lines, its general characteristics are to extend along the central axis of the lens and to assume as it progresses a fusiform shape. Posterior Polar Cataract. This is one which has its seat in the deepest layers of the lens, near the posterior pole, or which may, ac- cording to some, take its rise in the vitreous body. It may exist as a circumscribed and defined mass, but usually has one or more often- times spike-like projections leaving it in different directions, and * "Lehrbuch der Ophth.," p. 140. 156 TEXT-BOOK OF OPHTHALMOSCOPY. which usually take the curve and plane of the posterior capsule. These projections are sometimes so regularly arranged as to resemble the spokes of a wheel. The same effect may take place on the anterior capsule and its neighboring corticalis, or both capsules may be af- fected at the same time, while the intervening substance of the lens remains clear. Secondary Cataracts. These, whether the result of injury or of operative interference, show themselves in the shape of membranes in the pupillary space. Sometimes these membranes are so delicate as to be almost transparent in their entire extent, or again here and there minute opacities or pigment-spots may be scattered over them. On the other hand, these membranes may be so densely opaque as to be impervious to light, either from lateral illumination or the ophthal- moscope, and in this case they sometimes suggest the idea that a cata- ractous lens is still present. These membranes may also assume band-like forms, which then appear to run across from one border of the iris to the other, but which in reality have their attachments, as attempts to remove them show, in the neighborhood of the ciliary body. The size and position of foreign bodies in the lens, such as bits of steel or stone, can often be ascertained by oblique illumination, even when the surrounding substance has become so much disturbed that the imbedded fragments can not be detected with the ophthalmoscope. For this reason lateral illumination should never be neglected after such accidents. Sometimes, however, the lenticular substance sur- rounding the body remains perfectly clear, even for long periods after the accident, and then, if the fragment is a chip of steel or other pol- ished substance, the characteristic metallic reflex is obtained. So, too, we are often enabled to follow the track of a perforating body by con- densed light, and to trace its passage through the cornea and lens, either by the disturbances in transparency at the point of entrance, or sometimes through the entire thickness of the wound. We can thus become convinced that the foreign body, though no longer in sight, has entered the eye. When a cataract has become fully formed, oblique illumination is by far the best means of studying its peculiarities. This is especially the case after inflammatory processes, such as iritis and choroiditis, through which the lenticular substance has undergone degeneration. In these cases we can often detect with its aid what appears under ordinary illumination as a homogeneous whitish-gray substance, that is concrete masses of chalky degeneration, or a multitude of minute and glittering specks of cholesterine, which give a sparkling appear- EXAMINATION OF THE MEDIA OF THE EYE. 157 ance, or a satin-like sheen, to the surface of the lens. The lens may, moreover, even when no such degeneration has taken place, have a marbled or segmented appearance, such as the section of a piece of talc or isinglass shows when polished. The position of the lens, and whether in a given case it lies in its proper place or is dislocated, can often be determined by means of lateral illumination. Especially is this true when a perfectly trans- parent lens is dislocated into the anterior chamber, either partially or entirely. Through total reflection we then get a beautiful silver ring, which plays round the extreme edge of the lens. As a rule, however, this method, in ordinary dislocations, is not so satisfactory as that with the ophthalmoscope, and for this reason this subject will be more fully treated under that heading. Opacities in the vitreous are, as a rule, better studied with the ophthalmoscope than with lateral illumination. Still there are occa- sions where this latter yields the best results, such as profuse haemor- rhages from vessels lying in the anterior parts of the eye, and where we consequently iind it impossible to get a reflex from the fundus with the ophthalmoscope. So, too, with tumors or gummata situated in the ciliary region, or in diffuse hyalitis, from which we get a dull, and occasionally a rather bright, yellowish reflex, but never so bright as that which comes from glioma, or from metastatic choroiditis, which is the sequela of cerebro-spinal meningitis. More, however, will be said on this subject in its appropriate place. EXAMINATION OF THE MEDIA BY THE OPHTHALMOSCOPE. When light is thrown into the eye from the mirror alone, at the ordinary distance for the inverted image, the pupil is seen to glow with a uniform brilliancy, which varies somewhat in color and inten- sity, according to the pigmentation of the fundus and the portion of it which is opposite, for the time being, the pupillary space. Should anything be present which interferes with the passage of the light, and therefore with the transparency of the media, this manifests itself either by a general reduction in the intensity of the reflex in the pupil, or by isolated interruptions in the illumination, according as the opacities in the media are of a diffuse or concrete nature ; and it may be well to mention here that very delicate disturbances, especially of a diffuse character, are better seen with the weak-light mirror, since with the strong they are, from their delicacy, sometimes overcome by the excess of illumination. On the contrary, these opacities, although diffuse, may be so dense, from their consistency or numbers, as to re- quire all the illumination possible in order to get a reflex from the 158 TEXT-BOOK OF OPHTHALMOSCOPY. fundus. When this is so, either a plane or concave silvered mirror is demanded. With a little care in subduing the light, when occasion requires it, the common concave mirror may be made to answer every purpose. "When, however, the eye is very sensitive to light, that is, when the pupil contracts unduly, I prefer, without there are very strong indications against it, to use a mild instillation of atropine than to employ a weak-light mirror, as is recommended abroad, for the pur- pose of avoiding too great a contraction of the iris ; and especially in the case of patients of middle or advanced age, where there is rea- son to apprehend that there may be trouble in the periphery of the lens. All interruptions of whatever size in the field of the pupil, no matter where they are situated, appear with the ophthalmoscope, as a rule, black. This is due to contrast, for the rays thrown by the oph- thalmoscope directly upon these opacities are not reflected from these surfaces in sufficient quantities, as is the case with oblique illumina- tion, to give them much, if any, individual tinge ; while, on the other hand, the light reflected from the fundus is not strong enough, except in the case of thin membranes, to pass through them and thus give them a transparency. In rare instances, opacities in the media may be of such a nature as to reflect light in sufficient quantities to pro- duce a lustre of their own by direct reflection, as is the case sometimes with bits of metal or particles of cholesterine. Thin membranes, from their delicacy, often appear of a grayish hue in the midst of the otherwise reddish-yellow field. There are other cases in which, in spite of all our efforts at illumination, the entire pupillary space maintains a jetty blackness. This shows that there is some insurmountable obstacle to the penetration of light into the eye. Sometimes an otherwise uniform and bright reflex is suddenly in- terrupted by the appearance here and there of black specks, of a greater or less size, due to particles or shreds of mucus which have adhered for the moment to the surface of the cornea. Long, black, string-like formations may come suddenly into the field, due to the eye-lashes, and caused by the drooping of the upper lid. The first requires a little care not to mistake them for deeper-seated and permanent dis- turbances. They can be removed by rubbing the upper lid gently over the surface of the cornea. The true character of the latter is at once detected when once they have been seen. Besides the method of viewing the opacities of the anterior parts of the eye with the mirror alone and from a distance, we have two others by which they can be seen under an increased enlargement, EXAMINATION OF THE MEDIA OF THE EYE. 159 and many may be thus brought to view which would otherwise escape detection. This first method consists in placing a strong convex glass, -}- 10 D or -f- 12 D, behind the mirror, and then approaching carefully toward the eye till different levels cornea, aqueous, humor, anterior capsule, substance of the lens, and even anterior parts of the vitreous are brought successively into focus. In this way minute opacities in the cornea, and especially in the membrane of Descemet, are brought into view which would other- wise remain invisible. To reap the full advantages of this method of examination, a brilliant illumination and a dilated pupil are requisite, though a great deal may be done without the last condition being fulfilled. By slight to-and-fro movements of the head, we can bring differ- ent planes of the media of the anterior parts of the eye successively into focus, and thus gain some idea as to the antero-posterior position of the opacities, since the nearer we can approach the eye the accom- modation being as fully relaxed as possible the deeper seated must the disturbance be. The second method by which we get increased enlargement and more brilliant illumination consists of using the mirror at a short distance from the eye examined, say six or eight inches, and then in- terposing a convex lens between the mirror and the observed eye in such a way that the object viewed, the surface of the iris, for instance, shall be just within the principal focal length of the lens. The object- lens being held in front of the ophthalmoscope, acts in the double capacity of magnifier and condenser, and thus increases the amount of the illumination. By slight movements of the lens back and forth, we can bring successively into focus the different planes of the ante- rior media, and see them under a considerable enlargement. This manner of using the instrument is precisely the same as with the ordinary inverted image ; but the head of the observer is at six or eight instead of sixteen inches from the observer's eye, and the image obtained, instead of being inverted, is upright and magnified. This last method is not so comprehensive or satisfactory as the preceding, but is well adapted for studying the surface of the iris, small perfora- tions of the membrane, and minute posterior synechiae. A general or diffuse opacity of any of the anterior media of the eye only expresses itself as such under the ophthalmoscope by the dis- turbing influence which it has upon the fundus oculi, the brilliancy of which when slight it reduces, and the details of which -when dense it obscures or veils. 160 TEXT-BOOK OF OPHTHALMOSCOPY. The Cornea. From the reasons already stated in regard to illumi- nation, and from the fact that with the ophthalmoscope it is some- what difficult to judge accurately of distances, examination, not only of the cornea, but of all the anterior media, is, as a rule, more satisfac- torily performed by oblique illumination than with the ophthalmo- scope, still there are some cases where the former yields to the latter ; and this is manifestly the case wherever there are slight inequalities in the surfaces by which the media are bounded, and particularly is this true in the condition known as " fascettes " of the cornea, where, from the inequalities of the surface, the light reflected from the f undus is irregularly refracted, so that it produces, under slight movements of the instrument, the characteristic play of light and shadow. Some- times, too, very minute specks or opacities in the otherwise perfectly transparent substance of the cornea or lens are seen by transmitted light when they would have escaped attention under oblique illumina- tion. Especially is this the case where very small opacities lie deeply in the cornea, in the membrane of Descemet, or in the lens; and examinations with the mirror should never be omitted when the patient complains of a sensation as if something was in the eye, which oblique illumination has failed to detect. The ease with which these small objects can be seen can be in- creased, especially when the pupil is enlarged and the light strong, by placing a convex (-f- 10 D) glass behind the ophthalmoscope and ap- proaching close to the eye after the manner just described. I have, moreover, in this way often convinced myself that the membrane of Descemet, even when not the seat of actual deposits, has sometimes the appearance of being thrown into delicate folds or undulations, so deli- cate, indeed, as to escape notice except under the enlargement of the magnifier and the movements of the ophthalmoscope, combined, also, with the movements of the eye in different directions on the part of the patient. When this is done, the pupillary space, which with the mirror alone, and at a distance, had a perfectly uniform reflex, acquires a sheen-like appearance, as if light was reflected from delicate inequal- ity in the surface of a substance, the transparency of which was not, however, affected as a usual thing to any perceptible degree. Some- times, however, slight but annoying disturbances in vision are an accompaniment of the trouble, and it is important not to overlook them, especially after blows or other contusions of the eye or head. Whether, after all, this appearance is due to some change in the inner- most layers of the cornea, or is in the membrane of Descemet itself, may be a question. I am, however, inclined toward the latter view. Of its existence, which is often palpable enough, there can be no doubt. EXAMINATION OF THE MEDIA OF THE EYE. Aqueous Humor. The ophthalmoscope is of very little use in the study of the aqueous humor or the accumulations which take place in the anterior chamber. Minute particles can, however, when a magni- fying-glass is used behind the instrument, sometimes be seen as they rise above or sink below the borders of the iris, and thus show that they are in a plane anterior to that of the iris. i THE IKIS. The surface of the iris, like that of the cornea, is generally better studied by means of oblique illumination than with the ophthalmo- scope. Still, there are occasions where the instrument performs useful service even here, and when it is used it is better to place a high mag- nifier (-[- 10 D) behind the mirror, and then to employ as strong an il- lumination as possible while the observer approaches the eye until the plane of the iris is in focus ; or, even better still, instead of placing the magnifier behind the mirror, the two-inch object-glass can be held just in front of the eye to be examined, while the observer throws the light from the mirror through it. In this way the glass acts both as a condenser and magnifier. When used in this manner, the observer must approach close to the glass, which by slight to-and-fro move- ments can be made to focus the plane of the iris or anterior capsule of the lens. In this way minute bodies or apertures may be detected, condylomata studied, or even an increased vascularity of the mem- brane be seen under a greater enlargement. In this manner also the writer has been able to detect adhesions to the lens, especially in old people, where the pupil is very narrow and very sluggish to light. Light does not, under ordinary conditions, pass through the iris, at least in sufficient quantities to give any reflex of the fundus beyond. When, however, the membrane is destitute of pigment, as in albinos, or has undergone extensive degeneration through atrophy, sufficient light is returned to the observer to enable him to obtain a more or less feeble reflex through the membrane, or even in pronounced cases to discern the outlines of the ciliary bodies, which then appear as dark projections of various heights. In one case of extensive atrophy which I examined, the membrane presented alternate spaces of light and shade, radiating from the pupil like the fan-shaped sectors of a com- mon ventilator. Perforations of the iris and separations from its peripheric attach- ments and the remains of the pupillary membrane, provided the media behind have preserved their transparency sufficiently, betray them- selves by the red glow from the fundus, which then occupies the vacancv. The space may, however, especially after injuries, be the 11 162 TEXT-BOOK OF OPHTHALMOSCOPY. seat of a small haemorrhage or exudation, or masses of cortical sub- stance, so that no reflex can be obtained through them. The true nature of the obstacles can then usually be easily determined by oblique illu- mination. On the other hand, what sometimes seems under oblique illumination to be an interruption in the surface of the membrane covered with black pigment or with the remains of a layer of blood, proves with the ophthalmoscope to be a vacant space or cleft in the iris, through which we not only get a perfectly clear reflex, but can even discern some of the details of the fundus. For this reason the oph- thalmoscope is most advantageously employed in determining the con- dition of the pupillary space and its fitness for the passage of light, as, for example, after an attack of iritis, the performance of iridec- tomy, and especially that of cataract, where by its means we can judge at once whether the field of pupil is limited in extent, or whether adhesions have taken place from the borders of the iris, or whether the pupil is the seat of exudations, the remains of capsule, or cortical substance ; in fact, everything which relates to its clearness, size, shape, and permeability to light. THE LENS. Alterations in the curvature of the lens can not, as a rule, be told with the ophthalmoscope. One or two cases have been known, how- ever, even in the writer's experience, where a marked inequality in the surface could be detected. As with the other anterior media, diffuse opacity of the lens be- trays itself by a reduction in the brilliancy of the ophthalmoscopic picture, over which it casts a delicate haze. It is, as a rule, better ex- amined with oblique illumination than with the ophthalmoscope ; but in either case it requires the closest attention and care on the part of the observer not to overlook this delicate cloudiness, and whenever this is suspected both methods should be employed. Precisely the same appearances as those which have already been described in the case of the membrane of Descemet, and which sug- gest a delicate folding or ruffling of the surface, are often seen on the anterior capsule of the lens, or in the cortical substance lying just be- neath it. There can be little doubt that oftentimes this is a physiologi- cal condition and due to some peculiarity in the capsule, suggesting a continuation of the fold-like arrangement of the zonula on to the sur- face of the lens ; but, on the other hand, it is just as certain that these striae, or delicate minings, in the surface of the capsule are of patho- logical origin, as if due to some mild form of capsulitis of an idio- pathic form. I have also seen them as the result of injury to the eye, EXAMINATION OF THE MEDIA OF THE EYE. 163 and have now under observation a case of injury from a blow fol- lowed by a mild iritis, in which these stripes or folds developed. They ran horizontally across the upper half of the anterior capsule of the lens, the lower part being clear, as-was the entire substance of the lens. Sometimes, moreover, delicate irregularities are seen in the sub- stance of the lens, especially toward the periphery. These have usu- ally a twig-like course, and produce the impression as if they were inequalities in an otherwise transparent and homogeneous substance, having just enough difference in their construction and index of re- fraction to render them visible under the play of light from the oph- thalmoscope. Dust-like aggregations and minute spots are often seen in the peripherical portions of an otherwise perfectly clear lens. There can be no doubt that these appearances are often purely physiological. That they are not always so is proved from the fact that examinations repeated after successive intervals show that they do increase till the lens finally becomes cataractous. I would not wish to mislead the reader, or give the idea that any opacity in the lens is not a matter of serious consideration, which I freely admit it is, but I merely wish to point out the fact that opacities may exist for years without change in size or shape, while the rest of the lens remains perfectly clear ; and this is particularly true when the opacity is an isolated one with a clearly defined contour, as, for example, the small, round spots on the posterior surface of the lens, which are often attributed, whether rightly or not, to the remains of the central hyaloid artery. These spots may, however, exist in any part of the lens, not only on the pos- terior but also on the anterior surface, and not only near the centre, but also at the periphery ; and, moreover, they may be of any shape, either circular or cleft-like. This fact ought to make our prognosis a little more guarded than it usually is, and cause us to refrain from unduly alarming a patient about a threatening loss of vision, combined with a serious operation, when no occasion for either may ever occur. Especially is this true in patients who have for years been very my- opic, and whose eyes show an extensive posterior staphyloma, with other changes in the choroid. Defined opacities in the lens appear as black interruptions in a reddish-yellow field, since they lie, as already pointed out, between the observer's eye and the source of illumination, which in this case is the reflection from the fundus. As they reflect from their surfaces but little light when the angle of incidence and reflection is small, they do not appear as they do under oblique illumination in their true color, but, on the other hand, their position, extent, and outline are more clearly defined as they are seen against a brilliant background. 164 TEXT-BOOK OF OPHTHALMOSCOPY. It is certainly not worth while to exhaust the reader's mind with a long and detailed description of the multitudinous variations, either as to place, form, or extent, that these opacities may assume or the changes they may undergo. A single glance with the ophthalmo- scope at nature, or even a glance at the accompanying drawings taken from Jaeger's " Atlas," will give a better idea as to their true appear- ances than the longest and most minute verbal description. The pu- pillary space is supposed to be illuminated with the mirror, and the dark spots are seen by contrast against the lighter field. Fig. 56 represents an eye, affected with iritis, under the influence of atropine. The black points extending into the clear field of the pupil mark the points of adhesion between the iris and the anterior capsule of the lens. The festooned appearance of the membrane is due to the fact that the intermediate portions of the iris are still free from the capsule and are capable of dilatation. FIG. 56. FIG. 57. Fig. 57 shows the left eye of the same subject, in which the effect of the atropine has been sufficient to sever the attachments from the lens, the remains of which are seen on the anterior capsule. Care should be taken not to confound the remains of such attachments with cataractous opacities. In both eyes oblique illumination, even when the pupil was undilated, showed that besides the synechiae, which came clearly into view, there was a very delicate membranous opacity which extended over the central portions of the capsule. This was barely visible with the direct light from the ophthalmoscope. Fig. 58. This represents one of the many forms of cortical cata- ract. The disturbance is situated in the anterior portions of the lens, and in the centre of the field of pupil. For this reason the opacity does not appear to change its position from the centre of the field, and there are no parallactic displacements in its relation to the borders of the iris, whatever may be the position or movements of the eye of either patient or observer. EXAMINATION OF THE MEDIA OF THE EYE. 165 Fig. 59. This also represents another form of anterior cortical cataract. The disturbances here consist of four stripes of opaque cortical substance running from the different quarters of the equator of the lens toward its centre, where they are united by a fifth. There is, moreover, an isolated stripe running from below upward toward Fia. 58. FIG. 59. the centre. In looking at the central portion of these disturbances they would maintain their respective positions on movements of the head. Inasmuch as they are in the plane of the iris and centre of the field of pupil, their outer extremities would, however, have a slight parallactic displacement in relation to the borders of the iris, and the stripes would appear to become longer or shorter, accord- ing to the direction in which the eye was turned. Suppose, for ex- ample, that the isolated stripe is in the lower and outer quadrant of the lens, and the eye is looking directly forward. If, now, the eye is moved outward, the stripe will appear to move in the same direction and to become a little shorter. If the eye is turned inward, then the opacity moves inward, and at the same time lengthens. When the same or similar disturbances are found in the posterior layers of the lens, they form a posterior instead of an anterior cortical cataract, and present in the main the same ophthalmoscopic picture. As the opacities in this case lie at a considerable distance behind the plane of the iris, they can not be in focus at the same time with this membrane, as is the case in the anterior cortical or capsular cataract. These deep-seated disturbances seem to lie within and beyond the pupil and in its central portions, provided the eye looks straight to- ward the observer. On movement of the eye, however, the opacities make a greater or less excursion, according to the distance that they lie behind the plane of the iris. They always move, too, in respect to the iris, in a direction opposite to that in which the eye of the patient is moved, while it will be remembered that the disturbances in the anterior layers move in the same direction ; moreover, the 166 TEXT-BOOK OF OPHTHALMOSCOPY. opacities, as a whole, present a surface which is concave toward the observer. The image produced by the catoptric test is interrupted when it comes over the cataractous portions of the lens lying in front of the posterior capsule. Of course, the image from the anterior capsule will never in any case be interfered with, as the reflecting surface must lie in front of all lenticular disturbances, unless indeed the cap- sule itself should become so altered by disease as to give no reflection. There are still other cases where the anterior and posterior cortical layers are affected at the same time, and here we get the ophthalmo- scopic appearances which have just been described, united so that upon lateral movements of the eye of the patient the opacities of the two surfaces appear to pass each other. Fig. 60 represents such a cataract, the deeper black opacities representing the disturbances on the plane of the iris are seen to be in focus, while the most posterior, FIG. 61. from being out of focus, appear of a lighter hue and of a less defined shape. The drawing also shows where the iris has been torn from its attachments by a blow, allowing the light from the f undus to pass through the rent. Fig. 61. This illustrates peripherical disturbances in the cortical substance, and shows how important it is to make a thorough exami- nation of the periphery of the lens when disturbances of vision, however slight, are complained of. In this case the eye was myopic 9 D, and vision had been gradually decreasing for some years. In ordinary daylight and an undilated pupil, no abnormal appearances whatever were visible. The opacities lay in both the anterior and posterior cortical layers of the lens, and the ophthalmoscopic appear- ances were such as are represented in the drawing. These changes were supposed to be due to a long-continued form of choroiditis. The most interesting point in the case is the fact that, after a long- EXAMINATION OF THE MEDIA OF THE EYE. 167 continued treatment, examinations with the ophthalmoscope showed a gradual decrease in the disturbances, till finally at the end of five years they entirely disappeared, " no trace," according to Jaeger, " being left." I have myself often seen these peripheric opacities, especially in near-sighted eyes, remain in statu quo for years, and have occasionally convinced myself that they had gradually become reduced in size. I have, moreover, seen a case where, as Jaeger * asserts, opacities in the lens have entirely disappeared. Fig. 62 is of the same character as Fig. 61, only more pronounced. FIG. 62. FIG. 63. The reader must bear in mind that these cortical disturbances are not always clearly defined with sharp pointed processes, but, on the contrary, these may be obtuse or the whole disturbance a more or less ill-defined mass, as in Fig. 63, which represents an anterior and poste- rior cortical cataract. Fig. 64 is an example of a zonular cataract, which, as will be remembered, consists of an opaque layer of lenticular fibres lying between the nucleus of the lens on the one hand and the outer layers of the cortical substance on the other, both of these latter having preserved their transparency. Usually, as in the present case, the opacity is so delicate as to allow the light from the fundus to pass through it. Thus the central portions of the envelope present but little contrast with the rest of the yellowish- red field of pupil ; and the portion between the fine dark circle in the drawing and the borders of the iris is seen to be transparent. * " Wiener Zeitschrift fur praktische Heilkunde," 1861, Nos. 31, 32, E. Jaeger. " Ophth. Hand Atlas," p. 9, Taf. II., Fig. 9, E. Jaeger. " Annales d'Oculistique," B. i., iii., p. 201, Galezowski. 168 TEXT-BOOK OF OPHTHALMOSCOPY. From the angle at which the return rays strike the edges of the zonular envelope, these from total reflection appear of a much darker hue, and thus we get the appearance given in the drawing of a dark circle surrounding a central portion of a delicate reddish tinge. The size of the circle will, of course, vary, according as the opacity is nearer the circumference or centre of the lens. So, too, will the con- trast between it and the included space vary in proportion to the density of the disturbance. Zonular cataract may be accompanied with changes in the cortical substance, and then it forms a mixed cataract. The ordinary senile, or nuclear cataract, when it is most marked in the central portions of the lens, gives very much the same ophthal- moscopic picture as that just described. As the opacity increases, however, it loses the characteristic bright centre with a circular bor- der, and becomes a more or less dense and dark mass with radiating spokes. Dislocation of the Lens. Under ordinary physiological conditions the borders of the lens are not rendered visible with the ophthalmo- scope. This, however, may be the case, as, for example, when the iris is wanting either congenitally, or when it has been removed either in part or whole by surgical interference or accident, or when it has been separated from its attachments, or, under some conditions, when it has been dilated to its fullest extent with atropine, or is so wanting in pigment as to allow large quantities of light from the f undus to pass through it, as with albinos ; and, finally, when the lens itself has from any cause become dislocated. Under these conditions the bor- ders of the lens reveal themselves in two distinct ways, according as we view them with reflected or transmitted light. Suppose any of the above conditions suitable for the observation, such as a dilatation of the pupil to its maximum or a perfectly clean iridectomy, exists. When light is thrown into such a field of pupil by oblique illumination, the great mass of rays will, of course, pass directly through the lens into the vitreous beyond ; but the small por- tion of those which strike upon the very borders of the lens will, after passing through the intervening portions, meet the posterior capsule at such an angle that they will be totally reflected, and thus come back to the observer's eye ; consequently the very outermost limits of the lens will appear brilliantly illuminated. We see, therefore, the borders of the lens under oblique illumination as a finely drawn and glittering circle. This is very beautifully marked when the lens is entirely dislocated into the anterior chamber, preserving, as it some- times does, its perfect transparency. On the other hand, when we EXAMINATION OF THE MEDIA OF THE EYE. 169 use the ophthalmoscope, the rays which return from the fundus and strike upon the borders of the lens after passing through the posterior portions, meet the anterior capsule at such an angle that they are totally reflected and pass back again into the eye. The observer does not receive these rays, and consequently the border of the lens appears to him dark, and he sees the lens surrounded by a narrow dark rim. When, however, the lens is entirely dislocated into the anterior cham- ber, so as to expose the borders of the lens for its entire circuit, we can get, for the reasons stated above, the glittering ring even with the ophthalmoscope, by rotation and displacement of the mirror, com- bined with the movements of the eye on the part of the patient. The illuminated space between the dark border of the lens and the ciliary processes marks the position of the zonula of Zinn. Usually this membrane is so transparent as to be invisible ; but it has been asserted that under favorable conditions the folding of the zonula can be followed in the form of grayish stripes from the ciliary processes to the borders of the lens. I have myself seen something which sug- gests the above appearance on the marginal portions of the lens, but never any such appearances in the intervening space between its bor- ders and ciliary processes. The appearances just mentioned as to the borders of the lens will be more marked when the lens is dislocated, so that a part of its bor- der passes through the field of the pupil, as will be seen from Fig. 65. In such a condition the re- fraction would be very different in the two sections, and there would be, when the eye of the observer was placed so as to receive rays from each section, a doubling of the details of the fundus. The displacement of the lens is usu- ally downward, but may be in any direction. The iris is usually forced somewhat from its plane, and there is generally more or less trembling of the membrane. Instead of a partial dislocation this may be total, either into the anterior chamber or into the vitreous humor, where it sinks to the bottom of the eye, and presents the appearance, according to the amount of transparency which it has maintained, of either a pellucid or dark lenticular mass. Fracture of the Capsule of the Lens. Some ten years ago Dr. FIG. 65. 170 TEXT-BOOK OF OPHTHALMOSCOPY. Dyer published a paper * in which he described the fracture of the capsule and substance of the lens from violent hanging. The first subject examined was Probst, the famous murderer. The examina- tion immediately before death showed nothing at all abnormal ; that immediately after gave with the mirror the following results in brief : " In the right eye there was a line running transversely across the lens and about a line below the centre. From this at various angles ran short and long, but very fine lines. These ran close together, but in no regular arrangement. The transverse line had the appearance of a crack in a clear piece of ice. It was evidently a fracture, involv- ing the anterior capsule and extending in a horizontal plane backward into the substance of the lens." " The left eye showed a line difficult to distinguish but to be made out with certainty, corresponding in position with that of the right eye. It was undoubtedly a fracture of the anterior capsule. Experi- ments were afterward made on dogs with similar results." I mention these examinations of Dr. Dyer because I have several times seen very similar appearances from similar causes, that is, from violent concussions, of which the following may serve as an example : A gentleman while driving was thrown violently from his car- riage, striking, when he fell, directly upon his head. He consulted me a little later for a loss of vision in the left eye, which he knew to be the result of the accident. Examination showed that there had been an extensive rupture of the choroid. The media of the eye were, however, perfectly clear, and no disturbance in the lens could be detected. In the right eye, however, there was a delicate split- like opacity in the anterior capsule, which extended from the lower periphery of the lens toward its centre, so as to reach a little higher than the border of the undilated pupil. The rest of the lens was perfectly transparent. Hardly visible at first, this delicate opacity became in the course of a few weeks much more pronounced, and with the ophthalmoscope gave all the appearances that would a single and very delicate spiculum of an ordinary cortical cataract. Whether this disturbance was seated in the capsule or just below it could not be determined with exactness, though from the fact that it never in- creased in size it was inferred that it must be in the membrane, and that the continuity of this had not been broken, otherwise the lens would have become cataractous, which was not the case at least for the three years that the patient was under observation. During this time the opacity neither increased in size nor shape, or was the perfect transparency of the rest of the lens interfered with in the least. When * " Trans. Amer. Ophth. Soc.," 1866, p. 13. EXAMINATION OF THE MEDIA OF THE EYE. 171 Been again, six years after the accident, all signs of an} 7 fracture had disappeared. I have seen several such cases, the results of injury. An attempt has been made by many writers to divide cataracts into two great classes, the stationary and progressive. This classifi- cation should not, however, be taken too literally, as all cataracts have a tendency to increase, whatever may be their kind or situation. All that can be said is that certain forms, as a rule, show this tendency less than others, especially the zonular and polar varieties, which often remain unchanged for years, or even forever. Still, too much stress in the way of a favorable prognosis should not be laid, either from the situation or nature of the disturbance. The process in the formation of cataract in elderly people usually begins at the nucleus, which separates, as it were, from the cortical substance, and becomes denser and more opaque. This is followed in time by a cloudiness of the more superficial layers, till the whole lens becomes cataractous. When a nuclear cataract appears with a cortical one, it is called a mixed cataract. In young people, on the other hand, the disturbance usually begins in the cortical substance, and thence extends through the lens, forming what is called a soft cata- ract. VITREOUS HUMOE. The vitreous humor in a state of health is, under the ophthalmo- scope, a perfectly transparent body. It can, however, from the effect of morbid processes, become the seat of opacities which may vary in size and shape from the merest particle or filament to coarse, broad bands, and from the thinnest possible web, which hardly interferes in the slightest degree with the illumination of the fundus, to the densest membrane which may exclude all light from entering the deeper parts of the eye. As in the lens and aqueous humor these opacities may be of a gen- eral or diffuse nature, or circumscribed masses or membranes suspended or floating about in an otherwise transparent medium. From this fact they are usually classed as fixed and movable, conditions which are often important in a diagnostic point of view as to the true character of the vitreous, and whether in a given case it be of normal consist- ency or in a " fluid " condition. Whatever may be the nature of these bodies in the vitreous, and whether they spring from the formation of bands and membranes of the nature of connective tissue, or be the results of morbid exudations or haemorrhage, they appear, as a rule, black with the ophthalmo- scope, because they are seen by transmitted light in contrast with the 172 TEXT-BOOK OF OPHTHALMOSCOPY. surrounding medium, which is transparent, or, in other words, they are interruptions in an otherwise illuminated field. It is only occa- sionally that a membrane, when of considerable size or density and movable, so turns on itself as to reflect the light which strikes upon it. When this takes place, that part of the membrane from which the light is reflected changes from a black to a darkish gray, or even a grayish-white tinge. The same is true of bits of metal suspended in the vitreous, which frequently preserve their metallic glitter when- ever the angle of incidence and reflection is of such a degree as to carry the reflected ray to the observer's eye. "When this is not the case, and especially when encapsulated, they appear of a very dark hue or even black. Another remarkable exception to the rule that opacities in the vitreous appear black with the ophthalmoscope, is the effect due to minute particles of cholesterine which, under the movements of the eye, flash into view like minute motes of light, and then disappear to be replaced by others in the same or in a little different position. I have seen an eye so full of these minute particles as to resemble, more closely than anything I can think of, one of those globular paper weights which represent a mimic landscape in a snow-storm, and which upon being reversed are filled with a myriad of small and feath- ery particles. These particles of cholesterine may exist with an other- wise perfectly clear vitreous and normal condition of the other parts of the eye, and with perfect or nearly perfect vision. Such being the general aspect of all kinds of opacities in the vit- reous, it remains to study a little more in detail the three classes into which they are commonly divided. Diffuse Opacities. That such a condition may and does occur there can be no question, but that it occurs as frequently as is alleged I am inclined to doubt, and from my own experience and frequent mistakes I would strenuously recommend the observer to exhaust every method and detail of examination as to the condition of the an- terior media, the cornea, aqueous humor, and lens, and then the vitre- ous itself, for delicate stationary membranes before adopting such a diagnosis. To this end I would remind the reader that any existing error of refraction in his own eye should be corrected, and that an accurate adjustment of the accommodation, aided if necessary by the proper glasses, should be obtained for different levels or antero-poste- rior planes in the vitreous. The observer will often be surprised to see, after a careful examination of the anterior media, that what he had taken for a delicate diffused opacity in the vitreous resolves itself into a gauze-like but stationary membrane, which is only to be recog- EXAMINATION OF THE MEDIA OF THE EYE. 173 nized when the plane in which it lies is accurately in focus. "When this takes place the delicate membrane then betrays itself, much in the same manner and with much the same appearance as does the film on an unclean slide under the microscope ; that is, with here and there a minute dark speck, and here and there a fine, hair-like line or lines running transversely across the field. Diffuse opacity of the vitreous, when it is really present, shows itself rather by the effect which it has upon the distinctness of the fundus beyond, than by any marked peculiarity of its own, just as a delicate mist makes itself more apparent from the effect on surround- ing objects than it does from its own constituent elements. Here, again, under favorable circumstances, such as a good light and con- siderable enlargement produced by a somewhat strong convex glass behind the ophthalmoscope, this diffuse opacity may be made to resolve itself into small definite particles or shreds of membranes, or both. The want of clearness of the fundus from diffused opacity of the vitreous may vary from a scarcely perceptible want of definition of the details of the background of the eye to their almost total ob- scuration, in which the optic nerve is barely discernible as an indefinite white spot or disk surrounded by a dulled and blurred background, with no vessels apparent, or, if apparent, only to be detected upon the disk itself. When, however, the obscurity is as great as this, care is required on the observer's part not to confound a general haziness of the cornea, especially in glaucomatous affections, with that in the vitreous. It must be borne in mind, too, that any want of transpar- ency in the vitreous shows itself more readily with the upright im- age. Indeed, with the bright glare of the inverted image, these delicate and diffuse opacities often escape detection. As regards the etiology of these diffuse troubles, they may be said to be due, as a rule, to some form of choroiditis, especially that of a low type such as the serous variety. Mauthner says that they may also occur in glaucoma. Unfortunately for the beginner, no picture gives any adequate representation of these delicate and subtile changes in the vitreous, the most difficult to diagnosticate of all its troubles, and this, too, not only in regard to the media lying in front of the vitreous body, but also in regard to some morbid conditions of the membranes be- yond, especially those of the retina. It is often extremely difficult, sometimes impossible, to differentiate between a want of sharp defini- tion in the fundus coming from a slight disturbance in the transpar- ency of the deeper portions of the vitreous and that arising from a 1T4: TEXT-BOOK OF OPHTHALMOSCOPY. delicate and almost imperceptible haziness of the retina, that is, from some slight cedema, such as I feel convinced occurs in amblyopia po- tatorum, and other low types of retinal inflammation. Of some value, then, as a diagnostic mark is the diminution or entire want of the light-streak on the centre of the retinal vessels. Disturbances lying in front of the retina will, it is true, obscure to a certain degree the brilliancy of the image beyond, and thus proportionately reduce the brightness of the light-streak. This will, however, remain comparative- ly well marked, even when the general obscuration is of a considerable degree ; w T hile, on the other hand, should the want of transparency be in the retina itself, the slightest oedema will cause the light-streak to be diminished in size and brilliancy, or to disappear entirely. More will be found in regard to this matter under the head of " The Light-Streak as a Diagnostic Mark," Part II. Movable Opacities. These may be of any size or shape, varying from small, circumscribed black masses, with or without processes of different size and length, to long, snake-like membranes, which move with an undulatory motion through the vitreous on the slightest move- ment of the observed eye. Yet, notwithstanding this freedom of movement and extent of the excursion, which would lead one to be- lieve that these membranes are entirely free, they are often, if not as a rule, attached by filamentary bands to some peripheric portion of the fundus. When of moderate size, and present in considerable numbers, these movable opacities often produce the effect, as well to the observed as observing eye, of what is usually known as the mother in vinegar. Fig. 66 is taken from a chromo-lithograph by Jaeger, "Hand Atlas," Taf. III., Fig. 21. It represents a myopic eye affected with inflammation of the choroid with opacities in the vitreous. The lenticular system was perfectly clear, but the vitreous was, for the most part, in a fluid condi- tion. When the eye remained quiet there seemed to be, with the ophthalmoscope, a uniform haze over the entire field. If the FIG. 66. eye was moved, however, even to a slight degree, a great number of very minute as well as some larger opacities of a black or dark- brown color came into view, which rose and fell in a cloud-like man- ner, especially in the anterior and middle portions of the eye. When EXAMINATION" OF THE MEDIA OF THE EYE. 175 the eye became quiet again, the opacities gradually sank, the larger more quickly than the smaller ones. The back of the eye appeared less clear than usual, but still all the details of the fundus could be plainly seen somewhat veiled to be sure, but still sufficiently distinct and in their normal color. Fig. 67 (Jaeger, " Hand Atlas," Taf. III., Fig. 22) represents an eye in which there was inflammation of the retina and choroid with opacities in the vitreous. The examination with the ophthalmoscope showed that the lens was perfectly clear, as was, indeed, the vitreous body itself when the eye was motionless. The details of the fundus under this condition of rest preserved their usual clearness and defini- tion. On movement of the eye, however, the opacities in the fluid FIG. 67. FIG. 68. vitreous floated up at once into the field of the pupil as compact and untransparent masses of a nearly black hue, and of various sizes and shapes. On the eye becoming quiet again these masses gravitated to the bottom of the eye in the equatorial region, and passed completely out of view behind the iris. Fig. 68 (Jaeger, Taf. III., Fig. 23) is of the same character, only the opacities are larger and more pronounced. In this case the bottom of the eye was obscured, and the details of the fundus were veiled by the thick masses which only permitted the light to penetrate in re- duced quantities to the back of the eye. Under the head of movable opacities may also be classed clots of blood, the result of haemorrhage, either from disease or injury, which may assume the shape and form of circumscribed masses or mem- branes, such as are formed from other causes, and it is exceedingly difficult sometimes to say whether the disturbances in the vitreous are due to haemorrhage or arise from other formations. Mauthner ob- serves that, when due to bleeding, the edges of the opacities have a reddish tinge* This I have never noticed, these masses always ap- * "Lehrbuch der Ophthalmoscopie," p. 151. 176 TEXT-BOOK OF OPHTHALMOSCOPY. pearing black, as they necessarily must, unless, indeed, they turn at such an angle that the light returning from the fundus should so strike them as to be reflected again to the observer's eye, which, so far as my experience goes, never happens. There is nothing which so excludes the light from entering the eye as an extensive haemorrhage into the vitreous and in the immediate neighborhood of the lens. Not the faintest glimmer of the fundus can then be had ; the pupil- lary space preserving a jetty blackness even when condensed light is thrown into it by the oblique method. Sometimes, however, we do succeed by this last method in getting a reddish hue, when the pupil is dilated to its utmost, and the condensing lens is so held as to get the greatest angle of incidence and reflection, and especially is this true when the clot is of recent origin. The same want of transparency that exists with haemorrhage is also found in purulent exudations into the vitreous, arising either from injuries or disease, especially that from metastatic choroiditis, as seen in cerebro-spinal and puerperal troubles. Whenever, therefore, the pupil appears with the ophthalmoscope of a uniform blackness, and participation of the anterior media have been excluded by differ- ential diagnosis, it is necessary to have recourse to oblique illumina- tion to resolve the obscurity into its true color and shape. Even with this aid it is sometimes impossible to get a reflection from these abnor- mal formations unless they happen to be in the most anterior parts of the vitreous, that is, in close proximity to the posterior parts of the lens. Fixed Opacities. These present very much the same appear- ances as the movable ones would if deprived of motion, for like them they may be either circumscribed black points or bodies of various size and shape with or without numerous processes, which may be so arranged as to form with each other the appearance of bands stretched across the vitreous, either in the same or in different planes ; or, again, they may be so interwoven with each other as to give the appearance of a more or less regular network or cobweb, which may be either coarse or dense or of extreme tenuity. A favorite place for the forma- tion of these bands is just behind the teleform fossa ; especially are they found after an operation for cataract. They then appear to start from the neighborhood of the anterior parts of the ciliary body, and run backward in converging lines toward the centre of the eye. That they are due to some low morbid process which had also affected the nutrition of the lens, and were present before the operation and not the result of the healing process, would seem probable, at least in many cases. On the other hand, they often form after the operation EXAMINATION OF THE MEDIA OF THE EYE. 177 has been performed, sometimes even after a considerable interval has elapsed, either as the result of a mild inflammatory action following the operation, or sometimes without any apparent cause. At any rate, they are the despair of the surgeon as well as of the patient, as they often resist any and every effort at removal, closing at once over the passage made by the needle. These stationary opacities in the vitre- ous, if of any density, require but little skill or care in determining their true position and nature. But, as already pointed out under diifuse opacities, it is very different with these delicate stationary membranes, which offer so little resistance to the light as to appear perfectly transparent, except under peculiar conditions, and whose only expression of existence, on a cursory examination, is the vague and indescribable want of definition that they produce on the brill- iancy of the general fundus. Sometimes membranes of considerable density, either extended su- perficially or in the form of broad bands interwoven together so as to make a coarse network, are seen to protrude from different parts of the fundus into the otherwise clear vitreous. These give a grayish or greenish reflex, according to the angle under which they are seen, and are due evidently to some hypertrophy of the connective tissue, which would seem to be the product of some inflammatory action in the retina. They may become vascularized, and then, especially when movable, present a very beautiful appearance as they sway to and fro with every movement of the eye. These membranes, though com- mon enough to be mentioned by all authors, are nevertheless com- paratively rare. I have myself seen some dozen cases, and in two of these the point of origin could be traced directly to the retina. In the first case a delicate gauze-like membrane stretched across the tri- angle made by the first bifurcation of one of the ascending veins after it had left the nerve. It was of delicate structure, so that the red reflex from the fundus was but slightly dimmed. It lay in a plane close to the retina, and its surface was covered by a delicate and sprig- like ramification of vessels which seemed to be entirely of venous ori- gin. In the second case observed by me, the membrane was of larger extent, and apparently arose from along the course of one of the lower veins at a considerable distance from the nerve. Like the first, it was of gauze-like texture, and was covered with small vessels which had the appearance and ramification of minute veins. The membrane moved freely under every motion of the eye, and bore a close resem- blance, as a whole, to one of the more delicate sea-weeds, both in the gracefulness of its motion and the delicate tracings formed by the ves- sels upon its surface. 12 178 TEXT-BOOK OF OPHTHALMOSOOPY. Dr. Strawbridge * gives a description and drawing (Fig. 69) of an extensive membrane arising from the deeper-seated portions of the eye, and protruding into the vitreous to such a degree that its anterior limits could be viewed by oblique illumination. The membrane, which was traversed by numerous vessels, was dense and white in FIG. 69. some places and attenuated and feathery in others, and through these latter the fundus could be seen beyond, of a normal color and appear- ance. The retinal veins were, however, tortuous and overfilled. Jaeger f gives a drawing of an extensive membranous formation which surrounds the optic nerve like the frame to a picture, and then spreads out especially in a downward direction over the course of the principal vessels. The new growth is dense and opaque in some places, and attenuated and transparent in others, allowing the fundus to be seen in its normal condition. The web seems to be combined of layers and bands of connective tissue, so as to form superficial ex- tensions and bands in different places, producing a play of light and shade which gives to it a reticulated or honeycombed appearance. The optic nerve seen through the central aperture of the membrane is much reddened, though the membrane itself does not seem to be the seat of any vessels of new formation. * " Trans. Amer. Ophth. Soc.," 1875, p. 304. t " Ophthal. Hand- Atlas," 1869, Tab. XVIIL, Fig. 84. EXAMINATION OF THE MEDIA OF THE EYE. 179 Jaeger describes this membrane as others have under the head of troubles in the vitreous ; but it is evident in all these cases, as well from the ophthalmoscopic picture as from the descriptions, that these membranes are rather due to some form of retinitis, such as prolifera- tion of the adventitia or the connective-tissue elements of the limitans interna, than to a morbid process which affects in a primary manner the vitreous humor. These growths or membranes are evidently of the same nature, only exaggerated in form, as the hypertrophy of the radial fibres and connective-tissue elements of the limitans, which project from the inner surface of the retina into the vitreous, and which have been described by Iwanoff.* In this connection I might mention a case which at first sight I took for a membrane in the vitreous, but which, upon an exhaustive examina- tion, I was inclined to look upon as a fold of the retina itself. This fold extended from just beyond the macula lutea in a median line half-way toward the ora serrata. When the fold lifted itself up and down under movements of the eye, the transition from the normal part of the retina to the fold could be plainly seen. The vessels, too, could be observed to run over from the adjacent retina uninterrupted in their course, and were evidently the ordinary vessels of the retina and not those of new formation. This deformity was evidently congenital. Both eyes were highly myopic, and vision very much reduced. The patient was a young boy of eight years of age, and did not come of myopic parents. Neoplasms, strictly speaking, do not develop themselves in the vitreous proper ; still, Becker f mentions a remarkable case of a diaph- anous substance forming in the vitreous, and provided with vessels which seemed to have a connection with the retinal veins. The same writer also mentions two cases in which masses projected into the vitreous, one of which was an abscess upon which vessels could be plainly observed, while upon the second, which lay close be- hind the lens, the vessels could be plainly seen with the naked eye running from the periphery toward the centre of the abscess. In this case, from the first appearance of a general pinkish hue to the detec- tion of individual vessels, there was but the space of four days, while .the vessels had entirely disappeared after the thirteenth day. The writer once saw a very peculiar formation in the vitreous of a gelatinous nature, which resembled in consistency what is seen in the anterior chamber in spongy iritis. It gave the impression that certain parts of the vitreous had solidified into a spongy mass while other * " Archiv fflr Ophth," Bd. xi., Abth. i., p. 134. t "Bericht ueber der Wiener Augenklinik," p. 106. 180 TEXT-BOOK OF OPHTHALMOSCOPY. parts retained their normal clearness. It did not resemble the exuda- tion found in metastatic choroiditis, but rather that of coagulated white of egg. Through the clear places the fundus could be seen in certain districts as if through loop-holes, while it was completely con- cealed in others by the opaque substance. There were no vessels at all in the mass, nor did it suggest a tumor in any way, unless it might be one of those very rare cases of glioma, starting from the limitans interna. The vision was reduced to perception of light, and, as there was marked ciliary injection and some photophobia in the well eye, enu- cleation was proposed but refused, so that the true nature of the for- mation could not be determined. Abscesses of the Vitreous. These are described by Yon Graefe and others as giving with the ophthalmoscope, when the vitreous still preserves sufficiently its transparency, the appearance of globular, half- transparent or more or less opaque, and jelly-like bodies, which are attached to the inner membranes of the eye, and sometimes provided with a neck-like projection. The formation and retrogression of these bodies, when the condition of the media will permit, may, according to these authors, be watched from day to day with the instrument. I myself have never seen such an appearance with the ophthalmoscope, though I did observe, on one occasion, a more or less general yellow reflex with the oblique illumination. This seemed to come from the deeper portions of the eye, and proved on section at the time of enu- cleation to be due to an abscess the size of a small pea in the very centre of the vitreous. A diffuse purulent infiltration of the vitreous can only be surmised by the instrument by a total loss of reflex from the fundus. With the ophthalmoscope, where the angle of incident and reflected light is very small, we miss the yellowish-greenish reflex obtained under dif- fuse daylight and by oblique illumination, especially when the trouble is situated in the anterior parts of the vitreous. Foreign Bodies in the Vitreous. These follow the general rule of all foreign elements of an opaque nature in the media, and appear black with the ophthalmoscope, unless they happen to be of a metallic nature. Even then, bits of highly polished metal may look black, un-. less it so happens that they are either themselves fixed in such a posi- tion as to produce the right angle of reflection or this latter is brought about under the varying movements of the eye. Often light scales of metal seem to be suspended in the vitreous as if imbedded in a gelat- inous substance of sufficient consistency to support them. As a rule, however, 'a careful examination brings to light one or more delicate EXAMINATION OF THE MEDIA OF THE EYE. 181 thread-like attachments, which can be often traced far toward the pe- riphery, and sometimes even to the inner membranes. And especially is this the case when the foreign body lies in the anterior half of the globe, and near the posterior surface of the lens. Sometimes these bodies are thus suspended at only one end, and then swing about in the fluid vitreous, occasionally sending out a metallic lustre as they present the proper angle of reflection, and then becoming again per- fectly black. These foreign bodies may become either partially or entirely encapsulated, the membrane surrounding them being either opaque, as is the rule, and thus concealing entirely the true nature of the substance, or remaining transparent enough, which is very rare, to allow the body to be seen through it. According to Graefe, even the track made by the passage of these bodies through the vitreous can sometimes be traced a few hours after the injury by a delicate want of transparency, which may subsequently become a defined membranous extension or canal. The process by which these bodies become enveloped by mem- branes may extend either from the periphery toward the foreign body, thus gradually concentrating around it, as described by Jaeger and Berlin, or the membrane may form directly round the particle with- out the slightest participation of the inner membranes so far as can be detected either by the ophthalmoscope or on section a fact which must be looked upon as strongly corroborative of the view that the vitreous body is capable of independent morbid processes of an in- flammatory nature. One thing is certainly peculiar, and that is that bodies of consid- erable size, and whose specific gravity is greater than the vitreous, should be suspended in it, even when it is admitted that they are held in the position which they occupy by investing membranes and sup- porting bands. Since time is required for the formation of these bands, it would naturally appear that long before they could have been formed such objects as shot, bits of iron or glass, would have sunk from . their own weight to the floor of the globe, allowing even for the jelly- like consistency of the vitreous. It would seem, therefore, more ra- tional to suppose that they had been invested by membranes of new formation, and had been gradually lifted into their suspended position by the subsequent contraction of the bands, perhaps along the very course by which they had advanced into the eye. A very curious case occurred in my own practice which, I think, can only be explained in some such manner, although even this expla- nation seems far-fetched, even if not impossible. A gentleman of middle age was shooting in the company of a 182 TEXT-BOOK OF OPHTHALMOSCOPY. friend, who, mistaking his position, discharged his gun in such a direc- tion that a single shot, probably a glancing one, struck the right eye. The patient fell to the ground, probably from sudden f aintness. On getting up he felt the pain of the blow in and around the eye, but found that he could still see with it, almost if not quite as clearly as with the uninjured one. On the following day he came to town, and a careful examination revealed the following conditions : At the outer and upper angle of the globe, and just over the ciliary region, was a small elevation of tissue, with a few enlarged vessels running over it. This was no doubt the spot of entrance. The wound was, however, closed completely. The iris responded freely to light, and, except the trifling wound alluded to above, there was absolutely no external mani- festation that the eye had been injured. Vision was perfect, Y = --. There was no limitation of the field, and not a trace of any injury to the internal parts of the eye could be detected with the most thorough ophthalmoscopic examination. The examination was repeated on the following day, under atropine, for the purpose of definitely answering the question whether the missile had actually penetrated the globe. Nothing could be seen of it. Two alternatives presented themselves either the shot had entered the eye, and imbedded itself in the ciliary region without penetrating deeply into the tissue, or, as it certainly seemed more probable from the total absence of symptoms, the shot had struck the eye and glanced from it without penetrating the globe. This encouraging view was held by the patient, and I must say shared in by me. He was cautioned against all work and exposure, and told to report in a few days. Three or four days after this he again re- turned. He had been, he thought, a little imprudent, both as to the use of his eyes and exposure to weather, and had taken cold in the eye. The ball of the eye was inflamed, the wound more prominent, and there was the greenish-yellow reflex in the pupillary space so typical of hyalitis. The lens at this time seemed to be perfectly clear. As the patient was unwilling to have the eye removed, unless he could be assured that the shot was really in it, and as there was not the slightest trace of any sympathetic trouble in the other eye, enucleation was not performed. Two years after this, however, the eye was removed for a recurrent attack of inflammation, and the shot was found in the centre of the lens. How it got there is a mystery, unless it is supposed to have migrated there from its original position, in the same way as we see the migration of foreign substances in other parts of the body. Sometimes these foreign bodies strike the eye with such velocity as to traverse the entire vitreous and penetrate the opposite wall, EXAMINATION OF THE MEDIA OF THE EYE. 183 where they can be seen with the ophthalmoscope to remain, some- times for years, without causing the least disturbance to the surround- ing tissue. At other times inflammation ensues, either at the moment of the injury or at some later period. This is followed by atrophy of the tissue of the retina and choroid or altered new-formed tissue, leaving the foreign body as a dark speck in a white patch of atrophy, represented by the sclera, the healthy portions of the choroid being separated from the atrophic by segments, or, indeed, by an entire cir- cle of pigment. Sometimes an injury to the retina and choroid may be seen, either with the mirror or on section, at the back of the eye, while the foreign body itself occupies another position on the floor of the globe, usually at, or of tener still a little in 'front of, the equator. When this takes place, Berlin is of the opinion that the body has entered the eye with sufficient force to have traversed the vitreous, struck the opposite wall, and to have rebounded from this to fall finally by gravitation to the floor of the eye. Whether this be the true explanation of the occurrence or not remains to be proved. But that an injury to the inner membranes may be detected in one place and the foreign body seen in another is an established fact ; and for this reason when, after an injury has been discovered at the back of the eye, the observer should never neglect to make a diligent search at the periphery of the lower field for the body itself, as his line of ac- tion in regard to the removal of the eye may depend on the fact that the presence of a foreign body within the globe is recognized. It is alleged that separation of the retina is sometimes caused by cicatricial contraction of the wounded parts. This occurs, I can not help thinking, more frequently from some alteration in the vitreous. Separation of this latter, which is described by Iwanoff as not an un- common occurrence after penetration of the globe by foreign bodies, can not, so far as I know, be recognized with the ophthalmoscope, though, of late, attempts have been made to lay down some rules for that purpose. Air-bulbles in the Vitreous. I was indebted to Dr. Mittendorf for the opportunity of viewing the following very rare case, which was unique in my own experience and that of my colleagues. Dr. Mittendorf has, however, curiously enough, seen one other. The case, as reported by him, is as follows : C. K , aged twenty years, strong and healthy, a blacksmith by trade, presented himself at the New York Eye and Ear Infirmary November 6, 1883. There was a large irregular wound at the tem- poral side of the sclera 3 mm. from the sclero-corneal margin. The patient had been struck in the eye by a splinter of iron three or four 184 TEXT-BOOK OF OPHTHALMOSCOPY. hours before coming to the infirmary. No view of the fundus could be obtained, owing to intra-ocular haemorrhage, but there was hardly any doubt about the presence of a foreign body in the vitreous. The wound was irregular and slightly gaping, with the vitreous presenting. In the afternoon of the same day a partial view of the interior of the eye could be had with the ophthalmoscope. This disclosed a large clot of blood at the lower portion of the vitreous, and three round and highly refracting bodies with dark borders at the upper part. These resembled in every way air-bubbles or oil-globules under the microscope. They were undoubted air-bubbles, and situated im- mediately behind the upper portion of the lens, which remained per- fectly clear. The larger one appeared to be the size of a hemp-seed. The two smaller ones are hardly as large as rape-seed. The next morning the bubbles had coalesced and formed a flat vesicle at the posterior pole of the lens. After the patient had remained in the erect position for some time, the bubble gradually arose to the upper portion of the fundus and assumed a slightly elongated shape, and had the appearance of a small oil-globule rising in water. After a lapse of thirty-six hours the air became completely absorbed, and no trace could be seen of the bubbles on the third day. The eye remained free from inflammation for some time, and the patient left the infirm- ary doing tolerably well. No attempt was made to extract the for- eign body, as the patient objected to all interference with the eye. In order to establish the diagnosis, Dr. Mittendorf injected a small quantity of air into the vitreous of a rabbit, and the appearances of the bubble which formed were with the ophthalmoscope precisely those which have been described in the case related above, in which air had been either forced into the eye or liberated in some way from the piece of iron within it. DIFFERENTIAL DIAGNOSIS OF TROUBLES IN THE MEDIA. Most of the rules and expedients laid down for the proper exami- nation of the anterior media, the cornea, aqueous humor, and lens, are also applicable to that of the vitreous, and need not now be re- peated, nor need the method of exactly determining their antero-pos- terior position be further dwelt upon, as it has already been fully de- scribed in the chapter on determining the errors of refraction. Still, there are certain characteristic effects which are produced by opacities in the different media which may serve sometimes to make a differ- ential diagnosis more accurate, or at least more expeditious. Should, in a given case, the opacities float into view with now a rising and then a falling motion, it would be safe to conclude that EXAMINATION OF THE MEDIA OF THE EYE. 185 these were in the vitreous and not in any of the other media, and, moreover, a discrimination could be at once made as to their being " movable " and not " fixed opacities." Should, however, the dis- turbance move only in concert with the eye, and not have any motion of its own, then it is a fixed body, and may, so far as its appearance with the ophthalmoscope is concerned, give rise to a doubt whether it is in the vitreous humor, in the lens, aqueous humor, or even in the cornea. This, it is true, should not have been the case if the observer has fulfilled his duty by carefully examining the anterior media by means of oblique illumination. Still, the observer may, while the in- strument is still at his eye, remedy his want of care by attentively observing the behavior of the opacity in regard to the movements of the observed eye and its centre of motion, and the relation which it bears to the pupillary space and the borders of the iris. The centre of motion lies in the vitreous humor, somewhat behind the middle point of the visual line. Objects lying in front of this cen- tre will, when the eye moves, move in the same direction. If situ- ated at the centre they will have no apparent motion. If situated behind the centre they will move in the reverse direction from that in which the eye moves, and the farther the opacities are from the cen- tre of motion the greater will be their excursions. Thus, in a given case, if an opacity is seen to make a considerable excursion toward the right when the observed eye is moved toward the right, and passes rapidly out of the pupillary space in the same direction that the eye moves, the observer knows that it must be in the cornea. Should the amount of displacement be restricted, but yet still toward the right, then in all probability the opacity is on the anterior capsule. If the motion of the disturbance should be still more restricted, but yet in the same direction, then the opacity must be in the neighborhood of the posterior capsule. Should the opacity have no lateral motion whatever, then it must lie at the centre of motion, that is, the centre of the eye. Should, on the contrary, the motion of the disturbance be toward the left when the eye moves toward the right, then the observer knows that it must lie in the vitreous behind the centre of the eye, and the great- er its displacement toward the left the deeper its position. Suppose A (Fig. TO) to be a transparent sphere with various TIG. 186 TEXT-BOOK OF OPHTHALMOSCOPY. opacities situated along its central axis. Suppose it rotates toward the right, so that its axis a It occupies the position of the dotted line a! V . No. 1 will make a large excursion and appear to move toward the right ; Nos. 2 and 3 will make a less excursion in the same direc- tion. No. 4 will remain stationary, while No. 5 will move in the opposite direction, that is, toward the left. This is certainly very simple in theory^ and, provided the pupil is sufficiently large, or, better still, dilated with atropine, is often very advantageous in practice. But with a narrow pupil the inexperienced observer is apt to be misled, at least in regard to the opacities in the posterior portions of the lens, because the iris being in advance of these makes a proportionately wider excursion, and for this reason the opacity, though still in front of the centre of motion, appears to ap- proach the pupillary margin of the opposite side, and thus to move in a direction opposite to that in which the eye moves, which leads to the idea that the opacity is behind instead of in front of the centre of the eye, or, in other words, in the vitreous instead of in the lens. For this reason it is always well to mark attentively the relations which the opacity bears to the pupillary space and the borders of the iris under movements of the observed eye. If the opacity makes a wide excursion and passes rapidly out of the field of the pupil in the direc- tion in which the eye is moving, it must be in the anterior parts of the eye and probably in the cornea. Oblique illumination will then settle this at once. If, on the contrary, the opacity makes a wide excursion across the pupillary space in a direction opposite to that in which the eye moves, and passes rapidly behind the borders of the iris, then it is in the posterior parts of the eye, and the greater the ex- cursion the farther back it is. If, however, the excursion is limited, and the opacity appears to change its position but slightly in refer- ence to the borders of the iris, and this in the direction in which the eye moves, then the opacity is in the lens, and most probably on the anterior surface, and nearly in a plane with that of the iris. On the contrary, when the displacement is greater in reference to the pupil- lary space, and the opacity appears to pass across it rapidly in the opposite direction from which the eye is moving and disappears be- hind the iris, it is in the posterior part of the lens, and the greater the excursion the deeper it lies. To make a differential diagnosis with certainty as to whether a given opacity is in the anterior parts of the vitreous or the most pos- terior parts of the lens, say the posterior capsule, we must turn to a nicer and more delicate test which has been described very accurately and clearly by Mauthner in his text-book of " Ophthalmoscopie." This EXAMINATION OF THE MEDIA OF THE EYE. 187 consists in observing the behavior of the coraeal reflex in relation to the opacities on movement of the eye. When the observed eye looks directly at the hole in the observer's mirror, the visual axis of the observed eye coincides with that of the observer ; and as the path of the illuminating rays is also in the same line, the corneal reflex will be seen in the centre of the pupillary space, and will lie at the apex of the cornea ; consequently the visual line of the observer will pass through the centre of the reflex and also through the centre of motion of the observed eye. These two points will, therefore, act as fixed points, and always lie in the visual line of the observer the reflex, because it lies in the path of the rays, which can not change unless the position of the mirror changes and the cen- tre of motion because it is the point round which the eye rotates. For this reason an object situated in front of the centre of motion will appear in reference to the corneal reflex to move in the same di- rection as the eye moves ; if situated behind, it will move in an oppo- site direction. If the reflex covers the opacity, notwithstanding the various movements of the eye, then the opacity must lie at the very centre of the eye ; and Mauthner declares that in this way he has been able to convince himself that the small opacities which are some- times seen on the axial line in retinitis pigmentosa were really situ- ated in the vitreous, and not, as is commonly supposed, in the pos- terior capsule of the lens. My own observation would lead me to suspect that, for the same reason, the minute opacity seen so often in very high grades of myopia in the axis of the eye is not, as so com- monly supposed, a posterior polar cataract, is not in fact in the lens, but is in reality a minute collection of pigment in the vitreous. The delicacy of this test in regard to the lens depends on the fact that the centre of motion is not really in the centre of the visual axis, but, according to Donders, 1.77 mm. behind it. The fact that the posi- tion of the centre of motion varies in myopic and hypermetropic eyes has no appreciable effect on the apparent movement of these opacities. ENTOZOA. The presence and detection of entozoa in the eye have always been a very interesting study with ophthalmologists, and the number of recorded cases from the earliest days of ophthalinoscopy has grad- ually increased until the literature of the present day is exceedingly rich in them. The varieties hitherto met with are the cysticercus cellulosse and the filaria. The cysticercus has been found in every part of the eye and its 188 TEXT-BOOK OF OPHTHALMOSCOPY. appendages that is to say, under the skin of the lid, in the orbit, under the conjunctiva, in the cornea, iris, lens, in the vitreous, and be- tween the choroid and retina. A very remarkable fact in the history of this disease is the great frequency in which this parasite has been found within the eye in cer- tain countries, or even in certain districts of the same country, and its rarity or even total absence in others. Thus Yon Graefe, in some eighty thousand cases of eye-disease, observed the worm eighty times, or one case in every thousand. Hirschberg, out of twenty-one hun- dred new patients examined in the short space of six months, saw a cysticercus five times, or one in four hundred and twenty cases of eye- disease ; while Mauthner, in Vienna, among thirty thousand cases of general eye-disease of which he had cognizance, had never seen a single case of a cysticercus. Until very recently I had never seen even a doubtful case, nor did I know of a single well-authenticated case ever having been seen in the interior of the eye by any of my colleagues in this or the neighboring cities, or, indeed, in the entire country. Through the kindness of Dr. Minor, I have been permitted within the past few weeks to examine a case in which, from the oph- thalmoscopic appearances, there was reason to believe that it was a true case of cysticercus, although it was not absolutely proved to be so. As, therefore, I have little or no personal knowledge of this sub- ject, I must avail myself of the observations of others, and I therefore reproduce here an abstract of the description furnished by Becker for Mautlmer's work on the ophthalmoscope. These observations of Becker are prefaced by Mauthner by a short general description of the animal, as follows : The worm is provided at its posterior end with a round, cyst-like formation which acts as the receptaculum scolicis, into which the ani- mal can withdraw, presenting when in this position the appearance of a round, whitish body. A small fold marks the mouth of this recep- tacle. When the animal protrudes its head and neck out of the re- ceptacle its body appears to be sprinkled here and there with calca- reous deposits, and presents sometimes a smooth and sometimes a wrinkled surface. The body decreases in size toward the neck, to which is attached the head, with its four flattened-down but angular projections. A round-shaped snout can be projected by the animal from the centre of its head, and this latter is provided at its base with a double row of hook-like tentacles, which are capable of retraction. Each of the angular projections of the head is, moreover, provided with a rounded sucking apparatus. The most common seat for the EXAMINATION OF THE MEDIA OF THE EYE. 189 development of the animal is between the choroid and retina, and it occurs twice as often here, according to Graefe, as in the vitreous. As a rule, the worm is not inclosed in any sac, but on three occasions it was observed to have a peculiar envelope of its own, and on all of these occasions the animal was in the vitreous. The length of time in which the parasite can exist in the eye has not been determined, but Graefe has observed it for the space of two years. Its presence in the eye leads sooner or later (from three to fifteen months) to disturbances of vision, and to the production of irido-choroiditis, which can pass into true panophthalmitis, but the trouble usually runs a more chronic and insidious course, to a gradual atrophy of the bulb. In two cases only, in which the worm in the vitreous was encapsulated, were the form of the eye and a portion of the visual power retained. The case reported by Teal would appear to be unique, in which a free cysticer- cus was observed for two years without the eye suffering from the entozoon, and without the vision having decreased to any considerable amount. Moreover, as the sight of the eye had been bad from child- hood, there were fair grounds for supposing that the animal had main- tained itself in the eye from that period. The ophthalmoscopic appearances in the cases seen by Becker were briefly as follows : The retina was for a considerable portion of its surface disturbed and of a grayish-white color, instead of a bluish tinge. It was appar- ently raised but little above its ordinary level, and slightly folded, or perhaps irregularly thickened, so that its surface was not smooth and even, but apparently hollowed out in many places. The vessels were tortuous and bent, following the irregularities of the surface. They still conveyed their contents, and appeared red, but were here and there enveloped by extravasated blood. There was also the appearance of dark gray flecks or spots in the grayish-white retina. That portion of the retina which showed this kind of degeneration was in the posterior portion of the bulb, and included the macula lutea. The fact should here be emphasized that no other disease of the retina produces a simi- lar picture. In the neighborhood of that part of the fundus which had undergone the changes mentioned above there occurred an actual separation of the retina which then projected into the vitreous. The circulation in the vessels of the cyst-like elevation of the retina was not interfered with, as could be told from its red appearance. On two occasions, in which the retina remained, comparatively speaking, trans- parent, a cyst-like swelling of a bluish color could be observed. The walls of the bladder-like projection could be seen to bend backward with a convex surface, and to be distinctly separated from that of the 190 TEXT-BOOK OF OPHTHALMOSCOPY. retina. A critical examination led to the conclusion that the retina at this point was lifted up from the choroid by an independent bluish but depressed body with rounded contours, the walls of which con- tained no vessels. This lack of vessels speaks against the diagnosis of a new growth, and in favor of that of an entozoon. If the bladder perforated the retina, then the appearances were different, and a bluish cyst-like body, which varied in size from two to four diameters of the optic disk, appeared to project into the vitre- ous. The surface appeared finely granular and, under strong illumi- nation, produced a lively iridescence. The play of all the colors, in which a brilliant red predominated, was particularly noticeable toward the borders, and at some particular point there appeared a glittering white spot. The cyst-like body was in such cases attached by a neck-like pro- cess to a point of the retina which was then degenerated in the manner already pointed out. The appearances described above would in themselves suffice to mark the diagnosis, but a more convincing proof is obtained by the detection of the movements of the animal. If the observer riveted his attention upon some particular point of the projection, especially toward the borders, or, better still, upon the white spots just alluded to, he would be able to notice, after some moments of delay, and while the observed eye remained motionless, that suddenly an unmistakable change in form took place along the walls of the projection, or of the light-spot so often mentioned. This latter is then seen to be displaced in a certain direction to become greater or smaller in size, returning, after a short time, to its original condition ; or it might even assume a somewhat different shape and position. If the attention was fixed upon the border of the cyst, two kinds of movements might be observed. The contour itself might change its form, now bulging out, and then becoming concave, or a wave-like motion run along the surface, and at the same time a change of color occur, the blue places becoming white, and the white gray. Or the play of color might stop entirely, giving place to a dull shimmer on the surface. The move- ments upon the surface of the cyst and clear spots in its interior always happened at the same time. The clear spot then corresponded in position to that occupied by the head and neck in the receptaculum. Any movement, no matter how slight, in the position of these two made the cyst, which was full of liquid, tremble. The glittering effect which has been spoken of was caused by the minute calcareous deposits in the walls of the cyst. Much as these movements resem- bled each other, whether the cysticercus was in the vitreous or under EXAMINATION OF THE MEDIA OF THE EYE. 191 the retina, still certain peculiarities manifested themselves, due to the difference in position. For, if the free cyst extended into the vitreous, all the details described above could be more clearly perceived ; while, on the other hand, if the entire process was only seen through the retina, the changes in color were correspondingly dull, although, at the same time, the movements themselves were more conspicuous, since the observer could then estimate directly the amount of motion by comparing the excursion of the walls of the cyst with the retinal ves- sels, which do not share in the movements. In some cases, however, the movements of the animal were so energetic that the overlying retina was also implicated. It may be said that all doubt about the diagnosis is removed in these cases when the observer happens to hit, by chance, the time when both the head and neck of the animal are extended from the receptaculum. In such a case the head and neck may be seen to point, for a considerable time, fixed and immovable, toward one direction. The head, from its position, with its suckers somewhat retracted and its snout outstretched, then allows the circle of tenaculi to be divined, rather than clearly perceived, as fine, dark lines. In another moment, however, the neck may be seen to undergo, with comparative rapidity, all sorts of delicate undulations and changes in position. The neck becomes thicker and shorter, or extends itself to its full length, and then twists itself into every position, or even doubles upon itself ; while the head, by means of alternate projections and retractions of its sensitive suckers, and of the shorter but thicker snout, assumes the most wonderful and singular shapes. The sucking apparatus resem- bles precisely the tentacles of the snail, and constantly performs, like them, a ceaseless change in form and movement. It must be accounted as an exceptionally lucky occurrence when both the head and neck of the animal can be observed outside of the sac. In the short space of twenty or thirty minutes such a cyst-like formation has been observed to shove itself along under the retina for a space of several lines. In what way or by what mechanism these movements are performed has not yet been determined. The vitreous humor is interspersed with punctate disturbances, which are aggregated together in small collections. Membranous dis- turbances are only present after repeated operations have been per- formed without any successful result. Liebreich gives in his atlas two chromo-lithographs of the ophthal- moscopic appearances of the cysticercus. Fig. 5, Tab. VII., from which the drawing is made (Fig. 71), represents the animal after he had perforated the retina and was in the vitreous, in which it occupied 192 TEXT-BOOK OF OPHTHALMOSCOPY. FIG. 71. such a position that its movements and the contractions of the cyst could be plainly seen. Fig. 6 shows the cysticercus still beneath the retina, as is demonstrat- ^^ ed by the retinal ves- sels which run over it. The head and neck are within the bladder, and only appear very indis- tinctly through it (Fig. 72). Jaeger also gives a drawing of a cysticercus in his " Hand- Atlas," Taf . XYIIL, Fig. 83, as does Hirschberg, Graefe's " Archives," vol. xxii., Plates Y. and VI. The case alluded to, Flo 72 ^ reported by Dr. Mi- nor as occurring in New York, and described by him, is as follows : * " During the past summer a patient consulted me at the New York * " The Medical Pvecord," December 27, 1884, p. 703. EXAMINATION OF THE MEDIA OF THE EYE. 193 Eye and Ear Infirmary for impaired vision, and I made the diagnosis of cysticercus in the vitreous. The extreme rarity of such cases not a single authentic case, so far as I am aware, having been observed in America caused at first much doubt in my mind ; but the patient has been frequently and carefully observed since he was first seen, and I am now confident that the diagnosis was correct. And I am strengthened in my conclusion by the opinions of some of my con- freres of the New York Ophthalmological Society where the patient was shown who have seen cases of cysticercus in the vitreous in the European clinics. The patient has repulsed all overtures pointing toward an operation for the removal of the entozoon, and I simply desire to place the case on record, with the hope that I may, at some future time, add the result of the operation thereto. " J. M , aged sixty, male ; seen in July, 1884, when the fol- lowing notes were made : Ten days ago suffered great reduction in vision in the right eye, which has remained almost unchanged since. Vision in right eye = ^-f^, with excentric fixation, vision being pos- sessed only in the temporal half of the visual field. The ophthalmo- scope shows detachment of the retina throughout the temporal half of the fundus. Far forward in the supero-temporal quadrant, just behind the ciliary body, is a cyst, nearly transparent, of ovoid form, which contains (?) a cylindrical mass, appar- ently about one half of an inch long and one eighth of an inch thick, that terminates in a free somewhat pointed extremity. Just behind the tip on either side is a small black dot booklets and behind these a slight constriction the neck above which, after gradual enlargement, the tongue-like pro- cess reaches a point so far forward that it , i m 11 i -L j .c j v Fra- 73. As seen by the can not be seen. Two parallel bauds of deli- , . . direct method of ex- cate whitish tissue can be traced from the animation, neck up to the point at which the whole object is lost to view. The upper part of the cyst is lost to view at the same point. The retina, as it approaches the cyst, assumes a wavy and wrinkled outline, and presents a mottled appearance, being interspersed with a number of small grayish spots (see figure). The obliquity of the eye necessary for a proper view is such as to make it difficult to distinguish between movements of the globe as a whole and individual movements of objects in its interior. Yet I have sat- isfied myself, as others have done, that the tongue-like process does possess individual movements. I have observed slight lengthening 1 O 19tt TEXT-BOOK OF OPHTHALMOSCOPE and shortening, a little lateral movement and tremulousness of the process. The position of the entozoon is such as to make it impossi- ble to establish the exact relation of parts. The junction of the neck with the cyst-body can not be seen, and the cyst is so transparent that it can not be positively said whether the head and neck are contained therein, or whether they lie free in the vitreous, just in front of the cyst. I am inclined to think that the latter is the case, for with the inverted image a marked parallax can be obtained, which not only shows considerable depth to the cyst-cavity, but that the head and neck lie well forward in the anterior part of the cyst, or entirely in front of the cyst-wall." In regard to the second class of entozoa the filaria it can only be said that doubtful cases have been reported by Fano, Quadri, and Mauthner ; and the latter remarks that he saw in the perfectly clear vitreous of a man of forty years an object that was freely movable, but which had no independent motion of its own, but which he un- hesitatingly believed to be a filaria, though perhaps a dead one. I have myself seen a case which was presented at the New York Oph- thalmological Society, with the suspicion that it might be a case of filaria in the vitreous. The object in question presented the appear- ance of a long filiform body, which projected through the vitreous in the median axis from the optic disk to about two thirds the distance to the posterior surface of the lens. It had a graceful, undulatory motion when the eye of the patient was moved, but, like the case of Mauthner's, no independent motion of its own. It resembled, more than anything else, a very much attenuated and minute eel with a deli- cate, tapering neck, surmounted by a somewhat bulbous head. It was certainly wonderfully like a worm in shape and character ; but it was totally untransparent, and the general opinion of the society was that it was not a living organization of any kind, but either a delicate and filamentous band in the vitreous or the remains of the hyaloid artery. This opinion was strengthened by the fact that there was also a small black spot situated on the posterior capsule of the lens close to the posterior pole, and which forcibly suggested the idea that it was once the place of attachment of the anterior portion of the body, whatever it was. APPENDIX THE following remarks are intended only for those who are unac- quainted with the elements of optics. They illustrate, in a brief and, it is hoped, a simple way, the principles upon which the ophthalmo- scope depends, and only include such as are essential for the student to understand. A luminous body is made up of an infinite number of luminous points, from which lines of light radiate in all directions like the spokes of a wheel, the only difference being that the luminous point is the centre of a sphere, while the hub is only the centre of a circle. It is in the direction of these lines, or, as they are called, rays, that light is propagated in wave-like propulsion. Thus, in the diagram (Fig. 1), the straight lines radiating from the centre, or luminous point, may be looked upon as the ray which shows the direction in which the light travels ; while the sinuous lines show the manner in which it travels, or its undulatory motion. It is evident that the height of the wave has nothing to do with the direction in which the wave moves. Strictly speaking, the term ray is a relic of the old emission theory. The ray has no real existence, but is an imaginary straight line drawn from the luminous point, from which the light-wave starts, to the point against which it impinges. Still, as the height of the wave is to the human mind an inappreciable quantity, it is exceed- ingly convenient in optics to represent, not only the direction in which light travels, but also its wave-like motion, by straight lines instead of undulatory ones. A collection of luminous rays is called a luminous pencil. As luminous rays in nature always travel in straight lines, and FIG. 1. 196 TEXT-BOOK OF OPHTHALMOSCOPY. always diverge from each other as soon as they leave the luminous point, it follows that, strictly speaking, there can be, from natural sources, but one kind of rays that is, divergent rays. Thus, the rays from the sun and other heavenly bodies are, in fact, divergent ; but, inasmuch as these bodies are at an infinite distance, and inasmuch as the pupil of the eye is only from one to two lines broad, it follows that only those rays which travel nearly parallel to each other can find their way into the eye. Thus, if, in the diagram (Fig. 2), we suppose FIG. 2. the sun to be at an infinite distance, it at once becomes apparent that only those rays can enter the pupil which run parallel to each otlier. The slightest conceivable divergence would prevent this, and these rays would be excluded from the eye. Hence, when we see objects which are at an infinite distance, we do so by means of rays which are practically parallel. Such rays play a very important part in ophthalmoscopy as well as in physiological optics, as they form the standard by which we measure the power, not only of lenses, but also of the eye itself. Moreover, experience teaches us that it is not ne- cessary to go to infinity for parallel rays. Bays coming from any dis- tance greater than twenty feet are assumed, in physiological optics, to be parallel. When light coming from a luminous body strikes against the sur- face of a non-luminous one, part of it is absorbed by the body and part of it is reflected by it. There are two kinds of reflection : (1) that which takes place from a polished surface, and is called regular or specular reflection ; (2) that which is called irregular, because it produces no image, but only serves to render the object visible. Strictly speaking, perhaps all, certainly most objects, produce both kinds of reflection, but usually one so predominates over the other as to render the distinction a just one. Let a polished plane mirror be taken, and held about one foot from the eye, so as to catch the reflection of some luminous body, say the lighted chandelier, which we will assume to be at a distance of ten feet. It requires but a little abstraction of the mind to make one lose perception of the surface of the mirror, but what is seen is the fac-simile of the source of light in all its detail of form and color. Now, let a bit of paper, say an inch square, with some very fine print- ing on it, be pasted upon the centre of the mirror. Repeat the ex- APPENDIX. 197 periment under precisely the same conditions as before. Directing the attention to the image of the chandelier, this will be seen in all its detail, exactly as in the former case, excepting that the small portion of the image corresponding to the bit of paper is wanting. One is indeed conscious of this latter, even while looking intently at the image in the glass ; but it appears to the eye only as a blurred piece of white paper, on which not a letter of the type can be deciphered/- Now, fix the attention on the paper, so as to read it distinctly. One at once becomes aware of an effort on the part of the eye, and notices that the image of the chandelier has become blurred. Repeat this indefinitely, and it will be found that one never sees both the print and the image distinctly at the same time, although the bit of paper is at precisely the same distance from the eye as the surface of the mirror, and the chandelier, which is the source of light, is at precisely the same distance from each. That there is some difference in the condition of the rays which come from the surface of the mirror, and which go to form the image of the gas-flame, and those which come from the paper, is evident from the consciousness of tension and relaxation taking place in the eye when looking at the objects, and from the alternating distinctness and indistinctness of the objects themselves. The difference is precisely this : The rays coming from the source of light strike both the paper and the surface of the glass with precisely the same degree of diver- gence from each other ; but the polished surface of the mirror, after receiving the rays, gives them back exactly as it received them in every respect. It simply alters the direction in which the rays were travelling, but does not change their relation to each other. They leave the surface of the mirror with precisely the same degree of divergence that they had when they touched it, consequently the object appears just as it did before the reflection took place, only in a different position. But the slightly roughened surface of the bit of paper, although it received its rays from the same source and un- der precisely the same degree of divergence as the mirror, does not, like the latter, reflect them just as it receives them, but it absorbs the light, as it were, into itself, and then throws out such rays as it does not consume, just as if it had produced them itself, instead of bor- rowing them from another source. Thus, the rays coming from the paper enter the eye, in the above experiment, as if they diverged from the surface of the paper itself, which is at a distance of only one foot, while those which form the image enter as if they came from ten feet. Let A in Fig. 3 be the lamp, ten feet from the mirror m. Rays 198 TEXT-BOOK OF OPHTHALMOSCOPY. from this will strike the mirror, and be reflected from it with the same degree of divergence among themselves with which they struck it. Entering the eye, they will be projected backward till they inter- sect at A', where an image of the lamp will apparently be formed, just as far behind the mirror as the real lamp is in front of it, namely, ten feet. On the other hand, the rays striking upon the paper p will be absorbed practically into it, and then given off as if they came directly from it, and thus enter the eye as if they originally diverged from a distance of one foot. From this it will be at once apparent that the position of the source of light, from which the non-luminous body borrowed its light to become visible, has no effect on the direc- tion of the rays which are practically re-emitted, rather than reflected, from such a body. Thus, if we put the book which we read at twelve inches from the eye, and place the light at any distance we please be it one foot or twenty the rays will always enter the eye as if they came from a distance of twelve inches. And, further, we can change in various ways the direction of the incident rays so as to make them divergent, parallel, or convergent ; and still, as long as the book is held at a given distance, the rays will always enter the eye as if they diverged from the surface of the page. FIG. 3. This is " irregular reflection," and it is through this that we see the details of the bottom of the eye, in their due form and color, just as we see all other objects. It is for this reason that I have dwelt so particularly on this point; for, by keeping it in mind, the student will be aided essentially in understanding not only the theory of the ophthalmoscope, but also its practical application. Although there are in nature only divergent, or, at the most, par- allel rays, we have, as has just been stated, certain agents at our com- mand by which we can alter the direction of the rays so as to make them at will either divergent, parallel, or convergent. This is done APPENDIX. 199 by lenses and mirrors, and, as these are the two essential elements of all ophthalmoscopes, a thorough acquaintance with their fundamental properties, however elementary, is absolutely necessary. Convex Lenses. The simplest form of a lens, and one with which the reader's microscopical studies will have rendered him familiar as a condensing lens, is a piece of glass having a flat or plane surface on one side, and a spherical or convex surface on the other, hence called a plano-convex lens. Such a lens is represented in section in Fig. 4. The amount of curvature of the spherical surface depends on the radius of the sphere on which the glass is ground. Thus, in Fig. 4, R II would be the radius of the sphere on which the lens is ground, or, in the language of optics, the radius of the curvature of the lens. R N and R M would be likewise radii, as in fact would any line drawn from the centre of the sphere to any point on the surface of the glass. The ex- FlG 4 tent of the plane surface would, of course, depend on the size of the segment of the sphere taken. This might be only the size of the shaded portion in the figure, or what is included between the dotted line 8 G and the circumference ; or, in fact, the whole half -sphere. Yet, the curvature, and of course the radius, would remain the same. Consequently, the strength of the lens does not depend upon its thickness, though it is slightly influenced thereby. Suppose such a lens to be exposed to the waves of light coming from an infinite distance, and that consequently parallel rays strike upon its convex surface (Fig. 5). The width of a wave of light can not be estimated, of course, by the human eye. Nevertheless, the wave must have an appreciable breadth as compared with the point where it strikes the surface of the lens. We will suppose, for the sake of illustration, that the rays of light are enlarged to the extent shown in the diagram (Fig. 5), and are advancing, through the air, toward the lens in the direction of, and parallel to a straight line drawn through the centre of the lens, the radius of whose curvature is R H. For the sake of convenience, we will represent the light-waves by straight instead of curved lines. Take the upper beam in Fig. 5. One end of the beam (#), ad- vancing through the air, will come in contact with the glass at the point h before the end b does. As the glass is a denser medium than the air, the end a will be retarded somewhat in its progress, while b travels with its original velocity. This difference in speed will make 200 TEXT-BOOK OF OPHTHALMOSCOPY. 5 swing round #, describing a large arc, while a describes a small one, and this disproportionate rate of progress will continue until both ends of the beam, having entered the glass, are subject to the same retard- FIG. 5. ing influences, and then they will both advance at an equal rate of speed ; just as, with* a column of soldiers in marching into a street which runs at an angle with the one they are already in, the whole front of the column keeps moving, but the outer end of it moves with a greater rapidity than the inner till the line comes fairly into the street, and then both ends advance with the same rapidity. By contact with the glass the direction of the ray is changed at #, but, once the ray has fairly entered the glass, its direction will be maintained so long as it remains within it. But a glance at the dia- gram will show that, from the new direction in which the ray is mov- ing, the end b will emerge from the glass sooner than the end a ; and as 5 will, as soon as it emerges into the air, travel faster than a, it will make the same movement round a that it did before, and this will con- tinue until a emerges from the glass, and thus a new direction will be established. Thus the ray has been bent at two points : first, on en- tering, and, secondly, on leaving the lens. And it will be seen, by looking at the diagram, that the ray, at its first refraction at a, where it passes from a lighter to a denser medium, is bent toward the line R A, which geometry teaches is the perpendicular to the surface at the point of incidence wnen it assumes precisely the same appearance as the mirror now in uee, with the exception of the segment, which has been taken away. This, like Jaeger's and Dr. Wadsworth's mirror, rotates from right to left. With it we get abundant light for either method. APPENDIX. 249 The second modification is still simpler, and consists of cutting off both sides of the mirror, thus converting it into a parallelogram, as seen in Fig. 53. This is swung on two pivots, the inclination being 20, or, if wanted, 25. This mirror tilts both ways, and does not have to be rotated, and can be used perfectly well for both upright and inverted image. This mirror is usually known as the " tilting mirror." It is thirty- three millimetres long, by nineteen broad. In regard to the advantage of a mirror set at an angle for the use of the upright image, there can be no possible doubt in the mind of any one who has once seen the difference, in the ease of the illumina- tion and the clearness and brilliancy of the picture. By its use, a large quantity of light is saved, since the correcting glass, instead of being at a considerable angle with the axis of vision, and therefore in a position favorable to a largely increased loss of light through reflec- tion from the surface of the glass, is nearly at right angles to it, by which all the light possible is saved. This mirror gives also ample light for the inverted image, and I now use it entirely for all methods of examination. If, however, more light is needed, this can be obtained by making the shaded portions in the above drawings of mirror glass. A still more elegant though more costly way of obtaining the same result is to have a small mirror, circular in shape, and swung on pinions, a and 5, Fig. 54, and this surrounded by a concentric mirror, 6?, so that the two together form a mirror both in size and shape like that now used in ordinary ophthalmoscopes. The external portion would, of course, be set stationary, the central portion tilting to the right and left as occasion required. 250 TEXT-BOOK OF OPHTHALMOSCOPY. Fixed Ophthalmoscopes. These instruments, though numerous in kind, seem to have passed out of date, and they are very rarely seen at the present time, and still more rarely used. Among the earlier of these instruments, and one which was most frequently used, was Liebreich's. This consisted of the application of the inverted image through a tube similar to that of a microscope. This was fast- ened to a stand which allowed the instrument to be raised and low- ered as occasion required. It was also fitted with a rest for the pa- tient's chin. At one end of the tube a mirror was fixed, similar to that of Jaeger's ophthalmoscope, while at the other was the object- glass. The image was formed within the tube, between the object- glass and the mirror, precisely as it is with the inverted image. The picture was brilliant and clearly defined. For a further description, the reader is referred to Graefe's " Archives," vol. i, part ii, p. 348. Dr. Burke, in 1871, proposed a very ingenious fixed ophthalmo- scope, which had the rather unexpected merit, at this late day, of being founded, in part at least, on a new principle. This instrument consists of concave mirrors, mounted on stands, with sliding tubes, so as to permit of a change of elevation. The light from the source of illumination, striking upon the first of the mirrors (which is perforated with a focal length of thirty-three centimetres), is reflected against the second mirror. This latter is unperforated, is of nineteen centi- metres focal length, and is placed at just its focal distance from the observed eye. By this mirror, the light received from the first is cast into the eye to be examined. The fundus of the eye, being illumi- nated, reflects, in its turn, the light through the pupil back to the second mirror again, which, being concave, brings the rays to a focus at the focal length, where a very brilliant, reversed, and much enlarged image is formed. The head of the patient is supported by a chin-rest. Unfortunately, the practical handling of the instrument is not as easy as the theory is simple, and the result beautiful, when all things com- bine favorably. It often exhausts the patience of both the observed and observer before an image is obtained, and, even then, this is apt to be veiled, in spite of every care, by annoying reflections. Carter's Ophthalmoscope. Shortly after the appearance of Burke's instrument, Mr. Carter (" Report of Fourth International Ophthalmo- scopic Congress," London, 1872, p. 69), while keeping the general form of the stands, substituted for the second mirror a large convex object-glass. This simply reduced the instrument to a much enlarged but ordinary Liebreich's ophthalmoscope. The shape of the instru- ment and the principles on which it depends are precisely the same, the only difference being that one is fixed and the other portable. APPENDIX. 251 The apparatus requires the use of a table, which should be four feet long, and which need not be more than eighteen inches wide ; or it may be arranged across one end of an ordinary dining-table. This is, in many respects, the best demonstrating ophthalmoscope yet pro- posed, and the only objections to it would appear to lie in the large- ness of its dimensions, and the amount of separation, when in use, of its component parts. Binocular Ophthalmoscopes. After some previous attempts, for the purposes of getting perspective effect, Giraud Teulon produced (" Physiologic de Vision Binoculaire," Paris, 1861) his binocular ophthalmoscope, which was an exceedingly ingenious and beautiful application of the principles of total reflection by the means of prisms. Before the solution of this problem we were restricted, in our investigations of the fundus oculi, to the use of one eye, and no more forcible argument as to the advantages of seeing with two, and the absolute necessity of an instrument for this purpose, could possibly be brought forward, than the curious mistake universally made as to the true shape and conditions of the optic nerve in glaucoma now one of the best known of diseases, with one of the most striking oph- thalmoscopic pictures. That a deep excavation of the entire optic nerve, with its concavity toward the observer, should have been mis- taken, for several years, by observers then and forever famous, for a protruding convexity due to swelling of the entire nerve, seems now to be incredible. A single glance with the binocular instrument would have corrected this impression ; and, had it been invented in time to do this, Teulon's beautiful invention would have acquired for itself even a greater renown and a more extensive use than it now pos- sesses. But, curiously enough, the instrument is very rarely used, even in detecting the differences in level in the fundus, since we possess, with the ordinary ophthalmoscope, a means, not only of ascer- taining the existence of such variations, but also of measuring their exact extent. Still, the binocular instrument has virtues and beauties of its own, which will always command the respect and excite the interest of every careful student of ophthalmoscopy. The essential parts of the instrument and the manner in which the image is formed are shown in the beautiful drawing (Fig. 55) by Dr. John Green.* Since the discovery of the principles on which the ophthalmoscope depends, innumerable instruments have been invented with all possible kinds of reflecting surfaces, plane and curved, with their combinations of lenses and prisms ophthalmoscopes to be used with artificial light, daylight, and even sunlight, autophthalmoscopes, and ophthalmoscopes * " Recent Advances in Ophthalmic Science," Williams, p. 20. 252 TEXT-BOOK OF OPHTHALMOSCOPY. for one, two, or three observers. All of these, with the exception of those based on the plane mirror proposed by Helmholtz, and on the concave mirror introduced by Ruete, have yielded to the practical and FIG. 55. realistic tendencies of the day and passed into disuse. Not one in ten thousand of the examinations hourly taking place in all parts of the world is made with any other than the simple concave mirror of Kuete, and it has always struck me that but scanty justice had been APPENDIX. 253 done to one whose beautiful and comprehensive invention is the almost universally used implement of our art especially when it is taken into consideration that he also rendered practicable, even if he did not invent, a method of examination which forms an indispensable adjunct to that originally proposed by Helmholtz, and which has been used by the great majority of observers, even to the entire exclusion of the former. These more complex forms of the instrument are rather the solu- tions of interesting optical problems than the embodiment of any clinical or even physiological purpose, and the reader must be re- ferred to more technical works for their description. ADJUNCTS TO THE OPHTHALMOSCOPE. The most important adjunct to the ophthalmoscope, and one, indeed, which forms an essential part of it so far as the inverted image is concerned, is the object-glass. This glass varies in strength from a one to a four or even a five inch lens, according to the amount of enlargement and extent of field which we wish to obtain. These latter stand in inverse proportion to each other : the larger the field of view, the smaller do the details comprising it appear; the weaker the glass, the smaller the field, but the larger its detail. The best glass for average work is a biconvex lens of two and a half inches focal length. It should have a diameter of one and a half inch, and should be ground as thin as this dimension will per- mit. It should be made of the best glass, and as highly polished as possible. The comfort of working with a glass of this diameter, and the increased illumination, and the sharpness of the image which it gives, more than repay the little extra trouble and expense in pro- curing it. This glass serves also as a condensing lens for examining the media of the eye by oblique illumination. The writer, for the purposes of illuminating the anterior portion of the eye, has made use of the device shown in the drawing (Fig. 56). It is a modification of an idea suggested by Mr. J. E. Adams, of London, and consists of an arm, broken at the various points by ball- and-socket joints, so as to give a perfectly free adjustment to the lens in any direction, and at any distance up to the extreme length of the arm. This leaves both hands of the surgeon unencumbered, permits the use of fixation forceps if necessary, and does away with the neces- sity of an assistant to hold the lens. The arm is attached to an elastic head-band precisely like the head-band of an aural or laryngoscopical mirror. When in use, the band is slipped over the head of the patient in such a way that the 254 TEXT-BOOK OF OPHTHALMOSCOPY. hard-rubber support comes at the temporal region and on the side of the eye to be illuminated, the lens being then swung into the position desired. By having the plate at the temporal region, and the lamp well at the side instead of directly in front, we get rid of annoying FIG. 56. reflections, and avoid the irritating effects of the light from a strong condensing lens thrown directly through the pupil upon the patient's retina. If the lens is so arranged as to be a little within or a little without its focal length from the eye, the section of the cone of light is large enough to keep the cornea covered, even if the eye makes con- siderable excursions, while, as the lens is attached to the patient's head, this latter can be moved to a considerable degree without displacing the illumination from the eye. I have found it of great service in operating upon delicate membranes in the pupillary space, as it gives a much steadier illumination, and one which is more easily controlled than when an assistant holds the lens. By removing the lens from the clip and supplying a mirror, the instrument, from the character of its joints and the mutability of its position, can then be used as a fixed ophthalmoscope for the upright image, and can thus be used in demonstrating the fundus to a class, or in making a sketch of it without the observer being compelled to take up and lay aside the instrument at every look ; or the upper half of the ordinary ophthalmoscope can be inserted instead of a simple mirror, and then any optical combination that the refraction of the observed eye may require can be obtained. I have had a band made which carries two lenses, one on a shorter arm, which is then used as a magnifying-lens, but the single one answers every purpose, and for ordinary occasions is the most convenient. APPENDIX. 255 The instrument is also very useful for the removal of foreign bodies or magnifying small hairs, thus rendering their detection and removal much easier, or in performing any operation at night or whenever the light is poor. When, however, the light is sufficient, and only an increased enlargement is desired, the surgeon, by wearing the band on his own forehead and extending the arm to its utmost, can obtain a large amount of magnifying power, while by slight movements of the head he can successively inspect and keep in front any portion of the anterior surface of the eye or lid. Ophthalmo-Microscopes. For the purpose of examining the cor- nea, iris, and anterior portions of the vitreous, under an increased magni- fying power, Liebreich replaced the tube of his large ophthalmoscope with that of a microscope.* With this, in spite of the difficulty in keeping the patient's head immovable, he was enabled to see the cor- nea, iris, and disturbances in the lens and anterior part of the vitreous under an enlargement of ninety diameters. As the simple to-and-fro movements of the tubes were not sufficient to give a complete control over the instrument, it was subsequently f mounted on two rings, similar to those of a ship's compass, by which motions in all necessary directions were obtained. Wecker also constructed a small microscope, which, by means of a tripod, was made to rest firmly against the cheek and brow of the patient, lateral illumination being obtained by a condensing lens. This instrument gives an enlargement of eighty diameters.:}: A binocular ophthalmo-microscope has also been constructed. These instruments, though they deserve a mention here, are of very little practical value, and are rarely used clinically, a sufficient enlargement and illumination being obtained from a simple lens, or, sometimes, by a combination of two lenses. Artificial Eyes. It is often convenient, as well as instructive, for the student to have some mechanical contrivance which shall repre- sent the dioptric system of the eye. By its means he is often able to get at a glance a tangible idea as to the different errors of refraction and the manner in which images are formed, which would be impos- sible from any written description. One of the simplest of such arti- ficial eyes is what is known in the shops as " a cotton-counter," from the fact that dealers use it to magnify and thus count the number of threads in a given area of the fabric. It consists of a one-inch lens set in a short upright of brass, while another upright is placed just at its * Graefe's "Archives," Band 1, Ab. 2, p. 352. t " Monatsblatter f. Augenheilkunde," 1863, p. 486. t '' Etudes Ophthalmologique," 1864, vol. i., p. 272. 256 TEXT-BOOK OF OPHTHALMOSCOPY. focal length. A piece of card can be fastened to this second upright, which can then be looked upon as the retinal surface on which images may be formed or a picture of the fundus be painted. A little more extensive apparatus on the same principle is shown in Fig. 57. Here the upright screen which represents the plane of the retina is made movable by a screw, so that the space between the two uprights can be altered at will. The anterior upright is so made that lenses of dif- FIQ. 57. ferent power can be inserted. Among these is one, the focal length of which is 6.7 Paris lines. This gives precisely the same enlarge- ment as would be obtained with the ophthalmoscope in examining an emmetropic eye. This is a refinement, however, which is not essen- APPENDIX. 257 tial, as the ordinary one-inch lens answers every purpose. All the varying degrees of myopia and hypermetropia can be obtained by altering the length of the antero-posterior axis, and these can be con- nected by placing the corresponding glass in the clip in front. A more elaborate apparatus still is the artificial eye of Perrin, which has been in use for many years. It has the globular form of the eye itself, and is provided with different eye-pieces to represent myopia, hypermetropia, and astigmatism ; it is also furnished with a series of pictures of the normal and diseased eyes. It is, however, better adapted for the purposes of teaching the ophthalmoscopic ap- pearances to a class than for the study of optical errors. Other arti- ficial eyes have been invented by Badal, Parent, and Remy. In 1872 the writer showed to the New York Ophthalmological So- ciety, and in the following summer to the American Ophthalmological Society, the artificial eye shown in Fig. 58. It is the mechanical em- bodiment of Donders's reduced eye with a cornea ground on a radius of five millimetres with parallel surfaces, the media being represented by water. Every degree of refraction can be expressed upon it, the increase and decrease of the antero-posterior axis being noted in the metric system. It is also fitted with a compound dioptric system of lens and cornea, as well as with a cornea representing the aphakial eye. The instrument has been found very useful both by myself and others in the study and demonstration of every possible phase of diop- trics. It is made by W. II. Hunter, 1145 Broadway, New York. Later Landolt * introduced an eye on precisely the same principles, which, if not quite so comprehensive in its scope, is certainly more ele- gant in its shape and appearance. It can be obtained in this country of Meyrowitz Brothers, 297 Fourth Avenue, New York. It is often very important to be able to control the result of an ophthalmoscopic examination for refraction by comparing it with that obtained by glasses ; but, besides this, it is often of the greatest aid to the student, in arriving at a diagnosis, to know the amount and charac- ter of vision, for it often happens that what was at first eight taken for the well-marked signs of a morbid process, has under a careful examination resolved itself into some peculiarity either of a physio- logical or optical nature, while, on the other hand, the state and char- acter of the vision have called the observer's attention to some incipient and grave disorder in which there were few or no ophthalmoscopic signs. For this reason every ophthalmoscopic examination should be combined with a careful determination of the amount of vision, and the extent of the visual field and the condition of the refraction. * " Klin. Monatsblatter," July and August, 1876, p. 243. 17 258 TEXT-BOOK OF OPHTHALMOSCOPY. To do this in a manner at all satisfactory, a set of test-glasses and test-types are necessary. As a rule, these are more elaborate and more expensive than is absolutely essential. By the aid of the metric sys- tem, simple combinations can now be made without any knowledge of mathematics whatever. . A test-case has been designed by the writer to meet the wants of students and general practitioners. FIG. 58. The set contains seven pairs each of concave and convex spherical lenses, and five pairs each of concave and convex cylindrical lenses, and with these almost every combination possible in the most com- plete sets can be successfully effected ; moreover, as all the numbers are in pairs, both eyes can be examined simultaneously with glasses of equal strength. APPENDIX. 259 The case further contains a set of test-types and a triple-grooved, graduated trial-frame, into which one, two, or three lenses may be readily slipped to obtain the desired number. As mentioned before, the lenses are marked in the metric system. The simple numbers contained in the trial-case are as follows : Spherical, concave, and convex : .25, .5, 1., 2., 3., 4., 8. Cylindrical, concave, and convex : .25, .5, 1., 2., 3. The combinations made therewith are : Spherical : .25, .5, 1., 1.25, 1.5, 1.75, 2., 2.25, 2.5, 2.75, 3., 3.25, 3.5, 3.75, 4., 4.25, 4.5, 4.75, 5., 5.25, 5.5, 6., 6.25, 6.5, 7., 7.25, 7.5, 8., 8.25, 8.5, 8.75, 9., 9.25, 9.5, 10., 10.25, 10.5, 11., 11.25, 11.5, 12., 12.25, 12.5, 13., 14., 15. Cylindrical : .25, .5, .75, 1, 1.25, 1.5, 1.75, 2., 2.25, 2.5, 2.75, 3., 3.25, 3.5, 3.75, 4., 4.25, 4.5, 5., 5.25, 5.5, 6.* Dr. John Green and Dr. Roosa have also introduced excellent test-cases for students and practitioners. * This case can be had of Meyrowitz Brothers for the moderate sum of four- teen dollars. EXPLANATION OF PLATES. PLATE I. Fig. 1* represents the fundus of a normal eye in young adult life, of a type that was neither blonde nor brunette. The color of the back- ground is of a uniform hue, and only shows an increase in shade at the macula lutea, the centre of which is marked by the fovea, which, in this case, has the appearance of a small circular spot with the merest perceptible dot in its centre. The increase in hue which marks the central portions of the yellow spot is due both to an increase in the amount of pigment in the epithelial layer and to an increased density in the network of small vessels and capillaries of the choroid lying directly below this region, which is the finest of any in the entire body (p. 45). The uniformity in color and pigmentation is such that none of the choroidal vessels are individually visible. The retinal vessels leave the centre of the disk in a perfectly normal manner. The veins are differentiated from the arteries by a somewhat marked difference in color, while the light streak, though present on both arteries and veins, is more marked and more brilliant upon the former than upon the latter. The retinal vessels, after the usual sub- divisions, radiate toward the region of the yellow spot, and, having en- tered this, arrive within a short distance of the fovea centralis so that the region of the macula lutea contains quite a number of minute branches of the retinal vessels (p. 34). It is only the fovea itself which is devoid of any vascular twigs. * In looking at all ophthalmoscopic drawings, it should be remembered that they are made under artificial light, and that they should be examined by such to get an adequate idea of the shade of color. It should also be borne in mind that all ophthalmoscopic drawings are necessarily diagrammatic in so far that a much larger portion of the field is represented than can be seen at once. The extent of surface seen varies with the kind of mirror, the distance of the lamp, the size of the pupil, and the distance of the observer's eye from it. The extent of surface under view at one time, in the ordinary methods of making the examination by the upright image, is from \\ to 2^- or 3 millimetres. 262 TEXT-BOOK OF OPHTHALMOSCOPY. The nerve shows the usual concentric markings, with a slightly de- veloped choroidal ring. In this particular case the connective-tissue string is carried well forward along the vessels, and the nerve-fibres are so closely arranged that there is little or no physiological excavation. There is likewise no venous pulsation, which usually shows itself by an increased color of the vessel, just as it bends to enter the nerve-stem. The vascular portion of the nerve is perhaps somewhat more pro- nounced than it is usually, though not more so than is often found compatible with a perfectly normal development. Fig. 2 (Plate I.). This beautiful drawing is from Liebreich (Atlas d'Ophthalmoscopie, Taf. II., Fig. 2). It represents the fundus of an individual of a light blonde type, with a blue iris. From the clear- ness of the stroma and the weak development of the pigment epithe- lium, the choroidal vessels can be traced to their finest branches. (Lie- breich. ) Portions of the branches from the different venae vorticae are exposed to view. In the lower left-hand corner they are visible nearly to their trunks, but less so in the right upper corner. PLATE II. Fig. 1 (Plate II.). In this figure (Liebreich, " Atlas d'Ophthal- moscopie," Taf. II., Fig. 3) the pigmentation of the stroma is more marked, while, according to Liebreich, that of the epithelial layer is very feeble. This is the reason, in his opinion, why the choroidal vessels here appear to be separated by pigmented intervascular spaces. It is only in the right-hand lower corner, near the posterior pole of the eye, that these vessels are concealed by a dark and richly pigmented epithelium. If this explanation is correct, as already remarked (p. 44), it must be assumed that there are different degrees of pigmentation of a very marked character in different portions of the same fundus. A more natural explanation would appear to be, that in this part of the fundus there is a closer arrangement of all the vessels, large and small, and accordingly a denser and more uniform color to the fundus. It is this peculiar striped marking which is called the choroid tigre. Fig. 2 (Plate II.). This picture is diagrammatic, inasmuch as the peculiar concentric markings of the disk have been purposely exag- gerated somewhat in color and tone for the sake of defining in a better manner the positions of the different rings. The external ring is the " pigment" or "choroidal ring." The second or white circle is the " scleral ring." The third or colored ring is the " vascular portion " of the disk; and the fourth is the "non-vascular portion'* or "clear spot." (See text, p. 58.) Fig. 3 (Plate II.). This figure (Liebreich, "Atlas d'Ophthalmos- copie") is taken from a perfectly normal eye, although, from the size EXPLANATION OF PLATES. 263 of the disk and from the extent and depth of the excavation, the ap- pearances would seem to be due to a pathological condition. This ap- parent increase in size of the disk is due partly to a distended condition of the head of the nerve and partly to the fact that the choroidal open- ing is larger than usual, and drawn somewhat to one side. The nerve- fibres are here distended outward, allowing the lamina cribrosa to mani- fest itself at the bottom of the large and rather deep excavation. The true outer border of the nerve-entrance is shown by the grayish semi- lunar line, while the scleral ring, very much exaggerated in size, ex- tends to the outside of this. The inner edge of the excavation, or that to the left of the central vessel, is sharply defined and pierced by both veins and arteries as they leave the disk. This sharp edge to the excava- tion occurring within the surface of the disk itself is strongly corrobora- tive of the fact that the excavation is physiological, or at least congenital, and not due to pressure. (See text, p. 55.) Fig. 4 (Plate II.). This shows a precisely opposite condition that is to say, a reduction in the size of the choroidal foramen. This is occasioned by a continuation of the choroidal membrane over the bor- ders of the disk. Some of the larger choroidal vessels are visible, and one of these is so arranged that there can be no doubt as to the true nature of the anomaly. The picture is from an eye in which there was a high degree of compound myopic astigmatism. Another member of the same family had similar appearances in both eyes, although to a less degree. (See text, p. 98. ) Fig. 5 (Plate II.). This represents an anomalous collection of pig- ment in the choroid. There was no defect in the visual field corre- sponding to the pigmented plaque, and vision was perfect. Its dis- covery was purely accidental in a person who made no complaint in regard to the eyes, and who, rather singularly, was a pronounced blonde. (See text, p. 89.) Fig. 6 (Plate II.). This figure (Liebreich, "Atlas d'Ophthalmos- copie," Taf. XII., Fig. 2) represents the anomaly known as "opaque nerve-fibres," due to the continuation of the medullary sheath of the optic nerve-fibres as they pass over into the retina. This is the com- mon form under which the anomaly usually appears. The peripheric border ends in flame-like processes, which seem to shoot out over the retina, sometimes covering a vessel so as to completely hide it, and sometimes passing beneath it. The interior border, or that near the nerve, is sometimes separated from the papilla by a greater or less dis- tance, or sometimes encroaches upon the surface of the disk, the bor- ders of which it then entirely conceals. The plaque, instead of having the radiating tongue-like form, may have the shape of a white crescent with sharply defined contours, which then increases its resemblance to 264 TEXT-BOOK OF OPHTHALMOSCOPY. a pathological condition, and renders the diagnosis much more difficult. (Liebreich.) (See text, p. 98.) PLATE III. Fig. 1 (Plate III.). This figure (Jaeger, "Hand Atlas," Taf. IV., Fig. 28) represents the fundus of an albinotic person of the most marked type. The general fundus, instead of being of a uniform red, is of a yellowish-white color, and reflects a large amount of light. The central vessels of the retina are perfectly normal, although the veins are a little more tortuous than is ordinarily the case. The granular, or shagreen, effect of the general fundus is entirely wanting here, and it is only in the region of the macula lutea that there is any trace of any uniformity in color due to an increased degree of pigment in the epithelial layer and to a closer arrangement of the ves- sels. The external vascular layer of the choroid is sharply designed over the entire fundus, except in the neighborhood of the yellow spot, where it is somewhat veiled by the overlying layers and by an increased development of pigment, perhaps, in the epithelial layer. In certain places the choroidal vessels of the middle layer show themselves as band-like formations of more or less orange-color. These bifurcate and anastomose with each other in such a way that a some- what irregular network is formed, which usually is of a yellowish- white color, and at times of considerable brilliancy of color so much so, indeed, that one is convinced that this brilliancy is due to a reflection from the sclera. (Jaeger.) Fig. 2 (Plate III.). This figure (Liebreich, "Atlas d'Ophthal- moscopie," Taf. XII., Fig. 3) shows an opposite condition, or one in which there is an abnormal excess of pigment. These cases are exceed- ingly rare, and are known under the title of cyanosis of the bulb. The individual in this case had auburn hair and light eyebrows and eye- lashes. The iris of the left eye was of a light brown ; that of the right was of so deep a color that the pupil could only be distinguished with great difficulty. The cornea at some little distance from its border is marked by a collection of spots of a grayish color, which in some places pass into a violet shade. With the ophthalmoscope there was only a slight reflex from the fundus, and even this, when the patient looked directly in front of him, vanished almost entirely. With the inverted image the bottom of the eye appeared of a dark reddish tinge. It was only in isolated places that there were any traces of the choroidal vessels. The retinal vessels appeared darker than usual, and the light-streak on their anterior surface less brilliant. On the contrary, the substance of the retina revealed itself much more clearly than usual by a delicate grayish haze and by a curious play of light, which was produced, espe- EXPLANATION OF PLATES. 265 cially around the region of the yellow spot, with the various movements of the mirror. The macula lutea appeared almost black, the centre of which was surrounded by a deep-brown ring. The general surface of the disk was of a reddish hue, and the borders were sharply defined. The retinal vessels at their point of emergence were enveloped by masses of pigment, which cover about one third of the surface of the nerve, and make what is usually the " clear spot " in a normal eye appear here black. At the periphery also there was a narrow ring of pigment. The eye was myopic. The vision was good, and the organ appeared to be in an excellent condition. Fig. 3 (Plate III.). This figure (Jaeger, " Hand Atlas," Taf. XIX., Fig. 87) represents the eye of a young girl, who was affected with colo- boma of the choroid and iris on both sides. A description of the ap- pearances of the right eye has already been given in the text (p. 93). There was in this, the left eye, a coloboma of the iris which extended as far as the ciliary body. There was, however, no coloboma or other mal- formation of the ciliary body, so far as could be seen. The media were perfectly clear, and the fundus above and to the outer and inner side was perfectly normal, both as to color and general appearance. Below, on the contrary, corresponding to the coloboma, the effect produced by the mirror was that of a surface of large extent, of a yellowish-white, or a bluish-white, or at places even of a glittering-white color. The nerve was of an oval form, and normal in all its diameters. In the nerve-substance itself there was a deep excavation of a triangular shape, having its base below, with its angle pointing upward and extending as far as the centre of the nerve. From the fact that it extends to the lower borders of the nerve, and that at this place one of the branches of the lower vein makes a sudden bend over the steep edges of the ex- cavation, this latter bears a strong resemblance to one of those glau- comatous excavations of congenital origin. The coloboma taken as a whole has a pear-shaped form, and measures in its greatest breadth about five and a half diameters of the nerve. The upper border lies about one half of the diameter of the disk below the edge of the nerve. The an- terior border of the coloboma can not be perceived, as it lies too far for ward to be reached by the instrument, but this must be, from the direc- tion in which the lateral borders run to each other, on the other side of the ora serrata and immediately in front of the ciliary processes. The bottom of the coloboma is uneven and lies deeper than the plane of the choroid, and in some places even deeper than the inner surface of the sclera. The coloboma consists of three separate shallow excavations, which adjoin, and in a certain sense, pass into one another. The upper excavation is egg-shaped, and is of a whitish color when taken as a whole, while in its deepest portion it has a weak but decidedly bluish tinge. The middle and smaller excavation has rather a band-like form, 266 TEXT-BOOK OF OPHTHALMOSCOPY. and in its central third is a clear, yellowish white. The peripherical portions are of the same color, though of a somewhat lighter shade. The third excavation has by far the greatest extent, though it is the shallowest. It is in some portions of a light, and in others of a darker, grayish color. Over its surface especially toward the nose white stripes occasionally run. In some parts of the periphery of the colo- boma, toward the normal colored portions of the fundus, the choroidal tissue still manifests itself by light yellowish stripes. The epithelial layer is, however, wanting, and this allows (Jaeger) portions of the network of the larger vessels to become visible as light reddish stripes of a band-like character. Eemnants of pigment are also seen in different places at the lateral borders of the coloboma and at the boundary-lines of the different excavations. An extremely deli- cate and transparent membrane is stretched over the coloboma for its entire surface, all the inequalities of which it follows. The distribution of the central vessels is normal. They run in the usual manner over that part of the fundus in which the choroid has its normal appear- ance, but only small and delicate branches are continued over the re- gion of the coloboma. In this district, and below the plane of the retinal vessels, broader vessels appear, which have a uniform color across their entire surface. These divide into numerous branches, and run in an irregular and tortuous manner. These vessels spring in part from the region of the coloboma itself, and in part from beneath that portion of the fundus which has a normal color and appearance. They anastomose in certain places near the border of the coloboma with the choroidal vessels which are there visible. From this fact, and from their peculiar band-like character and light color, these vessels show them- selves to be really sclero-choroidal vessels. It will be noticed that in this case the coloboma does not include the optic nerve, but that there is immediately below the nerve a narrow strip of normal-looking tissue. That this strip still preserved its normal function was proved by the fact that Mariotte's blind-spot was separated from the defect in the field caused by the coloboma by a narrow band of visual field which still maintained its perceptive power. (See text, p. 92.) Fig. 4 (Plate III.). This figure represents a coloboma of the macula lutea, with a secondary defect between it and the nerve. These cases are very rare, and are apt to be confounded with an old exudation and subsequent atrophy of the tissue, especially as the rest of the fundus has a normal appearance. (See text, p. 94. ) Fig. 5 (Plate III.). This picture was taken from a highly astigmatic eye, in which the myopia was equal to 6 D in the vertical meridian, while the horizontal was emmetropic. The fundns, taken as a whole, presented a striated appearance, which, though very delicate, was still perfectly perceptible. This was due, of course, to the optical error, EXPLANATION OF PLATES. 267 and was not present when this was properly corrected. It will be seen that the upper and lower borders of the optic nerve are obliterated, while the lateral ones are sharply defined. It is the same with the vessels. Those which run horizontally are very much blurred, or else entirely obliterated, which is the case with the fine horizontal vessels which leave the nerve and run out toward the macula, when the ordi- nary spherical glass is used which corrects the vertical meridian. These horizontal vessels then come sharply into view, and the vertical vessels are correspondingly indistinct. In order to see both the horizontal and vertical vessels distinctly at the same time, a cylindric glass of 6 D must be used. It is this condition which is so liable to be taken for a case of neuritis by those who are unfamiliar with it. (See " Determination of Astigmatism," p. 116, et al) PLATE I PLATE INDEX. Abscess, in vitreous, 180. Accommodation, 222. equivalent to increased refraction, 225. in hypcrmetropic eye, 223. in myopic eye, 223. in normal eye, 222. non-relaxation of, in moderate hyperme- tropia, 111. relaxation of, 107. rules for relaxation of, 107, 108. Adjuncts to ophthalmoscope, 253. Age, effect on fundus, 84. Air-bubbles in vitreous, 183. Amblyopia, 113. Ametropia, 218. Ametropic observer, rules for, 127, 129. a hypermetrope, 131. a myope, 129. Anastomosis, arterio-venous, 105. between retinal and ciliary system, 29, 30. between vessels of sheaths of nerve, 28. of retino-choroidal vessels, 104. Anatomy, fundus of normal eye, 21. inner and outer sheath optic nerve, 21. of choroid, 38. of retina, 31. of the normal eye, 21. Anomalies, 86. abnormal transparency of nerve fibres, 100. arterio-venous anastomosis, 105. bifurcation of optic fibres, 101. choroidal opening, 97, 98. cilio-retinal blood-vessels, 104. coloboma of iris, 90. coloboma of sheath of optic nerve, 96. coloboma of the choroid, 92. coloboma of the lens, 92. coloboma of the macula, 94. congenital absence of iris, 90. discoloration of optic nerve, 101. of disk, 97. of the lens, 87. of the media, 86. of pigmentation of choroid, 88. of pigmentation of optic nerve, 89. of vessel wall, 102. opaque nerve-fibres, 98. persistent hyaloid artery, 103. pink spots at macula, 94. pupil, eccentric position of, 92. pupillary membrane, 91. vascular system, 101. Anomaly, anastomosis of retino-choroidal vessels, 104. Anterior - chamber, examination (oblique light), 148. Aqueous humor, 161. diffuse opacities of, 148. examination of, 148. examination with mirror, 161. filaria in, 149. pus in, 148. synechiae in, 149. Arachnoidal sheath (anatomy), 21. space (anatomy), 22. Arteria centralis retinae, 29. Arterial pulse, 74. " apparent " pulsation of, 75. character of, 74. diagnostic value of, 75. produced artificially, 75. Arteries, long ciliary, 39. persistent hyaloid, 103. ophthalmic, 28. short ciliary, 29, 41. variation in number, 102. inferior, of retina, 65, 66. subdivisions of, 66. superior, of retina, 66. Artery, hyaloid, 103. Atropine, disks for dilatation of pupil, 9. Artificial eye, 143, 255. Astigmatism, determination of, 116. determination by mirror alone, 136. determined by inverted image, 139. effect on fundus, 86. elongation of disk in, 117. hypermetropic, 119. irregular, 121. irregular, to be detected by mirror alone, 121. method of determining, 118. mixed, 119. myopic, 119. test for, 117, 118. Atropine, strength of, for purposes of ex- amination, 10. Axis, antero-posterior, 218. formulae for length of, 128. of eye, 217. Becker, method of illuminating cornea, 150. Blood-column, composition of, 70. bounded by bands, 103. 270 TEXT-BOOK OF OPHTHALMOSOOPY. Blood, difference in color between arterial and venous, 71. Bowman, membrane of, 146. Box, for studying passage of rays, 214. Briicke, experiment of, 229. Canal, central, 29, 65. displacement of, 65. Capillaries, choroidal, 45. Capsule, fracture of, 169. reflex from anterior, 152. reflex from posterior, 152. Cataract, anterior capsular, 154. as seen with ophthalmoscope, 164. cortical, 164, 165, 160. oblique illumination in, 156. oblique illumination, pcripheric, 166. posterior polar, 155. pyramidal, 154. secondary, 156. spindle-shaped, 155. zonular, 155, 107. Catoptric test, 152. Centre of motion, 185. Cholestcrin in iris, 150. in lens, 156. Choroid, anomalies of pigmentation, 88. attachment to solera, 38, 39. capillary net-work of, 45. coloboma of, 92. foramen of, 39. pigmented crescent of, 50. the (anatomy), 38. thickness of, 38. tigre 1 , 48. veins of, 42. vessels of, 39. anastomosis with retinal, 39. Choroidal opening, 97. Ciliary, long arteries, 39. short arteries, 41. vessels, 28. Circle, illuminated, 230. of dispersion, 230. of dispersion, size of, 231. of dispersion, varies with different mir- rors, 231. of dispersion, varies with distance of lamp, 230. of illumination, 230, 231. scleral, 30. Coloboma of iris, 90. of lens, 92. of macula, 94. of the vitreous, 88. Color of normal fundus, 46. Condensing lens, use of, in oblique illumina- tion, 5 (Fig. 1, p. 6). Congenital excavations, 60, 61. Connective-tissue ring, 57. variation in size, shape, and color, 57. Connective-tissue string, 29. effect on appearance of vessels, 66. Conus, 97. Cornea, 160. Cornea, abrasions of, 148. examination of, 146. examination of, with mirror, 160. foreign bodies in, 148. illuminated by Becker's method, 150. oblique illumination of, 146. reflex from, 152. reflex of, as diagnostic mark, 187. want of transparency of, 147. Crescent, pigmented, 50. Cylindric lens, 212. Cysticercus, description of, 188, 189. differential diagnosis of, 190. drawings of, 192, 193. ophthalmoscopic appearances of, 189. sac of, 188, 189. Cysts of iris, 149. Descemet, membrane of, 146. Descemitis, 148. Dioptric, definition of, 241. Dioptrics, conversion into inches, 242. Disk, anomalies of, 97. causes of elevation of surface, 62. change in form of, 138. change in, in astigmatism, 139. change in, in movements of lens, 140. clear spot of, 55. concentric markings of, 58. crescent round, 57. differences in size, 53. elevations of surface, 61. elongation of, in astigmatism, 117. excavation of, 58, 59. honeycombed appearance of, 55. plane of, 53. shape of, 51. variations in color, 55. variations in elevation, 58. variations in surface of, 54. vascular portion of, 56. . vessels of, 29. Dislocation of the lens, 87. Dispersion, circle of, 230. Dural sheath (anatomy), 22. Ectopia lentis, 87. Emmetropia, determination of, 109, 123. Enlargement, influenced by ametropia, 143. hypermetropia, 144. myopia, 145. Liebreich's method of, 16. produced by upright image, 142. Entozoa, 187. Examination by daylight, advantages of, 4. by inverted image, 12. by upright image, 18. of eye by artificial light, 5. of media of eye, 146. aqueous humor, 148. cornea, 146. lens, 150. iris, 149. vitreous, 157. INDEX. 271 Examination with ophthalmoscope, 8, 9. necessity for use of atropine, 7, 9. obstacles in the way of, 9. use of atropine in, 9. Excavation, " apparent," 60. congenital, 60, 61. measurement of, in glaucoma, 115. of disk, 58. physiological, 59. physiological characteristics of, 59, 60. Exudations upon lens, 150. Eye, ametropic, 218. artificial, 143. Donders's reduced, 257. of author, 257. of Landolt, 257. emmetropic (definition of), 218. equivalent to biconvex lens, 217. hypermetropic (definition of), 218. myopic (definition of), 218. Eyes, artificial, 255. Far-point, 221. Field, influenced by object lens, 239. of view, influenced by strength of object- glass, 14. Filaria, description of, 194. existence of, 187. in aqueous humor, 1 49. Focal length of eye, 217. of lenticular system, 142. Foci, conjugate, of mirrors, 216. Focus, alterations in, by change of object, 208 conjugate, 209. equal to radius in biconvex glass, 203. equal to twice the radius in plano-convex, 202. virtual, 210. Foreign bodies in cornea, 148. enveloped in membranes, 180. in vitreous, 180. rebound of, from back of eye, 183. suspension of, in vitreous, 130. Formula, to determine length of axis, 128. Fovea, appearance of, 79. distance from edp;e of nerve, 79. shape and appearance of, reflex of, 81. centralis (anatomy), 33, 34. increased pigmentation of surrounding tissue, 34. position of, 34. Fundus, differences in regard to age, 84. effect on, by optical conditions, 85. illumination of, 231. illumination of, by ophthalmoscope, 230. seen by irregular reflection, 232. variations in, owing to optical conditions, 85. visible by irregular reflection, 232. oculi, not a conjugate focus with source of light, 228. variation in texture of, 50. Glaucoma, measurement of excavation, 115. Glass, magnifying power of, 142. Halo, absence of, with upright image, 80. cause of, 82. surrounding macula, 78. the, not seen in all eyes, 79. why absent with upright image, 81. Helmholtz's weak-light mirror, 4. Hyalitis, 154. Hyaloid artery, 103. Hypermetropia, ability to determine '' total," with the mirror, 110, 111. as revealed by upright image, 110. determination of, 110, 125. determination of "latent," 110. non relaxation of A, in, 111. Ilypopion, in anterior chamber, 148. Illuminated circle, 230, 231. Illumination, oblique, importance of, 6. kinds of, 3. of the fundus, manner of obtaining, 10. Image, aerial, of myopic eye, 11. change in position of, by change of ob- ject, 207. enlargement produced by " upright," 142. formation of, by lens, 205. from concave mirror, 215. " indirect," principles of, 237. influence on life of, by refraction, 239. of fundus, production of, 11. place of reflected, 214. projection of, 143. reflected, 214. size of, as to object, 206. to determine whether erect or inverted, 11. virtual, in hypermetropic eye, 11. Incidence, angle of, 214. Increased enlargement, by inverted image, 16 Inequalities, in fundus, how to detect, 14. measurement of, 113. Inner sheath, vessels of, 28. Intervaginal space (anatomy), 21. (anatomy), 23. in myopic eyes, 23. Inverted image, examination by, 12 (Fig. 2). increased enlargement in, 16. Irido-choroiditis, 149. Iris, 161. absence of, 90. adhesion to lens, 150. cholesterine in, 150. coloboma of, 90. condylomata of, 149. cysts of, 149. examination of, 149. examination of, with mirror, 161. Liebreich's method of examination, 1 50. oblique illumination of. 147, 149. Iritis, 149. as seen with the mirror (Fig. 56), 164. Keratoscopy, 137. Lamina cribrosa (anatomy), 25, 26. vessels of, 28. 272 TEXT-BOOK OF OPHTHALMOSOOPY. Lamina vitrea, 38. Lamp, effect on circle of dispersion, 4. influence of position, 232. influence on circle of illumination, 232. position of, 3. source of illumination, 230-232. varieties of, 3. Length, focal, of eye, 217. Lens, adhesions to, 150. anomalies of, 87. coloboma of, 92. diffuse opacity of, 151. dislocation of, 87. dislocation of (as seen in the mirror), 168. dislocation of (oblique illumination), 157. dislocation of (as seen with mirror), 168. examination, 150. examination of (oblique light), 150. examination of, with ophthalmoscope, 161. exudations upon, 150. fracture of the capsule of, 169. opacities of (circumscribed), 154. physiological opacities of, 163. physiological reflex from, 151. stationary opacities in, 163. want of transparency in normal eye, 151. Lenses, action of, on light, 199. axes of, 204. biconvex, 203. bicylindric, 214. concave, 210. condensing, use of, 5. convex, 199. cylindric, 212. effect of changing curvature, 201. focus of, 201. image of, in case of concave lens, 211. image formed by, 204, 205. influence on size of image, 238. optic centre of, 204. plano-convex action of, 200. position of, 157. radius of, 199. sphero-cylindric, 213. strength" of, 19.9. strength of, expressed in a fraction, 203. Light, laws of, 195. pencil of, 195. quantity of, from different mirrors, 4. rays of, 195. Light streak, the, 75. increase and decrease of, 102. test for astigmatism, 118. theory of, 76. undulatory motion of, 195. Lymphatic spaces, 27, 35, 37. Luminous bodies, 195. Macula, spots at, 94. lutea, cause of color, 32. coloboma of, 94. distance from centre of disk, 32. how to examine, with upright image, 79. with indirect image, 77. increased pigmentation in region of, 49. Macula, increased pigmentation of region of, 80. not devoid of vessels, 67, 80. not synonymous with the i'ovea centralis, Y'J reflex round, with indirect image, 77. reflexions from, 77. region of, 31, 77. region of, with upright image, 79. situation of, 32. size of, 32, 33. vessels of, 35, 36. Magnifying-glass, power of, 142, 143. Media, anomalies of, 86. differential diagnosis in troubles of, 1 84. examination of, with mirror, 157. examination with ophthalmoscope, 157. Medullary sheath (anatomy), loss of, in nerve- stem, 24. Membrane, Bowman's, 146. determination of position of, in vitreous, 116. in vitreous, 177. of Descemet, 146. vascular in vitreous, 177, 178. Method, " indirect," principles of, 236. Metre, 241. Metric system, 241. conversion of, into inches, 242. Microscope, ophthalmic, 255. Mirror, concave, best adapted for general work, 4. concave, best for illumination, 231. conjugate foci of, 215. of Helmholtz, 230. modifications of, 247. plane, 214. proper focal length of, 4. tilting, 249. Wadsworth's, 248. weak-light, advantages of, in examination of media, 157. weak -light of Helmholtz, advantages of, 4. Mirrors, 214. concave, 215. Motion, center of, in eye, 185. Myopia, determination of, 110, 124. Neoplasms, in vitreous, 179. Nerve, discoloration of, 101. protrusion of, 115. Nerve fibres (anatomy), 26. abnormal transparency of, 100. bifurcation of, 101. opaque, 98. Nerve-stem, form of, 25. anatomy, 24. cross section (anatomy), 25. optic (anatomy), 24. transparent and non-transparent portion, 24. Neuritis, measurement of protrusion of, 115. Nodal point, 204. Normal eye, cause of color of fundus, 43. fundus of, 43. variation in shade and color, 46. INDEX. 273 Object-glass, 253. (jointed), 253. advantages of strong and of weak, in my- opia, 15. Oblique illumination, condition of the me- dia, 5. of iris, 147, 149. method of, 7. of cornea, 146. position of lens, 157. Opacities, determination of position, 1 59. in vitreous, 157, 171. in vitreous diffuse, 172. in vitreous fixed, 176. in vitreous movable, 174, 176. membranes in, 177. of lens (circumscribed), 154. (diffuse), 154. (physiological), 163. Opacity, determination of position in vitre- ous, 185. Ophthalmo-microscopes, 255. Ophthalmoscope artists, 254. Carter's, 250. construction of, 3. examination, elements of, 2. measurement of differences of level, 113. method of examination with, 10. remarks on, 11. theory of, 225. where superior to test by atropia and glasses, 112. Ophthalmoscopes, 242. binocular, 251. fixed, 250. Optic axis, dimensions of tables of, 113, 114. Optic centre (of lens), 204. Optic disk, objective point for examination, 12. Optic nerve, anomalous pigmentation of, 89. circulation of, 27. stem of, 24. cross section of, 25. diameter of, 52. diversity in shape and size, 52, 62. enlargement, as seen with ophthalmoscope, 52. entrance, 51. entrance, designations of, 51. entrance, form of, 25, 51. longitudinal section of, 23. Optics, physiological, 217. Optic nerve, coloboma of sheath, 96. Orthoscopc, 148. Papilla, 51. Parallax, how to obtain, 13, 14 (Fig. 3). Pencil, of light, 195. Phantom, 256. Physiological optics, 217. Pial sheath (anatomy), 21. vessels of, 27. Pigment ring, 58. Plasmic current, 70. 18 Position of observer's seat, 10. of patient's seat, 10. Pulse, absence of, in retinal vessels, 71. arterial, 74. venous, 72. Pupil, blackness of, 226. eccentric position of, 92. Pupillary membrane, 91. Pupiloscopy, 137. Purple, visual, 65. Radius, of lens, 199. Kays, convergent, 200. divergent, 210. divergent, in nature, 1 96. parallel (description of), 196. Reflection, angle of, 214. from plane mirror, 214. irregular, 196, 198. regular, 196. regular and irregular, 232. image formed by, 214. specular, 196. two kinds of, 196. Reflex, around macula, indirect image, 77. around macula lutea, shape of, 78. cause of, from yellow spot, 82. from lens, 151. from yellow spot, 77. of fundus, 10. Refraction, by cylindric lens, 213. cause of, 199, 201. conditions affecting, 201. determination according to inch standard, 122. emmetropia, 123. myopia, 124. hypermetropia, 125. determination of, 106. determination of, by mirror alone, 134. determination of, by inverted image, 137. diagrammatic representation of, 219. different degrees of, in various parts of the eye, 108. effect on appearance of fundus, 85. how to ascertain in a general way, 109. index of, 202. influence on circle of dispersion, 232. influence on size of image, 2 r :9. object-point for determination, 108. ophthalmoscope for, 106. smoke-box for study of, 214. Region of macula, 31. Retina, arteria centralis, 29. anatomy of, 31. diagrammatic section of, 33. differences in level of, 31. fold in, 178. layers of, 34. lymph-spaces of, 36, 37. parallactic displacement of vessels of, 63. pigment layer of, 36. principal branches of vessels of, 65. principal vein, anomalous exit of, 65. striation of, 64. 274 TEXT-BOOK OF OPHTHALMOSCOPY. Retina, thickest part of, 31. thickness of, as estimated with ophthal- moscope, 63. transparency of, 62. vessels of, 33, 34. vessels of, as seen with mirror, 63. vessels, principal branches of, 65. Retinal vessels, division of, 66. Retinoscopy, 137. Reversion, law of, 207, 217. Ring, connective-tissue, 57. pigment, 58. scleral, 57. simulating conus, 58. Scleral circle, 30, 31. Scleral opening, 49, 58. Scleral ring, 57. more pronounced in glaucoma, 57. simulating conus, 58. Sheath, arachnoidal, 21. dural, 22. external vessels of, 28. Sheath, medullary, 24. outer, inner, 21. pial, 21. Space, arachnoidal, 22. intervaginal, 21, 23. lymphatic, 27. subarachnoidal, 22. subdural, 22. sub vaginal, 21. Strabismus, 112. Subarachnoidal space (anatomy), 22. Subdural space (anatomy), 22. Subvaginal space (anatomy), 21. Synecliiae in anterior chamber, 149. System, inch, conversion into metric, 242. metric, 241. old style, 241. Table (III), decrease and increase of axis, 127. Table (IV), dimensions of axis, old style, 128. Table (II), showing increase of optic axis, 114. Table (I), showing shortening of optic axis, 113. Test, catoptric, 152. Theory of the ophthalmoscope, illustration of, 229. Tortuosity of vessels, 102. Tumors, 149. Tumors of iris, 149. Tumors, measurement of, 115. Upright image, position of observer and pa- tient, 18. method of performing, 18, 19, 20. Vein, diagrammatic section of, 35. principal, of retina, 65. inferior, of retina, 65, 66. Vein, subdivision of, 66. of choroid, 42. superior, of retina, 65, 66. subdivisions of, 66. variation in number, 102. Vena centralis, 29. Venae vorticosse, 42. ophthalmoscopic appearances of, 47. Venous pulse, 72. artificial production, 74. diagnostic mark of increased tension, 74. position of, 72. theory of, 72. Vessels, absence of, in macula, with in- verted image, 79. anastomosis of retino-choroidal, 104. ciliary, 28. cilio-retinal, 104. crossing of retinal, 67. diameter of retinal, 69. different size of, 69. division of retinal, 66. no anastomosis of retinal, 67. of choroid, 39. of disk, 29. of retina (with mirror), 63. plan of retinal, 66. temporal, as seen by inverted image, 67. by upright image, 67. temporal branches of retina, 67. the central, 29. tortuosity of, 102. tortuosity of retinal, 67. transparency of walls, 70. walls of, in retina, 70. Vessel-wall, anomalies of, 102. Visual purple, not visible with the ophthal- moscope, 65. Vitreous, abscess in, 180. air-bubbles in, 183. coloboma of, 88. examination of, 157. foreign bodies in, 180. neoplasms in, 179. opacities in, 157. position of membranes in, 116. Vitreous humor, 180. abscess in, 180. opacities (as seen by mirror), 171. Wall, vessel, decrease in transparency, 102. Yellow spot, absence of vessels with in- verted image, 79. color of, 78. how to find, with inverted image, 17. color of, 32. distance from nerve, 32. region of, 31, 77. situation of, 32. size of, 32. vessels of, 35, 36. END OF PAET I. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. Form L9-Series 4939 A 000 414514?