NRLF B M 3^T 5flD be Shadow Test I LIPRARY I I UNIVEKSWY Of I VCAUTORMIA y _ _ x^?^ «73 THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA GIVEN WITH LOVE TO THE OPTOMETRY LIBRARY BY MONROE J. HIRSCH, O.D., Ph.D. THE SHADOW TEST In Ocular Diagnosis Without prejudice as to method, mirror, distance or instrument BY GEO. A. ROGERS AUTHOR OF SKIASCOPY PRINCIPAL CHICAGO POST GRADUATE OPTICAL COLLEGE Professor of Optometry, Northern Illinois College of Ophthalmology and Otology President Illinois Optical Society THE OPTIC PRESS CHICAGO u'ff'^y^ ©PTOMETRY Copyright DP To Prefatory During the past five years the author has been asked many times, and often with a good deal of insistence, if he had, and why he had not, embodied his methods of teaching optics in permanent book form. Undoubtedly, aside from the facts involved in the study of optics, there is a good deal in the methods of imparting instruction to the initiate or new student of the science. Wliile there can scarcely be said to be a dearth of optical text books and general literature, perhaps the manner in which the subject is dealt with in a series of books, of which this is the initial volume, will be of assistance in preserving a favorite method of viewing the peculiar phe- nomena of optics and the author's explanation of their scientific meaning. This is the best excuse we can offer for perpetrating upon opticians and would be opticians a new series of optical text books. The series will embrace at least four separate volumes, none of them large enough to be unwieldy, but strongly bound, so that they can be used, in a pinch, to split kind- ling wood with, or be thrown out of a sixth story window without serious damage, as we feel sure some of their read- ers will be tempted to do. The series will be issued, if they are ever completed, in the following order: Vol. I, The Shadow Test, etc. Vol. II, Ophthalmic Lenses, Mirrors and Lens-Mirrors. Vol. Ill, The Ocular Muscles and Muscle Testing. Vol. IV, Practical Optometry (a general text book). The author hopes in these four volumes to embody all he knows about optics and perhaps considerable more. If he happens in the mean time to think up anything else it may possibly appear in a fifth volume, but there is no present intention of going farther. Chicago, May 15, 1905. G. A. R. Illustrations. 1. Shadow Testing-, Plane Mirror at One Meter. 2. Conjugate Foci, and Conjugate Planes. 3. Mirror and Source of Light. 4. View of Patient, through Peep Hole of Mirror. 5. Testing Emmetropia, Plane Mirror at One Meter. 6. The Fundus Reflex, and Motion with Plane Mirror. 7. Testing Hyperopia, Concave Mirror at 53 Inches. 8. Testing Astigmatism, Plane Mirror at one Meter. 9. The Reflex in Astigmatism, Band and Straightedge. 10. Movements of Real Light. 11. Peculiar Reflex Effects. 12. Shadow Test Devices. 13. The Geneva Retinoscope. 14. The Cross Retino Skiameter. 15. The Hardy Stigmatometer. 16. Shadow Test Practice with Schematic Eye. Introduction Since optometry as a practical science and art first ap- peared upon the stage, the most distinct advancement in method that has been made was that involved in the dis- covery of the shadow test. Its importance is due to two main facts: (1) it is a measurement of the complete re- fraction of the eye, and (2) it is an objective method, not requiring a quiz of the patient as to the visual effects of the lenses used. Since its discovery shadow testing has continued to be- come increasingly interesting and popular with those who are engaged in refractive work, and no well posted and equipped refractionist would think of ignoring or neglect- ing it. To the initiate in this work, as well as to many otherwise well posted refractionists who have thus far dis- regarded the method, our little book offers a means of be- coming thoroughly familiar with all of its practical fea- tures. It is put out for that purpose. But shadow testing is not a book affair. No one can be- come an expert at shadow testing by reading a book or a dozen boolvs. It is an art and as an art the essential thing is to learn to do hy doing. Unless one is ready to lay hold of the art and by practice acquire dexterity in it, this book and QXQYY other book bearing on the subject may as well be thrown aside. In the twelfth chapter a course of prac- tice with the schematic eye is given. Any one who follows the directions there given, amplifying them according to his need, will very quickly catch the whole meaning of the test. If that work is done in connection with reading the previous chapters, it will be all the better. In preparing the manuscript for this book it has been endeavored to make the treatment of any phase of the test as simple as the test itself. If the language at some points appears involved it is because that which the language attempts to describe is involved. A thing cannot be made, by any art of language, as simple as it is, although it can easily be made much more difficult. If our language does not give a clear idea at any particular point, go to the phenomenon itself and have the matter thoroughly ex- plained txj you. It is also most difficult to represent in a drawing the peculiar light effects that are obtained in the process of shadow testing an eye. If the illustrations do not seem quite real, go to the test itself for those effects. You can get them better there than anywhere else. Contents •CHAPTER I. The Shadow Test — General Character of the Method — Incident and Emergent Light — The Fundus Reflex and the Shadows — The ]\Iirror and Distance — Pupillary Ob- servation — Motion with and against the ]\Iirror — Neutral ]\Iotion — Subsidiary Phenomena . CHAPTER II. Conjugate Foci — The Principle of Conjugates in Shadow Testing — Conjugate Planes, Retina and Anterior Focal — Principal and Mongrel Conjugates — ^Favored Conju- gates in Shadow Testing, 40 in., 53 in., 27 in. — Dioptric Values of Testing Spaces — The Neutral Eye and Non- neutrals — Observing Eye out of Position and Effects. CHAPTER III. Physiology of Vision — Mobile Factors of Vision — Pupillary Control and its Purposes — Ciliary Action or Accommo- dation and its Purpose — Rotation of the Eyes and Binocu- lar Fusion — Natural Stimuli — Reflex Action or Spon- taneity — Range of Reflex Activities in the Eyes — Harmony or Unison of Ocular Reflexes — Effects of Accommodative Action on Position of Conjugates. CHAPTER IV. Shadow Test Requirements — The Dark Room or Darkened Space — The Light and its Position — The ]\Iirror, size and opening — ^Use of Both Eyes by the Observer — Circle of Illumination — ^Plane and Concave Mirrors — The Source of Light — Movement of Source of Light in Tilt- ing the Mirror — ^IMovement of the Reflex, the same or opposite to the IMirror — Aerial Image of the Reflex. CHAPTER V. Technique in Shadow Testing Emmetropia — Plane jMirror at One Meter — Conjugates in Emmetropia — Patient's Co- operation — Initial Movement in Emmetropia — Disturb- ing Factors — Insertion of Plus Sphericals — Reversal of Motion — Expansion of Reflex and Rapidity of Motion — ■ Reduction of Plus Values — Neutralization — Other Spaces and Mirrors — Mydriatics and Cyclopegics — Dynamic Skiametry. CHAPTER VI. Technique of Shadow Testing Hyperopia — Concave Mirror at 53 Inches Distance — Initial Appearances and Motion of Reflex — Action of IMirror and Relation to Motion — Efi^ects of Hyperope Accommodating for Distance — In- sertion of Plus Spherical Values and Effects — Reversal of Motion and Value Required for Reversal^Subsidiary Phenomena: Expansion of Reflex, Rapidity of Motion, etc. — The Neutralizing Lens — Deduction for Distance, Correction — Use of Atropine, Supposed Advantages — Pheripheral Refraction and Disadvantages — Myopia and its Technique — Other Spaces and IMirrors and Effects — Absolute Neutralization, Reversal and Deductions for Findings. CHAPTER VII. Technique of Shadow Testing Astigmatism — Compound Hyperopic Case — The Double Focus for Emergent Light —The First Meridian, most Hyperopic — Second ]Meri- dian, least Hj^peropic — Subsidiary Phenomena in Astig- matism — The Banded Appearance and the Straightedge — The Accommodation in Shadow Testing Astigmatism — Different Values Required for Principal Meridians — Spherical Reductions and Effects — Cylindrical Reduc- tions and Effects — Concrete Case and Order of Work — Spherical Changes and Effects in high degrees of Astig- matism—Deductions for Distance of Test — Application of Rule for Minus Changes. CHAPTER VIII. Technique of Shadow Testing Astigmatism continued — The Second Meridian in high degrees of Astigmatism — Its Manipulation to Preserve the Banded Appearance — Cylindrical Correction and Elimination of Band — ^Re- verse Cylinder and Preservation of the Band — Pro- ducing Band in Eyes not Astigmatic — Relation of Band to Axis of Cylinder — Emphasizing the Band — Relation of Band to Source of Light — Plane IMirror with Mobile Light — Concave Mirror with Mobile Light — ^Application of Principle of Conjugate Foci to Mirrors — Limits of both Plane and Concave Mirrors — Effects of Mobile Light on Band. CHAPTER IX. Difficult Cases — ^I'^oung Compared to Older People — Ef- fects of Complexion — A Too Brilliant Light and its Effects — Passivity of Eye Essential to the Test — Cases of Photophobia — Binocular Influences — Relation of Ac- commodation in Two Eyes — The Controlling Eye — Ani- sometropia in the Shadow Test — Shadow Testing and Fogging Both Eyes Together — Muscular Poise and its Relation to Shadow Testing — Effects of Imbalance, Exo- phoria — Temporary Prisms for Relaxation — The Dy- namic Method — The Atropine Route — ^Peculiar Reflexes — Eccentric Motion — Zonular Reflexes — The Scissors Movement. CHAPTER X. Shadow Test Devices — Frosted Electric Bulb — Skiascopic ■ Chimneys — Brackets for Mobile Light — Gas Illuinina- tion and Chimney — Kerosene and Acetyline Lamps — Mirrors of Various Forms — The Lens-Mirror — ^^The Schematic Eye and Practice — Auxiliary Cylinders — Pupillary Disc — Skiascopes — Luminous Eetinoscope. CHAPTER XI. Shadow Test Instruments — The Geneva Retinoscope — The Cross Retino-Skiameter — The Hardy Stigmatometer. CHAPTER XIL Practical Training — Shadow Testing as an Art — Mechan- ical Devices for Initial Work — Familiarity with Move- ments and How to Acquire it — Setting Schematic Eye and Verifying or Correcting it — Avoidance of Reflec- tions — Setting Schematic Eye at Known Points and Verifying — Setting it at Unknown Points and Determin- ing Findings — Deductions and Additions for Distance of Test — ^Use of Auxiliary Cylinders — Neutralizing Chief Meridians — Producing Banded Appearance, etc. — Pre- scription Forms for Findings and Final Results — Oblique Cylinders — Living Subjects. CHAPTER I. SHADOW TESTING. To be able to make an eye, in any state of refraction, reveal its true condition, without questioning the patient as to what he can or cannot see, would seem, to the uniniti- ated, a performance little short of the marvelous. And yet this is precisely what is done in Features shadow testing. While the requisite instruments for the work are essen- tial, they are also exceedingly simple. With a fragment of broken mirror and a lighted candle, the eyes may be successfully tested and their condition found in this way; but it is of course better to have a mirror with a small cen- tral peep hole, and a light of sufficient intensity to make the appearances perfectly clear and definite. Shadow testing is the study of light emerging from the eye at a definite view point before it, as at one meter, though different distances are preferred by different opera- tors. The distance, whatever it is, must be taken into account in determining the correction, inuimnation of ^^^^ -^ -^ important chiefly for that reason. To study light emerging from an eye The retina must be illuminated in some manner, in order to provide light of sufficient intensity to enable the observer to see and study the effects. A simple method of doing this is obtained by using a mirror in the manner shown in the illustration. The retinal illumination is of course small, for the action of the dioptric media reduces the area covered, but it is sufficient. Light from it emerges from the eye, passes across the space to the mirror, and mi- nute pencils pass through the peep hole and are admitted 11 into the eye of the observer. As a result of this arrangement the pupil of the eye under observation is lighted up by a sheen of diffuse, reddish light. It is really the illuminated spot on the retina seen through the dioptric media as through a lens. Such sheen of light is called the fundus reflex, and the dark non-illuminated areas surrounding it are the shadows, so called. The fundus reflex will appear in the pupil only when the mirror is so inclined as to reflect light upon the ob- served eye, for then only is there a bright spot on the retina to emit light. The observer's eye must also be di- rectly back of the peep hole and in '^'^Be^flex^''^ line with the emerging light to ''catch" the reflex. As the reflex is seen through the strong lenses that compose the dioptric media of the eye under observation, it is apt to be a very ** shifty" thing, and often has to be ''caught on the fly" as it is entering or disappearing from the pupil. There will also appear in the pupil other small and intense lights, moving quickly here and there. These are reflections from dioptric surfaces and are to be disregarded. The re- flex proper has a somewhat fiery appearance, taking its color from the blood vessels of the retina. At critical points in shadow testing it is so dissipated as to appear like a pale gray cloud in the pupil, which it entirely covers. Shadow testing is essentially a "movement" test. It involves the determination of the direction in which the reflex and its surrounding shadows move across the pupil of the observed eye when the mirror that reflects light to it is tilted in a particular direction. Movements. •^^' whcn the mirror is tilted in any direction, the reflex crosses the pupil in the same direction, motion is said to be with the mirror; but if the reflex takes an exactly opposite course from the tilting of the mirror, motion is said to be against the mir- 12 ror; if the reflex comes into the pupil so quickly that we cannot observe from what direction it comes, and goes out without our being able to observe its direction of depar- ture, the motion is neutral ^ or neither with nor against the mirror. It is all but impossible to get this effect abso- lutely; but other effects enable us to decide with sufficient accuracy when motion is neutral. It is through these movements and the alteration of effects that are produced by placing trial lenses before the eye being examined, that we are able to determine its condition of refraction, and what kind and the dioptric value of the lens the eye needs to wear. Along with the changes of movement in the reflex and its shadows, there are other effects that help to make the determination accurate, and to warn us of approach to the neutralizing point. These are as follows: (1) the ex- Dansion of the reflex and the elimina- Ph?nomena. ^ion of the shadows, (2) its taking on a faded or grayish color, or the dis- appearance of the red, (3) the rapidity with which the reflex moves, (4) the contour of the line of separation be- tween the reflex and the shadow. With wider diffusion of the reflex the line separating the reflex from the shadow becomes a smaller arc of a greater circle. If this circle of diffusion were completed outside of the pupil it would be many times the size of the pupil itself, every increase in diffusion extending it, until at neutralization it is infinite. 15 CHAPTER II. CONJUGATE FOCI. Shadow testing is based upon the principle of conjugate foci. Positive conjugate foci are two points so situated with reference to a phis lens that either point is the focus for light from the other point which passes through the lens. The two planes of the foci at cSuSesf ^^^^* angles to the principal axis of the lens are conjugate focal planes, for each point in either has a conjugate point in the other. There are an indefinite number of such conjugates for every plus lens. For instance, an 8 D. plus lens estab- lishes the conjugate relation (1) for infinity on either side of the lens with a plane at one focal length from the lens on the other side; (2) for two planes each at two focal lengths from the lens on opposite sides; (3) many other distances, as at 13 in. on one side and 8 in. on the other, at 20 in. on one side and 6 2/3 in. on the other, etc. The first set of conjugates above are the principal conjugates; the second are symmetrical conjugates; and all others "are mongrel or unclassified conjugates. In shadow testing, the conjugates selected for practical purposes depend upon the distance from the observed eye the operator chooses to w^ork. "Whatever the distance chosen, its plane forms one and the retina of the observed eye the other conjugate. If the ^^Deductions.^* working distance chosen is one meter, it is the external conjugate, the lens system of the eye, supplemented by whatever lens may be required to bring them into the conjugate relationship, be- ing the lens involved. Other distances often chosen are 16 at 53 in. and at 27 in. The dioptric equivalents of these distances are respectively as follows: for 53 in., 0.75 D., for one meter, 1.00 D., for 27 in., 1.50 D. These are therefore the deductions or additions to the dark-room, shadow test findings. Given a lens of specific value, if one conjugate is fixed the other is thereby fixed also, depend- ing upon the power of the lens and the position of the first conjugate. In the scheme of shadow testing we locate both conjugates, one being the retina and the other the chosen working distance, and then by using supplementary lenses before the eye as required bring the two into conjugate relationship. The lens required to bring this relationship about is then the key to the true condition of the refraction of the eye under examination. THE NEUTRAL EYE. In Chapter I we defined neutrality in shadow testing. It is that condition in which the reflex fills the entire pupil at once and leaves it without a trace of its direction of de- parture. This happens in only one condition of the eye under observation. It is at the point Motion^ when light from the retina of the ob- served eye focuses at the nodal point of the observing eye back of the peep hole of the mirror. Such an eye, if no accommodation is involved, is myopic to the extent of the distance of observation : . 75 D. for 53 in., 1.00 D. for 40 in., 1.50 D. for 27 in. Since light from the illuminated area of the retina of the observed eye is focused by that eye at the nodal point of the observing eye, it passes into the latter unrefracted, or precisely as though there were no dioptric factors there. The light of each pencil spreads over the entire occupied field of the retina, which is confined of course to the field occupied by the image of the pupil of the observed eye. There is noth- ing to differentiate the diff'erent pencils. 19 It is evident that from an eye in this refractive condi- tion no effect can be produced by tilting the mirror in any direction, except by so tilting it that light will not enter, and therefore not emerge, from it. If it both enters and emerges, and it will do both if it does ^obser^er°^ One, the entire pupil will appear filled with a sheen of light, and veins and arteries can only give a slight reddish tinge to the whole. The same effect is produced as when a small flame is fo- cused by a plus lens upon the pupillary space of any eye. To such an eye the flame, however small or distant, fills the entire area of the lens, except as aberration arranges it in rings or zones of fire around the poles of the lens. In shadow testing an eye, whether it gives these appear- ances in the first instance or is made to do so by the im- position of lenses, is said to be neutral. To move the ob- serving eye nearer or farther than such conjugate focal distance, whatever it may be, dispels these neutral effects. At a nearer distance motion is in one direction, at a far- ther distance it is in the opposite direction. Approach or recession of the observing eye to or from the neutral posi- tion also tends to cut down diffusion and to introduce a more decidedly reddish cast to the reflex. The border lines between the reflex and the shadows also begin to assume greater distinctness of contour, but they at no time become perfectly sharp. It will be apparent to those who are read up on the subject that neutralization is placing that which, in the parlance of the text book writers, is called the ' ' point of reversal" at the nodal point of the observing eye. NON-NEUTRALS. Since, for any distance of observation, a neutral eye establishes a degree of myopia corresponding to the space, it is evident that any greater or less degree of myopia than the space calls for would make the eye non-neutral 20 for that space. Myopia of 0.75 D. Concave Mirrors Plane and ^^,^^^j^ ^^^ ^^^^^^ ^^^ ^^^ neutral for one meter nor for 27 in., nor for any- other space than 53 in. Nor would 1 . 00 D. of myopia be neutral for 53 in. nor 27 in. nor any other space than 40 in. So also of 1 . 50 D. myopia, which w^ould be neutral for a 27 in. space only. Of course mj^opia of a" greater degree than any of these amounts would be non-neutral for all of them. Emmetropia and any degree of hypermetropia is of course non-neutral for all of them. Whether an eye in a hyperopic, mj^opic or emmetropic condition gives mo- tion with or motion against the mirror depends also upon the kind of mirror employed. A concave mirror, which focalizes the reflected light before it enters the observed eye, will give for any eye, except a neutral, precisely oppo- site motion from a plane mirror. This difference is due to the fact that it moves the real fundus reflex in the ob- served eye in the opposite direction from the way it is tilted, or from that of a plane mirror. The reason for this is explained in a later chapter. 21 CHAPTER III. PHYSIOLOGY OF VISION. The eye is primarily on organ of sense, a unit among the sensory agencies by which knowledge of the external world and of its panorama of events is conveyed to the mind. To discharge this function to the fullest degree it must have mobility, and thus be able Factors. * ^^ meet the varying requirements of changing circumstances. The eyes possess such mobility, and chiefly by the use of three motor factors. One of these controls the extent of the pupillary opening that admits light into the eye. By contraction of the sphincter muscle of the iris, with simultaneous relax- ation of the radial fibers, the pupil is made smaller. Two purposes are served by this action: (1) if the light is too brilliant, reducing the quantity in this manner tones down the images on the retina; but (2) as a diaphragm such closing of the pupil also tends to sharpen the definition of the images by minimizing diffusion. The iris acts like a shutter in a camera. By a second motor factor, the ciliary muscle or muscle of accommodation, the lens power of the eye may be in- creased. Without concerning ourselves as to the different theories of accommodation, it is accepted by all that accom- modation incre^es the curvature of Accomm^odation. ^^^ Crystalline lens, and chiefly of its anterior surface, thereby giving it greater dioptric power. This physiological power is needed to adapt the refraction of the eye to varying distances of the object viewed, or to preserve upon the retina a dis- tinct image even though the object is brought nearer or 22 remoxed to a greater distance from the eye. In eyes whose static lens power is not sufficient for distant light, the accommodation is used for distance, though this was not evidently the design in providing it with the power. The eye accommodates normally with the approach of the ob- ject, and accommodation is normally relaxed with the re- cession of the object ; or the accommodation normally acts for near objects and relaxes for distant ones. The third motor factors are those that rotate the two eyes, or either of them, to the relative position required for the fusion of the two retinal images, so that notwithstand- ing the duplication of the images on the two retinae, there will be but one mind picture, or what mnocuiar -^ termed binocular single vision. IMus- cles external to the eyes cause them to perform these rotations. There are three pairs of mus- cles for each eye, rotating them respectively on three chief axes at right angles to each other. But a given pair of muscles rarely acts singly, two or more pairs being com- bined in an action, such combination producing rotation in any desired direction, or on any desired axis. The use of these muscles merely to range the eyes from point to point is not strictly a binocular use of them, for such use would be necessary in a single eyed animal. Their use in pairs, one muscle for each eye, and those moving the eyes in oppo- site directions, so as to alter the relative directions of the two lines of vision, is a binocular use, and such movement is for the purpose of fusing the images only. NATURAL STIMULI. Nature has wisely provided for the control of these movements without involving the exercise of will power. The eyes are not only sensory organs but they are respon- sive, not to the will but to physiological stimulus. A de- 23 fective or anomalous sensory visual Action. Beflez effect causes the responsive stimulus that corrects or tends to correct the defect or anomaly. The action is what is termed in physi- ology "reflex action.". In a strong light the pupil con- tracts automatically, but nerve stimulus and muscular con- traction are none the less required. It is not the eye but ^ the mind that impels the action. We must take mental note of the excessive light before the action to reduce it takes place. The pupil will contract for a strong light only when the mind contemplates the brightness. It is not even necessary that the image fall upon the macula, al- though it is more usual for those things that are held in visual contemplation to be focused upon it, and it requires a special mental effort to visually contemplate an image not so located. In the same way the accommodation is aroused to action, not by the nearness of the object alone, nor is it relaxed by the mere distance of the object unless such object or objects are held in visual contemplation. There are always objects before the eyes, some of them ConTempLion. ^^^^ ^^^^ ^^me of them at a greater or less distance. We can, by the will, contemplate either the near or distant ones. That is the exercise of a mental faculty. But when we visually con- template the near object the accommodation acts involun- tarily so as to make a clear image of the object on the retina, the distant object being thrown out of focus by such action. But we may, also by mental process, with- draw our attention from the near object and visually con- template the distant one. This will involuntarily relax the accommodation, and thereby the near object will be thrown out of focus. That the mind is a factor in the pro- cess, and that the position of the image relative to the macula is not, is shown by looking through a fine wire net- 24 ting, say 13 in. from the eyes, at distant objects. Both the wires and the distant object, which are in the same line of vision, are on the macula together, but we adapt the accommodation to and see distinctly only that which the mind contemplates, -and we can, by will power, visually contemplate the one we choose, or first one and then the other, without changing the position of the eyes. The fusion stimulus is of the same general character as those noted above. The action is a reflex or spontaneous action. The sensation of separation of the images, or ten- •dency to separate, spontaneously calls into action the requi- site stimulus for fusion, and the eyes ^Reflexes.^' are brought into proper alignment for single vision. But in this as in all physiological actions, nerves and muscles perform their allotted part; and if the correction of the anomaly is not within the range of the power of the muscles required to overcome it, or if for any reason the nervous impulse re- quired cannot be provided, the mobile factors succumb to the anomaly. There is nothing else for them to do. The intense light, though painful, pours into the eye unhin- dered, unless the lids are closed or some artificial screen is held before it; blurred images are formed upon the retina and vision is impaired, except as we are able to screen it down by the iris and using what accommodation we can ; or we see double, two objects instead of one, every- thing being visually duplicated. In the last case a partial correction is no improvement, and so obnoxious is it to the sense of vision that an effort is made to suppress vision in one of the offending eyes. This effort is something more than merely *' disregarding" the vision of one eye, for it quickly results in absolute loss of visual power in one of the eyes in a majority of cases. These motor factors in the eyes are all more or less anited, acting in unison. A strong light upon the eyes, 25 tending to cause pupillary contraction, also tends to stimu- late the accommodation, for the nerves controlling the sphincter muscles of the iris are of ^un^Bon*"^ the same system as those stimulating the ciliary muscles, having a common nerve center in the brain. But the muscles that rotate the eyes inward, or toward the nose, are also stimulated from the ^me nerve center, and there is a tendency to converge the eyes during ciliary action. Conversely, a condition of the muscles that demands excessive activity on the part of the internal recti muscles, such as converging the eyes in order to parallel the visual lines for distance, tends to in- cite ciliary action and to cause contraction of the pupil. In this manner an action by one set of muscles involves action, or a tendency to act, by others, and complete relax- ation of any of the motor factors depends upon relaxation of all of them together. In the study of the refraction of the eyes these influences cannot be ignored, nor, in the study of the muscular condition, can the refraction be treated as a negligible quantity. When the eyes accommodate the position of the plane that is conjugate to the retina is brought nearer, for by accommodation the refraction of the eye is increased, and since the retina is fixed in position, its conjugate, external to the eye, takes a position corres- Effects on ponding to the increased refraction, conjugrates. Thus, if a normal eye accommodates 0.75 D. its conjugate plane is at 53 in. from the eye; for 1.00 D. accommodation the conjugate plane is at 1 meter; and for 1.50 D. accommodation the conjugate plane is at 27 inches. In shadow testing the eyes it is therefore important either (1) not to involve the accommodation, or (2) if it is involved, to know to what extent it accommodates. We endeavor usually to secure,' as nearly as possible, a relaxed accommodation; but there 26 are advocates of another system, a system of measuring the refraction during acconmiodative activity, or relaxing it for a point within infinity. This method has been styled '' dynamic" skiametry. Of course the proper deductions or additions are made for the distance of the point fixed by the observed eye during such an examination. Like every other mode of testing the eyes, shadow testing in- volves all factors contributing to the result or tending to conceal the true refraction. It extends through all the dioptric media of the eyes, and is therefore a measure of the whole refraction, regardless of the separate values of the cornea, crystalline lens, etc. 27 CHAPTER IV. PRIMARY REQUIREMENTS. Shadow testing, without special instruments, requires a space screened from general light, or a dark room. Other- wise the phenomena are less distinct than required. The special light may be a frosted electric bulb or a gas or lamp flame. Unusual brilliancy, such as is ^for^est.^ developed by a Welsbach mantel, is not necessary, unless a skiascopic chimney, which screens all but a small area of the light, is also used. As to the necessity of such a chimney, it is by no means imperative, an ordinary bulb or flame entirely uncovered answering every purpose. But an unfrosted electric bulb is unsatisfactory for the reason that the wires stand out too prominently and tend to give an appearance of astigmatism whether there is any present or not. The position of the bulb or flame must be such that, while the light will fall upon the mirror and be reflected by it to the observed eye, it cannot reach the eye directly or by any different course. A position back of the patient 's head, and either above or to one side ^ight^ of it, is necessary. The extent of the pencils of light reflected to the ob- served eye depends upon the size of the reflecting surface of the mirror ; but whatever its size only pencils of the lat- eral width of the pupil can enter the eye to which light is reflected. The pencils should be of such extent that the operator can readily follow their course and easily direct them to the pupil. With a mirror of from one to two inches in diameter this can easily be done. The reflection from the mirror makes a bright round patch of light wher- ever it falls, and its course is followed, when tilting the 28 P.M^___— -^-^^^ ^ ll-^--;:::::r3= ^=4^.^i^ Direct Tief lection. . ' ^ f|S,^-'-"",'. \ — = -.V'^-' rilUd Upu^ard ■ : ^^-.^ ~~ -- -^__ P.M. ^^^7?ec/ /.f^/i> Tilted DoLunivard ^\.^^ CM..,.--'" ,.'"r;^ Upujard \ .'' ^ — =^i7?eaJ Li^ht CM. Tilted r^^^^^^^^^ .1 Mirrors anc/ Sou/^ce 0/ L ^/./ mirror, by noting the position and tracing the movements of this lighted spot, which is round the same as the mirror. The eye that is not used in the shadow test, that is, the one not back of the peep hole of the mirror, is easily trained to follow the movements of this patch of light and help to guide it in the right direction. Until it is sufficiently trained for the work a small paper card may be held in position to show where the light is. The catoptric principles involved in shadow testing are exceedingly simple. A plane mirror produces a virtual image of objects before it, the images being as far back of the mirror as the objects are in front of it. We may re- gard this image as the ''source of ^^^^glT °^ li^^*" t^at is directed into the pupil. If the light is in a line perpendicular to the face of the mirror, the virtual image, or source of light, will be in the same line projected back of the mirror. But if the light is to one side of the perpendicular, the reflected light goes to the opposite side, and this places the virtual image to the same side of the perpendicular as the light itself. Hence, with a stationary light, if the mir- ror is tilted in any direction the virtual image and source of light is moved in the opposite direction. Tilting the mirror downward therefore throws the source of light up- ward, tilting it upward throws the source of light down- ward, and the same inverse principle holds true for tilting it to right or left. A concave mirror, which focalizes the light received before it enters the observed eye, makes a real image of the flame or bulb at that focus, and this image becomes the source of light. Since tilting the mirror in any direction moves this image in the same direc- ^^Mirror!*^^ tion, the source of light moves in the same direction as the mirror is tilted, and this is a directly opposite movement, for the same tilt- 31 ing, from that produced by a plane mirror. Hence the motion rules for plane and concave mirrors are opposite to each other. But neither motion of either mirror gives a definite direction to the movement of the reflex, for the eye examined is also a factor in the direction of motion — the last determining factor. With a concave mirror the source of light is necessarily nearer the observed eye, for it is only a part of the space between the two eyes from the latter. With a plane mirror, on the other hand, the source of light is the sum of the two spaces, from light to mirror and from the mirror to the observed eye, distant. This is one reason why the plane mirror is preferred by many of the best refractionists. It is especially advantageous in low degrees of astigmatism, where a distant source of light is needed; but a concave mirror, which provides a near source of light, is equally advantageous in high de- grees of astigmatism. So far as the movement of the reflex is concerned, which is the principal determining phenomenon in shadow testing, there is no choice between plane and concave mirror. It is only in the minor phenomena, such as the banded ap- pearance in astigmatism, that one ^rlctors'^'' may be better than the other. Shadow testing is "not dependent upon the kind of light nor the manner in which it is reflected to the eye, except as stated above, nor is the focalizing of the light in the eye in any particular manner sought for, so long as it does enter the eye and brightens an area of the retina, which it will do whether focused at the retina or not. It is with the light emerging from the eye through the dioptric media that we have to do, for that shows us the condition of refraction. If emergent light is focused hy the observed eye at the observing eye, motion of the reflex is neutral; if focused beyond the observing eye, or negatively back of the observed eye, we see the actual move- 32 ment that the reflex makes ; if focused between the observed and observing eye, we see the motion of the aerial image of the reflex, which is opposite to the motion of the reflex itself. The kind of motion that is produced by different mirrors, at different distances of observation, and for the different refractive conditions of the eye observed may be conveniently tabulated as follows: PLANE MIRROR 1. Hypertnetropia of any amount 2. Emmetropia 3. Myopia of less than O. 75 D. ( 1. Motion With I 1. At 53" i 2. Motion Neutral j 1. Myopia of O. 75 D. 2. At 40" L 2. Motion Against \ 1. Myopia of more than O. 75 D 1. Motion With 2. Motion Neutral ) 1. Myopia of 1.00 D 1. Hypermetropia of any amount 2. Emmetropia 3. Myopia of less thon 1.00 D. I 3. Motion Against j 1. Myopia of more than 1.00 D. ( 1. Hypermetropia of any amount ' 1. Motion With ] 2. Emmetropia ( 3. Myopia of less than 1.50 D, 3. At 27" ^ 2. Motion Neutral j 1. Myopia of 1.50 D. I 3. Motion Against 1. Myopia of more than 1.50 D. In the use of a concave mirror the only difference from the above is that where motion is with, with the plane mir- ror, it will be against with the concave mirror, and where it is against with the plane mirror it will be with, with the concave mirror. The neutrals are pre- cisely the same. As to the use of spe- cial instruments for shadow testing, of which there are several on the market, we defer a discus- sion of their special qualities and value to a subsequent chapter devoted to that subject alone. Variation for Concave Mirror. 33 CHAPTER V. TECHNIQUE. The purpose of the following four or five chapters is to describe in detail the technique of practically fitting eyes by the shadow test, taking cases in the following order : (1) emmetropia, (2) hypermetropia, (3) myopia, (4) as- tigmatism. While shadow testing is condiMons. ^ Valuable method when used simply to corroborate the trial case or sub- jective findings, we will assume it to be, in the following, the initial method, and that its findings are corroborated by the trial lenses. We introduce emmetropia into the series not because emmetropes are frequent patients but be- cause emmetropia, being the normal or model condition of refraction, is the standard of physiological action of the eyes. EMMETROPIA. Emmetropia may be defined as that condition of the re- fraction of an eye in which, without accommodative action, light from a distant source (infinity = o o ="20 ft. or far- ther) is focused upon the retina, producing sharply de- fined images of such distant objects; conditicm^ and which for all points nearer to the eye than infinity requires, in order to make the images clear, accommodation in proportion to the dioptric space separating the object from the eye; or which, failing to accommodate for the required (normal) amount, focalizes the light back of the retina and there- fore produces blurred images upon it. In emmetropia, since no accommodation is required for distance, to relax the accommodation all that is necessary is to have the patient fix a distant object, or merely to look 'into space without seeing any definite thing. Light emerging from 34 an emmetropic eye, in such state of relaxation, emits plane waves or parallel rays of light. The retina and infinity are conjugate to each other. Suppose our case, but that fact unknown to us at first, is an emmetrope. We seat the patient in the dark room in such position that the light to be used for shadow testing is back of her head, but either sufficiently above it or to one side to allow its light to fall upon the mirror when held in the position shown in the illustration, Chapter I. ^for*Te*sr* We take our position also as shown in the figure. The patient is direct-, ed to look at some object, perhaps dimly seen back of the operator, for all light, except that from the special light used in the test, is excluded, or at least the space is made reasonably dark. We so incline the mirror that the re- flected light from it falls upon the patient's face, and tilt the mirror so as to cause the light to pass over first one eye and then the other. Suppose we are using a plane mirror and our distance is one meter from the patient. As the light falls upon either eye, we notice the red reflex spring into the pupil. The patient is apt at this point to look at the light seen in the mirror. If she does the reflex disappears. We direct her to look at the distance again, at a card or object on the wall so placed that her line of vision is, for her right eye, just past the operator's right ear, or for the left eye past the left ear, although both eyes can be tested when looking either way. Having properly fixed her vision upon distance again, we so tilt the mirror as to cause the reflected light to sweep across one eye, and as it crosses that eye, we note whether the reflex, and its surrounding shadows, cross the pupil in the same or in the opposite direction. "^^^Tes^ *^® Being an emmetrope, if the accommo- dation is relaxed the reflex will cross the pupil in the same direction as the light ; motion will be 37 with the mirror. The other eye will show the same motion. We tilt the mirror vertically, up and down; and horizon- tally, to right and left; or obliquely, and everywhere get motion with the mirror. We know that our patient's eyes are either less than 1 D. myopic, emmetropic or hyper- opic. The conjugate of the patient's retina cannot be be- tween her eye and ours. Notice the proviso above, "if the accommodation is re- laxed. ' ' This is put in for the reason that, if the patient vis- ually contemplates the light, though not looking directly at it, reflex action will cause the pupil to constrict, and it will tend to accommodate in spite of its CompUcaSons emmetropia and fixation of the dis- tant object. Some people are very difficult to shadow test on this account. There are also conditions of the muscles tending sympathetically to excite the accommodation that require attention before full cili- ary relaxation is possible, despite the fact that the eyes are emmetropic. These conditions are often regarded as pointing to a spasmodic action of the ciliary, but are ac- counted for by muscular imbalance. Exophoria is one of those imbalances tending to induce ciliary action. To eliminate these causes for ciliary activity may be difficult, but a temporary prism, base in, over one eye will tend to relieve the muscular influence during the test. However, some eyes, because of the above, or because of an exceeding darkness of the reflex, cannot be successfully tested in this manner, except perhaps by the most expert. But, granted no such factors interfere with the test, we have decided motion with the mirror. This, with the plane mirror, calls for plus lenses. We adjust a pair of +2.00 D. spheres in a trial frame made for the purpose, and again make the test as before. Reflections ^^Kst** °^ from the lenses are easily avoided by moving slightly to one side of the position that gives them. With the -f^.OO D. motion in 38 JEin m ef'rooi a 1 06se/'i^//7t^ Eye ryect Lye ^^-^''""^ ~Hh ^ Inci'denf Lt'q/if -P/ane Mirror ^ /0^^ ,'<' ^ ^/^^^ y~ ^v^.y vv- ^ V_>^ ^ /^^?^^ Xi^ fcr-Mi] ' ~~~~— ^=-1-=— — \ ■---^ yy- /fof/on /J^a/ns^ 4i4t ^ --e- y -iff- '\\ \'^^^^~~~ — BS^A .^ A/of/on ^Gainsit ^ irff ~~0\ Afo;^/6^7 /Veul^ral 4!^ ^y ^/ane Atirror of one Ne^er- each eye is decidedly against the mirror. That is, light coming from the illuminated spot on the retina focuses on its way to the observing eye, forming an aerial image of the fundus at the focus. It is the motion of this image, which is opposite to that of the real fundus reflex, that we watch, and therefore get reversed motion. Reduce the lens to -f-1.50 D. and motion is still against. We notice also that the reflex seems to cover a larger area and to more completely fill the pupil ; it also moves on and off the pupil with greater rapidity. A reduction to +1.25 D. augments the effects last named — enlarges the reflex and makes it move more rapidly — but gives motion against the mirror still. The reflex also has a less reddish cast, as though the color had been dissi- pated through the larger area, and is ^McTt^on^^ taking on more of a pale grayish color. I cut my lens down to +0 . 75 D., making a drop of one-half diopter, and, while motion is not made more rapid, nor is the reflex apparently altered in extent, motion has reversed, and the reflex now goes with the mirror. With +1.25 D. I have motion against, with +0.75 D. I have motion with. Evidently my neutralizing lens lies somewhere between the two. I substitute a +1.00 D. and I get very nearly the neutral effects, but I think motion is still slightly with the mirror, and I am unsatis- fied. Measuring my distance, I find I am 36 inches from the eyes, instead of 40 inches ; moving back to the required distance I find as near absolute neutralization as I am likely to get. The whole pupil is illuminated at once, no matter in what direction the mirror is tilted, and it entirely passes off the pupil in the same manner. In this condition the slightest touch of the circle of light upon the pupil fills it with the sheen of light, and it stays in the pupil until the last edge has passed off. The eyes have been made to focus at one meter by a 41 +1.00 D. spherical lens. Without that lens light from the retina will focus at infinity and vice versa. The retina is conjugate to infinity and infinity is conjugate to the retina, for a +1.00 D. sphere establishes the ^prnding-^^ Conjugate to the retina at one meter in front of the eye. The eye, and both of them, is therefore emmetropic. The dark room finding at one meter is +1.00 D. sph. The correction is 1 D. less, or absolutely no lens at all, or a piano. At 53 in. a +0.75 sph. would neutralize motion ; at 27 in. a +1.50 sph. would do the same. With a concave instead of a plane mirror, at one meter initial motion would be against the mirror; +2.00 D. would make it with; +1.50 D. with; +1.25 D. with; +0.75 D. against. But a +1.00 D. would neutralize the eye. These results would be obtained from an emmetropic eye only. It is seen that, at the critical point in the test— that is, when motion is neutralized — the eye being tested is fogged for distance by a plus lens. It is endeavored, in this way, to relax the accommodation at this point, and, so far as fogging the eye is capable of relaxing ^ydriasis^' accommodation, it will be relaxed. Many practitioners in the medical profession prefer to be fully assured of this fact, and em- ploy a cycloplegic for the purpose. This also enlarges the pupil and gives a wider field of view of the reflex. But this fact is not devoid of disadvantage. By admitting the extra-visual areas of the crystalline lens into the test, a somewhat different refraction is obtained than when the test is applied to the visual areas (the normal physiological pupil) alone. It is also generally admitted that the test under thorough cycloplegia is not accurate, but that de- ductions are required for the findings under those circum- stances, and there is no certainty among those who use the drug as to •the amount of the deduction. 42 Dynamic shadow testing is the opposite of mydriasis and cycloplegia. It engages the accommodation for a definite amount by having a card upon the operator's forehead, or elsewhere, for the patient to look at (visually contemplate) during the test. If the patient is aShod*^ able to accommodate for the requisite amount, such card becomes, by ac- commodation, conjugate to the retina of the observed eye, and since the observing eye is practically in the same plane, the eye examined is neutral for the distance. Increasing plus lenses are then imposed until motion is reversed. At one meter a +1.00 sph. should be the neutralizing lens — neutralizing, in this case, the accommodation previously engaged. It is claimed by some refractionists that in this manner latent hypermetropia is uncovered. Mr. A. J. Cross of New York is the originator and principal advocate of this method. 45* CHAPTER VI. CONCAVE MIRROR 53 IN. It was originally supposed, in shadow testing, that the position of the "source of light" was a factor in the mo- tion of the reflex. Accordingly, under this theory, a con- cave mirror of 10 in. focus held before the observer 's eye would focus at about 13 in. before the 53 in space. mirror; or in a space of 53 in. at 40 Origrin of ■ ^ in. from -the observed eye. This would place the source of light 40 in. from the eye being exam- ined. The theory undoubtedly led to the use of a testing space of 53 in. It is employed exclusively by many opti- cians. But the position of the source of light has no effect upon the direction of the motion. Motion of the patch of light in the eye is always exactly opposite to the motion of the source of light. But with a concave mirror the source of light goes in the same direction as the mirror is tilted, and the reflex therefore goes in the opposite direc- tion, and so appears to the observer in emmetropia. Hence, if the observed eye focuses nearer than 53 in., the aerial image of the reflex goes opposite to the motion of the real reflex, and appears to move in the same direction that the mirror is tilted. This accounts for the reverse effects of using plane and concave mirrors. HYPERMETROPIA. We will, in this case, suppose the observed eye to be 1.50 D. Hyperopic, and that it accommodates for the amount in the dimly lighted dark room when the eyes are fixed on objects back of the operator ; but that, on account of the hyperopia, the patient com- Hyperop^a. plains of eye strain. We seat the patient in the proper position with reference to the light and take our position at 53 46 in. with a concave mirror. Reflecting light upon the eye we get motion against the mirror. That is, emergent light focuses beyond the observer 's eye and the true motion of the reflex is seen. A +1.00 sph. is imposed, but since that merely relaxes the accommodation to that extent, no change is seen, either in the direction of motion or expan- sion of the reflex or greater rapidity of motion. A +2.00 D. sph. relaxes all accommodation and actually causes the focus of emergent light to approach the observer, but it is still back of him. There is therefore no change in the di- rection of motion, but the reflex expands considerably and the motion is quite rapid. The dissipation of the color also shows that we are approaching neutralization. A +2.50 sph. is substituted, and this reverses motion making it with the mirror. Since the 2.50 sph. is a 1.00 D. over- correction of the hyperopia, it focuses the observed eye at 40 in., and this is forward of the position of the observ- ing eye. It is the aerial image of the reflex that now comes into view, and its motion is the opposite of that of the true reflex. Reducing our lens to a +2.25 sph. we obtain the nearest to neutralization it is possible to get. All of the phenomena of neutrality are atjbheir best — enlarged, pale reflex and very quick motion. Since a +2.25 sph. has neutralized the observed eye, with the lens imposed light from the retina of the observed eye emerges and focuses at 53 in., the testing distance, or at the observing eye. It has therefore been made, by the lens, 0.75 D. myopic. To correct the ^pind^g-"^ eye, or make it normal for distance, would require 0.75 D. less plus, or +1.50 D. It is seen that with the concave mirror at 53 in. the only differences to be observed from the plane mirror test at 40 in. are: (1) the directions of motion are reversed, and (2) the deduction or addition is 0.75 D. in- stead of 1.00 D. The phenomena of enlarging the reflex, 49 increasing the rapidity of motion, and the dissipation of color are precisely the same. The difference between hy- peropia and emmetropia only result in requiring more plus to produce neutralization, for until the accommodation is relaxed the observed eye will continue to focus at infinity. In a case of hyperopia where the accommodation is unable to hold infinity in focus, whether it be because of excessive hypermetropia or a lack of accommodation, mo- tion will be correspondingly slow for the amount of such insufficiency of the refraction. Or ^Mouon.^^ if atropine is used and the accommo- dative function is thereby suspended, the motion is then slow at the beginning but increases in rapidity with the imposition of plus lenses until the point of neutralization is reached. This is no particular advan- tage since lenses will ordinarily relax the accommodation before you can arrive at the point of neutralization. The seeming advantage of a large pupil is also nullified by the fact that upon central areas you are likely to have motion contrary to that which appears in the periphery of the pupil. It is because of these contradictory phenomena that many who use atropine also employ a pupillary disc cutting out the peripheral effects. The advantage of atro- pine, if there is any advantage, is thereby reduced to its cycloplegic effects entirely. MYOPIA. If our patient is a myope for an amount in excess of the dioptric value of our testing space, as for example 3.50 D., the initial motion for a concave mirror, without lenses, is with the mirror. That is, motion of the mirror in any direction, as downward, causes the Myop^f true fundus reflex, or lighted area of the retina, to move upward. But, since light from this reflex emerges and focuses at about 50 111/2 in. from the observed eye, the aerial image of the fundus will move downward — in the same direction as the mirror is tilted. And this motion shows to the observer that the focus of the observed eye is forward of the observ- ing eye, and, that being the case, a minus lens of the cor- rect value will bring it to the observing eye. We impose a — 1.00 sph. and motion is still with; a — 2.00 sph. also gives motion with; but a — 3.00 reverses motion, and is therefore too strong for the purpose. Reducing it to — 2.75 sph. neutralizes motion, or focuses the observed eye at 53 in., our position. This lens leaves the eye 0.75 D. my- opic. Hence a lens 0.75 D. stronger than the neutralizing lens, or — 3.50 D., is the required correction. We add to the minus lens that is found to neutralize motion the diop- tric value of the testing distance, in this case 0.75 D. This is the same as subtracting an equal amount of plus. Some practitioners do not attempt absolute neutraliza- tion, but stop with the weakest lens that reverses motion from the original direction. To compensate for such in- accuracy in the case of minus findings, instead of adding 0.75 D. the addition is cut a quarter ^°F^ding^. °^ ^^ ^ diopter, making the addition for 53 in. 0.50 D. This method gives the operator the distinct phenomenon of reversal to go by in- stead of the elusive one of neutralization. It is on the same principle as if the marksman set his forward sight low so as to shoot a little above the mark and then aimed his rifle low so as to counteract that effect. It is always well to reverse the initial motion, whatever it may be, for then only is one sure of having passed the apex of correction. But if he has only passed it an eighth of a diopter, and such a small value will sometimes produce distinct reversal, the addition of 0.50 D. will not be quite sufficient, although it is on the safe side of a myopic correction. It would seem to us just as essential to make the deduction 0.50 D. 51 for plus findings, admitting that the lens finally used is a slight overcorrection, which it would be if motion is re- versed. Such a deduction would also be on the safe side. 27 IN. SPACE. The reason for employing this space, or even a shorter one, is that it brings the observer near enough to the pa- tient to make any changes in the lenses called for without getting up, and thereby lessens the danger of altering the uniform distance of making the ference between it and other spaces is the amount of the deduction or addition from the dark room. findings, which is 1.50 D. ; or for a 20 in. space 2.00 D. The shorter spaces, because of nearness to the observed eye, give a greater visual angle to the pupil, thereby en- larging the field of observation. The phenomena of neu- tralization are the same for all spaces, all mirrors and all distances, as are also the phenomena of approach to the point of neutralization. 52 CHAPTER VII. ASTIGMATISM. In considering the diagonsis of astigmatism by the shadow test it will not be necessary to differentiate between the use of different mirrors and different testing spaces. These things are questions of individual preference merely, and one may become skillful in the A^r^matirm practice of shadow testing with the mirror and space of his own choosing. Whatever space he chooses to employ is a matter of conse- quence to nobody but himself. By any of the methods there is one point at which all agree — the point of neutral- ization — and reversal of motion is the same by one method as another. At the point of neutralization the reflex is greatly expanded ancl diffuse; at either side of this point motion is very quick; and with neutralization the reflex assumes the faded out or colorless appearance. Of these subsidiary phenomena, the expansion of the reflex is one of the surest signs of astigmatism. The characteristic feature of astigmatism, of whatever kind, is the double focus. One meridian of the eye pos- sessing the highest dioptric value and the other at right angles to it having the lowest, establishes two focal points, one for each meridian, within the eye, ^^pocu^^^ for light from any object. But if, by the mirror reflection employed in shadow testing, a bright spot of light is produced on the retina, light from it will emerge from the eye and have also two points of focalization. The retina, instead of be- ing conjugate to only one plane in front of it, is conju- gate to two such planes, the space between them being the 53 so-called interval of Sturm. The two principal meridians are of different refractive value for emergent as well as incident light. It is evident therefore that, in shadow test- ing such an eye, the observing eye cannot be at both of these focal points at the same time, and that, if it is at one of them, the other will necessarily be back or in front of the observing eye. To neutralize one meridian of an astigmatic eye there- fore leaves the other principal meridian out of focus and un-neutralized. Consequently, in the neutralized meridian, you will get all the phenomena of neutralization, while in the opposite meridian motion remains Meridians distinctly with or against the mirror, as the case may be. The problem in the shadow testing of an astigmatic eye is to determine the value of each principal meridian and thereby get also the difference between them, and thus measure the whole de- fect. A cylindrical value will be required to equalize the difference between the meridians, and a spherical lens will correct the uniform error after such difference is deter- mined and corrected. The determination of the difference is the more difficult part of the problem, but in some re- spects this is even easier than measuring the simple spheri- cal part of the error, for there are distinctive phenomena for it. While shadow testing is essentially a motion test, the subsidiary phenomena to which we have referred become of great importance in astigmatic cases, especially the phe- nomenon of the expansion of the reflex along the neutral- ized meridian. A round rubber disc stSSht^dge. ^^ equally curved at all points of its circumference, but if it is stretched by pulling at two opposite sides, the edges between assume practically a straight line, or take the form of a straight edge. This effect gives to the reflex, in contrast to the 64 Conjj. Hyp. /iJih^ mutism Jnctclen} Lt^h> ^Jain Mirror- 1 Meter meri^eni Liqfit Motion h/ith shadowed areas that surround it, what is known as the ** banded" appearance. The band or straight edge extends in the direction of the neutralized meridian. There is no distinct motion either with or against the mirror if tilted in that meridian. The reflex flows across the pupil in one continuous stream, and has no defined end. But when one meridian is so neutralized the other will show distinct mo- tion either with or against, and by tilting the mirror in that direction the straight edge crosses the pupil. If the vertical meridian of the eye is neutralized the band and straight edge will extend vertically. "When the mirror is tilted vertically the reflex will "flow" along that me- ridian without a distinct ending, and the problem then is to find what reduction or increase Tf 'BaneT ^^ ^^^ ^^^^ power is required to cause the band to assume the horizontal position and show the horizontal straight edge. As there are but two chief meridians, it cannot be made to assume any other direction than those of such two chief meridians, be they vertical and horizontal or oblique, and whatever meridian is made neutral or to show the straight edge, the other or opposite meridian will show motion. To get these effects successively, first for one meridian and then for the other, the lens changes must all be spherical, one value being used for the highest meridian, the other for the low- est, for a proper cylinder with its axis along the neutral meridian will make all meridians neutral and dispose of the band. But working with sphericals alone exposes the test to the danger of accommodative action, as may be seen. One focal point in astigmatism is iiecessarily back of the other. It is either nearer to the retina when both are forward of it, back of it when either is back of it, and far- ther back if both are back of the retina. All spherical 57 changes in the lenses allow these foci Ac^commod\«on. ^^ remain apart and put them in one of the above relations to each other. Now, the accommodation resists the focalizing of any me- ridian^ back of the retina. Wherever there is a tendency of even one focus to go back of the retina, the accommoda- tion becomes active and holds the focus from such retro- gression. Hence, when in shadow testing, we endeavor by a spherical reduction to neutralize the meridian of greatest refraction, which is focalized forward of the other, and the astigmatism is of a greater dioptric value than the di- optric equivalent of the testing space, we arouse the resis- tance of the accommodation, which, acting equally for all meridians, prevents neutralization of the second meridian, at least until a sufficient reduction is made to overcome the resistance of the accommodation. This is apt to give the impression that there is a great deal of astigmatism where there is in fact but little. But the employment of cylinders to neutralize the sec- ond meridian after the first has been neutralized, takes away the distinctive banded appearance and straight edge, which is so useful in testing astigmatic eyes. Either of the methods therefore has certain dis- ^^^''^Band.^''^ advantages in shadow testing. The problem of avoiding both difficulties is not so hard however as it would seem. As to the prac- tical use of such a method we will deal with that in a con- crete case. In such case we will specify no special form of mirror nor distance, but refer to the case as ' ' requiring + " or "requiring — ." In all cases it is important not to give either meridian a focal foothold on the retina with which to resist* further reduction of the lens. This prin- ciple is of equal importance in shadow test instruments in which the reductions are spherical. 58 CONCRETE CASE. Suppose our case is one of compound hyperopic astigma- tism, showing eventually that a correction of +1.50 sph.=+0.75 cyl. ax 90, or ♦ +2.25 sph.=— 0.75 cyl. ax 180 is the needed correction. At the ~ Testing chosen distance and with the chosen AstigrmatiBm. mirror we reflect light upon the eye and the motion indicates that plus is required in all merid- ians^ no definite marks of astigmatism being at first ap- parent. We impose increasing plus spheres until motion is opposite from the initial motion in all meridians. "We then reduce gradually until the horizontal meridian (the one requiring the greater amount of plus) is decided to be neutral. This would be in the above case, for 53 in., +3.00 D., for 40 in., +3.25 D., and for 27 in., +3.75 D. In this case the band extends across the horizontal meridian, and the straight edge when seen is also horizontal. The latter is only seen when we tilt the mirror vertically, and when the reflex comes into or leaves the pupil. Horizontally the reflex has no defined beginning or end, but streams across the pupil in a continuous flow. If we now use a cylinder its axis must be placed at 180, or along the neutralized meridian, to neutralize the other meridian; and such cylinder requires to be minus, for the vertical is the least hyperopic and has therefore been made, by the plus sphere employed, the ^cyuifder most myopic. A —0.75 cyl. ax. 180 wdll be found to be the cylinder re- quired. But it will not be so easy a matter to decide that it is just the value needed, for a — 0.63 cyl. or a — 0.88 cyl. come very close to the correction. The difficulty in distinguishing which is preferable is partly due to the fact that either of the three cylinders so reduce the astigmatism 61 that only the most finely trained eye can detect the dif- ference in motion, for the banded appearance is practically eliminated and serves no longer as a guide to the test. But to reduce the sphere 0.75 D., leaving the astigmatism un- corrected, exposes the test to the danger of accommodative resistance, although in this particular case that danger is avoided by the low degree of the astigmatism. In this case therefore, by such spherical reduction, the vertical meridian v^ould become neutral, and the band and straight edge would shift from the horizontal to that meridian., The banded appearance would be in the vertical and a hori- zontal tilting of the mirror would show motion and the vertical straight edge. If these results were set down we would have as follows: At 53 in. At 40 in. At 27 in. +2.25 +2.50 +3 +3 +3.25 +3.7 Deduct 0.75 Deduct 1 Deduct 1.50 +1.50 +1.50 + 1.50 +2.25 +2.25 +2. All of the findings reduce, after making the proper reduc- tion for the testing space, to the same correction, which is of course the prescription first given. Had the case been one requiring minus in all meridians the initial test before a lens was inserted would have shown that condition. We would then have imposed increasing 62 minus spheres until one, the least myopic, meridian was neutralized and the- straight edge ap- AstT matism peared. With a minus cylinder with its axis along the neutral meridian, or by a straight spherical increase of the minus value, the other meridian would have been neutralized. The correct- ing cylinder over the first found minus sphere would neu- tralize all meridians together and eliminate the banded ap- pearance more and more as the correction was approached ; but a spherical change from one principal meridian to the other, while preserving the band, would expose the test to the danger of accommodative action the same as in the case last described. The deduction in the case of minus findings would depend upon whether the test was carried merely to the point of neutralization or to the reversal of motion. A reversal of motion would of course show an overcorrection, and in that case the addition would need to be correspondingly reduced to make up for the testing distance. For a 53 in. space, for instance, the. addition might be 0.50 D. instead of 0.75 D., all meridians being treated the same. Cases of shadow testing give frequent examples of eyes requiring, for neutralization, a plus value in one prin- cipal meridian and a minus value in the other. These are not necessarily cases of mixed astigmatism, for the deduc- tions and additions may take them out Astiginatism. ^^ ^^^* ^^^^^' ^^^ t^^^ ^^^ mixed find- ings. If the eye is neutralized to give the findings, each should be corrected for the precise value of the testing space, no more and no less. But if both findings are an overfinding or reversal, the plus finding contains, as a finding, too much plus ; and the minus finding contains, as a finding, too much minus. It is customary among those who practice this method to deduct the full 63 space value from the plus finding but to add a quarter of a diopter less than the space value to the minus finding. That is, for a space of 53 in. the findings and correction would be shown below: Findingfs: —1.25 +0.75 Correction: -1.75 That is, since the findings themselves tend to show more astigmatism than there is, the correction is so modified, and in favor of less minus, as to negative the overcorrection. 64 CHAPTER VIII. THE SECOND MERIDIAN. The banded appearance, or straight edge between reflex and shadow, made to show in shadow testing astigmatism is more pronounced in the higher and less pronounced in the lower degrees of that optical defect. It is of so dis- tinctive a character that its preserva- ^^^•^''^•.f^'''*''* tion throughout the test is desirable. Neutralizing the second meridian with a minus cylinder, after the first has been determined, corrects the astigmatism and eliminates this apearance; while making spherical reductions for the second meridian exposes the test to the danger of arousing accommodative action, as has been explained. To avoid both of these com- plications involves special methods. When the first meridi- an has been neutralized, supposing it to be the horizontal and that the other meridian shows motion requiring minus, a minus cylinder of the right value, axis 180, w^ill neutralize the vertical; but a minus cylinder of a higher value than the astigmatism will cause the vertical .focus to take a posi- tion back of the horizontal and reverse the astigmatism, or make it artificially against instead of with the rule. If the astigmatism is thus overcorrected for more than the dioptric equivalent of the testing space, it will tend to arouse accommodative action, or stimulate the resistance of the accommodation. Since astigmatism is merely the difference in the refrac- tion of the two principal meridians, and the measure of it is the cylinder that unifies them, it is evident that whatever 65 minus cylinder will neutralize the second meridian after the first has been neutralized, an Astigmatism. ^^^^^ P^^^ Cylinder with its axis at right angles to the neutralized merid- ian will also correct the astigmatism, and that a higher plus cylinder similarly placed will also reverse the astigma- tism. The latter cylinder would have its value or power along the neutralized meridian and destroy its neutrality, but as that has become a finding, we no longer care for ii. Such a cylinder will not expose either meridian to the danger of stimulating the accommodation. .Therefore, having neutralized the first — the most hyperopic or the least myopic meridian — with a sphere, we set the result down as a finding for that meridian, and then impose a strong plus cylinder with its axis ^across the neutral merid- ian over the sphere, thereby placing it out of accommo- dative danger, and then proceed to reduce the sphere for the other meridian. When it is neutralized we have our second finding. The cylinder thus imposed must be suffi- ciently strong to reverse the astigmatism, and may be in- creased if found insufficient, to preserve the characteristic band and straight edge. With the neutralization of the vertical in this manner the band and straight edge become vertical. Care has of course to be exercised in placing the axis of the cylinder exactly at right angles to the meridiaii) first neutralized. An eye having no astigmatism can of course be measured by the same procedure, a plus cylinder creating artificial astigmatism and a spherical lens being used to neutralize the meridian lying along the axis of the cylinder ; then re- versing the position of the cylinder, ^^Tests*^^^ in the new position the meridian under the axis should with the same sphere be neutral also. If this test shows that a different spherical value is required for neutralizing: the axial merid- ians astigmatism would be shown, notwithstanding its nonappearance under a spherical test. A cylinder may also be used to determine whether the position of the chief meridians of weak astigmatism has been correctly deter- mined or not. If the position of the axis of the cylinder inserted does not correspond to one of the chief meridians of the eye being tested, the effect will be that of cross-cylin- ders with oblique axes, and the banded appearance and movement will not then be along the chief meridians of either the eye or of the inserted cylinder, but at some inter- mediate meridian. As a verification in a difficmt case this method of corroboration is worth trying. EMPHASIZING THE BAND. Having discussed the distinctive quality of the banded appearance in shadow testing astigmatism, and stated that it is more pronounced in the higher degrees of astigmatic error, there is another important fact and factor in giving it the fullest emphasis. The band is ^iffu^sion°^ distinct in proportion to the diffusion in one meridian and the absence of diffusion in the other or opposite meridian. In other words, it is the contrast between the neutralized and the un-neu- tralized meridians that gives the band its emphatic features. This is of course greater the higher the degree of astigma- tism. But we get the most out of a given degree of astig- matism when the source of light is at one of the anterior focal points and the observing eye is at the other. When the source of light is at one of the focal points, it and the retina are, for that meridian, in conjugate focus. Since the other meridian is, at the same moment, focused at the observing eye, the latter is also conjugate to the retina, but by the action of another meridian. Now, further, as it is the source of light that produces the true reflex, that re- 67 flex is most diffuse in the meridian that is focused at the observing eye and least at the other. Emergent light from that reflex will therefore be slightly diffuse for the meri- dian conjugate to the source of light, and greatly diffuse for the meridian conjugate to the observing eye. With a plane mirror, which places' the source of light as far back of the mirror as the light is in front of it, these respective positions are attainable only for ^ low degree of astigmatism: thus, if the testing space is one meter, the observing eye is at the 1 D. distance, ^^T •!!J!1.''"° w^hile the light is at most not more than at a little over two meters, or 0.50 D., distance, and this limits the astigmatism that can be reduced to the positions to 0.50 D., being less the nearer the true light is to the mirror. A concave mirror places the source of light in front of the mirror, and its distance from the observed eye can be varied at will: (1) by moving the light toward the mirror, causing its focus (the source of light) to approach the observed eye; or (2) by the opera- tor taking a nearer distance, which also brings the mirror nearer to the light and projects the focus toward the ob- served eye. If it is desired to maintain a uniform distance for the test, the light may -require to be brought in front of the observed eye, and should, in that case, be so screened by a chimney as to prevent direct light from it reaching the eye under examination. With a concave mirror of 10 inches focus, the usual form of concave mirror employed in shadow testing, with the operator at one meter from the patient, and with the light 20 inches from the mirror, the source of light is placed 20 inches forward of the mirror and therefore 20 inches from the observed eye. In these positions if the observed eye is 1 D. myopic in the hori- zontal meridian and 2 D. myopic in tlie vertical, the hori- zontal meridian will focus at the observing eye and the ver- tical at the source of light. These positions will make the 68 Re:u/ , ^/^// ^ i A nea/ L/g/if^ . ^■. ■'=^=:^::i: — :n \r~~~ — ~^ ^' ^^\^^ ^^^.^ ffca/ ^iS^\ _— — — — -r====^"^ '^^^^^^^^Tlf5) J V— ^==-^=^1?^^ ^~x3^ ^^J^eaf L/'^hf" V--^^^^^- ^|f^^^~— ^ ^ =^ c/if skj^eaf Liq/if' P/ane anf/ Concavt^ A^/rror-s, ^ banded appearance most distinct for this degree of astig- matism (1.00 D.). Whatever degree of astigmatism there may be in an eye, the imposition of spherical lenses before it does not increase or diminish the amount, so whatever the initial refraction of the eye, aside from the 1 D. of astigmatism, a spherical value may be found that will neu- ^°^iffht* °^ tralize the meridian of least refrac- tion, and that value will necessarily focalize the meridian of greatest refraction one diopter nearer the observed eye, so that the respective positions of the two anterior foci are at 40 in. and 20 in., or, one diopter apart, the former position being that of the observing eye, the latter that of the source of light. Working on the basis of the meridian of lowest refraction (i. e. the most hyperopic or the least myopic) being the first meridian neutralized, the other meridian w^U focus nearer the ob- served eye, and enough nearer to make the interval be- tween the foci the equivalent of the astigmatic value, what- ever it may be. If there is less than one diopter of astig- matism, the source of light can be moved farther from the observed eye by moving the light farther from the mirror, for the position of the true light and its focal point, the source of light, is governed by the principle of conjugate foci the same as a lens. The conjugate of the true light, for this mirror, cannot however be brought much nearer than 13 inches, or 27 inches from the observed eye for a one meter space. To bring it nearer the true light would have to be moved farther than one meter away, and a two meter distance would only bring the conjugate to about 12 inches, and that would be impracticable. The amount of astigmatism represented by the interval from 27 inches to 40 inches is 0.50 D., and that is the lowest amount of astigmatism that could be made to meet the requirements. 71 But a plane mirror would enable one to get any lower de- gree, by bringing the light nearer to it. A much higher degree of astigmatism than one diopter could be managed with the concave mirror however, by bringing the true light closer to the mirror. With the approach of the true light toward the mirror, the focus recedes toward the observed eye very * co^ave^ Mwor. rapidly. Starting from a position at 20 inches from the mirror, where it focalizes at 20 inches from the observed eye, at 16 inches the mirror would focus the light at 27 inches, or 13 inches from the observed eye. The interval between this point and the observing eye is equivalent to 2.00 D., and this would meet the requirement for that amount of astigma- tism. A position of the true light 13 inches from the mir- ror would focalize it at the observed eye, and that would be past the limit of the highest degree of astigmatism, or an infinite amount. The dioptric value of the interval grows very rapidly from a 20 in. to a 13 in. position of the light, for that represents all points from 20 in. to in front of the observed eye. For a point or position nearer than 13 in. the mirror focalizes back of the observing eye, or acts, so far as motion is concerned, precisely like a plane mirror. The movement of the light is therefore practically confined to a space extending from about 13 inches to one meter forward of the mirror. The object of moving the light nearer and farther is not to determine the dioptric value of its position, but to bring out with the strongest emphasis the banded appear- ance of the reflex, so that by it the position of the axis of a correcting cylinder is "determined ^Band**° with a greater degree of accuracy than can usually be obtained subjec- tively. Even if the light approaches that position the band 72 becomes more definite, and no great accuracy in the location of the light is needed. It is simply moved away or nearer, and stopped in the position that shows the clearest banded appearance across the pupil. Taking the meridians succes- sively, as previously described, each confirms the other, for the two bands are necessarily at right angles to each other. 73 CHAPTER IX. DIFFICULT CASES. There are several causes operating to defeat the best endeavors of the refractionist to shadow test particular cases. While a majority of people are readily and success- fully tested in this manner, an outline of the difficulties that interfere in some cases will not er people, those whose statements cannot be relied upon in a subjective examination or who are too young to answer intelligently, are most easily shad- ow tested. The reflex is vivid and its motion is readily determined. In older people there is more or less cloudi- ness and lack of brilliancy and also a small and fixed pupil- lary area. But the rule is only a general one, some old peo- ple being very easily shadow tested while some young ones are exceedingly difficult. Light complexioned people are as a rule more easily tested than dark ones, for the^ fundus partakes in color tone of the same general character as the complexion, — is light in the light people and dark in the dark ones. This is no doubt due to the saturation of pig- ment in the choroid immediately back of the retina, the darker colors more fully absorbing the light and giving a less brilliant reflex. Negroes are not easily shadow tested as a rule. Attention has been called to the tendency of the eye, under the influence of the brilliant light that is cast upon it in shadow testing, to accommodate and thus give a find- 74 ing not in accordance with the real static refraction. But an eye that does not at first give a Sensitiveness. satisfactory reflex is not therefore to be regarded as being a ''hard case,'* for the imposition of a plus lens, relaxing the accommo- dative effort, often causes the reflex to at once show up and the eye to become entirely submissive to the test, not- withstanding the fa.ct that it at first gave back no satis- factory motion. But a too brilliant light — one that daz- zles the eye — is not the best sort to employ. Cases with real photophobia, inability to submit to the test because of supersensitiveness of the retina, cannot be tested satisfac- torily by the method. The light causes a general nervous agitation that no power of the will can overcome, and a shadow test to be reliable requires, above everything else, a state of complete passivity. BINOCULAR INFLUENCE. Beside the difficulties enumerated above there is another class of complications that arises from the binocular rela- tionship of the eyes, or their habit of acting, not as single organs, but as a team working together. It is known that the two eyes under the usual circum- ^^'^^Eye^^^ stances of vision accommodate and relax together, and for equal amounts ; and furthermore it is the active eye that controls, not the passive. If the two eyes are in such a refractive condition that one is compelled to -accommodate whilq the other need not, the eye requiring to accommodate will do so and the other eye will be compelled to accommodate equally at the same time. For eyes habituated to such binocular harmony of accommodative action, Ho artificial means of putting them in a different relationship will be effective in suppressing the habit. Hence, in shadow test- ing a case, to test one eye while the other is uncovered ex- 75 poses the test to the binocular influence tending to give a false finding for the eye tested. The accommodation re- quires to be relaxed in both eyes to be relaxed in either. This danger arises in hyperopic cases only, but that in- cludes a large percentage of all cases. In isometropia (equal refractiQji or refractive error) this difficulty must be specially guarded against, for the habit of accommodative unison is strong, indissoluble. In anisometropia (unequal 'refraction or refractive error) the habit is not so indissoluble, but it metropia. Cannot be ignored in any kind of a case. In shadow testing a pair of eyes we are not of course informed to begin with in what state the eyes are in this respect. It is feasible, however, to treat them as equals until their true relationship is as- certained. This is done by imposing equal lenses before them until the motion of the shadow is reversed in both eyes. They may reverse together or one may require a higher lens than the other. By selecting the eye requiring the higher plus lens as the one first to be neutralized or reversed, leaving the other eye in the meantime in the fog; and then, with the neutralizing lens on the first eye, simi- larly neutralizing the other, gets us over this difficulty. We will find out by the test whether the eyes are equal or not, but while doing so have eliminated the binocular uni- son of accommodative action as a disturbing element in the test. In cases of astigmatism the meridian requiring the great- est amount of plus, as well as the eye requiring the great- est amount, have both to be looked to, for astigmatism is nothing more than anisometropia of different meridians of the same eye. To eliminate all Binocular tendencies to accommodation, the Seiaxatiou. ' more hyperopic meridian of each must be ' ' plussed ' * out of that tendency, not only for that 76 eye in particular but for its influence on the accommoda- tion of the other eye. The rule therefore should be "Get myopic motion in all meridians of both eyes before attempt- ing to neutralize, by reduction, the least myopic meridian of either." Having fogged both eyes under this rule, one is left so covered, the one requiring the most plus of the two, and the first meridian of the other eye is then neutral- ized by reducing the sphere. The procedure from this point has already been described under astigmatism. With the neutralizing lens for the first eye before it, the other eye is then treated in the same manner. This method is better than merely covering one of the eyes with an opaque disc while the other is being tested, for it insures the co-opera- tion of the two eyes under the test, as they have been ac- customed to co-operate. , MUSCULAR POISE. But there is still another binocular influence to be reck- oned with in shadow testing the eyes. The connection be- tween the reflexes by which the eyes accommodate and con- verge, or relax those functions together, is well understood. If there is a normal poise of the extra- *~ctret^enc"."* °<'^^^^ i»"scles, no abnormal influ- ence is exercised by them over the accommodation; but in certain muscular imbalances, par- ticularly that imbalance that is known as exophoria, the influence may be considerable., That is, exophoria, since it is a tendency of the eyes to turn outward, naturally arouses counteraction by the internal recti muscles. The tendency to diplopia that the outward turning of the eyes, or tendency so. to turn, awakens by reflex action the coun- ter stimulation of the internal muscles. As these muscles are innervated by the same pair of cranial nerves that con- trol ciliary activity, the ciliary is involved, or apt to be 77 involved, and that results in accommodation, even though there is no direct cause, aside from such influence, to pro- duce it. To relax the accommodation of an eye, it is therefore not only necessary to give that eye no cause for action, but the accommodation of the other eye must also be suppressed, and now a pair of muscles entirely outside of the eyes must be made inactive also. This influence can be overcome by excluding one of the eyes from vision — that is, by covering it with an opaque disc. But it can also be overcome, for the time being, by inserting over either eye a prism, base in, of sufficient power to relax the internal muscles, or to allow the eyes to turn outward ac- cording to their tendency without producing diplopia. Lest the complications here described- discourage the would be shadow test expert, let me say that such compli- cations are infrequent, and they are brought up here for the purpose of giving the student of shadow testing an understanding of some of the cases Special ^YiSi^ might otherwise defeat his best Metnoas. efforts, and cause him to forswear the use of the method under any and all circumstances. As to the method that has been christened by its inventor ''dy- namic skiascopy with a retino-skiameter" I would say that while I am sure that that erudite and euphonious phrase ought to be sufficient to paralyze the most obstinate ciliary spasm that ever came out of the woods, I have only been able to verify the fact that it has the effect of paralyzing the tongue of one who tries to repeat it verbatim. And as to the use of atropine, or any other drug, as an aid in determining the refractive condition of the eye, either by the shadow test or any other method, about all the impor- tance that attaches to it is that ''it is a convenient means of discovering, while the patient is alive, what kind of lenses will be adapted to his eyes after he is dead." Or, 78 e ^^^^H I ZOA 1 1 Ex centric T^effex 1 1 1 ■■ la m £:xct '/1/r/c ne^ J ex