The refraction of the eye; including a complete treatise on opthalmometry; a clinical text-book for students and practitioners

Front matter

LIBRARY

OF THE

UNIVERSITY OfS/V^nik

Preface

Sixce the introduction of the perfected ophthalmometer into ophthalmic practice, rapid strides forward in the art of the refraction of the eye have been made. With its aid, the practice of fitting glasses quickly and accurately and, as a rule, without the aid of any mydriatic whatever has been attained. It is to the end of demonstrating the clinical and practical use of the ophthalmometer, and of recording the advances made in the science and practice of the Refraction of the Eye, that this book has been written. Some half dozen books on Ophthalmoscopy and Retinoscopy have been written, and the time is opportune for one on Ophthalmometry. We have one such book in French, Javal's Memoires d' Ophtalmometrie, but none in English.

While the present book is intended more especially for beginners, and for those who have not had the advantage of personal instruction in the use of the ophthalmometer, it is hoped that its clinical details will interest those in active practice, and who are well versed in the use of the instrument of which it treats. I am especially desirous that it shall be read by a certain rather considerable number of oculists who have the ophthalmometer in their offices, but who, from the want of a proper understanding of it, through faulty instruction or a lack of personal instruction, do not use it ; or, if they do know how to use it, do not take into consideration the limitations of the instrument, and abandon it on that account. Through the citation of a great number of clinical cases, together with numerous diagrams illustrating them, I have

PREFACE

Since the introduction of the perfected ophthalmometer into ophthalmic practice, rapid strides forward in the art of the refraction of the eye have been made. With its aid, the practice of fitting glasses quickly and accurately and, as a rule, without the aid of any mydriatic whatever has been attained. It is to the end of demonstrating the clinical and practical use of the ophthalmometer, and of recording the advances made in the science and practice of the Refraction of the Eye, that this book has been written. Some half dozen books on Ophthalmoscopy and Retinoscopy have been written, and the time is opportune for one on Ophthalmometry. We have one such book in French, Javal's Memoires cT Ophtalmometrie, but none in English.

While the present book is intended more especially for beginners, and for those who have not had the advantage of personal instruction in the use of the ophthalmometer, it is hoped that its clinical details will interest those in active practice, and who are well versed in the use of the instrument of which it treats. I am especially desirous that it shall be read by a certain rather considerable number of oculists who have the ophthalmometer in their offices, but who, from the want of a proper understanding of it, through faulty instruction or a lack of personal instruction, do not use it ; or, if they do know how to use it, do not take into consideration the limitations of the instrument, and abandon it on that account. Through the citation of a great number of clinical cases, together with numerous diagrams illustrating them, I have viii PREFACE

tried to show the virtues of the ophthalmometer, while I have not omitted to note its limitations. In that way, I have hoped to present the instrument in the true light and to justify the claims made for it.

In composing the book, I have departed from the beaten path, and have devoted the greater part of it to the report in detail of clinical cases illustrating practical points in the use of the ophthalmometer. In other words, instead of a theoretical and didactical discourse, I place a sufficient number of cases themselves (one hundred and fifty in all) before the eye of the reader, which are reported in full, so as to be easily understood. To be more explicit still, I may say I have made my teaching correspond, so far as it is possible in a book, to the instruction that we give at the Post-Graduate Medical School, where the instruction is entirely clinical.

I have given an Index of Cases at the close of the book, so that the reader who has a case that he does not fully understand, may turn to this index and look for cases in it similar to his, and then refer to the full report in the body of the book. By comparison he may get a solution of the case that is puzzling him. I have done this in order that the student may not be " lost with a case," as is too often true when he refers to the larger text-books wherein no such index is given. It has been my experience that more can be taught the student by one concrete case illustrating a point in question, than by many pages of abstract deduction concerning cases which have never been presented to the student himself.

After giving a brief description of the instrument and the rules for its use, with some general considerations, I have treated successively, in separate chapters, of its practical use in cases of Simple Hypermetropia and Hypermetropic Astigmatism, Compound Hypermetropic Astigmatism, Simple Myopia and Myopic Astigmatism, Compound Myopic Astigmatism, and Mixed Astigmatism, giving many cases and using diagrams to show the

PREFACE ix

point of focus of the principal meridians, so that the merest tyro must understand them. Incidentally throughout the book, I have endeavored to show the utter uselessness of a mydriatic in fitting glasses in the vast majority of cases, even in young subjects. If the Ophthalmometer is correctly used and a good routine method followed in putting the glasses in the trial frames in the subjective test, as here suggested and fully explained, the use of a mydriatic is, with rare exceptions, never necessary in order to give the right glasses.

I desire to express my sincere thanks to Professor St. John Roosa for his kindness in looking over the manuscript, and for many valuable suggestions both as to the matter and the form of the composition.

Mr. Fred Stuart has given me much assistance in proofreading, which I here acknowledge with thanks.

Mr. Norman P. Findley has made the original drawings for the book. For the cuts of instruments I am indebted to Mr. E. B. Meyrowitz and the publishers of the book.

A. EDWARD DAVIS..

New York, December, 1899.

PAGR

Chapter II

Principle of the Application of the Ophthalmometer in measuring Astigmatism — Rules for its Use — Astigmatism "with the Rule"

— Astigmatism " against the Rule" — Why the Mires overlap in Astigmatism with the Rule and separate in Astigmatism against the Rule — Why we deduct half a Diopter from the Reading of the Instrument in Astigmatism with the Rule and add a half Diopter to the Reading when it is against the Rule — Rule of Procedure when the Main Meridians are at 45° and 135° — Principle of the Application of the Ophthalmometer .... 13

Chapter III

General Considerations in the Use of the Ophthalmometer — Simple Hypermetropic Astigmatism — Simple Hypermetropia — Illustrative Cases 36

CHAPTER IV Compound Hypermetropic Astigmatism — Illustrative Cases — Spasm

of Accommodation 80

CHAPTER V Simple Myopic Astigmatism — Myopia — Spasmodic or False Myopia

— Rule for prescribing Near or Reading Glasses in High Degrees of Myopia — Presbyopia and the Transposition of Glasses from Distance to Reading in Myopes when it is Present . . . 122 xii CONTEXTS

Chapter XI

Exceptional Cases — Variations in the Amount and Axis of the Astigmatism as shown by the Ophthalmometer and as Indicated by the Glasses Accepted by the Patient — Illustrative Cases . . . 348

Improvements on the Javal-Schiotz Ophthalmometer: (a) Davis's Double-movable Mires ; (b) Valk's Gear-wheel Attachment : (c) Skeel's Perpendicular Lever Adjustment ; (d) Metal Base and other Minor Improvements — Reid's Ophthalmometer, a Description of it and how to use the Instrument — Other Ophthalmometers ... 383

Chapter I History Of The Ophthalmometer — Description Of The

INSTRUMENT

History of the ophthalmometer. — The ophthalmometer is an instrument designed to measure the radius of curvature of the cornea in its various meridians. By its use the presence or absence of corneal astigmatism is ascertained ; if present, it gives the amount and the axis of the astigmatism.

The instrument was invented by Helmholtz who, as early as 1854:, published a description of it together with his conclusions as to the exact form of the cornea, as measured by the instrument.1 Although very accurate in its measurements, the instrument, as constructed by Helmholtz, was not a practical one. In order to use it the patient was placed six feet in front of it, and from fifteen to twenty readings made ; then, before the astigmatism was ascertained, mathematical calculations had to be made. As such, it was used in the laboratories of only a few men and for strictly scientific purposes.

It was not until 1880, when Javal and Schiotz made alterations and improvements in the instrument, that it became practical for office use, and it was not until 1889 that they perfected the instrument into its present model. As now constructed, it has about reached the limit of improvement, except as to minor details ; consequently the purchaser is safe in buying it and with the assurance that it will not soon be a back number.

Dr. Swan M. Burnett, of Washington, was the first Ameri-

can to use the Javal ophthalmometer. As early as 1885 he published a paper in the Archives of Ophthalmology, Vol. XIV,

Fig. 1. — The ophthalmometer complete.

under the title of " Ophthalmometry with the Ophthalmometer of Javal and Schiotz, with an Account of a Case of Keratoco-

DESCRIPTION OF THE OPHTHALMOMETER 3

nus." Dr. Henry D. Noyes, of New York, began using the instrument about the same time. Both of these instruments were old models. In 1887, Dr. Burnett gave a description of the old model instrument in his Treatise on Astigmatism ; and in the same year, 1887, in the Reference Hand Book of the Medical Sciences, Dr. John Green, of St. Louis, gave a description of the instrument with a cut. The instrument remained comparatively unknown, however, in this country until 1889.

When the new or " 1889 model " came out it found among its advocates, among others, Dr. D. B. St. John Roosa, of New York, who by his earnest and persistent advocacy of the instrument, especially in the class-room and in the hospital, where practical demonstrations of its use and value were given, did much to bring it into general favor. Other writers in America who have helped to bring the ophthalmometer into esteem are : Speakman, Roller, Ring, Weiland, Van Fleet, Wurdeman, Swasey, Woodward, Valk, De Schweinitz, Norris, myself, and others.

Construction of the instrument. — To be able to use the ophthalmometer well the oculist should at least be somewhat familiar with its construction.

The instrument is composed of the following parts : —

1. A telescope on an upright, supported by a tripod.

2. A graduated arc, which is the quarter of a circle and attached to the telescope at right angles to it.

3. Two mires or reflectors which are attached to the graduated arc.

4. A large steel disk (Placido's) attached to the telescope, just back of the graduated arc.

5. The planchette or base for the instrument to rest on. The telescope. — The telescope is made of brass and has a

fixed length. It contains : (a) an ocular or eye-piece (0, Fig. 2, A) of .7 inch focus or 56 diopter power ; (5) double objectives (L and L', Fig. 2, A) of 11.2 inch focus each, or about 4 diopter power ; (c) a cross-thread to show when the eye-piece and objectives are in adjustment ; (d) and a double refracting Wallaston prism (W, Fig. 2, A).

(a) The eye-piece can be made to approach or to recede from the objectives by means of a small pin which is fixed on the side of the brass ring that holds the eye-piece, sliding in an oblique groove in the side of the telescope. When the cross-threads in the barrel of the telescope are brought into view by this means, it shows that the eye-piece is in proper focus with the

Fig. 2.

A, showing vertical sections of the telescope and its component parts. B, horizontal section of the telescope.

proximal objective (Z', Fig. 2, A) ; and when the distal objective (Z, Fig. 2 A^) is brought into exact focus with the eye observed, a perfect image of the mires is possible. If the observer is myopic, he has to push the eye-piece inward or to the right to get the cross-threads in focus ; if he is hypermetropic, the eye-piece has to be pulled outward or to the left to properly focus them. The eye-piece should always be properly adjusted for the cross-threads before focussing the instrument on the observed eye. The imported instruments, made by Goubeaux, of Paris, have graduations along the oblique slit in which the pin on the eye-piece slides. These graduations are so placed that

DESCRIPTION OF THE OPHTHALMOMETER 5

each corresponds to a displacement of the eye-piece to the extent of 1 mm., each millimeter of displacement corresponding to a change in the observer's eye of 3 diopters. For example, when the pin on the eye-piece stands at zero an emmetropic observer should see the cross-threads in the telescope plainly, while a myope of 3 diopters would have to turn the pin one graduation to the right, and a hypermetrope of 3 diopters would have to turn the pin one graduation to the left in order to see the cross-threads distinctly.

(5) The two objectives are exactly alike. Each has a diameter of 40 mm., or 1.6 inches, and a focal distance of 280 mm., or 11.2 inches. They are the most perfect lenses made, being both achromatic and aplanatic.

They are so placed in the barrel of the telescope that the crown of one is turned toward the observed eye, and the crown of the other toward the observer. By this means the flints of the two objectives are kept opposed and next to the bi-refracting prism.

(e) The cross-threads are two very fine wires stretched at right angles to each other across the barrel of the telescope about 1 inch in front of the eye-piece and about 11.2 inches behind the first objective, 27. They are there simply to show when the eye-piece is in proper focus with the objectives.

(d) TJie bi-refracting prism (Wallaston) placed between the two objectives is in fact two prisms, placed apex to base and base to apex. In this country, at least in the instruments manufactured by Meyrowitz and Georgen, these prisms are made from the best mountain crystal quartz. They possess the power of doubling objects, that is, are bi-refractive, if ground in a certain direction with regard to the axis of the quartz. The amount of the deviation or doubling produced by each prism depends on the angle at which it is ground.

One of the prisms is ground diagonally with the grain of the quartz (a, Fig.. 3), while the other is ground at right angles

Fig. :'». — The bi-reto it (a\ Fig. 3) ; see cut, looking down on them from above as they are placed in the telescope of the instrument. Thus placed, their axes are at right angles to each other and at the same time transverse to the axis of the telescope. Each prism when ground at a certain angle causes a definite amount of deviation; and by using two prisms, apex to base and base to apex, the deviation takes place from each side, thus getting twofold the deviation that would be caused by one prism and at the same time keeping the doubled images nearer the center of the field. Furthermore, these prisms are placed in the tractive prism telescope with their plane of doubling in ex-

as placed in the . . . , , , r -. , ,

telescope. ac^ ^ine Wlth the plane ot the graduated arc,

which latter is fixed to the telescope of the

instrument at right angles to it by two screws in a brass

collar.

It is very important, therefore, that these two screws should not be meddled with; for, if moved in the least, the arc and the plane of the prism is altered, and the instrument cannot be used again until readjusted by an expert.

The prisms in Javal's instrument produce a deviation of 2.95 mm. when the instrument is focussed on an object at double the focal distance of the objective, or 460 mm. When, therefore, the instrument is properly focussed on the cornea, the latter is doubled by the prism, and each point of the image reflected from the cornea is displaced to the extent of 2.95 mm. Consequently, if the image of the object reflected from the cornea happened to be just 2.95 mm. in length, the deviation of 2.95 mm. caused by the prism would allow the edges of the doubled image to just touch, as in Fig. 4.

Say the image of the arrow 1-2 is just 2.95 mm. in length, and by the deviation caused by the prism each of its points are displaced correspondingly the distance of 2,95 mm. ; then the

DESCRIPTION OF THE OPHTHALMOMETER 7

tail of the secondary image, l'-2', will just touch the head of the primary image, 1-2.

In this way we are enabled to measure the size of the corneal image by the amount of displacement it is necessary to

1 2 1 2

Fig. 4. — Showing the extent of displacement in the Javal-Schiotz instrument.

give to each point of the image in order to have the edges of the doubled images just touch.

Instead of an arrow, Javal takes for his object the distance between the inner edges of two mires or reflectors, 1 and 2, Fig. 7. Here, as in the case of the arrow, the prism, from its fixed position in the telescope, causes a deviation of 2.95 mm. Consequently, if the two mires are so arranged on the arc of the instrument that, by this deviation of 2.95 mm., the inner edges of the images of the two mires are just touching, it is quite plain that the diameter of this image must be just 2.95 mm. Furthermore, it is equally plain that the distance between the inner edges of the two mires, in this instance, is equal to the size of the object, in fact, is the object which gives a reflected image 2.95 mm. in diameter.

The bi-refracting prism in the Javal-Schiotz instrument causes a fixed deviation of 2.95 mm.,1 the arc on Avhich the mires move has graduations to show the distance apart of the two mires, and thereby the size of the object; and twice the focal distance of the objective determines the distance of the object from the cornea. With these three points known it is easy to find the fourth, the radius of curvature of the cornea

1 An extra tube with a prism causing less deviation and therefore a smaller image is furnished with the instrument which is of use in cases of marked variation from the average radius of curvature of the cornea.

in its various meridians, and thereby ascertain the presence or absence of astigmatism — the object of the ophthalmometer.

The graduated arc is an arc with a radius of its inner edge of 290 mm. When focussed on the observed eye it is concentric with the cornea. The posterior edge of the arc is graduated into equal spaces and numbered, the numbering beginning at the center and extending in each direction to 40 spaces. Each one of the divisions on the posterior edge of the arc, taken in connection with the doubling of the image by the prism, stands for a diopter mark. For example, if, with an eye under observation and the arc in the horizontal meridian, the images of the mires just touch when the mires on each side of the arc stand at the 20 mark, it shows that the refractive power of the horizontal meridian of the cornea is 40 diopters. If now we turn the arc to the vertical meridian of the cornea and the images of the mires overlap, say three steps, it shows 3 diopters of astigmatism, which may be verified by the graduations on the posterior edge of the arc in the following way. While still looking at the images through the telescope as they appear overlapped there, move the graduated mire outward along the arc till the images are left just touching again. Then by looking at the posterior edge of the arc we will find that the graduated mire has moved the distance of just three graduations ; thus verifying the amount of astigmatism present and at the same time showing the vertical meridian of the cornea to have a refractive power of 43 diopters.

On the right side of the arc on its inner edge are some fine graduations and some figures. On the instrument with the single movable mire these figures go from 6 mm. to 10 mm. ; on the instruments with double movable mires (improved) from 5 mm. to 13 mm. By noting the position of the graduated mire on the right side of the arc in relation to these graduations when the images of the two reflectors just touch, in any meridian whatever, the number corresponding

DESCRIPTION OF THE OPHTHALMOMETER 9

indicates the radius of curvature of the cornea in that particular meridian in millimeters. These figures are very important, therefore, and should be noted carefully, for by them we are able to register the radius of curvature of the cornea in millimeters in its various meridians.

Two mires or reflectors are attached to the arc. One of them is a parallelogram, 60 mm. long by 30 mm. wide, and, in the unimproved instrument, is fixed at 20 on the left-hand side of the arc. The other is a graduated mire, each graduation or step is 10 mm. long by 5 mm. broad, and counts as 1 diopter. There are eight of these steps.

Dividing the mires into halves are two narrow black lines,

called guide-lines. The lines are parallel with the planes of

the arc. They serve to show when the arc is in one of the

chief meridians of curvature of the cornea, that is, when it

is in the meridian of longest radius of curvature, or in the

meridian of the shortest radius of curvature.

They do this by showing perfectly straight and

opposite each other when the arc is turned to

either of the chief meridians of curvature (see

v m Fig. 5.

Fig. 5), but run obliquely toward each other in

all other meridians (see Fig. 6). Of course where there is no

corneal astigmatism, the cornea being uniformly and evenly

curved, they will remain straight and opposite

each other in all meridians. As we have to find

one of the chief meridians of the cornea, that

is, get the "primary position" or starting point

in measuring corneal astigmatism, these lines are

of much importance. A small pointer or indicator is attached

to the outer side of each mire, which points to figures on the

periphery of a large disk, where the axis of the meridian is

marked in degrees of a circle. These short indicators on the

reflectors serve as a check to a long indicator which is attached

to the middle of the graduated arc and at right angles to it.

Fig. 6.

This long indicator shows the direction the arc is in when the long black lines dividing the reflectors become straight with each other. For example, say the black lines dividing the mires become straight when the arc is in the horizontal meridian of a cornea having astigmatism with the rule. The long indicator, since it is at right angles to the arc, will be pointing directly downward (directly upward, however, as seen in the telescope, because the image is an inverted one) to 0°, which is the same as regards axis as 180°, for 180° just completes the half of a circle.

It will be noticed that 0° or 180° is marked on the big disk directly above and directly below, and does not occupy the horizontal meridian, as is usually the case. This is due to the fact that the long indicator is at right angles to the arc whose direction it indicates. Therefore, when the arc is really in the horizontal meridian (0° or 180°) the long indicator is in the vertical meridian, consequently the 0° has to be put there. This explains why 0° is marked in the vertical meridian and 90° in the horizontal meridian on the disk.

When the long indicator points to 0° the short indicator should point exactly to 90° ; in this way the latter serves as a check to the long indicator, as above stated.

The disk (Placido's) is a large circular sheet of steel 640 mm. (25.6 inches) in diameter attached to the telescope at right angles to it and just back of the graduated arc. Upon this disk are concentric white circles on a black background, also radiating lines extending from its center. The concentric white circles are five degrees apart, numbering from the center to the periphery a distance of 45°. They are constructed on the law of tangents, that is, the radius of each circle represents the tangent of an arc drawn from the center of the graduated arc.

The circles marked 15° and 30° are broader than the others, and on the 30° circle beginning above, the radiating lines from

DESCRIPTION OF THE OPHTHALMOMETER H

the center of the disk are numbered in the degrees of a circle from 0° to 360° — a complete circle (see Fig. 1). By numbering both the concentric circles and the radiating lines in this manner, this disk can be used as a perimeter ; for the same reason it can be used to make observations on the cornea outside of the visual line/

At the periphery of the disk, between the 40° and the 45° circles, is a large white border. On this white border are large inverted figures 15° apart. Instead of numbering from 0° to 360°, as did the small figures on the 30° circle, they stop at 180°, then begin again and number up to 180° or 0°, where they first began (see Fig. 1). These figures appear upright or straight when viewed as a reflected image from the cornea, for this image is inverted.

On the right side of the disk in the horizontal meridian the numbers 3 mm., 4 mm., and 5 mm. appear. These are meant to aid in measuring the diameter of the pupil. In order to do so, however, an extra strong objective has to be put in the telescope, and an extra brilliant illumination obtained. If the pupil seems to extend out to the circle marked 3 mm., it is 3 "mm. wide, etc.

On the opposite side of the disk are seen the figures 35, 40, 45, and 50. When viewed in the corneal image, if any one of these circles so numbered become tangent to itself (through the doubling caused by the prism), the figures denote the power of refraction, or dioptric power, of the cornea in that meridian. For example, say the circle marked 40 becomes tangent to itself — thus 00 — in the horizontal meridian ; the refractive power of the cornea in that meridian would be 40 diopters.

The reason that the numbering at the periphery of the disk begins at 0° and goes to 180°, then repeats itself from 0° to 180° again instead of completing the circle of 360° (as in the 30° circle in small figures), is that both ends of any corneal meridian under measurement may be indicated by the same number on each side of the disk. For this reason each mire has a short pointer on it. These pointers not only point to the same number of degrees on each side of the disk, but serve as a check at the same time on the long pointer or indicator. For example, when the short pointers each point to 0°, the long pointer should be exactly at 90°, at right angles. Again, by means of these short pointers and the double numbers on the disk, the angles of the chief meridians can be seen at once from the reflected image. This is one strong reason why this big disk should not be removed from the instrument and replaced by a smaller black velvet disk and upright numbering on a small medal disk facing the observer, as is now sometimes done by some Americans.

For a description of the improvements made on the Javal- Schiotz instrument and modifications of it, and for descriptions of other ophthalmometers, see Appendix.

Chapter II

PRINCIPLE OF THE APPLICATION OF THE OPHTHALMOMETER IN MEASURING ASTIGMATISM — RULES FOR ITS USE — ASTIGMA- TISM "WITH THE RULE"— ASTIGMATISM "AGAINST THE RULE" — WHY THE MIRES OVERLAP IN ASTIGMATISM WITH THE RULE AND SEPARATE IN ASTIGMATISM AGAINST THE RULE — WHY WE DEDUCT HALF A DIOPTER FROM THE READ- ING OF THE INSTRUMENT IN ASTIGMATISM WITH THE RULE, AND ADD A HALF DIOPTER TO THE READING WHEN IT IS AGAINST THE RULE — RULE OF PROCEDURE WHEN THE MAIN MERIDIANS ARE AT 45° AND 135° — PRINCIPLE OF THE APPLI- CATION OF THE OPHTHALMOMETER

The principle on which the ophthalmometer acts in measuring the radius of curvature of the cornea in its various meridians, and thereby marking the corneal astigmatism, consists simply in the measurement of the size of a small image reflected on the cornea.