Popular Science Monthly/Volume 12/November 1877/Effects of Study on the Eyesight
|EFFECTS OF STUDY ON THE EYESIGHT.|
A POPULAR error has long existed as to the real character of short-sightedness; and even medical men have to some extent participated in it. It is not an indication of strength of vision. It is a disease, always inconvenient, and sometimes dangerous. Its character, cause, and progress, have enlisted the earnest attention of the most eminent oculists, especially during the last decade. The movement received its first impulse from a suggestion of Prof. Donders, made in 1864. It originated, therefore, at the very fountain-head of influence and authority in ophthalmology; for Donders was one of the three men who led in what is now styled "The Great Reformation," wrought some twenty-five years ago, in the treatment of defects and diseases of the eye. To illustrate the character of this change, Dr. Agnew, of New York, in his analysis of 1,065 cases of asthenopia (weak sight), thus describes the standard treatment for this disease only thirty years ago:
The suggestion of Prof. Donders is found in his work, "Accommodation and Refraction of the Eye," and is as follows:
About two years after this, Dr. Cohn, of Breslau, published the startling result of his investigations, which had taken the form of an inquiry into the effects of study on the eyesight. Similar investigations followed in various parts of Europe.
A like movement is progressing in this country, which was initiated by Dr. Cornelius R. Agnew, of New York. Under his auspices, examinations have been made in New York, Brooklyn, and Cincinnati. Dr. Edward G. Loring, Jr., and Dr. Peter A. Callan, of New York; Dr. Lucien Howe, of Buffalo; and Dr. Hasket Derby, of Boston, have reported investigations in the same direction.
In some of these investigations the suggestion of Donders has been literally followed; while in most of them the effect of several successive examinations of "a particular category of men" has been sought to be realized by one examination of several classes of students in the various stages of advancement in study.
In the thirty-three schools of Breslau, including its university, Dr. Cohn examined 10,060 pupils of all grades, and found that 1,004 of the number, distributed among all the schools, were near-sighted; and that only twenty-eight of these had near-sighted parents. Of the children who were yet in their first half-year of school-life, only 0.4 per cent, were near-sighted. Thence, upward, through seven biennial grades, the percentage increased till it reached 63.6 per cent, of those who had been fourteen years at school. The disease was found also to be progressive in degree.
Results bearing a striking correspondence with these have since been reported by various eminent European oculists, chiefly the following: Of 4,358 examinations by Dr. Erismann, of St. Petersburg, in 1871; of 1,058 by Dr. Reusse, of Vienna, in 1872, '73, '75; of 3,036 by Dr. Conrad, of Königsberg, in 1874-'75; and of 1,846 by Dr. Pflüger, of Lucerne, in 1876.
The interest excited by these reports was not confined to European circles. But the conditions of school-life in this country were believed to be so much more favorable than in Europe, that these deplorable statistics, it was thought, could have no parallel here. Nevertheless, the examinations which have been made, as we shall show, furnish occasion for the deepest solicitude.
In New York the examinations were made by Dr. W. Cheatham; in Brooklyn, by Drs. Prout and Matthewson; and in Cincinnati, by Drs. Ayers and E. Williams. They had been furnished by Dr. Agnew with elaborate tables or forms, arranged like Cohn's, which they returned to him filled for summing up and comparison. In this he was assisted by Dr. Webster. The results are as follows:
Brooklyn Polytechnic, 300 students: Academic Department, ten per cent.; collegiate, twenty-eight per cent.Cincinnati, 630 students: district schools, ten per cent.; intermediate, four-teen per cent.; normal high, sixteen per cent.
This report was read by Dr. Webster before the Social Science Congress at Detroit in 1875, and again by Dr. Agnew at the Medical Congress in Philadelphia, September, 1876. In the report of the proceedings of the latter body, for the Medical Record, October 14th, it is stated that "the section unanimously recommended to the Congress that the paper be published, with the statistical tables in full." Nevertheless, the paper has not yet been printed; but some of its conclusions may be found in the Medical Record, January 20th.
In February last, Dr. Lucien Howe was appointed, by the Buffalo Medical Association, to examine and report upon the effects of study upon the eyes of pupils of the public schools of Buffalo. In March he reported that he had examined 1,003 scholars, of whom he found twenty per cent, to be near-sighted, and twelve per cent, over sighted; that not a single case of near-sight was found among the children six years old and under; but that at seven years of age five per cent, had acquired near-sight; at eleven there were eleven per cent.; at thirteen there were nineteen per cent.; and at eighteen twenty-six per cent. Among those who had continued in the schools beyond the age of twenty-one years, he found no less than forty-three per cent, with near-sight. He says that Dr. Agnew had sent him blanks for the name, age, sex, and height; for the exact size of desks and seats; also, for each room, the color of the walls, number of windows, and whether to the right, left, front, or rear; the number of square feet in each window, and the distance of adjoining buildings which might obstruct the light. Also, for methods of teaching by large objects, the hours of study, number of recesses, methods of heating and ventilation, and for the cubic feet of air to each individual. The greatest care was exercised to record: 1. The precise condition of the pupils' vision, whether healthy or not; and, if abnormal, to what degree. 2. The usual position of the body when studying. 3. Illumination of the school-room. 4. The relaxation given to the eye alone, or to the whole body. 5. The general hygienic surroundings of the pupil.
He then describes the process of individual examination: Haifa dozen scholars at a time were sent into a class-room, on one of the walls of which had been hung a card of letters known to oculists as "Snellen's test-types." The scholars were placed at a distance of twenty feet from these letters, and asked to read the lowest line, the letters being 8 inch Gothic. Those who can pass this test are not near-sighted. Then there is held before the eye of each a weak convex glass, such as old people are accustomed to wear. If he cannot see so well as without it, he is not far-sighted. In some cases of unusually imperfect vision, the ophthalmoscope was employed.
During the summer of 1876, Dr. E. G. Loring, Jr., of New York, assisted by Dr. R. H. Derby, examined the sight of 2,000 pupils of the Twelfth Street public school and the normal school in Sixty-sixth Street, New York. Their ages ranged from six to twenty-one years. As in the other examinations cited, myopia was found to affect a very small percentage of the pupils in their first year, and to increase yearly and largely thereafter, to the close of school life; and that the average degree of near-sight increases with the age up to twenty-seven years. His report was read before the Medical Congress in Philadelphia, in September, 1876.
In the fall of 1875, Dr. Hasket Derby, of Boston, commenced a series of examinations at Amherst College, with the purpose of noting the progress of near-sight in the same class and in the same individuals. The freshman and sophomore classes—1,880 and 1,879—were required to report to him; and twenty-seven per cent, of the former and twenty-eight per cent, of the latter were found to be near-sighted. In the fall of 1876 they were again examined, when the disease was found to have progressed in one-half the number of those previously found to be myopic. In January, 1877, he examined the eyes of 122 volunteers from the freshman class of Harvard College—a little more than half the class—of whom 29.5 per cent, were found to be near-sighted. Of these, twenty-two per cent, had supposed their sight to be normal. He describes his blank-printed forms as—
In his report to President Eliot, he urges the advantages to the student of—
His report closes with an illustration of the development of near-sight in a person born free from it, but inheriting a strong tendency to it. During nine years—from the age of ten to nineteen—suggestions several times offered with regard to rest and treatment having been unheeded, a progressive change had occurred, ranging from perfect soundness in one eye, and a very slight degree—represented by "0.75"—of near-sight in the other, to a high degree of near-sight, represented by "5.50" in each. If advice and warning are still unheeded, he thinks "an amount of structural change may be brought about incompatible with the integrity of the eye through life."
But while it appears to be conceded that near-sight is of infrequent occurrence among the illiterate classes, the question is a very natural one, "Have examinations been made, for comparison, of the eyes of any classes of young persons other than those engaged in study?" Dr. Cohn examined the eyes of many peasant-children, living in a state of comparative simplicity, and having little or no occasion to tax or strain the sight, and found that hardly two in a hundred of them were near-sighted. Examinations have been made also of the sight of young factory-operatives in large manufacturing towns in Europe, and the results exhibit a low percentage of myopia, corresponding to that of the peasant-children here cited. Dr. Howe says:
Donders remarked this difference between his private patients—representing the wealthy and cultivated class—and his hospital patients: that while over-sight was distributed between the two classes in nearly equal proportion, near-sight occurred much more frequently among his private patients.
The investigations of Dr. Peter A. Callan belong in this category, with a qualification. He examined the sight of 457 colored-school pupils, aged from five to nineteen years, of the New York public schools, Nos. 3 and 4, and he found but 2.6 per cent, of them near-sighted. This field was selected because it was thought to furnish the nearest approach to the normal eye to be found in this locality. The Southern freedmen, he thinks, would afford the best possible field for this special line of investigation. As a class, the colored people of New York, prior to this generation, had very limited educational advantages, and the occupations which tax the sight, like engraving, etc., have never been known among them. But as these 457 subjects are now receiving the best school-training that the city affords, the superior condition of their sight must be referred to their freedom from hereditary tendency to myopia. The conscientious painstaking and thoroughness of Dr. Callan's work, as exhibited in his report, are manifest and noteworthy.
The uniform drift of results in all the examinations here referred to, and relating to over 26,000 individuals, may be regarded as sufficiently establishing the following propositions:
1. That, as a rule, near-sight originates in school-life.
2. That a large percentage of the scholars are thus afflicted—the percentage progressing with the stage of advancement in study.
3. That near-sight is progressive in degree, according to the length of school-experience.
But, though the demonstration of these points is now complete, further and successive examinations will still be useful to determine the improvement consequent upon the adoption of means to that end, and to furnish a standard of comparison between different schools in respect to material or methods, or both—that is, first, in respect to arrangement of building, amount and direction of light, character and position of desks, seats, etc.; and, second, in respect to methods of teaching, especially in the earlier years, and generally to the intelligent observance and enforcement by the teachers of hygienic conditions. Dr. Howe's report is interesting in this feature, showing that "in schools where the hygienic conditions relating to the position of the pupils and the amount of light are disregarded, the proportion of near-sighted pupils grows larger; and conversely, where these relations are observed, the number diminishes;" and he gives numerical rank "from an ophthalmic point of view" to the different schools examined by him.
Here arise two questions: 1. Can near-sight be cured? 2. Can it be prevented?
All authorities agree that it is incurable, and all agree that it may be prevented.
The answer to this may be made more satisfactory if first we rapidly sketch a few well-known physiological facts, and get an understanding, approximately correct at least, of what near-sight is, and what causes it. Incidentally we shall have occasion to notice some of the methods and appliances for detecting both near-sight and over-sight.
When we see any object clearly, it is because the rays of light reflected or radiated from it enter the eye and produce a perfect picture of the object upon the retina. But the perfection of the picture depends upon the distance, size, and illumination of the object relatively to the powers and condition of the eye. The distance determines the angle at which the rays enter the eye. Whatever this angle, the rays must converge upon the retina, or the picture will be defective. This convergence it is the office of the lens to effect. From remote objects the rays are parallel, or nearly so. These, passing through the lens, are converged by it upon the retina. As the distance diminishes, rays entering the eye from any given point of the object become more and more divergent. Now, unless there be a corresponding increase in the convexity of the lens, these divergent rays will not be focalized at the same point as were the parallel rays; because, with the same power of lens, the focal distance must increase as the rays diverge; they will not, therefore, have converged when they reach the retina. A perfect picture will not be formed, and distinct vision will not be realized. But a change does take place in the lens corresponding to the change in the angle of the rays which enter the eye. As they diverge, its convexity increases. This is effected by the contraction of a muscle called, sometimes, the muscle of accommodation, which encircles the lens. Thus, the point of convergence is maintained upon the retina, in spite of the varying angle of the entering rays.
The normal location of the retina is that point at which parallel rays are converged, the lens being at rest. But if the eyeball loses its normal shape, and becomes elongated in the direction of its visual axis, the retina is thereby set back beyond the focal point. Convergence may be effected within the normal distance, but never beyond it; for, while the lens may become changed from its passive state to one of greater convexity, it cannot assume a convexity less than that of its passive state. Consequently, when the eyeball becomes elongated from front to back, the convergence will be at a point in front of instead of upon, the retina. This is near-sight, as it may he recognized by object-tests or trial-glasses. But near-sight is sometimes simulated. This is caused by a spasmodic action of the muscle of accommodation. To determine absolutely, therefore, whether or not the eyeball has taken this abnormal shape, or whether the apparent near-sight is due to this spasmodic action of the focalizing muscle, the oculist must paralyze that muscle. He does this by a simple and, in his hands, a harmless application of a weak solution of sulphate of atropia. Then the object-tests and trial-glasses will determine the question with certainty. But, if it be impracticable to apply the atropia, then the ophthalmoscope must be resorted to, as offering the nearest approach to certainty of results when the accommodating-muscle cannot be paralyzed, because its contraction is not very likely to occur under the operation of that instrument. Thus provided, the oculist proceeds to examine the interior of the eye, and, his own eye being normal, and his own accommodation relaxed, if he sees the retina of the examined eye perfectly, he pronounces the refraction to be correct; or, technically, the eye is emmetropic. But, if he finds the retina is not clearly visible, there being no opacity of the refracting media, he knows it can only be because the rays reflected from the ophthalmoscope have not converged upon it. Assuming it to be a case of anterior convergence, he interposes a concave glass, which lengthens the focus and removes the point of convergence back upon the retina. Thereupon he pronounces the eye near-sighted; or, technically, myopic, of a degree indicated by the strength of the glass.
Near-sight, then, is that condition of the eye in which the rays from distant objects reach the retina after convergence.
On the other hand, if, instead of the eyeball becoming elongated, it is flattened, then the visual axis is too short; that is, the retina is brought too near the lens, which consequently requires the contraction of the accommodating muscle to focalize the parallel rays upon the retina; whereas, had the eye been normal, the lens would have performed this function while in a state of rest, and would have required the contraction only for divergent rays.
This condition is known as over-sight, technically, hypermetropia. When it exists in a degree beyond the adjustability of the lens, it may be recognized by object-tests and trial-glasses; but in less degrees it may escape detection by these means, because of the accommodating action of the lens. As in the case of near-sight, therefore, atropia must be employed for its exact observation.
Over-sight may, then, be defined as that condition of the eye in which parallel rays, passively transmitted by the lens, reach the retina before convergence, because of the shortened axis.
While the subjects of this malformation are numerous, some investigators finding them even to exceed largely those of the opposite condition, and while the eyes so malformed are usually not diseased, as in myopia, yet numerous local and general disturbances are found to exist in very many of the cases. These are the result of over-use, or straining of the muscle of accommodation. A special interest has recently been excited in reference to them by an address of Dr. George T. Stevens, of Albany, read last December before the Albany Institute, in which the relation of cause and effect is claimed to have been established by the author, between certain visual defects, particularly over-sight, and such functional nervous affections as neuralgia, the more common forms of headache, epilepsy, St. Vitus's dance, hysteria, and insanity. About six months previously he had presented this theory to the New York Academy of Medicine, but he then limited its application to St. Vitus's dance. These views were "new and unexpected to the profession," and were controverted by Dr. Charles S. Bull, of New York, in a paper read before the New York Medical Journal Association, in April last. He reports thirty-one cases of St. Vitus's dance in his own recent practice, in which special attention was given to the discovery of any such relation as Dr. Stevens affirms to exist. Fifteen of the thirty-one had correct and sixteen had defective vision (over-sight). Of the latter only five could be induced to purchase and wear the necessary correcting glasses. But in these five cases there should have been some improvement, at least, in the nervous symptoms consequent upon their wearing the glasses; this being, by the admission of Dr. Stevens himself, "the crucial test" of the correctness of his theory. Yet no such result was observed. Nevertheless, in his later essay, he insists that "correction of the eyes of the patients does relieve their nervous symptoms. . . . This is no place," he says, before the Albany Institute, "to relate cures in medical practice; but, after a sufficiently extended and careful series of observations, continued during more than four years, I can safely prophesy that this principle will be found of more universal application, and more successful in its workings, than any which has been advanced for the mitigation of this class of affections."
The distressing confusion and disappointment resulting from the unbalanced action, in the over-sighted eye, between the arrangement for adjusting the lens and that for converging the eyeballs, is very clearly explained by Dr. Stevens in the same paper. Referring to its effect upon school-children he says:
Resuming now the consideration of near-sight, we proceed to suggest some of its principal causes, as follows:
1. Too early use by school-children of books, slates, and writing-paper, or copy-books, when blackboards and models would be better. Type and script letters and figures, and their primary combinations, at least, should never be taught from books, but from large and perfectly-formed models, printed on cards and hung on the wall. When the eye and the memory are sufficiently trained to easily recognize and name each letter and figure at sight, and when some knowledge has been gained of the power of letters and figures in combination, then the same forms in books will be at once familiar as old acquaintances, and may be studied without straining the sight. To train the hand without straining the sight presents a greater practical difficulty. In the large schools, of course, all the children cannot go to the black-board. But a considerable practice in drawing large lines and simple objects on good-sized slates, in a sort of free-hand style, should precede the formation of letters and figures; and, when these are begun, they should be made of generous size. A correct position, meanwhile, should be an imperative requirement; and, until it becomes habitual and easy, good work should be held to be of secondary importance. Hard slate-pencils and greasy slate-surfaces should not be permitted; both should be subject to systematic inspection.
2. Ignorance or laxity on the part of parents and primary teachers, in permitting faulty positions of the head, body, and book, during reading, study, and writing; and in not seeking early to secure the intelligent coöperation of the pupil by simple and appropriate physiological instruction.
3. A prolonged and steady looking at an object or at objects near the eye, though at proper distance, without rest or frequent change of the visual focus, as in long and absorbed novel-reading, intense study, or persistent diligence in needlework.
4. The practice of reading or otherwise using the sight at too short range. This results in part from insufficient light; or from its faulty direction, so that the hand or body throws a shadow on the page; or so that the direct rays fall upon the eye, causing undue contraction of the pupil, while the page is in shadow. It results also from improperly graded desks, from small and poor type and inferior printing-ink, and from faulty color and quality of printing-paper; also from pale writing-ink—pale when used—and from the substitution of the lead-pencil for the pen, especially in the evening.
5. A prone or forward position of the head too long maintained, or frequently repeated, and becoming a habit. This results from reading or studying with the book in the lap, and from the use of desks not graded to the height of the pupil. Dr. Howe reports pupils varying eighteen inches in height seated at the same grade of desks. The distance of the eye from the page should not be less than twelve nor more than eighteen inches. Having the desks set too far from the seats also induces this faulty position. The front of the desk should overlap the seat one or two inches.
Donders says, "In the hygiene of myopia the very first point is to guard against working in a stooping position." He favors high, sloping desks, and indicates "rectilinear drawing on a flat surface" as a class of work which is especially objectionable.
6. Since a vitiated atmosphere is a frequent feature of the school-room, it may not be amiss to add here that the effect of bad air is indirectly to injure, if not to destroy, the sight.
7. Allowing a sun-glare on the page while reading; also transitions from cloud-shadow to sunshine.
8. Reading and studying in railroad-cars is known to be a fruitful source of injury.
9. But insufficient light, perhaps more than any other cause, produces disease of the eye and derangement of the vision. This is not confined to the schools. Sadly frequent as it is found to be there, it is believed to be yet oftener illustrated at home, both by daylight and in the evening, in preparation for the school and otherwise. Artificial illumination is faulty at best, but, even in the most favored homes, the elder group is apt to monopolize the shaded drop-light or student-lamp, while the schoolboy with his text-books is found somewhere in the outer circle.
Twilight-reading is much practised, and is especially pernicious—that is, prolonging the study or reading after daylight has begun to decline. The change is so stealthy that, when the interest is excited, and the mind absorbed, the growing darkness is unheeded or unobserved, till serious mischief is done.
A curious and interesting case of injury to the sight by study is that of Prof. John Nott, late of Union College, Schenectady. Over thirty years ago his sight was permanently destroyed for all literary purposes, "by attempting," as he says in a recent letter to the writer of this, "too much study without thought of the necessity of care for the eyes." How many are following after him! In the same letter he thus describes his case as diagnosed by Dr. Alexander, of London, who alone of all whom he consulted was able to afford him even temporary and partial relief: "Thirty-six very small glands in the eyelids make oil for the eye, the same as oil for your lamp. When these glands become dry, reading is impossible, although in other respects the eye may be perfect. This was my disease—no oil was supplied to the eye." He makes or implies this noteworthy suggestion, which is hereby commended to authors, publishers, and school-boards: that a brief and appropriate caution be conspicuously printed or pasted in the front of every school and college text-book, by authority of commissioners, superintendent, trustees, or faculty. Something like the following would perhaps realize his idea:
Caution.—Reader, your eyesight is worth more to you than any information you are likely to gain from this book, however valuable that may be. You are therefore earnestly cautioned—
1. To be sure that you have sufficient light, and that your position be such that you not only avoid the direct rays upon your eyes, but that you also avoid the angle of reflection. In writing, the light should be received over the left shoulder.
2. That you avoid a stooping position and a forward inclination of the head. Hold the book up. Sit erect also when you write.
3. That at brief intervals you rest the eyes by looking off and away from the book for a few moments.
And you are further cautioned to avoid as much as possible books and papers printed in small type, and especially such as are poorly printed; also to avoid straining or overtaxing the sight in any way.
Boys may need to be reminded of the great importance of thoroughly cleansing the eyes with soft, pure water both morning and evening.
To many readers it would no doubt be interesting to consider how each of the practices and conditions we have pointed out as producing near-sight tends to effect the elongation of the visual axis. But while there might be no disagreement among oculists as to the fact that the practices and conditions named do thus tend, there may not be a consonance so general as to the precise process in every case A few general suggestions, however, are submitted:
1. The rationale of the effect of the premature use of books, etc., during the more plastic condition of the eye is sufficiently obvious.
2. A prolonged tension of the sight lessens the muscular elasticity.
3. The contraction and consequent thickening of the muscles which pull the two eyes inward, so as to focalize the sight upon a near object, causes a side-pressure, and a corresponding transverse or length-wise protrusion. The nearer the object, the stronger must be this action of the muscles, and the more marked the effect.
4. The prone position of the head causes the blood to settle in the eyeballs, increasing the tension of the fluids, exciting inflammation and consequent softening of the coatings, and resulting in permanent distention.
The attentive reader cannot have failed to observe that we have enumerated causes of injury to the eyes from study, other than those which produce near-sight. Of these, only one seems to require reference—the effect of bad air in the school-room.
Dr. Loring read a paper in February last before the Medico-Legal Society of New York, answering four questions relating to the care of the eyesight, which had been submitted to him by that Society. The first of the series inquires the effect of bad air on the sight. His reply, given at some length, supports the statement herein made.
In a recent conversation with the writer, Dr. Loring advocated examinations of the sight of all children when they first enter school, and at such subsequent stages of their education as might seem desirable. The position of a child's seat relatively to the blackboard, etc., would often be governed by such an examination. He thought, too, that glasses would be recommended in some cases by the examining oculist—a permanent official he would have him to be—and that, if necessary, they should be furnished at the public expense, or out of some special fund; the glasses to be worn during school-hours at least, if not continuously. He related the circumstance of a lad having been recently brought to him by his father from the West. An examination verified the boy's statement that he could see to read usually very well; but that sometimes, in a moment, his sight would be so affected that reading became impossible. This had led to his repeated punishment at school, his averment of inability not being credited by his teacher.
- The circumstance that one of the children of the writer is temporarily withdrawn from school because of injury to his sight contracted in study, has led him to look into this subject, and this paper is the result. The startling extent, the rapid increase, and the serious character, of these visual defects in our schools, and the fact that the greater part of them originated there, and might have been prevented, should awaken universal interest, that the proper remedies may be applied to arrest the evil as speedily and effectually as possible.
The writer having submitted this paper to Dr. David Webster, of this city, takes this occasion to acknowledge, with great pleasure, his obligation to him for important suggestions.
- These are approximate tests.
- Boston Medical and Surgical Journal, March 22, 1877.
- Though this is frequently done with individual patients, yet schools have generally objected to it. Dr. Cohn enjoyed an exceptional opportunity to examine the eyes of 240 scholars after the application of sulphate of atropia. Dr. Callan's colored subjects, he relates, refused to permit this application. Therefore, wishing "to place the results of his examination beyond dispute" in point of accuracy, he adopted the alternative course, and "kept both of his own eyes under the influence of a four-grain solution of sulphate of atropia, applied three times daily during a period of five weeks, so that the accommodation was completely paralyzed for that length of time." Sometimes the examining oculist has acquired the power to perfectly relax his accommodation at will. But the relaxation of the accommodation of the subject, as well as that of the examiner, is essential to entire accuracy.
- A small mirror with a hole in the centre. The mirror is held close to the patient's eye, so as to reflect into it the light of a gas-jet back of him. The oculist then places his eye close to the hole, and looks into the illuminated interior of the eyeball.
- This is not a disease, like near-sight, but a condition; and it is not acquired, but is congenital, always. It is also called far-sight and long-sight; but it is thus liable to be confused with an acquired condition producing a similar result, as in the sight of old people which is not a flattening of the eyeball itself, nor of the cornea and the lens, but it is an impairment of the power of accommodation due to the hardening of the lens, which usually occurs at about the age of forty-five years, and is often called old sight, but is technically known as presbyopia.
- See "A Preliminary Analysis of 1,060 Cases of Asthenopia occurring in the Practice of C. R. Agnew, M.D.," which shows hypermetropia 359 to myopia 121, or nearly three to one.
- New York Medical Journal for June.
- Medical Record, June 2d.
- "Accommodation and Refraction," p. 419.
- Medical Record, April 14th.