# Popular Science Monthly/Volume 19/May 1881/Eyes and School-Books

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* EYES AND SCHOOL-BOOKS.
By Professor HERMANN COHN.
IT was formerly considered, and some recent text-books have repeated the error, that the qualities of near-sighted and long-sighted eyes were opposed. The investigations of Professor Donders, of Utrecht, have, however, shown that not only is long-sightedness not the opposite of near-sightedness, but that the two defects may be associated in the same individual. The real opposite of short-sightedness, according to Professor Donders, is over-sightedness. He distinguishes three kinds of eyes: 1. Those whose axis is of the proper length from front to rear, normal-sighted or emmetropic (ὲν μέτρω ὼψ, seeing at the right distance); 2. Those whose axis is too long, short-sighted, or myopic (from μύειν, to blink, from the habit common to near-sighted persons of partly closing the eyelids in looking at distant objects); and, 3. Those whose axis is too short, over-sighted, or hypermetropic, seeing beyond the measure. To see at a distance, the emmetrope needs no glass, the myope a concave glass, the hyperope a convex glass.
All three kinds of eyes may become far-sighted or old-sighted as their near vision becomes weaker in old age. This kind of far-sightedness is no more a disease than the turning gray of the hair; it depends upon the diminished force of the muscle that curves the crystalline lens for near vision.
​Myopy is seldom congenital. All experts remark that it is rarely found in children of less than five years of age. All agree likewise that it arises from a too steady application of the eyes to close objects, especially during the school age. The attention of the authorities in Baden was directed to this fact forty years ago, by the number of students in the gymnasia who wore spectacles. Their inquiries were followed up by Dr. Szokalsky in Paris. Professor C. von Jäger, of Vienna, in 1861, was the first person who made a systematic examination of the eyes of children in reference to this point. Out of two hundred children, he found fifty-five per cent. of those in an orphan house, and eighty per cent. of the pupils in a private school, to be short-sighted. He did not, however, consider his investigation extended enough to justify his drawing a general conclusion.
I began in 1865 to examine the school-children of my native city, and believed, after I had gone through thirty-three schools of all grades, up to the gymnasium, containing 10,060 children, that I was justified in announcing the three following laws: 1. Short-sightedness hardly exists in the village schools—the number of cases increases steadily with the increasing demands which the schools make upon the eyes, and reaches the highest point in the gymnasia; 2. The number of short-sighted scholars rises regularly from the lowest to the highest classes in all institutions; 3. The average degree of myopy increases from class to class—that is, the short-sighted become more so.
My investigations have been repeated in many cities of Europe and America, and my conclusions have been everywhere confirmed. I may cite the examinations of Dr. Thilenius at Rostock in 1868; of Dr. Schultz at Upsala in 1870; of Dr. Crismann at St. Petersburg, and Dr. Maklakoff at Moscow, in 1871; of Dr. Krüger at Frankfort, and Herr von Hoffmann at Wiesbaden, in 1873; of Dr. A. von Reuss in Vienna, Dr. Ott and Dr. Ritzmann in Shaffhausen, Dr. Burgl in Munich, and Professor Dor in Bern, in 1874; of Dr. Conrad in Königsberg in 1875, of Dr. Scheiding in Erlangen, Dr. Koppe in Dorpat, Professor Pflüger in Lucerne, and Drs. Loring and Derby in New York, in 1876; of Dr. Emmert in Bern, Drs. Kotelmann and Classen in Hamburg, Professor Becker in Heidelberg, Drs. William, Agnew, and Derby, in Cincinnati, New York, and Boston, in 1877; Dr. Niemann in Magdeburg, Dr. Seggle in Munich, Professor Dor in Lyons, Dr. Haenel in Dresden, and Dr. Reich in Tiflis, in 1878; Dr. Just in Zittau, and Dr. Florschutz in Coburg, in 1879. We have in all more than thirty accurate reports of competent oculists, giving the results of the most careful investigations among more than forty thousand scholars.
The final results of all these observations, when combined, show, that in the village schools hardly one per cent., in the elementary schools five to eleven per cent., in the girls' schools ten to twenty-four per cent., in the real schools twenty to forty per cent., and in the ​gymnasia between thirty and fifty-five per cent. of the pupils are myopic.
University students have so far been examined only in Breslau and Tübingen. I found in 1867 fifty-three per cent. among the Catholic theologues, fifty-five per cent. of the law students, fifty-six per cent. of the medical students, sixty-seven per cent. of the evangelical theologues, and sixty-eight per cent. of the students of philosophy, to be short-sighted. In July, 1880, I again examined our medical students, and found that fifty-two per cent. of those who had not passed the examen physicum, and sixty-four per cent. of the candidates who had already stood the examination, were myopic; and I am convinced that the work of preparing for the examination in this as well as in the other departments contributes to the increase of near-sightedness. Dr. Gärtner, between 1861 and 1879, examined six hundred and thirty-four students of the Evangelical Theological Seminary in Tübingen, and found that seventy-nine per cent. of them were myopic.
If we inquire into the bearing of nationality on the development of the affection, we find that in the gymnasia at Upsala thirty-seven per cent., at St. Petersburg thirty-one per cent., at Dorpat fifty-five per cent., at Lyons twenty-two per cent., at Tiflis thirty-seven per cent., at New York twenty-seven per cent., at Boston twenty-eight per cent., of the students are myopic. In the gymnasia of St. Petersburg thirty-four per cent. of the Russian, and only twenty-four per cent. of the German scholars; at Tiflis, thirty per cent. of the Russians, thirty-eight per cent. of the Armenians, and forty-five per cent. of the Georgians, were short-sighted. Of five hundred and twenty-nine teachers in Lucerne, fourteen per cent. of the Latin Swiss, twenty-four per cent. of the German Swiss, were affected. Loring and Derby observed in New York, in 1876, that fourteen per cent. of the children of Irish, twenty per cent. of American, and twenty-four per cent. of German parents, were near-sighted. At the International Congress of Physicians, held in Paris in 1867, I confidently addressed every one who wore spectacles in German, and was sure to receive a German answer. It is possible that the Germans have become more than ordinarily predisposed to short-sightedness, by the operation of compulsory education through several generations; but this can not yet be taken for granted, for relatively only a small proportion of non-German school children have been examined. The statements of all the authorities establish, however, that everywhere, and in all institutions, the number of myopes increases from class to class, and becomes really formidable in the secunda and prima of the gymnasia and real schools, and the corresponding classes of other schools. It ranges at between thirty-five and sixty per cent. of the whole number of scholars; but the proportion has been found to exceed sixty per cent. in the prima of several German gymnasia, and to rise to eighty per cent. at Erlangen, and one hundred per cent. at Heidelberg. Taking the ​average of the results of the examinations in twenty-five German and Swiss gymnasia with 9,096 scholars, the percentage of short-sighted pupils rose from the sexta to the prima as follows: 22, 27, 33, 46, 52, 53.
These numbers speak plainly enough. Still there are persons who doubt that children become short-sighted at school. In order to make this more clear, I examined the pupils of the Friedrichs Gymnasium at Breslau in 1871, and repeated the examinations upon the same persons three semesters afterward. Seventeen pupils who had been found normal-sighted at the first examination had become short-sighted, and more than half of those who had appeared near-sighted at first had become more so. Similar results have been obtained by Dr. A. von Reuss in the Leopold Stadt Gymnasium at Vienna, by Dr. Seggle in the Cadet Corps at Munich, and by Dr. Derby at Boston.
It is evident that we are threatened with a great national affliction, which is likely not only to be detrimental to all peaceful occupations, but to impair the military efficiency of our people. It is important to seek out the causes of this ever-growing evil and contest them with energy. We can not discuss here all the causes that tend to produce myopy. All protracted looking at close objects may contribute to it. Among the more active causes may be mentioned badly-constructed school-benches, imperfect lighting, too much reading, bad writing, and bad type. The matter of the style of typography which is most compatible with the preservation of the eyesight deserves especial consideration. The most important point is the size of the letters. We can not determine this by the measurement of the em, as the printers do, for that regards the shank of the type, of which readers know nothing; but it must be judged by a special measurement of the visible letter. I have adopted as the standard of measurement the letter n, that being the most regular and symmetrical in shape in both the Roman and German alphabets. I have found that the n in pearl type is about 0·75 millimetre (or about 3/100 of an inch) high, in nonpareil 1 millimetre (or about 1/25 of an inch), in brevier (petitschrift) 1-1/4 millimetre (or about 1/20 of an inch), in long primer (corpusschrift) 1-1/2 millimetre (1/17 inch), and in pica (Ciceroschrift) 1-3/4 millimetre (1/14 inch).
We have hitherto had no definite rules concerning the smallest size of letters which should be permitted for the sake of the eyes. The distance at which a letter of any particular size can be seen does not afford a guide to it, for it does not correspond at all with the distance at which matter printed in the same type can be read steadily, at the usual distance in reading. I believe that letters which are less than a millimetre and a half (1/17 inch) high, will finally prove injurious to the eye. How little attention has hitherto been paid to this important subject is exemplified in the fact that even oculistic journals and books ​frequently contain nonpareil, or letters only a millimetre (1/25 inch) high.
Many of the text-books required by the school authorities are badly printed. The officers should go through every school-book with a millimetre-rule in their hands, and throw out all in which the letters are less than a millimetre and a half high, and should give the preference to those establishments which do not use letters of less than two millimetres (1/13 inch).
The distance between the lines is an important factor in respect to ease in reading. As is well known, the compositors often insert thin leads between the lines so that the letters which project above the average height and those that fall below the line shall not touch. Every one knows that legibility is improved by contrast; the darker the print and the clearer the paper, so much easier is the reading. When the lines are close together, or the matter is printed "solid," the eyes become tired sooner, because the contrast is lessened. The lines tend to run together, and the effort to separate them strains the eyes. In fine editions the lines are widely separated. I consider a book well leaded in which the interlinear space, measured by the shorter letters, amounts to three millimetres (1/8 inch). The lines will really seem to be closer, for the projections of the longer letters will encroach upon the interlinear space; and cases may occur, when those letters predominate, in which the space may seem to be only one millimetre. The narrowest interval that should be permitted is, in my opinion, two and a half millimetres (1/10 inch).
The thickness of the strokes should also be regarded, for it is obvious that the form of the letter is more readily and more clearly impressed on the retina when the stroke is broad and distinct than when it is fine. Letters having a stroke of less than one fourth of a millimetre (1/100 of an inch), in thickness should not be admitted into school-books. Ample space should be allowed between the letters. Laboulaye recommended that every two letter should be separated by a clear space at least as broad as the distance between the two strokes of the n.
Javal believes that the extension of the lines beyond a certain limit of length contributes to myopy, by forcing the eye to endeavor to adjust itself to the varying distances from the eye of the ends and the middle of the line. This has not been demonstrated, but it is not improbable. Every near-sighted person is aware of the pain it occasions him to read a number of long lines without spectacles. The shorter the lines, the more easily they are read, because the eye does not have to make wide excursions. The most suitable length of lines for school-books appears to be about ninety millimetres, or three and a half inches.
Javal has observed that the rectangular Roman letters are liable to be reduced in apparent size, and have their corners seem rounded by ​irradiation from the white paper, and recommends a thickening of the cross-strokes at the ends to obviate this defect. This observation is less applicable to the German letters, for they already have broken lines and knobbed expansions at the ends of the strokes. Many physicians, particularly those who are not Germans, believe that the shape of the German letters is more tiresome to the eyes than that of the Roman letters. I have never been able to perceive this, nor any reason why it should be so, provided the German print is large and thick enough, and the lines are far enough apart. Use has doubtless much to do with the matter. For myself, it is always pleasant, after a long reading of the monotonous Roman print, to return to "our beloved German."
Even the thickest and largest letters, the shortest and best separated lines, and the most excellent printing, may speed the progress of myopy if the light is bad. At home, every one can find a light place to read—by the window on dark days, by a bright lamp at night. It is different in schools and offices. Fifteen years ago, after measuring the ratio of the window-space to the floor-space in the schoolhouses of Breslau, I declared that there could never be too much light in a schoolroom, and estimated that unless the house could be furnished with a glass roof, at least thirty square inches of window-space should be provided for each square foot of floor-space. In many schoolrooms as at present arranged, the pupils nearest the windows may be sitting in a glare of light, while those farthest away are not able to study for the obscurity. Notwithstanding all that has been written and all that has been done in the last fifteen years for the improvement of schoolrooms, enough is still left to be done in nearly every town.—Deutsche Rundschau.