( Originally Published 1899 )
WE are now to study the king of all the senses —the sense of sight. It, like sound, is not a contact sense. Rays of light are transmitted through space by an intangible medium called ether. So faithfully does it do its duty that the eye is thus permitted to see objects lying hundreds of millions of miles away, a distance so great that no one can form any adequate conception of it. While the telephone transmits the human voice so that it can be heard a thousand miles away, the telescope extends the power of the eye so that a vast multitude of heavenly bodies are brought to view which otherwise would not have been known to exist. The wonderful resources of this sense and its vital importance in every moment of our waking hours give it the high place above assigned.
In structure its mechanism is not so difficult to understand as that of the ear, though the rods and cones underneath the retina perplex the student somewhat. At birth the eyes of some children are more fully developed than those of others, though it is probable that none of them at first have more than the faintest sensation of light. In a few days they begin to notice any bright light, as that of a lamp, but the most painstaking investigators incline to the belief that there is very little discrimination among objects for a fortnight, and then only among those of bright colors.
Compayré reminds us that the child at first sees only in front of him and that he does not see objects to the right or left. This can be shown easily by shifting a light or a bright colored object either way in front of him. He soon loses it and gazes vacantly into space. The same authority also cites the fact that all young children are myopic, seeing objects only at short range. The first is due to the fact that the child has not yet learned the art of moving its eyes so as to change the field of vision; the second, to the fact that the eye is not yet completely developed and that the power of focal adjustment has not yet been attained. Experiments of this nature during the first four or five months of a child's life will reveal some very interesting things about the growth of sight perception, among them the surprising fact that nearly all children are cross-eyed at birth and some of them for many months after. The co-ordination of the movements of the muscles controlling the eyeballs is necessary before rapid progress can be made in distinguishing objects by sight; this is often not fully attained before the age of four or five.
The intellectual value of this sense needs no particular discussion here. So much of our knowledge comes through it that the value of the other senses is often overlooked. If one sees a thing, he is supposed to know all about it. Seeing has become the synonym for understanding, and when we have explained a matter to any one we quickly ask, " Do you see it?" The direct knowledge given us by the eye is of hue, tint, and intensity. By hue is meant the more or less positively defined colors; by tint, the varying shades due simply to the small quantity of a color or hue showing itself in a mixture or background of white or some leading color; by intensity, the amount of light received from an object by the eye. The first is dependent upon the relative rapidity of the wave movements, red being the lowest and violet the highest; the second and third are already sufficiently explained. By the infinite number of combinations of these three, the perception of the external world is made so definite that no two human beings out of the billion and a half now living appear exactly alike to the cultivated eye; no two of the endless quintillions of leaves that cover the earth are found to agree in every detail. Every-where is variety; the bright and the somber, the red and the gold, the light and the dark, the green and the yellow, the blue and the crimson, the glow of the evening sunset, the dancing of the silver-tipped waves, the wild sprangles of the restless lightning, are ever revealing through the eye the nature and the resources of the universe of matter and of force.
The purely visual function of the eye is greatly multiplied and extended by its union with the muscular movements of the body, the neck, and the eyeballs, as already intimated. By the, aid of the first two the whole range of the horizon, around and above, can be swept almost in an instant, and objects distinguished and located with surprising accuracy. At first consciously, then more or less unconsciously, the muscular sensations serve as a measure of the angles passed over in the movement and the visual sensation is the only one prominent in the perception. But when the eyeballs of children of school age or of adults are observed, they will be seen to be as restless as globules of mercury, turning hither and thither and everywhere on the slightest occasion. Few of these movements are purposeless. They are made so as to take in the whole of an object and its surroundings; they are repeated and reversed again and again, that each detail of color and tint and shade and form and relation may be verified. These muscular sensations also merge in consciousness with the purely visual, and the knowledge de-rived is usually attributed to the latter. Then there are two sets of delicate ciliary muscles inside the eyeball itself; one adjusts the size of the pupil so that the proper amount of light may be admitted to the internal eye, the other adjusts the lenses of the eye in looking at objects at varying distances, so as to focus the rays coming from them upon the retina. Though the movements of these internal muscles are so slight, they evidently enter into conscious sensation fully enough to assist eye-perception in determining the shape, distance, and size of objects.
The dependence of sight upon touch has already been mentioned. At first all objects seem flat to the child, and right up against him, as it were. Exercising a natural impulse to touch them, he puts out his hand and finds that they are a little distance from him, or even beyond his reach. Through a long course of experimenting, he learns to measure in a rough way the distance to any object by the amount of muscular effort necessary to reach it. In like manner also he gets an idea of its form and size, including its depth as well as its height and breadth. The eye follows all these movements, and the associated visual and muscular sensations of the eye proper become so assimilated with them that on their recurrence, without touch, they serve to symbolize the touch sensations, and thus give knowledge which touch alone had been supplying. So by this wonderful principle of symbolism the eye gradually usurps this function of touch, and tells us whether objects are rough or smooth, liquid or solid, fibrous or crystalline, round or elliptical, oblong or square, flat or in relief, sharp or dull, large or small, fixed or moving, far or near; and all of this by the minute differences seen in the shades and colors of the various parts of a body or of different bodies. Thus it not only enhances the value of touch, but makes itself almost a universal sense, for this principle of symbolism enables it to act in place of other senses also, as explained in Chapter II.
The aesthetic value of the senses also reaches its climax in the sense of sight. Bright colors awaken interest and pleasure in a very young child. Their combinations in almost any fantastic way gratify and delight him. With the development of his intellectual nature the feeling of harmony is aroused only as certain colors are associated, and, later, esthetic taste finds satisfaction in tints and colors of the rarer hue.
Even in the most cultivated minds Nature and art never cease to kindle the emotion of beauty through color and shade alone. But the perception of form, as touch drops out, also awakens the emotion of the beautiful. Order, proportion, symmetry, and grace in form appeal to the finer and less sensuous elements of our nature more easily than does color. Form itself serves to purify and spiritualize the aesthetic feelings. Certain classez of movements, particularly those of animals, possibly due to the concrete forms they suggest, beget similar emotions. When color and form and movement are harmoniously combined, the most pleasurable effects are produced.
A liberal education and a successful life are so clearly dependent upon the perfection and skill in the use of the eyes that their care and training ought to constitute a large part of the responsibility of every parent and teacher. It is a long distance from that vacant, expressionless look of the newborn babe to that eye so full of meaning and understanding in the richly endowed man, and some intelligent hand must help to its attainment. The aid to give children with normal eyes is suggested in the next chapter.
In certain families almost every child is troubled with some affection of the eye; in others, weak or diseased eyes are unknown. Heredity shows its trail in no other sense more clearly. Many of these diseases are of the eyelids, not affeeling the eyeball at all, and are merely temporary; others, though external, are very serious and gradually extend to the eyeball, even to the optic nerve. The surface of the eyeball is subject to diseases of a similar nature, sometimes originating there and extending to the eyelids. All such disorders should be treated by physicians or by experienced nurses. The orders they give should be strictly followed, even though " there is no danger." Many eyes have been ruined by the carelessness or indifference of those whose love and interest ought to have taught them better.
These disorders are easily seen, but those that directly affect the sense of sight are usually discoverable only by closer examination. The experiments with the lighted candle or lamp for discovering the first sight sensations, range of field to right and left, distance at which objects are evidently lost to view, constitute a series which should be repeated at first from day to day, and then from week to week until such time as there seems to be but little change. The progress, rapid or slow, which the child makes in extending his range of vision by association with muscular movements and with touch should be most carefully noted. At times he will be found to have made great progress, and too much care can not be taken to discover the cause. Bright objects, as balls of colored yarn, may early be substituted for the lighted candle, afterward being varied with those of softer colors. No attempt should be made to stimulate the eye to undue activity nor to test its endurance at any time, particularly with little children. The eyes of children are often injured greatly by gazing too long at a bright light. I remember, when past thirty, experimenting with an electric light to discover its power, and, though I was soon able to stare it out of countenance, I found, as the cars started off, that I was totally blind. Fortunately, the paralysis was temporary, but how much the contest has affected my sight since has always been a problem. A student of mine was blind for several days and suffered with weak eyes for years as a result of walking a mile at midday with the reflections of the bright sun-light from the snow crystals pouring into her face at every step. Reading from a brightly illuminated page has a similar effect. These experiences are so common and so well known that any one who endangers a child's eyes in such a way is little short of a criminal.
Should these experiments with the babe reveal any peculiarity at any time, there ought to be no alarm. It sometimes happens that a child appears to be making considerable progress for several days and then apparently loses all power gained. The cause may be interest in something else, or weariness, or a slight temporary weakness in the eyes. If the child is later in observing the light than other children, it may be the better for him, as earlier appreciation might do him harm. If, however, he pays no attention to it when ten days old, a physician's advice should be promptly sought, possibly even before that time if suspicions are aroused. Should the retrogression above mentioned continue for a few days, or should no progress be making, the same ever-safe counselor should be called in.
Not only should objects of different colors be used, but also of different sizes and forms, especially as the child is running around and getting acquainted with the outside world. Though, as stated, all small children are short-sighted to some extent, ability to adjust the eye to objects within reasonable range should be clearly showing itself as the child enters school. If parents do their duty, they will inform the teacher of any defects in vision. By noting the ease or difficulty with which the children read writing on the blackboard or the words in their books, teachers will at once discover reasons for further tests. The short-sighted children should be placed where they can see the work on the board, and they should be permitted to keep their eyes near the paper as they read or copy or figure. Weak eyes should not be confused with myopic eyes, for the former see with difficulty at any distance, while the latter see easily within their own range. The former need more light; the latter, a proper focus, which proper distance only can give, though suitable glasses will aid both. Among older children, long-sighted, hyperopic, eyes will occasionally be discovered. In serious cases of myopia or hyperopia, expert oculists should be consulted and proper glasses secured. The reason for consulting a specialist is that the child should not only have glasses that will enable him to see well, but that will also serve to gradually correct his defect. Where the cases are not very serious, the child should be seated in the schoolroom as suggested, and permitted to hold his book or paper at the distance best adapted to his eyes. He should, however, be encouraged in a friendly way to move his book a little nearer the normal distance from time to time, in order to stimulate readjustment to the new focus. There should be no haste about this, for if the child has made appreciable progress in correcting defects in four or five years it is cause for congratulation. It is probable that the increase in skill in apprehending words and objects will also relieve the embarrassment in myopic and hyperopic children, as they soon learn to get along without such clear eye pictures as their more fortunate neighbors are accustomed to have.
The most difficult cases to manage are those known as astigmatic, and those in which the foci of the two eyes are at unequal distances, thus con-fusing the image, particularly at certain ranges. There seems to be no remedy for these defects save in glasses properly fitted. The former is quite common, and is a prolific source of headache. Thousands of cases of chronic headache have been promptly cured by the use of glasses. Though the astigmatism may be very slight, the constant strain on the fine nerves and muscles of the internal eye produces most acute pain in the head. This same effort in myopic and hyperopic cases produces the same result. A ministerial friend tells me that a teacher forced his son, who was afflicted with myopia, to hold his book at the "regulation distance " and in the regulation position as he read or studied, and that the headache resulting threw him into such nervous disorders that at least once a fortnight he was obliged to keep him out of school for three or four days. A lady friend tells me that her little daughter had been coming home every day for months with a bad headache, and that she was losing all interest in school, when the writer visited the city and urged the teachers to test the sight and hearing of their pupils. This girl was found defective in eyesight and given a front seat. In two weeks her headache was all gone, and her interest in school had returned. A multitude of similar cases might be given, but these must suffice. If this paragraph awakens its readers to a fuller understanding of the intimate connection between overstrained eyes and head-ache among children and adults, somebody will be remembered most kindly by them.
For a little more definite test of the defects just named, Snellin's cards, bought of jewelers and dealers in spectacles nearly everywhere for ten cents, will be found serviceable.
The fact has already been mentioned that the eyes of little children are often crossed more or less, and that the power to move both together may develop but slowly. It is important that nothing be done which will tend to cause a child to try to look in two directions at the same time. Slowly moving an object not too small, in various directions at some distance before him, carefully excluding anything from the right or left which might attract him, will encourage the two eyes to move together. This repeated from day to day will assist the child in co-ordinating the muscles and attaining the power to move them together. Very small objects should not be used, neither should anything be placed so near as to force the child to try to look over his nose. The disposition to show a child off by having him look cross-eyed is vicious and criminal.
Cataract is a well-known disease of the eye, but its early symptoms often escape notice, and sight is gone before any attempt is made to pre-serve it. At the first suggestion of a discoloration of the pupil, medical aid should be sought.
Children are continually getting something in their eyes a particle of dust, a cinder, a thorn and everybody ought to know how to remove it. Put a toothpick above the eyelid and quickly re-verse the lid over it, thus usually exposing the foreign substance. With a silk handkerchief gently remove the intruder. If the substance be imbedded in the eyeball, great care must be exercised lest permanent injury result to it. Only an expert should be permitted to handle this delicate organ if the case be serious.
In the selection of text-books and reading matter generally for children, fine print and masses of letters and figures should be avoided. Eyes may be ruined in a fortnight by too close application to solid matter of this kind. In visiting a class recently, I found twenty boys, four-teen to seventeen years of age, complaining about weak eyes. Many of them had never thought of weak eyes before entering the class, but a month of study over fine print and compact columns had caused them incalculable distress. Good, clear type, well leaded, on white paper will prevent such trouble. Some blackboards are not fit for use. Half of the pupils do not write their work on the board so that it can be seen without strain. The light in many schoolrooms is very poor; often too much, often not enough; often from the right when it ought to be from the left.