Jasper County Democrat, Volume 5, Number 3, Rensselaer, Jasper County, 26 April 1902 — THE EYE. [ARTICLE]

THE EYE.

The following is a part of an ad. published in the Rensselaer Journal some time ago by Mr. , claiming to be an optician. He apparently desires to lit the optic nerve with glasses tbat will givo it rest. His ad follows. You’ve noticed that your eyes pained you at times—haven’t you? Do you know what caused it ? This pain is caused by a continual strain on the optic nerve—it hasn’t come about in one or two years—but the incessant use of your eyes, for all purposes, at all times, has gradually caused this optic nerve to become weaker and weaker until now—this little, but essential body is tired (just as you are after a days work) —it needs rest, but the only way to give it that desired relief is to secure a pair of perfectly tested glasses, perfectly fitted to your eyes. Our testing apparatus will tell just what style of lens will give your optic nerves that desired relief, then you are absolutely guaranteed a perfect vision. Comment of Chas. Vick, the optician, on the above ad. EYESIGHT. This subject is a wide one, involving, as it does, the sciences of anatomy, physiology and optics. It has enlisted earnest and distinguished workers from all, and has accumulated a literature of its own, which an ordinary lifetime is hardly long enough to master. That an intelligent care of the eyesight requires some knowledge cf the structure and functions of the organ of vision is a proposition too plain to ad mit of argument. Nor has this much abused organ had fairer play in practical use than in theoretical knowledge, for many who would give to tired limbs or back the needed rest, or nurse a lame leg with the most tender care, will goad on their willing but disabled or over-strained eyes in the most reckless way. To understand anything of the physiology of vision, it is necessary to have a general idea of the way in which images of objects are formed by refracting surfaces. In an effort merely to popularize established facts and accepted theories which have become the common property of scientific men, it will, of course, be understood that no originality is claimed and it will not be necessary to weary the reader with reference to authorities. About one-tenth of an inch to the inner side of the yellow spot is the point of entrance of the optic nerve, which is the only portion of the surface of the retina from which the power of vision is absent. It is important for the optician that he possess a clear idea ol the relative positions of the yellow or sensitive spot and the optic perye entrance or blind spot. In what way the retina Is influenced by light, what the change in its elements is when light falls upon it, has never been fully explained. It seems certain, however, that some change is wrought in it and that this imoression is conveyed through the nerve fibres of the optic nerve upward to the brain, and that there it is interpreted as light. You remember very well, I am sure, that the optic nerve itself is incapable of receiving this impression and you remember the familiar experiment in physiology by which you may find the “blind spot” in your eye. This bl nd spot corresponds to the entrance of the optic nerve. THEORY OF VISION. Having learned what a convex lens is let us follow the example of Frances Maurolycus, who made the first approach to correct phyosophy of vision in 1575, by comparing a convex lens to the lens in the human eye. Let us take a convex lens No. 10, in one hand and a sheet of paper in the other, if rays of light coming from an object twenty or more feet away fall upon the lens they will be united in one point (the focus), ten inches behind the lens. Ifour sheet of paper is placed here we will find a bright, round spot. If the paper is carried a little further back, a sharp, distinct, i .verted image of the object, is formed on the paper. This is exactly what takes place in the normal eye when at rest. The cornea and lens is represented by the glass lens. The space between paper and lens, represents Lhe dark qhamber of the eye. The paper represents the retina. The minute inverted linage formed upan the retina is conducted to the brain through the optic nerve, and thus the simple visual act is complete. Although Maurolycus rejected his own theory upon the ground that the image must all be seen inverted, nevertheless this was the path by which the correct theory of vision was reached. The next step after Maurolycus’ discovery was made by John Baptist Porta, the inventor of the camera obscura. He compared the instrument invented by him with the human eye. He compared the dark chamber with the chamber of the eye, but of the part which the ground glass screen represented, he had an entirely incorrect idea; he supposed the cornea alone acted upon the light and that the inverted image was formed on the anterior surface of the lens. A clear theory of vision we have already given in one experiment with glass lens and paper was first given by John Hepler, 1604. Des Cartes, in 1631, was probably the first to practically demonstrate that an inverted image is formed upon the retina. He removed all the coatings of the eye from its posterior pole and placed in the opening a piece of ground glass, upon which he had the satisfaction of seeing the retinal image formed. Optical defects requiring the use of glasses may be classified as follows: 1. Presbyopia—a disease, or error, or failure in accommodation, or in the power of adjusting the eye to vision at different distances; a refraction of the near point, 2 Hypermetropia—insufficient refractive power of the eye usually dependant upon shortening of the anteroposterior diameter of the eye-ball. 3. Mypoia—or near sightedness; the eye is too long or deep, and its refraction causes parallel rays of light to focus before they reach the retina. 4- Astigmatism.—Unequal refraction ot two meridians of the same eye, or of one and the same meridian. 5. Asthenopia—or weak sight; due to a weakness of the ciliary muscle or of the recti muscles. 6. Diplopia—or double sight; where the two eyes cannot be directed to the same object. Vision is a function which is more nearly even in man than any other function of the body. There is a certain power of vision which is the birthright of all men. There is the widest difference in the faculity of hearing in man and no standard has been absolutely set down as normal. How much more true is this of taste and smell and feeling T Yet we can make a standard in the vision, and say that man must have vision equal to that or fall below the standard. The retina, the third or nervous membrane, is the most important of all, indeed, ail the other structures of the eye may be considered subservient to this one, for on it are formed the images of external objects by means of which we are said to see them. It is a very complicated and extremely delicate structure,offering endless difficulties to the investigator; and although an immense amount of labor has been expended upon it by many mastery in science, its minute anatomy can hardly yet be considered settled. The cure of headache, vertigo and other symptons, by the use of correc live glasses While there has been much of exaggeration in some of the claim* that have been made for the cure of headaches, vertigo, and more serious affections, by the use of glasses it still remains true tbat many symptons that do not appear to be related to the eye are often removed by the use of corrective glasses. a Thus far the act es vision is a strictly physical process; the rays of light can be traced to the retina as definitely and accurately aa they can be followed to lhe screen of the magic lantern or the plate of the photographer’s camera. But beyond this point we find ourselves in the minty region of theory and speculation and the something that enables the image to excite a sensation, and converts (he sensation into a mental proceas-that evolves thought and reason—like an ignis fatuua, eludes the grasp of science. What is essential in glasses is that they shall be perfectly clear, of uniform density, and free from flaws, and shall be properly ground with the

right curvature. These essentials are by no means always to be found in cheap glasses, so tbat spectacles are not good things to economize in. Yours Truly, Chas Vick, The Optician. Office second door west of Rensselaer Bank, Rensselaer, Ind.