|THE CAUSE, NATURE AND CONSEQUENCES OF EYESTRAIN.|
NO questions are so often asked of the oculist by his patients as, 'Why do so many people, and even children, have to wear spectacles nowadays?' 'Are we deteriorating?' 'Are eyes so much poorer than formerly?' 'My grandfather did not wear glasses,' etc. Each oculist meets the questioning in his own way, but the public still remains unconvinced, suspects there may be some mistake about the whole matter, and is at least mystified.
It is hard to give satisfactory answers, at the best and with all one's good will. Not a little of our inability to throw light on the subject comes from our own indecisions and nonunderstandings. About many of the phases of the matter we have not reached a common conclusion and our professional differences of opinion bring further doubt to our patients. Concerning other parts we are also utterly unknowing ourselves, because the mechanics and neurologies of sensation, mentation and even of nervous force and transmission, still remain utter mysteries to all. Of these things the most learned are as ignorant as the most unlearned. We see or conclude that certain trains of ether-waves with a vibrational periodicity of some 400 to 700 trillions per second are transformed somehow into retinal and neural bundles of forces traveling only at the rate of about 125 feet per second; thence proceeding to the cortical visual center they are again transformed into what we call sensations of form, light and color. And innervational forces are sent back to the muscles of the eyeball, which move it as a whole, or modify its internal functions. Although we can know nothing of the intimate nature of these mechanisms and forces, we can deduce many definite, though crude, conclusions as to their causes and their results.
The dominating demand which governs all the processes concerned is for an accurate and accurately kodak takes a picture. To realize the difficulty of the kodak of the living eye, one must have an adequate conception ofimage upon the retina of the object upon which the eye is trained. All human physiology centers in that success, and much of our pathology follows from its failure. That there shall be two such images upon 'identical points' of the two retinas only heightens and complicates the difficulty. The clearly defined perfectly-representing image upon the retina is purely a matter of optics, physical and physiologic, and may be understood by any one who knows how his