736 POPULAR SCIENCE MONTHLY. 



THE CAUSE, NATUKE AND CONSEQUENCES OF 



EYESTRAIN. 



BY GEORGE M. GOULD, M.D., 

 PHILADELPHIA. 



~VTO questions are so often asked of the oculist by his patients as, 

 -^ ' Why do so many people, and even children, have to wear spec- 

 tacles 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 our- 

 selves, 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 travel- 

 ing 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 focussed image upon the retina of 

 the object upon which the eye is trained. All human physiology cen- 

 ters 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 kodak takes a picture. To realize the difficulty of 

 the kodak of the living eye, one must have an adequate conception of 



