EYESTRAIN. 743 



contraction of the ciliary muscle, can never be renounced. This con- 

 stitutes the predominant source of eyestrain. 



There are several other misfortunes or imperfections of the accom- 

 modation mechanism which may not be neglected if we wish to under- 

 stand the matter in all its bearings. The crystalline lens must of 

 course be transparent, hence it can not be nourished directly by the 

 blood with its red corpuscles. Its healthful action is, therefore, de- 

 pendent upon nourishment by blood-serum alone — plainly a difficult 

 task, especially as this serum must reach it indirectly by osmosis, filtra- 

 tion, etc. It has also no nervous connection with the brain, and the 

 three conditions named conspire to bring about two most noteworthy 

 faults in its life-history. It is prone to become non-transparent or 

 opalescent and, finally, almost opaque in the old, and this is cataract. 

 Its elasticity also decreases steadily from childhood until it is so in- 

 elastic at about 45 years of age that the ' range ' or degree of accom- 

 modation becomes too limited to enable it to focus the images of 

 objects clearly on the retina except by holding the book, for instance, 

 too far from the eye. This is the beginning of l presbyopia ' ; at 

 about sixty all the elasticity of the lens is lost and accommodation is 

 at an end. Moreover, oculists have been hitherto unmindful of the 

 fact that the accommodation may be less than normal in many young 

 patients, even for short tasks. It is always so for long and continuous 

 ones. For presbyopia, there is no prevention and no cure. There 

 is a makeshift device (spectacles) whereby we may supply the lost 

 focusing power of the living lens, by glass lenses placed in front of 

 the crippled ' crystalline lens.' Of cataract, however, there is a pretty 

 sure method of prevention, and this, again, is spectacles. 



The science and art of correcting or neutralizing these optical 

 defects of the eyes — myopia, hyperopia and astigmatism — is by means 

 of artificial optical lenses. First, be it noted, it is a medical art and 

 science, which no optician can compass. He has neither the legal 

 nor the ethical right to attempt it, and surely he has not the scientific 

 and medical knowledge requisite for its accomplishing. However 

 poorly the medical man has executed his task, the optician will do it 

 far more blunderingly. This verbum sapienti should be sufficient 

 warning until, as with the druggist, we have also with the optician, 

 passed laws to prevent him from attempting to fill the office of physi- 

 cian. There will then not be so many ruined eyes, and far less suffer- 

 ing from eyestrain. 



Spectacle lenses have the power of changing the shape and direc- 

 tion of the image-forming cone or bundle of rays of light entering the 

 eye so that its faulty optical construction and powers are neutralized, 

 and the image is at last accurately focussed, and perfectly pictures the 

 object. The outside lenses are in a way reversely unnatural, so that 

 the inner eye-defect is met with an outer cancelling modification, 



