THE NEW OPHTHALMOLOGY 423 



in such ways as the circulatory or metastatic transfer of inflamma- 

 tory or infectious diseases from the eye to other organs, nor to the 

 extension of localized inflammations to adjacent or even distant ones. 

 That is another matter, and of it the old ophthalmology took suffi- 

 cient cognizance. The field of study of the new ophthalmology is 

 topographically well defined, its title clear, its methods, instruments 

 of culture, the seed, and the crop itself, distinct, both genetically 

 and evolutionally. 



The abnormal conditions of the eye which set up morbid sys- 

 temic results may in strictness scarcely be called abnormal except 

 by a strain put upon the word. At least they are per se not morbid. 

 They might better be called physiologically aberrant or variant. 

 They do not originate in inflammatory or pathologic conditions, but 

 simply in optical ones. But for us all physical optics leads to physio- 

 logic optics. Primarily and fundamentally it pertains to the eye as an 

 optical instrument, but as a living one, a physiologic camera obscura. 

 If the photographer's camera had an elastic lens instead of a rigid 

 one, and if its refractive power were spontaneously governed by the 

 desire of the camera for an accurate focus of the picture, the analogy 

 would be almost perfect. But the photographer's camera can neither 

 direct itself, nor renew its own sensitive plate, so that in spontaneous 

 choice of scene, change of focus, and renewal of sensitive plate, the 

 living camera is superior to the dead one. The natural difficulties 

 of the choice of scene and of the resensitization of the plate have 

 been beautifully overcome in the eye by the God of evolution, but 

 other obstacles have not been overcome. The ocular camera, for 

 instance, is double, and stereoscopic, and accurately to superpose 

 the images of both cameras is frequently impossible even after ages 

 of workmanship. As all physiology leads to pathology, so, for phy- 

 sicians, all physiologic optics ends in pathologic optics. The twelve 

 ocular muscles have a highly complex and skilled task; hence 

 heterophoria and strabismus. Moreover, the spontaneously elastic 

 lens grows inelastic in forty-five years, and presbyopia, at least be- 

 fore the days of spectacles, was a frightful tragedy. Lastly, the 

 transparent lens could not formerly retain its transparency in old 

 age, and the blindness from cataract at the end of life has not yet 

 been entirely prevented. 



But the chief difficulties of the mechanic of the living camera 

 were to secure to 1,500,000,000 human beings, and to their successors 

 in each generation, eyeballs which did not vary more than about 

 TJ-^-Q of an inch from a given diameter, and to make all corneas of the 

 same radius of curvature in all meridians. These difficulties have 

 been so great that there has probably never been such a mathe- 

 matically perfect and optically exact pair of eyes in the world. 

 Those chosen by natural selection, the elimination of the unfit, 



