DISOEDERS IN RELATION TO THE EYE T61 



complete opacification of the lens in connection with grave degenerative 

 forms of cyclitis and of iritis involving a loss or change of color in that 

 membrane. 



Dryness of the skin, brittleness of the nails, and baldness, combining 

 to form a syndrome of ectodermal pre-senility are dramatically checked 

 by the administration of thyroid extract (Starr) and the action of the 

 iodides, internally or in the form of subconjunctival injections in senile 

 cataract are suggestive in this connection. 



Corneal Changes in Senility. Arcus senilis, gerontoxon. The ap- 

 appearance of a gray crescent or semicircle just within the clear cornea 

 near the limbus was from the earliest times associated with baldness or 

 white hair as a sign of aging. 



The influence of endocrin factors is indicated by the varying age inci- 

 dence of these conditions in healthy individuals, by comparatively early 

 onset after continued disturbances of nutrition, and by their sudden ap- 

 pearance in exceptional but undoubtedly genuine, cases immediately after 

 severe emotional shock. It is a question whether the highly pigmented 

 eyes and hair of brunettes indicate a type which tends to premature gray- 

 ness. The latter, like precocious development, is generally attributed to 

 thyroid influence, and might be explained on the basis of a relative hyper- 

 thyroidism setting in with an all too early gonad deficiency. 



Ocular Pigment. The biologic significance of pigment is by no means 

 simple or completely understood. There are indications that it is in 

 some way connected with all sources and manifestations of energy, cosmic 

 as well as vital. Sunlight and heat are the primal sources of all energy 

 and of all pigment (cf. coal, carbon, chlorophyll, hematin, and skin- 

 pigment) , and the coloring matter in the human economy is related to and 

 probably derived from iron (hemO'siderin). Ocular pigment, uveal 

 as well as retinal, is a melanin derived from the pigment of the blood or, 

 more probably, from protein chromogen. 



The biological relation of light and in fact of all radiant energy to 

 pigment in organic life is indicated by phototropism and heliotropism 

 not only of organisms in lower life but of all plant and animal cells. Photo- 

 taxis acts on all protoplasma, only part of which becomes differentiated to 

 light sensory cells. Light of high intensity affects not only the visual cells 

 but all ectodermal elements as shown in dermatitis, sunburn and freckles 

 and in the therapeutic effect on epithelial neoplasms. 



Photochemical reactions in the retina associated with pigment are not 

 thoroughly understood or uniformly interpreted. Visual purple is a prod- 

 uct of an acid metabolic reaction and decolorizes phenol phthalein (Put- 

 ter). Its action is probably a sensitizing one on the visual cells which 

 themselves have a secretory function. The actual chemistry of the visual 

 process may be explained as simple splitting, analogous to the decomposi- 

 tion by light of hydriodic acid ; as a more complicated process of alternat- 



