LENTICULAR OPACITIES 



121 



lens, the liability to cataractous conditions is increased. The trade 

 cataracts mentioned above are usually attributed to the overheating 

 of the eye as a whole with consequent disturbed nutrition of the lens. 



Fig. Ill— 11. Correction of a corneal opacity by a transplant from an enucleated 

 eye. (a) Corneal opacity before operation, (b) Transplant 4 mm square taken 

 from an enucleated eye of a stillborn child. Photographs by courtesy of A. Marfaing. 

 For details on keratoplasty see R. Castroviejo, Am. J. Ophthalmol., 17, 932 (1934); 

 for bibliography, see Arch. Ophthalmol., 22, 144 (1939). 



The near-infra-red rays, though freely transmitted by the cornea, are in 

 large part absorbed by the iris. This excessive local absorption may 

 in turn produce an abnormal stimulus to the processes controlling the 

 secretion of the humor and thus may cause nutritional'disturbances in 

 the lens. 



Retina 



The retina (pars optica retinae) may be said to be formed by the radial 

 expansion of the fibers of the optic nerve which enter the eye at the 

 inner side of its posterior pole, pierce the sclera and choroid, and spread 

 out over the inner surface of the eyeball. The retina is considered to 

 extend forward from the entrance of the optic nerve (optic disk) as far 

 as the posterior margin of the ciliary body, where it apparently ends 

 abruptly with an indented border, the ora serrata. During life the 

 retina is perfectly transparent, despite its complex cell structure, with 

 the exception of its pigment layer. It presents on its inner surface a 

 slightly elevated yellow spot, the macula lutea, which is located at the 

 posterior pole of the visual axis. The fovea centralis, a slight depression 

 in the center of the yellow spot, is the result of an apparent thinning of 

 the retinal layers at this point. 



The retina, if considered in detail, is made up of ten layers (Fig. 



