The relative absorption of thermal energy in retina and choroid.

The production of thermal lesions in the ocular fundus depends, among other factors, upon the spectral quality of the light incident on the cornea, and the energy-density gradient in the fundus. The latter depends, in turn, upon the concentration of pigment within the granules and the space distribution of the granules within a given stratum or layer. The distribution of pigmented granules varies in both pigment epithelium and choroid, but most markedly in the latter. Absorption of radiant energy in pigment epithelium may be greater than in the choroid or vice versa depending upon the individual. It is estimated on the basis of experiments on albino rabbits that the blood pigments absorb approximately 10 per cent of the light incident on the human cornea. Energy absorption in the retinal pigment epithelium is the most important factor leading to the development of mild or so-called threshold burns.