Introduction Since the degree of pigmentation in the fundus plays a major role in the absorption of radiant energy,1 the relationship between absorption and reflectance of light by the fundus has been investigated in an attempt to develop an in vivo method of predicting the susceptibility of the individual eye to retinal burns. It is hoped that the method described here will prove useful in assessing the optical hazards of nuclear fireballs and lasers as well as in providing an aid to the clinical applications of light coagulation. A method of measuring quantitatively the variation in pigment density among individuals removes one of the principal sources of error in predicting the thermal dose required to produce a lesion of a given severity. Method Fifty-eight eyes from Chinchilla gray rabbits exhibiting a very uniform fundus pigmentation within the individual eye but a large variation in pigmentation from one animal to