Cataracts and photochemical damage in the lens.

The possibility is considered that ultraviolet radiation, from sunlight and other ambient sources, is a major causative factor in certain human cataracts. Epidemiological and experimental data from the literature are reviewed and new experimental results on exposure of rat lenses to UV laser radiation in vitro are presented. This UV irradiation of lenses is shown to cause: (i) photochemical alteration of tryptophan residues in lens proteins, resulting in loss of tryptophan fluorescence, (ii) new ultraviolet absorption bands attributable to photo-oxidation products of lens proteins, and (iii) cross-linking of polypeptides in lens proteins, detected by sodium dodecylsulphate-polyacrylamide gel electrophoresis. It is noted that the UV radiation-induced lens changes reported are quite similar to the changes found when normal human lenses develop cataracts. In order to establish the degree to which UV-exposed lenses resemble naturally occurring cataracts, a comprehensive comparison of anatomical, histological and biochemical parameters for normal, cataractous and UV-exposed human lenses is proposed.