Lens UVA photobiology.

Although UVA radiation was considered to be benign as a factor that could contribute to cataract formation, the studies briefly summarized herein show that UVA may provide the more damaging radiant energy involved in the formation of human cataract. Of the UVA impinging onto the eye from sunlight, a sufficient dose does reach into the lens to enhance cataractous changes. The adverse physiological and biochemical effects on lens epithelial cells and their ability to differentiate into clear adult lenses include cell growth inhibition, cell membrane and cytoskeletal anomalies, and enzyme inactivation. Many of the damaging events are related to the excitation of sensitive UVA absorbing chromophores which generate singlet oxygen and free radicals. This process enhances lens oxidative stress. Some protection against this damage is provided by vitamin E and tea polyphenols. Thus, an imbalance between photooxidative stress, antioxidant protection, and repair processes would increase the potential to produce cataracts.