Epidemiological studies of sunlight and cataract: the critical factor of ultraviolet exposure geometry.

Despite the large body of laboratory evidence that ultraviolet radiation (UVR) is cataractogenic, epidemiological studies of the relationship between age-related cataract and chronic UVR exposure have provided apparently conflicting results. An explanation for these conflicting results could be related to errors in dosimetry. Failure to account for the biophysical, physiological and behavioral factors, as well as ground reflectance, which determine the level of UVR exposure of the lens can lead to completely wrong assignments of lifetime exposure. It is argued that by overlooking these factors, past epidemiological studies of UVR and cataract could readily be expected to produce conflicting results.