In vivo cataract after repeated exposure to ultraviolet radiation.

The purpose of this study was to investigate the effects of repeated close-to-threshold ultraviolet radiation (UVR) doses in the rat lens. Sprague Dawley rats received two UVR exposures (lambda(max) = 300 nm, lambda0.5 = 10 nm) separated by different time intervals. The animals were unilaterally irradiated with 4 kJ m(2-1) UVR in each exposure. The intervals between both exposures were: 6 hr, 1 day, 3 days, 9 days and 30 days. At 1 week after the last exposure both lenses were removed, microphotographs were taken and intensity of forward light scattering was measured. Evaluating the difference between exposed and non-exposed eyes, the forward light scattering in the 6 hr and 1 day interval group was not significantly different. The most intense forward light scattering was found in the group that was allowed 3 days interval between exposures. Thereafter, the intensity of scattering decreased as the time interval between exposures increased. The lowest intensity of forward light scattering was detected in the 30 days interval group. Three days after a UVR exposure, the lens showed the highest sensitivity for a second UVR exposure. One month after the first exposure lenses undergo physiological repair and interactions between exposures seem to decrease.