Influence of exposure time for UV radiation-induced cataract.

PURPOSE It is believed that for a certain ultraviolet radiation (UVR) exposure, the biologic effect depends on the product of irradiance and exposure time (the reciprocity Bunsen-Roscoe law). The purpose of this study was to investigate the validity of the reciprocity law for UVR-induced cataract. METHODS Two experiments were conducted. In the first one, 100 Sprague-Dawley rats were exposed to UVR divided into five groups according to exposure time: 7.5, 15, 30, 60, and 120 minutes. In the second experiment, 80 Sprague-Dawley rats were exposed to UVR divided into four groups according to exposure time: 5, 7.5, 11, and 15 minutes. All the animals were unilaterally exposed to the same dose of UVR (8 kJ/m(2)) in the 300-nm wavelength region. One week after exposure both lenses were removed to measure the intensity of forward light scattering and for microphotography. Groups were compared by evaluating the difference between exposed and nonexposed eyes. RESULTS The group exposed to UVR for 5 minutes had the lowest intensity of forward light scattering. The highest intensity of forward light scattering was found in the group that was exposed for 15 minutes. With longer exposure intervals, the intensity of forward light scattering decreased as the exposure time increased. No difference in intensity of forward light scattering was found between the groups exposed for 60 and 120 minutes. CONCLUSIONS; Exposure time strongly influenced cataract formation after low-dose UVR. In this model of UVR-induced cataract, the photochemical reciprocity law was modulated by a biologic response.