Maximum Tolerable Dose for Avoidance of Cataract After Repeated Exposure to Ultraviolet Radiation

Abstract

Abstract: : Purpose: To investigate the impact of interval between repeated exposures on maximum tolerable dose (MTD) for ultraviolet radiation induced cataract. Methods: A total of 100 six weeks old female Sprague–Dawley rats were randomly divided into 5 groups of 20. The different groups were assigned to one of the inter–exposure intervals 6 hours, 1, 3, 9 or 30 days. Each inter–exposure interval group was sub–divided into 5 dose subgroups, with 4 rats in each subgroup. One eye of each rat was exposed to ultraviolet radiation (_max=300 nm, _0.5=10 nm). The dose incident on the cornea varied between 0∼5 kJ/m² and the exposure time was 15 minutes. One week after the second exposure, the rats were sacrificed and both lenses were extracted. The intensity of forward light scattering was measured and morphological changes were documented by photographs under microscope with dark–field illumination. MTD of each inter–exposure interval group was estimated based on the experimentally determined dose–response function. Results: The MTD_2.3:16 was 2.6, 2.5, 2.7, 2.9, and 3.4 kJ/m², respectively, for the 6 hours, 1, 3, 9 and 30 day inter–exposure interval group. The highest MTD_2.3:16 was found in the 30 days inter–exposure interval group. The light scattering difference between exposed and non–exposed lens decreased with increase of interval between two repeated exposures. Conclusions: MTD is higher for repeated UVR–B exposure with long inter–exposure interval (30 days) than with short (6h∼9days). One month after the first UVR–B exposure, lenses probably have undergone some biological repair.

Keywords: cataract • radiation damage: light/UV • pathology: experimental