The lens response to daily in vivo exposures to UVR

Purpose Epidemiological data indicate correlation between life long exposure to ultraviolet radiation and cortical cataract. There is no experimental data on the effect of daily repeated in vivo exposures of the eye to UVR. This experiment was designed to verify whether the dose additivity for UVR exposures holds through periods of time up to 30 days. Methods Eighty rats were conditioned to a rat restrainer five days prior to exposure. All animals were divided into 4 exposure period classes of 1, 3, 10 and 30 days of exposure to UVR. Each exposure period class of 20 animals was randomly divided into five cumulated UVR dose sub‐groups. Eighteen‐week‐old non‐anesthetized albino Sprague‐Dawley(SD) rats were exposed daily to UVR‐300 nm for 15 minutes. One week after the last exposure, animals were sacrificed. The lenses were extracted for macroscopic imaging of dark‐field anatomy and degree of cataract was quantified by measurement of intensity of forward lens light scattering. Maximum tolerable dose (MTD2.3:16), statistically defined standard for sensitivity for threshold for UVR cataract, was estimated for the periods of exposure and plotted with a linear regression as a function of days during which dose was accumulated. Results All exposed lenses developed anterior subcapsular cataract with varying appearance depending on the period of days exposed to UVR. Small single doses of UVR accumulated to cause cataract during the periods up to 30 days. MTD2.3:16 for 1, 3, 10 and 30 days of repeated exposures was estimated to 4.7, 4.74, 4.8 and 6.0 kJ/m2, respectively. Conclusion The tolerance to UVR‐B for 18 week old SD rat increases with increasing number of days being exposed. With lower single dose and longer duration for daily exposure the lens is more tolerant to UVR.