Estimation of a Safety Limit for Ultraviolet Radiation-B (UVR-B) Induced Cataract in an in vivo Pigmented Rat Model

Abstract

Abstract: : Purpose: To establish a threshold measure, maximum tolerable dose (MTD), for UVR-B-induced cataract in the pigmented Brown Norway rat. Methods: Twenty-five Brown Norway rats, 6 weeks of age, were divided into 5 groups of 5 rats each. Pupils were dilated bilaterally before exposures. The rats were unilaterally exposed to UVR-B in vivo, receiving between 0-7.1 kJ/m² over a duration of 15 minutes. Each rat was sacrificed 25 hours after exposure. Lenses were extracted and photographed in vitro. Intensity of forward light scattering was measured for each lens. The data were analysed with regression using a second order polynomial model, considering the first order term to be 0. The applied MTD concept is based on the dose response curve obtained for the Brown Norway rat. Results: All the rats exposed to UVR-B developed cataracts in the anterior subcapsular region. MTD for avoidance of UVR-B cataract in the rat was estimated to be 4.2 kJ/m². Conclusions: The MTD for avoidance of UVR-B-induced cataract in the pigmented Brown Norway rat is comparable to the threshold obtained by Pitts et al. in the pigmented rabbit. MTD is an appropriate method for estimation of toxicity for UVR-B-induced cataract in the pigmented Brown Norway rat. The pigmented rat is less sensitive to UVR-B exposure than the albino rat.

Keywords: radiation damage: light/UV • cataract • ocular irritancy/toxicity testing