Estimation of a safety limit for ultraviolet radiation-B (UVR-B)-induced cataract in an in vivo pigmented guinea pig model

Purpose: To establish a threshold measure, maximum tolerable dose (MTD), for avoidance of UVR‐B‐induced cataract in the pigmented guinea pig. Methods: Thirty female guinea pigs, five to nine weeks of age, were divided into 5 groups of 6 guinea pigs each. Pupils were dilated bilaterally before exposures. The guinea pigs were unilaterally exposed to UVR‐B under anesthesia in vivo, receiving between 0 and‐84.9 kJ/m2 over a duration of 60 minutes. Each guinea pig was sacrificed 24 hours after exposure. Lenses were extracted and photographed in vitro. Intensity of forward light scattering was measured for each lens. The data were analyzed with regression using a second order polynomial model, considering the first order term to be 0. The applied MTD concept is based on the UVR‐B dose response curve obtained for the pigmented guinea pig. Results: All of the guinea pigs exposed to UVR‐B developed cataracts in the anterior subcapsular region. MTD for avoidance of UVR‐B‐induced cataract was estimated to be 69.0 kJ/m2 in the pigmented guinea pig. Conclusions: The MTD for avoidance of UVR‐B‐induced cataract in the pigmented guinea pig is significantly higher than 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 guinea pig. The pigmented guinea pig is less sensitive to UVR‐B exposure than the pigmented rabbit, pigmented rat, and pigmented mouse.