Maximum tolerable dose for avoidance of cataract induced by ultraviolet radiation-B for 18 to 60 week old rats.

The purpose of the present study was to investigate the maximum tolerable dose for avoidance of UVR-B-induced cataract in rats in the age interval 18-60 weeks and establish the functional relationship between age and sensitivity to UVR-B. Four groups of 20 albino Sprague-Dawley rats each, aged 18, 26, 40 or 60 weeks, were included. Each age group was divided into five UVR dose sub-groups. The rats were unilaterally exposed to ultraviolet radiation (lambda(max)=302.6 nm, lambda0.5=4.5 nm). The incident dose on the cornea varied between 0 and 9.2 kJ m(-2). One week after exposure, the rats were sacrificed and both lenses were extracted. The intensity of forward light scattering was measured and photographs were taken. The functional relationship between age and sensitivity to UVR-B was estimated as the maximum tolerable dose based on rats age from 3 to 60 weeks. The maximum tolerable dose for 18, 26, 40, and 60 weeks, respectively, was estimated to 5.2, 4.9, 4.7, and 5.1 kJ m(-2). The sensitivity to UVR-B for Sprague-Dawley rats increases with increasing age during the first third of the rat life span, and then stabilizes to a constant level during the remaining two-thirds.