Lens growth and protein density in the rat lens after in vivo exposure to ultraviolet radiation

PURPOSE. To investigate lens growth after different doses of ultraviolet ra diation (UVR) and to investigate the long-term effect of a near-threshold U VR dose on the refractive index distribution in the lens. METHODS. Sprague-Dawley rats received UVR (lambda (MAX) = 300 nm) unilatera lly during a 15-minute period. The exposure dose ranged from 0.1 to 20 kJ/m (2), and the rats were kept for up to 32 weeks after exposure. Intact lense s were photographed and lens wet and dry masses were measured. The protein density was estimated by quantitative microradiography. Freeze-dried lens s ections were used fur contact x-ray photographs. From the transmission of t he microradiographs, protein density and refractive index profiles were cal culated along the lens radius with a resolution of 2.5 mum. RESULTS. Lens dry mass in exposed eyes was lower than in nonexposed eyes at one week after exposure. Lens water content was decreased after low UVR do ses but increased after high doses. The difference between exposed and none xposed lenses in dry mass and water content increased with time after expos ure. No significant difference was found for the mean protein density in ex posed and nonexposed lenses. The protein density increased linearly in the lens cortex, from a minimum in the superficial cortex of 0.26 g/cm(3) to a maximum in the deep cortex of 0.81 g/cm(3). This corresponded to a refracti ve index of 1.38 and 1.48, respectively. CONCLUSIONS. Lenses exposed to UVR grew more slowly than their nonexposed c ontralaterals. This growth inhibition was dose dependent. Near-threshold do ses led to decreased water content in the lens whereas high doses led to sw elling. Six months: after near-threshold UVR exposure, no global change of the refractive index was found. However, local variations of the refractive index caused a subtle cortical light scattering.