Light scattering parameters of rat lenses with calcium-induced cataracts

Light scattering intensities of rat lenses obtained in the I,, and I+ modes were analysed using the random density and orientation fluctuation theory. Rat lenses incubated in calcium rich media had the same density fluctuation parameters as rat lenses incubated in control (low-calcium) media. However, the correlation length of the orientation fluctuations decreased during cataract formation by 100 to 200 nm while the amplitude of the fluctuations increased. The correlation length, or the size of the optically anisotropic domains, is related to the size of the cytoskeleton, especially vimentin. Vimentin has been shown to degrade when calcium activates calpain. This has been observed in SDS-gel electrophoretic experiments in rat lenses in calcium rich media. The amplitude factor of orientation fluctuations, that is, the mean squared deviation from the average refractive index, increased between two- and seven-fold during cataractogenesis. These results indicate that calcium cataract formation at the beginning (first 72 hr incubation) has little to do with aggregation or syneresis but it is largely the result of changes in the intrinsic birefringence of the lens due to vimentin degradation.