The number and localization of rods and cones in the retina

All-trans-retinal and its condensation-products can cause retinal degeneration in a light-dependent manner and contribute to the pathogenesis of human macular diseases such as Stargardt’s disease and age-related macular degeneration. Although these toxic retinoid by-products originate from rod and cone photoreceptor cells, the contribution of each cell type to light-induced retinal degeneration is unknown. In this study, the primary objective was to learn whether rods or cones are more susceptible to light-induced, all-trans-retinalmediated damage. Previously, we reported that mice lacking enzymes that clear all-trans-retinal from the retina, ATPbinding cassette transporter 4 and retinol dehydrogenase 8, manifested light-induced retinal dystrophy. We first examined early-stage age-related macular degeneration patients and found retinal degenerative changes in rod-rich rather than cone-rich regions of the macula. We then evaluated transgenic mice with rod-only and cone-like-only retinas in addition to progenies of such mice inbred with Rdh8Abca4 mice. Of all these strains, Rdh8Abca4mice with a mixed rod– cone population showed the most severe retinal degeneration under regular cyclic light conditions. Intense light exposure induced acute retinal damage in Rdh8Abca4 and rodonly mice but not cone-like-only mice. These findings suggest that progression of retinal degeneration in Rdh8Abca4 mice is affected by differential vulnerability of rods and cones