Visual field loss in RCS rats and the effect of RPE cell transplantation

The consequences of progressive retinal degeneration on central visual function were studied by recording single and multiunit receptive fields (RFs) across the surface of the superior colliculus (SC) of pigmented dystrophic RCS rats. Retinal morphology was used to provide a correlation between function and histological appearance. In addition, the potential protective effect of retinal pigment epithelium (RPE) transplantation was studied in a similar manner in dystrophic animals in which RPE cells were injected into the subretinal space, or the vitreous humor, at between 21 and 28 days of age. The visual responsiveness of SC units in dystrophic rats differed markedly from those in nondystrophics. Dystrophic rats developed a relative scotoma beginning in the central visual field by 42-45 days of age and expanding to include 50% of the visual field by 97-107 days. In contrast, following subretinal RPE transplantation, there was photoreceptor rescue correlated with a partial to complete preservation of RF representation when examined at 85 to 108 days of age. The majority of photoreceptor rescue occurred in the region of graft placement with possible low level rescue across the central retina. Dystrophic animals that had received intravitreal RPE transplants showed poor photoreceptor survival as well as minimal functional preservation. Our results indicate that there is a progressive central to peripheral loss of visual responsiveness in the SC of dystrophic RCS rats which can be limited by subretinal injections of healthy RPE cells.