ABSTRACT Age-related macular degeneration (AMD) is a common cause of severe vision loss. Recent studies have shown that a layer of capillaries called the choriocapillaris is affected in AMD, both in “dry” AMD in which the blood vessels degenerate, depriving the retina of nourishment, and in “wet” AMD in which the cells become activated to grow abnormally, damaging the retina. To a large extent the biochemical changes in the choriocapillaris that accompany AMD are poorly understood. In this proposal we will study how a gene that is affected by the complement system and is enriched in AMD cells contributes to the processes associated with the choriocapillaris in AMD. We will also utilize a new technology (single cell RNA-sequencing) to discover the molecular signatures of endothelial cells from the choroid at the single cell level of resolution in health and different forms of AMD. A better understanding of how these cells are altered in disease will provide insight into how to protect them from damage and death.