Scientists report that tiny tube-like protrusions called primary cilia on cells of the retinal pigment epithelium (RPE) -- a layer of cells in the back of the eye -- are essential for the survival of the retina's light-sensing photoreceptors. The discovery has advanced efforts to make stem cell-derived RPE for transplantation into patients with geographic atrophy, otherwise known as dry age-related macular degeneration (AMD), a leading cause of blindness in the US.