Rhythmicity of the Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) forms the outermost layer of the retina. Its interactions with outer segment portions of rod and cone photoreceptors are essential for vision. Among the many essential support functions of the RPE for photoreceptors, the contribution of the RPE in photoreceptor outer segment renewal is strictly rhythmic occurring once a day for both rods and cones. RPE cells contribute to shedding of distal outer segment tips of photoreceptors and are solely responsible for the concomitant clearance of shed debris by phagocytosis. Here, we discuss current knowledge of how the diurnal rhythm is established and how the rhythm translates into synchronized activation of the phagocytic machinery of the RPE.