Retinal pigment epithelium melanin granules are phagocytozed by Muller glial cells in experimental retinal detachment

The ability of retinal Muller glial cells to perform phagocytosis in vivo is studied in a rabbit model of experimental retinal detachment where pigment epithelial cells are occasionally detached together with the neural retina. While macrophages and/or microglial cells phagocytoze most of the cellular debris at the sclerad surface of the detached retinae, some Muller cells accumulate melanin granules. The granules are virtually intact at the ultrastructural level, and are surrounded by a membrane. They are often located close to the sclerad end of the cells, but some are distributed throughout the outer stem process up to the soma. It is concluded that rabbit Muller cells in vivo are capable of phagocytosis and of transporting the phagocytozed material within their cytoplasm.