The process by which cells engulf materials (e.g., bacteria, dead cells) that are eventually killed, destroyed or digested. The outer segment tips of photoreceptor cells are phagocytosed every day by RPE cells.
Phagocytosis is the cell's process of engulfing solid particles by the cell membrane, forming an internal "food vacuole" or "sack". This sack is internalized and the contents are subsequently degraded and either released or retained for recycling. Some retinal degenerative diseases (e.g., some forms of Stargardt disease) are thought to be caused by problems with this phagocytosis.