The pigment epithelium has two types of processes: (1) relatively slender, fringe-like villi projecting between the outer segments of the photoreceptors, and (2) broad, rampart-like cytoplasmic sheets encompassing the tips of the outer segments. The latter processes play an important role in the normal cohesion between neuroretina and pigment epithelium. In addition, they are capable of phagocytosing the tips of outer segments by protruding inward from all sides. This leads to the formation of pigment epithelial inclusions termed "phagosomes." The phagosomes disintegrate in the pigment epithelium, which results in a change of their morphology. A classification for these morphologically different pigment epithelial inclusions is proposed.
Spitznas M, Hogan MJ. Outer Segments of Photoreceptors and the Retinal Pigment EpitheliumInterrelationship in the Human Eye. Arch Ophthalmol. 1970;84(6):810-819. doi:10.1001/archopht.1970.00990040812022