Phagocytosis of photoreceptor outer segments during retinal development in utero.

The retinal pigmented epithelium of the fetal guinea pig was examined for evidence of phagocytosis and degradation of outer segments. Beginning at the early stages of outer segment formation and continuing through the remaining fetal period, pigment epithelial cells contained large and small phagosomes with multi-lamellated internal structure. Thus, mammalian retinal photoreceptor cells which normally develop and mature in utero in the absence of light undergo a process of phagocytosis of outer segemnt fragments comparable to that found in species whose retinae mature postnatally outside of the uterus.