Pigmentepitel

Pigmentepitel, or retinal pigment epithelium (RPE), is a monolayer of pigmented epithelial cells located between the neural retina and the choroid. The cells contain melanin pigment, which absorbs excess light and helps prevent photo-oxidative damage, contributing to visual quality and protection of photoreceptors.

The RPE rests on Bruch’s membrane and forms part of the outer blood-retina barrier via tight junctions between adjacent cells. It maintains retinal homeostasis by actively transporting ions, water, and metabolic waste, and by phagocytosing shed outer segments of photoreceptors on a daily basis. The RPE also supports the exchange of nutrients and metabolites between the retina and the choroidal blood supply.

A central function is participation in the visual (retinoid) cycle. Retinal isomerization and regeneration occur partly in the RPE, with enzymes such as RPE65 and LRAT catalyzing key steps to produce 11-cis-retinal. This molecule is delivered back to photoreceptors to restore visual pigment, aided by retinoid-binding proteins in the interphotoreceptor space.

Development and clinical relevance: the RPE originates from neural ectoderm during development and remains essential for photoreceptor survival. Dysfunction or degeneration of the RPE is central to multiple retinal diseases, most prominently age-related macular degeneration (AMD) with geographic atrophy, and several inherited dystrophies such as Best disease. Therapeutic approaches include strategies aimed at preserving, repairing, or replacing RPE function.