pigmentepithelium

Pigment epithelium, commonly known as the retinal pigment epithelium (RPE), is a pigmented monolayer of cells located between the neural retina and the choroid. It forms part of the outer retina and plays a critical role in photoreceptor maintenance and visual function. The RPE derives from the outer layer of the optic cup.

Anatomy and structure: RPE cells are polygonal, highly pigmented due to melanin, and are joined by tight junctions that create the outer blood-retinal barrier. The apical membranes have densely packed microvilli that interdigitate with photoreceptor outer segments; the basal side interacts with Bruch's membrane and the choroid.

Functions: The RPE absorbs excess light to reduce scatter and protect photoreceptors. It participates in the visual cycle, regenerating 11-cis-retinal via enzymes such as RPE65. It phagocytoses shed photoreceptor outer segments daily, recycling disk material. It transports nutrients, ions, and fluid between the choroid and retina, and maintains the outer blood-retinal barrier. It also secretes factors such as PEDF and VEGF to regulate the choriocapillaris and inflammation, and participates in immune surveillance.

Clinical relevance: RPE dysfunction is central to several diseases, notably age-related macular degeneration (AMD), which can cause geographic atrophy or neovascular AMD. Other conditions include inherited maculopathies and retinal detachment involving the RPE. Advances in understanding RPE biology underpin therapeutic approaches such as cell transplantation and gene therapy.