Function
The RPE shields the retina from excess incoming light. It supplies omega-3 fatty acids and glucose, the former for building photoreceptive membranes, the latter for energy. Retinal is supplied by the visual vitamin A cycle. Water is removed from the retinal side to the choroid side, at a rate of 1.4-11 microliters per square centimeter per hour. It maintains balance of pH, and routinely phagocytoses the oldest outer segment discs of the photoreceptors. It has a self-contained immune system, which is connected with the immune system proper to either shut down interactions when healthy, and when there is disease, it teams up with the main immune controls. Finally, it secretes substances to help build and sustain the choroid and retina.
The retinal pigment epithelium also serves as the limiting transport factor that maintains the retinal environment by supplying small molecules such as amino acid, ascorbic acid and D-glucose while remaining a tight barrier to choroidal blood borne substances. Homeostasis of the ionic environment is maintained by a delicate transport exchange system.
In some clinical studies, RPE auto transplant has been used in treating Macular degeneration. Also experimental studies have reported in vitro expanded RPE used in similar studies.
Read more about this topic: Retinal Pigment Epithelium
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