RETINAL PIGMENT EPITHELIUM
The retinal pigment epithelium is a monolayer that lies between photoreceptor outer segments and Bruch’s membrane. The estimated number of retinal pigment epithelial cells is about 4-6 million cells per eye. This epithelium has many functions, including matrix production for photoreceptors, phagocytosis or outer segments, barrier protection, and active transport. These cells are large; are polygonal in shape; and contain abundant cytoplasm, round nuclei, and single nucleoli. The cytoplasm contains large distinctive ovoid and elliptical pigment granules. The retinal pigment epithelium has a remarkable potential to proliferate and undergo metaplastic transformation. RPE cells in the macula (in a 4 mm diameter region) are taller and more pigmented than elsewhere in the retina. At the ora serrata RPE cells are flatter and wider.
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