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The retinal cellular structure. A) The inner blood retinal endothelial cells (RECs) form the blood-retinal barrier (BRB). B) The outer pigmented epithelial cells (PECs) form the retinal pigmented epithelial barrier (PREB). As polarized cells, both retinal endothelial and pigmented epithelial cells possess tight junctions and traverse of nutrients are selectively controlled by transport machineries as carrier-mediated transportation and receptor-mediated transportation.
