Retina

"The retina is highly vascularized and consists of various types of cells that are precisely organized into three layers of neural cell bodies: (1) the outer nuclear layer (ONL) filled with the nuclei of photoreceptors, (2) the inner nuclear layer (INL) housing the nuclei of bipolar, horizontal and most of the amacrine cells, as well as (3) ganglion cell layer (GCL) including the nuclei of RGCs and some displaced amacrine cells. In addition, axons and terminal endings of these retinal neural cells form two synaptic layers: the outer plexiform layer (OPL) and the inner plexiform layer (IPL). Dual blood supply is present in the retina to support its daily metabolic demand: the choroidal vessels provide oxygen and nutrients to the photoreceptors located at the outer most layer of the retina while other inner retinal cells, such as RGCs are nourished by the intra-retinal circulation. These retinal micro-vessels contain an inner lining of non-fenestrated endothelial cells surrounded by pericytes and glial processes. More importantly, all of these components are joined together by tight junctions in order to maintain the integrity of the blood retinal barrier.