retina

Light-sensitive layer of the eye. In vertebrates, looking from outside, there are four major cell layers: (i) the outer neural retina, which contains neurons (ganglion cells, amacrine cells, bipolar cells) as well as blood vessels; (ii) the photoreceptor layer, a single layer of rods and cones; (iii) the pigmented retinal epithelium (PRE or RPE) ; (iv) the choroid, composed of connective tissue, fibroblasts, and including a well-vascularised layer, the chorio capillaris, underlying the basal lamina of the PRE. Behind the choroid is the sclera, a thick organ capsule. See retinal rods, retinal cones, rhodopsin. In molluscs (especially cephalopods such as the squid) the retina has the light-sensitive cells as the outer layer with the neural and supporting tissues below.