Retina of the eye. Light micrograph of a section through the retina from a human eye. From top down: nerve fibres of the optic nerve and a blood vessel; several layers of neurons (nerve cells) and synapses (nerve junctions); vertically arranged photoreceptor neurons terminating as rods or cones. These make contact with the thin, brown pigmented epithelium. Beneath this is a wide zone making up the heavily pigmented and vascularised choroid, and finally the tough, collagen-rich and protective sclera. Magnification: x139, when printed 10 centimetres high.