Fundus camera image of a normal, healthy retina of a human eye. In the centre is the optic disc (yellow area), where the retinal veins & arteries leave & enter the optic nerve (healthy, intact blood vessels can be seen radiating from this area in the image). The retina is the innermost coat of the eye & is the expanded portion of the optic nerve; it consists mainly of nervous tissue. When an image is focused on the retina, photosensitive cells (rods & cones) translate light energy into nervous impulses, which are conducted through the optic nerve to the brain.