The retina is a thin film of nervous tissue, about the consistency of wet cigarette paper. It actually an extention of the brain. It covers the inside wall of the eye, like wallpaper covers the inside wall of a room. Since the eye is more or less spherical, the retina is also more or less spherical. At the back, it is attached to the optic nerve, which is a ribbon of brain tissue connecting the eye with the brain. In the front, the retina stops around the apparatus that directs light rays to the retina. This apparatus is composed of the cornea and the crystalline lens. Since it is awkward to represent the retina on paper, because the retina is roughly spherical, doctors sketch the retina as if it were flat
The retina is a light-sensative and it covers about 65% if the interior surface of the eye. Light enters the pupil, is focused and inverted by the cornea and lens, and is projected onto the back of the eye. At the back of the eye the retina, processes the light and converts a light signal into a neural signal ("signal transduction"). The actual photoreceptors are the rods and cones, but the cells that transmit to the brain are the ganglion cells. The axons of these ganglion cells make up the optic nerve, the single route by which information leave.