SEM of rods and cones, showing the structure of the eye retina. The retina is a thin tissue layer on the inner eye responsible for sight. Light strikes from the top. At top are nerve fibers which combine to form the optic nerve to the brain. Nerve fibers have round cell bodies with branching dendrites. Rods are long nerve cells which respond to dim light, enabling images to be detected. Cones are shorter cone-like cells which detect color. Rods and cones pass visual signals through the optic nerve to the brain. Pigment cells block light from passing further. Magnification: unknown.