Retina. Coloured scanning electron micrograph (SEM) of a section through a freeze-fractured retina, showing the light-sensitive rods and cones and their associated neurones. Light entering the eyes passes through the bipolar neurones in the nuclear layers (grey, lower frame). It then hits the rods and cones (pink yellow, upper frame). The rods, used in dim light, are found at the retinal margins. The cones, which control colour vision and acuity (sharpness), function best in bright light. They are concentrated in the centre of the retina. Information from both is passed to the neurons, which relay it to the optic nerve (not seen).