The retina is made up of photoreceptors—rods and cones. These are located along the outer surface of the retina adjacent to the pigment epithelium. The blood supply of the photoreceptors is derived from the choroid and not from blood vessels on the inner retinal surface. There are about 120 million rods and only 7 million cones in each eye. Rods are uniformly distributed throughout the retina and are responsible for night and monochromatic vision. They contain the pigment rhodopsin. Cones, however, are concentrated in the fovea and are responsible for bright and colour vision. Cones contain opsins that are sensitive to red, green and blue.
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