Layer of nerve tissue covering the back two-thirds of the eyeball. Light focused onto the retina by the lens of the eye stimulates two types of light-sensitive cells: rods, which are sensitive to low light levels, and cones, which provide detailed vision and colour perception. Chemical changes in these cells trigger nerve impulses, which are assembled by complex connections among retinal nerves into a pattern to be carried through the optic nerve to the visual centres of the brain. Disorders affecting the retina or the macula in its centre decrease vision and can cause blindness. Seealso detached retina; macular degeneration.

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Separation of most layers of the retina of the eye from the choroid, the pigmented middle layer of the eyeball. With age, small tears can develop in the retina, and the vitreous humour inside the eyeball leaks through, separating the retina from the choroid. The disease retrolental fibroplasia or accidents can also cause retinal detachment. It usually develops slowly, without pain. Floating black spots and flashes of light appear in the affected eye, and vision becomes increasingly blurred. Without prompt treatment, it causes permanent blindness. Draining the fluid behind the retina and applying heat, a laser beam, or extreme cold causes scarring that seals the tears and prevents the retina from detaching again.

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