retina defined in 1951 yearretina - retina;
retina - Layer lining interior of vertebrate eye, except in front (in region of ciliary body); it is sensitive to light. It has an outer pig-mented layer, next to the choroid; and an inner transparent nervous layer next to cavity of eye-ball. The nervous layer contains light-sensitive rods and/or cones in contact with pigmented layer; and nerve-fibres, intermediary nerve cells, bloodvessels and glia, interposed between incoming light and rods and cones. Embryologically part of the brain. Develops as hollow out-pushing of brain wall, whose outer end becomes dinted in to form a stalked cup; the double-walled cup forms the two layers of the retina, the stalk forms optic nerve. See also: Fovea; See also: Blind spot. In molluscs the retina is formed not from the nervous system but from the external ectoderm, and the light-sensitive cells are external to the nerve-fibres, etc.
near retina in Knolik
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