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retina |
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retina: see vision vision, physiological sense of sight by which the form, color, size, movements, and distance of objects are perceived.
Vision in HumansThe human eye functions somewhat like a camera; that is, it receives and focuses light upon a photosensitive ..... Click the link for more information. ; eye eye, organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many ..... Click the link for more information. . retinaLayer 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. See also detached retina; macular degeneration. |
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| The flare was momentary, followed by black darkness, in which, however, the apparition still showed white and motionless; then by insensible degrees it faded and vanished, like a bright image on the retina after the closing of the eyes. "And isn't strange, said the young lady, passing with startling suddenness from Sentiment to Science, "that the mere impact of certain coloured rays upon the Retina should give us such exquisite pleasure? Mellowed in the drowsy sunlight of a summer's afternoon, Wargrave, nestling where the river bends, makes a sweet old picture as you pass it, and one that lingers long upon the retina of memory. |
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retina
