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Of or pertaining to chemical action of light, or produced by it; as, the photochemical changes of the visual purple of the retina.

the retina, held in solution by fats, and slowly decolorized by light; distinct from the photochemical pigments of the rods of the retina.

An image of external objects fixed on the retina by the photochemical action of light on the visual purple. See Optography.

The production of an optogram on the retina by the photochemical action of light on the visual purple; the fixation of an image in the eye. The object so photographed shows white on a purple or red background. See Visual purple, under Visual.

at which the visual rays unite; the position of the eye. -- Visual purple (Physiol.), a photochemical substance, of a purplish red color, contained in the retina of human eyes and in the eyes of most animals. It is quickly bleached by light, passing through the colors, red, orange, and yellow, and then disappearing.…