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Visual \Vis"u*al\, a. [L. visualis, from visus a seeing, sight: cf. F. visuel. See Vision.]

  1. Of or pertaining to sight; used in sight; serving as the instrument of seeing; as, the visual nerve.

    The air, Nowhere so clear, sharpened his visual ray.

  2. That can be seen; visible. [R.]

    Visual angle. (Opt.) See under Angle.

    Visual cone (Persp.), a cone whose vertex is at the point of sight, or the eye.

    Visual plane, any plane passing through the point of sight.

    Visual point, the point 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. Also called rhodopsin, and vision purple. See Optography.

    Visual ray, a line from the eye, or point of sight.

    Visual white (Physiol.), the final product in the action of light on visual purple. It is reconverted into visual purple by the regenerating action of the choroidal epithelium.

    Visual yellow (Physiol.), a product intermediate between visual purple and visual white, formed in the photochemical action of light on visual purple.


n. (context biochemistry English) A light-sensitive pigment in the rod cells of the retina; it consists of an opsin protein bound to the carotenoid retinal


n. a red photopigment in the retinal rods of vertebrates; dissociates into retinene by light [syn: visual purple, retinal purple]


Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction. It is named after ancient Greek ῥόδον (rhódon) for “rose”, due to its pinkish color, and ὄψις (ópsis) for “sight”. Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 45 minutes.

Rhodopsin was discovered by Franz Christian Boll in 1876.

Usage examples of "rhodopsin".

The molecule of rhodopsin is made up of two parts: a protein, opsin, and a nonprotein portion, very similar in structure to vitamin A, which is retinene.

The shape of cis-retinene is such that it can combine with opsin to form rhodopsin, whereas trans-retinene cannot.

In the presence of light, cis-retinene is converted to trans-retinene and, if it already makes up part of the rhodopsin molecule, it falls off, leaving the largely colorless opsin behind.

In the dark, trans-retinene changes into cis-retinene and joins opsin once more to form the rhodopsin.

The molecule of rhodopsin is made up of two parts: a protein, opsin, and a nonprotein portion, very similar in structure to vitamin A, which is retinene.

The bleaching of rhodopsin and the narrowiviy of the pupil on re-emergence into full light is light adaptation.

It is commonly called visual purple (though it is not purple), but its more formal and more accurate name is rhodopsin (roh-dop'sin.