\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.
                                               --Milton.
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.