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.
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.