n. a visual pigment associated mainly with function of the retinal rod cells. Rhodopsin consists of the vitamin A aldehyde 11-cis retinal bound to the protein opsin. When activated by light (photons), 11-cis retinal is transformed into all-trans retinal, which detaches from the opsin. This initiates a cascade of events that results in visual transduction. Also called visual purple. See scotopsin; visual cycle.