– 11-cis Retinal is a chromophore that binds to opsin in the mammalian visual system as an inverse agonist forming the inactive conformation of rhodopsin. When 11-cis retinal absorbs a photon of light, it isomerizes to form all-trans retinal beginning the phototransduction cycle, which is the basis for mammalian vision. A G121L mutation in opsin allows 11-cis retinal to bind as a partial agonist and activate rhodopsin in the absence of light. In a moth model of carotenoid deficiency-induced low visual sensitivity, 11-cis retinal application to compound eyes restored visual sensitivity almost completely.