11-cisRetinol is an isomer of vitamin A . It is formed from vitamin A,viaatrans-retinyl ester intermediate, by the enzyme RPE65 in the retinal pigment epithelium and then converted to 11-cis retinal as part of the visual cycle.1,211-cisRetinol is an agonist of salamander and human red rod opsins expressed in COS cells and an inverse agonist of salamander red cone opsin, as well as human red and green cone opsins expressed in COS cells.3It promotes pigment formation in cone, but not rod, photoreceptors.