Editing Vitamin A (section)

====Vision====
{{Main|visual cycle}}
The role of vitamin A in the visual cycle is specifically related to the retinal compound. Retinol is converted by the enzyme [[RPE65]] within the retinal pigment epithelium into 11-''cis''-retinal. Within the eye, 11-''cis''-retinal is bound to the protein [[opsin]] to form [[rhodopsin]] in rod cells and [[iodopsin]] in cone cells. As light enters the eye, the 11-''cis''-retinal is isomerized to the ''all-trans'' form. The ''all-trans''-retinal dissociates from the opsin in a series of steps called photo-bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. After separating from opsin, the ''all-trans''-retinal is recycled and converted back to the 11-''cis''-retinal form by a series of enzymatic reactions, which then completes the cycle by binding to opsin to reform rhodopsin in the retina.<ref name=PKIN2020VitA/> In addition, some of the ''all-trans''-retinal may be converted to ''all-trans''-retinol form and then transported with an interphotoreceptor retinol-binding protein to the retinal pigmented epithelial cells. Further esterification into ''all-trans''-retinyl esters allow for storage of ''all-trans''-retinol within the pigment epithelial cells to be reused when needed. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin, and will lead to one of the first symptoms, night blindness.<ref name=PKIN2020VitA/><ref name="Combs2008">{{cite book |title=The Vitamins: Fundamental Aspects in Nutrition and Health | vauthors = Combs GF |year=2008 |edition=3rd |publisher=Elsevier Academic Press |location=Burlington, MA |isbn=978-0-12-183493-7}}</ref><ref name="Miller"/>