I. ˈre-tə-nəl, ˈret-nəl adjective
Date: 1838
: of, relating to, involving, or being a retina
II. ˈre-tə-ˌnal, -ˌnȯl noun
Etymology: retin- + -al (III)
Date: 1944
: a yellowish to orange aldehyde C 20 H 28 O derived from vitamin A that in combination with proteins forms the visual pigments of the retinal rods and cones