Cis-Trans Isomerism in Vision

Introduction

The retina, the light-detector layer in the back of our eyes, contains colored compounds called visual pigments. They are insoluble in water and can be extracted from the retina with aqueous detergents. In the dark these pigments are reddish (their name, rhodopsin, comes from a Greek word meaning rose-colored), but the color fades upon exposure to light (Craig & Chen: 47).

The change in rhodopsin conformation is eventually transmitted to the nerve cells in the eye and then the brain. The stereoisomerism of retinal is thus an important part of the vision process. Note that only one of the ...