What is "photoisomerase"

n. (context enzyme English) Any of a group of enzymes that catalyse the isomerization of photopigments

A photoisomerase is a protein in the eye that is responsible for isomerizing photopigments.

In order for the eye to function properly, a special chemical called a chromophore is bound to a protein known as an opsin. When a photon strikes the chromophore, it changes shape (isomerizes). It is this change in conformation that the protein detects and eventually leads to vision. Before the chromophore can be reused, it must be converted back to its original conformation. The photoisomerase is the protein responsible for this change. In the mammalian retina, they are believed to be confined to the retinal pigment epithelium.