Pigment drives muscle movement in cats' eyes

Pigment in iris can control cats' pupils

source: New Scientist vol 212, no 2837, November 5 2011 p18

A pigment in the iris of a cat's eye can control the movement of the pupil. This is also true of hamsters, dogs and other animals which are active at dawn, dusk and during the night. Previously, messages from the brain were seen as the way the pupil changed size. A team led by King-Wai Ya, from Baltimore's John Hopkins University, have found that a pigment called melanopsin also controls pupil size. This may help prevent such animals from being dazzled by sudden bright light. Fish, amphibians and birds use the pigment in the same way.