Scientists at the University of Tromsø in Norway have discovered that the eyes of arctic reindeer change colour in the course of a year. The colour transition alters the sensitivity of the animal’s retina to different intensities of light. During the summer, their eyes are gold coloured – enabling them to reflect bright light back directly through their retinas. With the arrival of winter, their eyes change to a dark blue – which reflects less light. The new colour helps the reindeer spot predators in the Arctic’s low winter light, increasing their chance of survival.