Reindeer are a species of deer native to the Arctic, sub-Arctic, tundra, boreal, and mountain regions of northern Europe, Siberia, and North America. People require contact lenses to change the colour of their eyes. Scientists have discovered that the reindeer’s beautiful eyes change colour radically between summer and winter to adapt to extreme changes in luminous intensity. In summer, the eyes of reindeer are golden and in winter, they become deep and rich blue. This change in colour allows reindeer eyes to catch more light during the dark Arctic winter months.
SepThese colours each has a different visual advantage, either by allowing them to see through the dark, or by preventing them from squinting in the sunny glare. The part that changes colour is a layer of tissue that rests behind the retina known as tapetum lucidum. As this layer is reflective, the light is reflected on the retina by increasing the amount of light available for photoreceptors. Reindeer apparently increase the pressure inside the eyeball during the winter to compress those fibres together and the reduced spacing between those fibres makes the eyes reflect blue light. In summer, it becomes golden in numerous reindeer, reflecting most of the light through the retina, helping the reindeer to face the almost continuous daylight of the Arctic summer.
