The eyes of the reindeer hide an inner variation. Behind the retina is a reflective layer, the tapetum lucidum. It sends light back to the sensitive cells, giving them a new possibility to capture it. In the reindeer studied, this internal mirror changes with the seasons.
In summer, the light he reflects looks golden. In winter, it turns blue. This change accompanies increased sensitivity in the prolonged darkness of the Arctic regions. It is not an iris that recolors as an accessory: the transformation concerns a structure located at the bottom of the eye and the way it interacts with light.
A proposed explanation involves pressure in the eye, related to the prolonged dilation of the pupil. The collagen fibers in the mirror would get closer, altering the reflected wavelengths. This mechanism remains an explanatory hypothesis. The observed fact is striking: the same animal has a different eye reflection between summer and winter.
What we know
The pressure mechanism remains a proposed explanation.
To go to the source
References consulted on September 21, 2026. Linked pages may be in another language.
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