Different Season...Different Eyes

[amy]

Reindeer, such as the adult female seen here , change the color of their eyes in response to the seasons.




During the 24-hour darkness of winter, reindeer eyes reflect the predominant colour of blue (inset right), while in the continuous sunlight of the summer, the eyes shine yellow.
Scientists say the animals change their eye color and structure with the seasons in Arctic regions where permanent summer sunlight is replaced by 24-hour darkness in winter.


The visual alterations appear to be an adaptation to deal with polar light extremes, according to the researchers from Norway and the U.K., who add that the phenomenon has never before been recorded in mammals.


The researchers studied reindeer from the Lapland region of northern Scandinavia and found that eyes removed from animals culled in winter appeared deep blue when light was shined into them.

But the eyes of summer reindeer were yellow in color.


Scientific Reason

For reindeer, the key may be changes in the reflective membrane behind the eye's retina called the tapetum lucidum ("bright carpet").

The blue of winter reindeer eyes "helps the retina make the best of its signals when the lights go down," explained co-researcher Glen Jeffery of the Institute of Ophthalmology at University College London.

"The blue is favoring a dark environment," he added.


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