The eyes of a reindeer are not only gorgeous, but they are also a scientific marvel. As summer fades into winter, the animal’s eyes shift from golden to deep blue, allowing it to see in radically varied light levels.
In 2011, scientists revealed that reindeer had a built-in air conditioning system to protect their natural fur coats from overheating. There is also evidence that their eyes change hue to aid vision. Reindeer have yellowish-gold eyes in their natural environment during the day, but during the winter, the eyes become a distinct shade of blue. The only mammal whose eyes change color depending on the season is the arctic reindeer.
The tapetum lucidum is the portion that changes colour. Some animals can see in the dark thanks to a glossy, reflective layer below the retina. When light enters the eye, a large portion of it is absorbed by the retina’s sensitive cells. However, it occasionally misses the point. The tapetum lucidum provides the eye with a second opportunity to perceive light by reflecting it back towards the retina. This reflective coating in many animals, glows gold all the time. While reindeer eyes are gold in the summer, they become blue in the winter.
Glen Jeffery, a neurologist at University College London, argues that since blue light is dispersed more, photons continue to bounce inside the eyes, boosting their chances of being caught by the retina. However, Dan-Eric Nilsson, a vision researcher at Lund University, believes that the enhanced sensitivity is due to higher amounts of light-sensitive pigments in the retina.
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