Why reindeer eyes change color over the course of the year

What's golden in summer but blue in winter?  Reindeer eyes. Here is why they are so unique.

Transcript

00:00In summer, it's the same colour as most other mammals. It's a golden colour and you find

00:22that in cows, you find that in sheep, you can find it in your cat. However, in winter

00:28it turns to a very, very deep blue.

00:58It's a very, very deep blue.

01:28That is the primary problem for the reindeer. Can I see something moving? That is a potential

01:54threat. I've got to run, I've got to move. So he needs to be sensitive to low light levels

01:59and he needs to be sensitive to movement at low light levels. That's what this animal

02:04does.