Twice a Year, Reindeer Eyes Pull Off a Wonderful Magic Trick

Of all the eyeballs in Glen Jeffery’s office, only a very small minority are his.

“Oh, I’ve got an office full of eyes,” Jeffery, a neuroscientist at University College London, told me. Over Skype, he fished one of his favorites out of an opaque vial: About the size of a golf ball and fringed with white tissue, it looked a bit like a poached egg with a slate-hued yolk. The prized specimen was a reindeer eye, an organ that has captivated Jeffery for decades because of the beguiling metamorphosis it undergoes each year in the animals’ Arctic home.

During the summer, when the sun spends , the inner parts of the animals’ eyes, a structure called the tapetum lucidum, gleam a shimmering of winter, their eyes turn a rich blue. The change isn’t easily noticeable in live reindeer, simply strutting about. But the first time Jeffery dissected both summer and winter eyes in his lab and spotted the difference, “I nearly fell off my seat,” he said. “I’d never seen an animal able to its tapetum.”