How reindeer eyes change colour in winter to help them see in the dark

It turns out reindeers’ amazing night vision is thanks to a strange ‘mirror’ in their eyes called the tapetum lucidum that is extra sensitive to UV light

Life



14 December 2022

By David Robson

AS SURPRISE presents go, two pots of reindeer eyeballs are hardly at the top of most people’s wish lists – even if you are a vision scientist like Glen Jeffery.

It was 2008 when the macabre packages arrived. They had been sent by two of Jeffery’s colleagues in Norway, who wanted him to investigate how reindeer manage to see in the winter, when the sun fails to rise above the horizon for months on end. “Half the eyeballs were collected in midsummer and half the eyeballs were collected in midwinter,” says Jeffery, who is based at University College London. To begin with, he wasn’t optimistic. A quick dissection, he suspected, wouldn’t reveal anything of particular interest.

But, to his surprise, when he took an eyeball from each pot and cut them open, a striking difference was visible straight away. Whereas the inside back surface of the summer eyeball was golden with a turquoise halo, the winter one was an astonishingly deep blue. It suggested that the eyes of reindeer – known as caribou in North America – could change with the seasons.

Jeffery’s curiosity was piqued. And so began his mission to understand the mysterious colour-changing structure in the eyes of reindeer, and the impact it has on their ability to see in the dramatically different seasonal light conditions of the Arctic.

Like all good scientists, Jeffery is keen to pay his debt to his forebears. He admits he is standing on the shoulders of the British photographer and ophthalmologist George Lindsay Johnson. Working in the late 19th and early 20th centuries, Johnson spent days in a darkened room at London Zoo …