Reindeer Eyes Designed for the Arctic

The eyes of reindeer, also known as caribou, are different from those of any other mammal. The retinal tissue known as tapetum lucidum in reindeer eyes changes color from gold in the summer to vivid blue in the winter. Many nocturnal mammals have this mirror-like layer that reflects light, causing “eye shine” and allowing the photoreceptors to sense dim light. Only in reindeer eyes does it change color with the seasons.

Lichens are a main staple of the reindeer diet and are very common in northern latitudes where reindeer live. A lichen known as “reindeer moss” is an off-white color, making it difficult to see in the snow. However, snow reflects ultraviolet (UV) light, and the lichen absorbs it. The changing color of the retinal tissue is designed to make the lichen stand in dark contrast to the white snow.

UV light damages the eyes, so the cornea and lens suppress the UV radiation in most animals. Some of us have experienced temporary snow blindness caused by UV light, and excessive exposure can lead to cataracts. However, reindeer eyes are designed to admit up to 60% of UV light. Reindeer moss has “impressive antioxidant properties,” which may help prevent UV light damage. Also, reindeer feed on the buds and leaves of Arctic willow and dwarf birch, which have high levels of Vitamin C (ascorbic acid), which helps repair damaged cells.

From September to April, animals such as reindeer living above 70 degrees latitude experience the violet-blue of twilight for 8-11 hours daily. Reindeer eyes display another example of a specialized design unique to one species, giving the animal tools for survival in its environment. Predatory white wolves are well camouflaged in the snow but appear relatively dark to a reindeer detecting UV light.

The color-changing tapetum, unique to the reindeer species, is difficult to explain by gradual chance mutations. We suggest it is another example of how God has produced special equipment to enable an animal to survive in a challenging environment.

— John N. Clayton © 2024

Reference: “Reindeer and the quest for Scottish enlichenment” in i-Perception, Sage Journals