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.
Why do birds have eyes? That sounds like a silly question. Suppose you said, “So they can see,” you would be correct. But that’s not the only purpose for a bird’s eyes.
Bird’s eyes also serve to cool the bird’s body. People sweat, dogs pant, but birds have another cooling system. Flying is a high-energy activity, and it can raise a bird’s body temperature so much that the heat could damage its central nervous system. A bird’s eyes are designed to eliminate this problem.
As the wind rushes past the eyes of a flying bird, it evaporates water from the surface. This evaporation cools the blood in the nearby veins. The cooler blood prevents the temperature of the bird’s brain from going too high. Scientists proved this by putting hoods over the heads of some birds. If the eyes were covered, the brain temperature rose dramatically. If the eyes were uncovered, the brain temperature stayed constant.
You might be surprised to know what animal has the most sophisticated visual system. Its eyes have at least twice as many types of color receptors compared to human eyes. They have three focal points while human eyes have only one. This animal can see both ultraviolet and infrared light, which our eyes cannot do. It has six polarization channels in each eye with high polarization sensitivity and hyperspectral imaging. What is the animal with this incredible visual system? It’s the mantis shrimp–a marine crustacean of the order Stomatopoda.
Researchers studying this animal’s eye say that it not only surpasses the sensitivity of our own visual system, but also captures more visual information, uses less power, and takes up less space than the most sophisticated state-of-the-art cameras. Scientists at the University of Illinois have developed a color-polarization camera based on the mantis shrimp’s visual system. The camera can aid in the early detection of cancer.
Mantis shrimps communicate using polarized light which cannot be detected by predators. They polarize the light by sending it across a reflector rather than the conventional method of sending the light through a lens. Researchers are copying this method of the mantis shrimp to develop a single chip, low-power, high-resolution color-polarization camera. The National Science Foundation and the Air Force Office of Scientific Research are sponsoring the project. The mantis-copied camera concept has great potential for a variety of applications.