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Birds’ Eye Design - Bar-headed goose — Bar-headed goose (Anser indicus)

A group of biologists has finally solved one of the great mysteries of biology. For decades, scientists have wondered how birds can have keen eyesight without blood vessels to supply oxygen to the retina. Blood vessels provide vital oxygen to the retinas of other animals, but the birds’ eye design is different.

Without blood vessels that scatter the light reaching the retina, the birds’ eye design enables sharper vision. How can the retinal cells function without dying from lack of oxygen? The answer, according to researchers at Aarhus University in Denmark, is anaerobic glycolysis. “Anaerobic” means without oxygen, and “glycolysis” refers to the process of breaking down the sugar glucose. Anaerobic glycolysis is less efficient than oxygen-based metabolism, and birds’ eyes need a lot of energy. How can they get enough energy with this less-effective method?

The birds’ eye design features a unique structure that no other species has. A comb-like network of blood vessels called the pecten oculi protrudes from where the optic nerve enters the eye and moves freely within the vitreous humor, the fluid filling the eyeball. The pecten oculi transports glucose into the vitreous humor while removing carbon dioxide and lactic acid that could harm the retina.

This discovery explains how birds like bar-headed geese can fly at elevations over 6000 meters, where oxygen is scarce. The DNA of these birds is coded to overcome specific environmental challenges while maintaining sharp vision. Encoding requires an intelligent programmer who understands what birds need to survive. Bird’s eye design, like every scientific discovery, gives us a window into the creation of life on planet Earth.

Reference: “Briefings” in American Scientist for March/April 2026, page 77.

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.

So now you know. If someone asks you, “why do birds have eyes,” you can tell them, “To keep their brains cool.” We see many other amazing designs in birds. (Why do they fly north in spring? Why don’t they have ears? Why do some birds stand on one leg?) The design we see in all of life truly shows the wisdom of God.

Tag: bird eyes

Birds’ Eye Design

Why Do Birds Have Eyes?