Bird retinas work without oxygen – solving an old biological puzzle
Neural tissue normally dies quickly without oxygen. Yet bird retinas − among the most energy-demanding tissues in the animal kingdom – function permanently without it. This allowed birds their razor sharp vision and ability to migrate at high altitudes.
Most animals need a constant supply of oxygen to their neural tissue – but not birds. Now, a new study in Nature reveals how birds manage without and maintain vision in a retina that functions permanently without oxygen.
The discovery overturns centuries of assumptions about eye biology and may eventually inspire new approaches to treating stroke.
The work was led by biologist and Associate Professor Christian Damsgaard from Department of Biology – Zoophysiology at Aarhus University and had contributions from a number of colleagues, including Professor Coen Elemans from Department of Biology at SDU. The team’s own scientific article in Nature can be found here.
Nature's Own Design is a Paradox
Bird retinas contain no blood vessels, a feature that sharpens vision by allowing light to reach the photoreceptors without obstruction. This design has long posed a paradox, as the retina is one of the most energy-demanding tissues in the body and should be unable to function without a continuous oxygen supply.
Using advanced physiological measurements the research team has now shown that the inner retinal layers rely entirely on anaerobic metabolism – an energy process typically associated with short-term survival rather than continuous function.
The findings prompted a reevaluation of the pecten oculi, a mysterious comb‑shaped structure in the bird eye that has historically was assumed to deliver oxygen to the retina. Through imaging techniques, spatial transcriptomics and metabolic analyses, the researchers demonstrate that the pecten serves a completely different purpose: it transports large amounts of glucose into the retina and removes lactate, the waste product of anaerobic metabolism.
In this way, birds maintain a vessel-free retina that supports high visual performance while avoiding the optical interference caused by blood vessels. Evolutionary evidence suggests that this strategy emerged early in the dinosaur lineage leading to modern birds.
What it Means for Researchers in Strokes
“Establishing the function of this enigmatic structure in the birds’ eye is super cool”, Coen Elemans says. “This pecten allows a snake eagle the incredible acuity of vision to spot a tiny still lizard from great heights, but also may have had a crucial role in allowing birds to migrate. That is wild!”
The results offer new perspectives on how tissues can survive long-term oxygen deprivation. Conditions such as stroke involve both reduced oxygen delivery and buildup of metabolic waste. Understanding how bird retinas avoid these problems may help inspire future medical solutions.
The study represents eight years of interdisciplinary work involving physiology, imaging, and molecular biology.
Elemans adds “This study is really a tour de force and a beautiful piece of work that combines the expertise and hard work from many people.”
Meet the Researcher
Coen Elemans is a Professor at Department of Biology. His studies include animal sound production and communication.