The sharpest eyes in the animal world: How does the birds' record-breaking sharp vision work?

Birds have the sharpest vision in the animal kingdom. For example, a white-tailed eagle can spot a fish in the water surface from a height of one kilometre, and even small birds see far more sharply than other animals of the same size.

The secret behind the falcon's gaze is that birds do not have blood vessels in their retinas that would shade the light intake. 

Within the animal kingdom, it is only the birds that lack blood vessels in the nerve tissue that is the retina. In other animals, the blood vessels perform an important function by transporting oxygen and nutrients around to the nerve cells.

»In birds, you have a naturally formed nerve tissue that works without any blood vessels being present, and which does not have the nutrient supply and oxygen supply that all other nerve tissues have. They are exciting from a sensory physiology perspective to understand how extremely sharp vision has evolved among birds,« says Christian Damsgaard, assistant professor at the Department of Biology at Aarhus University, and continues: 

»It is also interesting to understand how nature has solved some of the health problems seen at the clinic, where patients with reduced blood supply to the brain can suffer permanent brain damage in a matter of minutes or hours.«

With support in the form of a Sapere Aude grant from the Independent Research Fund Denmark, Christian Damsgaard will lead a research project that will investigate how the birds' retinas actually function without a constant blood flow.

The chicken is the chosen bird species

In addition to Christian Damsgaard, the research group will consist of a PhD student and a postdoc. They will start from scratch, because there is a limit to how much research has been done on the physiology of the bird retina.

»The sensory biology of the bird retina has been intensively studied, and it has been known for more than 50 years that the bird retina lacks blood vessels. But to make the connection that you can use the bird retina as a model system to understand the physiological adaptations to the extreme environment inside a bird's retina, is something no one has done before,« says Christian Damsgaard.

In order to map the physiology of the bird retina, oxygen and pH levels will be measured in chickens' retinas and the metabolism of the sensory cells will be studied with new molecular biology methods. 

The choice is not accidental, because just like in mice, the genome of chickens has been thoroughly mapped. This makes it possible to study the cell biology of birds in high detail.

»By studying cells from chickens, we will be able to block the production of certain proteins that may be part of the tolerance to not having a blood supply. Then we can see if the animals are no longer able to tolerate having no blood vessels in the retina,« explains Christian Damsgaard.

Perhaps birds can solve people's problems in the long term

When the project group sets out to try to find out how the cells in the retina can exchange nutrients and waste products with each other, the researchers start from a working hypothesis.

The retina contains some support cells, called glial cells, that go all the way through the retina. Therefore, they have the potential to constitute a highway for nutrients and waste products that blood vessels are in other animals.

Whether the hypothesis holds up, the four-year research project will hopefully be able to show.

»We hope to map the fundamental mechanisms that make it possible for the bird retina to function. It's crazy that the blackbird that sits and chirps out in our garden every single morning has some mechanisms that solve some of the problems that make many people sick,« says Christian Damsgaard.

He therefore also hopes that the results of the research can directly benefit people in the long term.

»If we are able to transfer the tolerance mechanisms to mammalian cells, we can potentially treat some types of circulatory diseases in humans. You could say that here we are doing the reverse model of what is typically done in biomedicine, where you try to induce a disease in an animal model. Instead, we look at how nature has solved the same physiological problem,« concludes Christian Damsgaard.