Photo by: iPhoneLomo.com
It’s an age-old question: Why did the chicken cross the road?
And here’s an answer you’ve never heard before: To see all that colorful stuff on the other side.
As the results of a recent study indicate, chickens do a better job of perceiving color than you and I, which researchers attribute to the way their retinas are organized and structured.
The study mapped five types of light receptors in the eyes of chickens. It determined that their light receptors are laid out in “interwoven mosaics” that maximize their ability to see many colors throughout the retina.
Dr. Joseph C. Corbo, of Washington University School of Medicine in St. Louis, Missouri, the study’s author, says, “The color receptor organization in the chicken retina greatly exceeds that seen in most other retinas and certainly that in most mammalian retinas.”
Why would chickens end up with better color vision than us? Somehow, it just doesn’t seem fair.
The answer likely can be found in the evolutionary history of poultry and other bird species; specifically, their dinosaur ancestry. Dr. Corbo speculates that birds developed acute color vision because they did not spend any part of their evolutionary history in the dark. Apparently, while dinosaurs were out cavorting during the day, most mammals became nocturnal (a logical way to avoid becoming a meal for T-Rex and his friends).
Because they do not have a lengthy nocturnal period in their history, birds developed more retinal cone cells (which function best in relatively bright light) than mammals. Cones are also the vision cells responsible for color perception, and different cones detect different wavelengths of light. You and I have three kinds of cones that allow us to see red, green and blue. But birds have an extra cone, which allows them to see violet and ultraviolet light.
This line of research is important because it may help pave the way for the use of stem cells and other new techniques to treat the nearly 200 genetic disorders that can cause various forms of blindness.
What may be surprising is the connection between Dr. Corbo’s research and Acucela. Because mammals spent much of evolutionary history as being nocturnal, we developed rod photoreceptors and ultra-sensitive retinas, compared to chickens’ cone-photoreceptors, which are more tolerant to light. It is our rod dominance that is believed to be the underlying cause age-related macular degeneration (AMD). With excessive daytime light exposure, the rods will be over stimulated and produce toxic byproducts, including A2E, which is implicated in AMD. Because rod photoreceptors are also known to be more susceptible to the prolonged light exposure, we want to specifically avoid the over stimulation of rod photoreceptors, to reduce the accumulation of toxic byproduct and subsequent cell death. This is the underlying scientific base for Acucela’s visual cycle modulation treatment paradigm for the treatment of dry AMD.
So let’s not be jealous of our feathered-friends’ outstanding color vision—our understanding of it may prove to be very helpful in treating human vision problems in the future.
