Dogs have been close companions of humans for tens of thousands of years, and the objects of close scientific study for many centuries.

Yet researchers at the School of Veterinary Medicine and the Perelman School of Medicine have recently discovered something brand-new about canine eyes that has the potential to improve treatments for blinding retinal diseases in humans.

“It’s incredible that in 2014 we can still make an anatomical discovery in a species that we’ve been looking at for the past 20,000 years, and that, in addition, this has high clinical relevance to humans,” says William Beltran, an assistant professor of ophthalmology at Penn Vet and co-lead author of the new study with Artur Cideciyan, a research professor of ophthalmology at Penn Medicine.

Beltran, Cideciyan, and colleagues, including Gustavo Aguirre of Penn Vet and Samuel Jacobson of Penn Medicine, have been studying blindness in dogs for years. Previous research has shown that several conditions that rob the sight of dogs affect humans in similar ways. But it was commonly understood that dogs lacked a feature of primate eyes called the fovea—a tiny pit in the center of the retina that is jam-packed with the photoreceptor cells called cones and crucially important for tasks like reading and driving.

In this study, however, published in the journal PLOS ONE, Penn researchers have turned that assumption on its head. Using advanced imaging techniques that allowed them to characterize the retina layer by layer, they discovered a miniscule region of very high cone density in the center of the retinas of dogs.

Counting the cells in this region, they found densities of more than 120,000 cells per square millimeter, a number several times higher than any previously reported in canines, and on par with cone densities in primate foveas.

Taking the finding a step further, they examined dogs that had mutations in two genes that can cause macular degeneration in humans and found that the fovea-like region of dogs was affected similarly to how the disease affects people.

“Our findings, which show the canine equivalent of a human genetic disease affecting an area of the retina that is of extreme importance to human vision, are very promising from the human point-of-view,” says Cideciyan. “They could allow for translational research by allowing us to test treatments for human foveal and macular degenerative diseases in dogs.”