Two veterinary scientists that specialize in canine vision have discovered that a dog's retinal area may be exactly like humans. In a recent research paper, both Dr. Artur Cideciyan, University of Pennsylvania, Perelman School of Medicine and Dr. William Beltran, University of Pennsylvania, Veterinary School of Medicine focus on the retinal area in a dog's eye.
What Function Does The Fovea Have?
A human's fovea is filled with cone photoreceptor cells and helps us with our central and sharp vision skills. We use the fovea for reading books, driving cars and watching things. Both professors found similarities in how the fovea region in dogs is just as easily affected with the same genetic eye diseases that their owners may be prone to. These diseases may result in blindness in both humans and dogs.
A Dog's Eye
All dogs have a retina. The center of the retina is surrounded by the area centralis. It is in this area that there are many more cone photoreceptors than elsewhere in the eye. But while humans have a pit formation with many cells, dogs do not. Before this new research took place, it was thought that the cone photoreceptor cell density was not as high in dogs as it is in humans.
Previous Studies By Other Researchers
Past studies were not accurate in that they never took into account a tiny section of a dog's eye that showed increased cell density. Dr. Beltran and his colleague, Dr. Cideciyan, discovered a retinal degeneration disease in one of their canine patients. At this time, they found that there indeed was a thinning of the eye area that involved the retinal layer and photoreceptor cells.
Both scientists decided to focus on this particular area of the eye. In a study, they used imaging, where they were able to examine the different layers of a dog's retina. By doing so, the researchers were now able to see the small area of peak cone density. Cone cells are next to each other in the fovea centralis of the eye.
Both Dr. Beltran and Dr. Cideciyan counted the number of cone cells they observed. This interesting research showed cone densities that were more than 120,000 cells per square millimeter. This demonstrated that dogs had the same amount of cone density in their eye as humans do. Dr. Beltran and Dr. Cideciyan found that there was also a region that worked together with a region of retinal ganglion cells (a type of neuron that is found on the inner surface of the retina).
When people have macular degeneration, they lose photoreceptor cells. With this research, both scientists wanted to see if the fovea region in dogs was similarly affected. To do so, they studied macular degeneration in dogs, and they also studied healthy dogs that were not affected by macular degeneration. They studied mutations in two genes that caused macular degeneration, Best 1 and RPGR. "This gives us a structural basis to support the idea that dogs might have a higher visual acuity than has been measured so far," explains Dr. Beltran via Science Daily. "It could even be the case that some breeds have an especially high density of cells and could be used as working dogs for particular tasks that require high-level sight function.
This research demonstrated that cone densities spanned more than 120,000 cells per square millimeter in the fovea-like region of the centralis region of the eye. This density is similar to that found in primates foveas.
People that suffer from macular degeneration will lose photoreceptor cells. These are the rods and cones that process light. This happens near or at the fovea area of the eye, and results in the loss of central vision. "Why the fovea is susceptible to early disease expression for certain hereditary disorders and why it is spared under other conditions is not known," adds Cideciyan, via Science Daily "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. They could allow for translational research by allowing us to test treatments for human foveal and macular degenerative diseases in dogs."
In addition, "This gives us a structural basis to support the idea that dogs might have a higher visual acuity than has been measured so far," explains Dr. Beltran via Science Daily. "It could even be the case that some breeds have an especially high density of cells and could be used as working dogs for particular tasks that require high-level sight function."