Dogs see a different world than people do, but it’s a myth that their view is just black and white. Canine eyes lack the light receptors that allow people to see a full spectrum of colors from red to violet, but they can see yellow and blue.
What we see as red or orange, dogs probably view as a shade of tan. A bright orange ball lying in green grass will look like a tan round object lying in another shade of tan. But a bright blue ball will look similar to both dogs and humans.
Vision researchers are unable to interview dogs about what they see, but dogs have been trained to touch illuminated color discs with their nose to get a treat. When well-trained dogs can’t figure out which disc to press, it becomes obvious the they can’t distinguish differences in certain colors. But the experiments also showed that dogs can see yellows and blues.
In human eyeballs, retinas contain three types of special cone-shaped cells that are responsible for color vision. Using a technique called electroretinography to measure the way dogs’ eyes react to light, researchers found that canines have fewer kinds of these cone cells. While people have three kinds of cone receptors in their eyes, dogs have only two types of cone.
Not only do dogs see fewer colors, but they probably don’t see as clearly as humans. Tests show that both the structure and function of the dog eye leads them to see things at a distance as more blurry. Whereas perfect vision in humans is 20/20, the vision in dogs is closer to 20/75. This means that what a person with normal vision sees from 75 feet away, a dog would need to be just 20 feet away to see as clearly.
Not all dogs are the same, however. There is a lot of difference in visual ability between breeds. Over the years, breeders have selected sight-hunting dogs like greyhounds to have better vision than dogs like bulldogs.
Dog vision may not have the colors or acuity that humans enjoy, but they have far superior night vision. People have a tough time seeing clearly in dim light, but dogs see as well at dusk or dawn as they do in the middle of the day. This is because dog retinas have a higher percentage of rod cells which, because of their shape, function better in low light than cone cells.
Dogs also have a reflective tissue layer at the back of their eyes that helps them see in less light. This mirror-like tapetum lucidum collects and concentrates the available light to help them see when it’s dark. The tapetum lucidum is what gives dogs and other mammals that glowing eye reflection when caught in headlights or night photos.
Source: Nancy Dreschel, Associate Teaching Professor of Small Animal Science, Pennsylvania State University
