Experts believed for a very long time that dogs see only in black and white.
However, research has dispelled that myth and it has been proven that dogs can see some colors, but the tones of color that they do see is quite different from that of humans.
One of the main reasons for the difference is that dogs have only 20 percent of the cone photoreceptor cells that humans have. Photoreceptor cells are the portion of the eye that controls the perception of color.
Obviously, dogs are not able to take a trip to the eye doctor to read a color chart so much of the research is based on behavioral tests that suggest that dogs see in shades of yellow and blue and lack the ability to see the range of colors from green to red. This means that dogs basically see the colors of the world as yellow, blue, and gray.
One might wonder how scientists know this. One method is based on shining beams of colored light into dogs’ eyes. The experts then analyze the spectrum or pattern of light that is reflected back to them. The same process is then repeated on human beings and the results are compared.
Another determining method is to train dogs to “tell” the experts what they see. This is done by teaching dogs to select certain colored lights with their noses. In test where dogs are shown three lights, two of which are the same color, dogs have been able to choose the one light that differs from the other two.
The function of human and dog eyes differ. One reason is that dogs have two cones, which are photoreceptor cells in the retina that function best with bright light. Humans have three different cone types that contain a photo pigment that is sensitive to separate wavelengths of light. It is the wavelengths that make the detection of color possible. Thus, dog eyes are not as sensitive to the separate wavelengths of light.
The rods also play a role in the difference between canine and human vision. Canines have more rods in their eyes than do humans. Rods work best in low light. This is why dogs have better night vision than human beings.
Another important difference between canine and human eyes is the fact that a dog’s visual acuity is less developed than that of people. It is thought that dogs may have 20 to 40 percent of the visual acuity that we do. This accounts for the fact that humans can see an object more clearly than dogs can when viewed from the same distance. However, it also provides for the fact that dogs can see better in dimmer light and they are able to detect motion more easily than humans can.
The next time you go shopping for dog toys, consider this information so that you can choose a toy that your dog can easily see. Stay away from red and green toys. More than one dog has been accused of being stupid because they ran right past the bright red ball. Remember, red looks like a dark brownish gray and may easily blend into the background.