Dog Vision (or How a Dog Sees)
What do dogs see? Many of my clients are aware that dogs do not see exactly the same as we do. The retina is composed of receptors for gray tones, called rods, and receptors for color vision, called cones. Rods are also sensitive to motion. Dogs have many more rods than we do, which make it easier to see in low light, and easier to detect motion, which are valuable assets for hunting. In addition to this low light advantage, dogs have a tapetum lucidum, which is a reflective layer in the retina that we do not have. This reflective layer acts to magnify the available light, thus allowing dogs to see even better in very low light. Another low light advantage is the degree to which a dog’s pupil (the aperture of the iris) can dilate to allow more light in. Their pupils can dilate to the point that barely any of the iris (colored area) can be seen.
So is a dog able to see color? Dogs have only two types of cone receptors in their retina, while we have three types of cone receptors, as well as having a larger number of cones than dogs do. This allows us to see a broad range of color, as well as seeing color more intensely. Research shows that a dog is more akin to a person who is red-green colorblind. Dogs can’t distinguish between red and green very easily. Shades of red will appear yellow, and green appears to be white. However, dogs can detect the colors yellow and blue, although the intensity of the color is probably more subdued than what we see. This may explain why, if my dog doesn’t see a ball land, he uses his nose to look for it, and often misses it lying there in the grass. In the future I will go for blue or yellow balls, as they may help my dog pick out the ball from the grass. Incidentally, everything that is said here for dogs also goes for cats, except that cats are even better at night vision due to a more reflective tapetum lucidum!