Canine Vision Explained
The eyes of dogs contain specialized cells known as cones that catch light and respond to color. Dogs have fewer cones in their retinas than humans, which means they can't see as many colors as we can. Furthermore, the colors dogs see don't look as rich and vibrant to them as the colors we see do to us. This limited range of color vision is referred to as dichromatic vision, because they possess only two of the three types of light-catching retinal cone cells.
The Colors Dogs See
Dogs can't see the full range of the color spectrum, but that doesn't mean they can't see colors at all. Dogs can't tell the difference between orange, yellow and green. All of these colors look yellowish to a dog. The color red appears dark brownish gray or black to dogs.
Dogs can see the color blue, but violet shades appear blue to them. Blue green shades appear gray to dogs. Therefore, while dogs are not completely colorblind, they do in fact display partial colorblindness that inhibits them from perceiving shades of green and red. This type of colorblindness also occurs in humans and is known as deuteranopia.
Researchers believe that dogs can distinguish shades of gray indistinguishable to humans. This is because the canine retina contains a larger number of the rod cells that perceive shades of gray. These rod cells need less light to function than do the cone cells that perceive color. Because of this, dogs can see well in dim light situations.
Other Facts About Dog Vision
Dogs are more capable than humans of detecting flickering light. Because of this, they're more able to perceive motion, and can detect smaller amounts of motion. However, researchers believe that dogs may perceive television screen as constantly flickering, rather than as a continuous moving image.
While dogs are not colorblind, they do tend to be nearsighted. Dogs lack the ability to focus on the shape of objects. An object that a human with perfect vision would be able to see from 75 feet away remains indistinguishable to a dog at distances of more than 20 feet.
Dogs also have limited peripheral vision. The extent of peripheral vision varies according to the breed of the dog and the size of its head, but in general, dogs can't see in detail things to the size or behind them.
While dogs can detect movement from a great distance, they don't possess what is known as "depth of field" vision. When a dog looks at a distant object, only those things in the center of his vision appear in focus; the objects in the background remain indistinct. This means that dogs can't see stationary objects at a distance.