Thursday, February 23, 2012
Cats and Dogs CAN See Some Color
Many adults think that dogs and cats cannot see any colors, only shades of gray. But this is not true. Cats and dogs can see some colors but not all of them. So in a sense they are like adults who are colorblind. Cats and dogs have cells in their eyes that respond well in bright and dim light. At night, cats and dogs use cells called rods that are sensitive to dim light. They are found in a lining at the back of the eye called the retina. When light falls on the rods, they send a message to the brain to explain the image that they see. For the bright light of day, you need cells called cones. But having cones in your eyes also means that you can also see color. Humans have three kinds of cones that allow them to see blue, red and green. So humans (and monkeys!) can see in full color. Dogs and cats only have two kinds of cones sensitive to blue and green light. So they do see some colors. By the way, if you have a horse or pony at home, they have red and blue cones. Horses see some colors, but they can't tell green from gray.
Now, do cats' eyes glow in the dark? No they don't. Cats and dogs have some cells behind the retina that act like a mirror. These cells are found in a part of the eye called the tapetum. This mirror reflects light back, giving the rods and cones a second chance to pick up the small amount of light available at night. It is this tapetum that makes cats' and dogs' eyes seem to glow in the dark.
Humans don't have a tapetum. You may have noticed that if you use flash to take a photo, humans tend to look like they have red eyes. This is because there is a reflection of the red blood vessels behind our retinas. If you took a flash picture of your dog, you might see yellow or orange eyes instead. This is a reflection of the light of the flash by the dog's tapetum.