Dogs, cats and almost all domestic animals have a special reflective layer in the back of the eye termed the tapetum, which enhances nocturnal vision. Light passes through the animal's retina from outside of the eye and is then reflected back through the retina a second time from the reflective tapetal layer beneath the retina. This double stimulation of the retina helps these species to see better than humans do in dim light situations. The color of this tapetal layer varies to some extent with an animal's coat color. A black Labrador retriever, for example, will usually have a green tapetal reflection.
at 10:34 PM on Jan. 26, 2009