June 13, 2006

bright carpet eyes

another snippet from the new york times:

Q. When I photograph a person using a flash, I often get "red eye," but when I photograph my dog, I get "blue eye." What difference in their eyes accounts for this?

A. The difference lies in the layers of cells at the back of the eyeball, where the flash of light strikes. When people are photographed in dim light, their pupils are wide open to let in enough light to see. As the flash hits the retina, which is richly supplied with blood vessels that are close to the surface, a red reflection may result.

In most dogs, and in most cats as well, there is a reflective layer beneath the light receptors of the retina called the tapetum lucidum, Latin for bright carpet. This mirror helps the animals maximize their seeing ability in dim light by reflecting any light not absorbed during its first passage through the retina back for a second opportunity to be absorbed.The color of the tapetum varies, and with it the color that is reflected back to the camera, but for most adult dogs the resulting flash is blue or green. Blue-eyed dogs and cats may lack pigment in this layer, and so huskies and Siamese cats often show red eyes in photos. Puppies and kittens are also likely to show red eyes because their eye structures have not finished developing.

In case you don't know what these people are talking about:

this picture was taken at a fancy boarding kennel. two caregivers tried hard to make brandy look really happy. but how happy can you look with bright blue carpet eyes?

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