Name: Sophie Hunt
Why do dogs eyes glow in the dark?
They have a reflective surface behind the retina (light sensitive
back surface) of the eye which bounces light from, for example, your
headlights back at you somewhat like highway reflectors. The purpose of
the surface is to increase the ability of the retina to detect faint
light -- that is, the ability of the animal to see in the dark -- by
making the light pass *twice* through the retina. Humans don't have this
surface, but very bright light will bounce back from the retina itself
enough to be seen. Since the retina is red (from its ample blood supply)
you see a red reflection, and this is the source of the "red spot" in the
eyes in photographs of people who looked at the flash.
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Update: June 2012