Why does my pet...?
Why do my cat's eyes glow in the dark?
Short answer: Behind the retina, cats have a mirror-like layer called the tapetum lucidum. It reflects light back through the eye for a second chance to catch it, which helps in dim light and causes the eyeshine you see in photos.
Updated
The wild side
Many night-active wild animals, from wildcats to foxes, have the same reflective layer.
Try this
Turn off the flash for nicer photos, and keep a little light on if your cat likes to move around at night.
See it in the episode
Why Your Cat Goes Wild at 3 A.M. (Wild Cousins, episode 1)
Questions people ask
Why do my cat's eyes glow in the dark?
Behind the retina, cats have a mirror-like layer called the tapetum lucidum. It reflects light back through the eye for a second chance to catch it, which helps in dim light and causes the eyeshine you see in photos. This is general information, not veterinary advice. If anything about your pet's behavior or health worries you, ask your vet.
Sources
This is general information, not veterinary advice. If anything about your pet's behavior or health worries you, ask your vet.