The glow is actually light reflected back from a layer of special cells behind the retina, called the tapetum lucidum, which is Latin for "luminescent tapestry." (We love showing off our Latin, even if we had to look it up first!) The retina is the light-sensitive tissue lining the back of the eye. Its job is to convert light into electrical impulses that are sent to the brain. The job of the tapetum lucidum is to catch all the light that didn't enter the retina directly and reflect it back in, so every tiny bit of light can be processed.
Add in the fact that a cat's pupils can dilate to three times the size of ours and they also have a larger cornea (the eye's outermost lens), and you can see why a cat has no need for night-vision goggles. The bottom line: A cat can see in conditions that are more than five times less bright than what we require.
Perhaps this ability to hunt by night has contributed to the alley cat claiming the award for one of the most successful predators in the animal kingdom.
Long before a cat ever was caught in the headlights, the ancient Egyptians had another theory for why the cat's eyes glow at night: They believed the eyes of a cat reflected the sun, even at night when it was hidden from humans.
Q. Why do cats' eyes contract to a vertical slit?
A. If cats wore sunglasses or didn't evolve into creatures who have the nighttime munchies, they probably would have round pupils like ours.
But they're nocturnal hunters and see well in very dim light. Just as we adjust our headlights from normal headlights to brights, a cat's eyes adjust to different lighting conditions. In the daytime, cats have precise control over the amount of light reaching their eyes. This enables them to gaze out the window and zero in on that errant squirrel in the tree or big bird on the feeder.
Having eyes that reduce the pupils to slits rather than tiny circles gives the cat greater and more accurate control in different types of lighting; this ability is particularly important in bright sunlight.
Vertical slits also have another advantage over horizontal slits. Because the cat's eyelids close at right angles to the vertical pupil, a cat can reduce the amount of light even further by bringing her eyelids closer and closer together. Similar to the shutter on a camera, this combination of the vertical slits of the pupils and the horizontal slits of the eyelids enables the cat to make the most delicate adjustments to accommodate different lighting. And these actions, in combination, protect the eyes better than sunglasses.
It's a perfect set-up for a nighttime hunter who loves to bask in the daytime sun.
This adaptation sets the domestic cat apart from her majestic relative, the lion. Because the lion hunts by day, her pupils do not have the same sensitivity to light as the domestic cat. The lion's eyes contract -- like ours do -- to tiny circles, not vertical slits.
Q. Do cats dream?
A. Cats definitely remember things -- in fact, they have great memories -- so it makes sense to believe they have the ability to dream, just as people do. After all, dreaming is a normal part of organizing and re-organizing memories. Kind of a subconscious filing system, you could say.