Joel Hunter, MD Refractive Surgeon, Hunter Vision Updated 05/08/17 1:16 PM
I guess I should put a disclaimer at the beginning of this to say I am not a "cat person." But honestly, I feel like it is more accurate to say every cat I've met is not a "person cat." If you love cats, then please know that I respect cats, and even more, I respect you. If you're a "cat person" it means that you have self-confidence in abundance, and that unlike me you've never let a cat make you wonder "why am I so uninteresting and stupid?"
If cats could talk, they would probably use that ability as a another way to ignore you by not talking to you, only on purpose. But if they did talk to us, I imagine the conversation would be mostly about how much better cats are than people. And in one area, they would be 100% correct. Cats have night vision that is far superior to ours. They hunt at night and have no need for artificial light to do it. They see prey in the dark that we could never see without a flashlight. Owls have the same ability to an even greater degree, but they are less smug about it. Probably because of their wisdom.
For an eye to see something, enough light has to hit the retina (which lines the inside of the eye) to activate its photoreceptors, called rods and cones. For humans, the quality and sharpness of vision is a much bigger deal than night vision, so our photoreceptors sit on a dark, pigmented layer that absorbs extra light which could otherwise bounce around inside the eye and blur vision. But for animals that need to see in the dark, the eye is adapted to increase night vision even if it means a decrease in sharpness of vision.
Nocturnal animals' eyes have a retina that sits on a layer called the tapetum lucidum, and it is basically a built-in reflector. This reflecting layer bounces light that has passed through the retina's photoreceptors back into the eye so that every little bit of light will provide the most vision possible. It lets them "see in the dark," but that only encompasses what looks dark to us but isn't. Have ever been outside at night and looked up and seen the moon, and then looked around you and seen only darkness? The same light from the moon that your eye focused on your retina when you looked at it is also shining on everything around you, you just can't see it. Cats, with their tapetum lucidum, are able to look at that same scene and see the details of it bathed in moonlight.
So if you've ever seen a photo where the flash turns the people's eyes red, and a cat's eyes into glowing orbs, now you know the reason. You were looking at retinas that absorb light next to one that reflects light. Or that cat was possessed.