Sometimes when I wake up in the middle of the night and stumble downstairs for a drink of water, I find myself startled by two glowing green orbs in the darkness. I quickly realize that is just one of the cats eying me from across the room.
I’ve always assumed that the glowing ability of their eyes made it easy for them to see in the dark. Cat’s eyes are a little more complicated than that.
How They Glow
Cat’s eyes glow because of a tissue in their eye call tapetum lucidum. According to Animal Planet, this tissue is made up of mirror like cells. These cells take the light that comes into their eyes and reflects it back. This allows cat’s to see in dim light. Many mammals have these cells in their eyes, but cats have an especially thick layer of tapetum lucidum cells. Contrary to what many believe, cats can’t see in the dark, but Wikipedia says they can see at one-sixth the light level needed for humans.
What Big Pupils You Have
Cats have very large pupils, which constrict to small slits in bright light and dilate to spheres in dim light. When the pupil constricts to a slit in the light it keeps cats from getting overwhelmed by the sparkling sunshine. The opposite occurs at night, when the dilation of their eyes allows them to have better vision in the moonlight.
Humans have an upper and a lower eyelid. When we look at cats, we assume they are made the same. Cats actually have a third eyelid. According to Animal Planet, this eyelid appears white or opaque and come up from the inner corner of the eye. You probably have seen your cat’s third eyelid when they wake up from a nice lazy nap. Third eyelids only come out when a cat is sleeping or blinking. It’s interesting to note that cats don’t actually blink that often (which is why they always win the staring contest when they want some food).
Why do they need a third eyelid? It helps to keep the eye moist and dust free. My guess is that because they don’t blink much, they need an extra layer of moisture for their eyes. Of course, that leads to the question of why they don’t blink much.
Prey In Sight
Cats are natural hunters. They are always looking for some small creature moving about. I believe that is why they don’t blink as much as humans do; they don’t want to miss anything.
Cat’s eyes are built for catching prey. According to Animal Planet, the numerous rods in a cat’s retina make it easier for them detect motion. This is why they love toys that move back and forth.
While cats can be trained to recognize different colors, they mostly pick up on different shades of grey. This also helps them when they are in dimly lit environments.
“Eyes & Vision,” Animal Planet
“Tapetum Lucidum,” Wikipedia