How a Cat's Eyes Work in Little Light and Why They Glow

You can laugh with a cat, but never let them know you are laughing at them. It hurts their feelings and they do know if you are laughing at them. Although it's sometimes hard not to laugh at things cats do. I'm always amazed and amused at the tiniest bug or spider they can see. I'll find one of my cats sitting motionless staring at the floor or a wall in a room with dim lightening watching something. How can they see tiny bugs with little light to work with? Cat's have amazing vision, but just how do cat's eyes work?

Cats hunt anytime during the day or night, but their vision is designed to see best in dim light and a cat's eyes are perfect for locating movement at sunrise or sunset. Like all predators, cat's eyes are on the front of their face which gives them good depth perception and allows them to measure distance before they leap. A cat's peripheral vision can pick up movement much better than we can and they have a total field of vision of 250 to 280 degrees. Instead of having round pupils like us or a dog, cats eyes have vertical slits and a third eyelid that allows the cat to completely control light entering their eyes. If a cat doesn't feel well, we can see the third eyelid partially closed, but it can also mean your cat is contented, so you need to pay attention to any symptoms of illness in your cat if you see the third eyelid. It also helps protect the eye from becoming dry or damaged.

Any eye, human or animal, has cells that are sensitive to light called cones and rods which make up the retina located at the back of the eye. Light passes through to the retina where a unique layer of cells called tapetum lucidem catch the light and reflect it back to the retina where it can be picked up by rods. This is what causes a cat's eyes to glow in the dark. The glow we see is excess light from a flashlight or car headlights that wasn't absorbed by the rods. Cones aren't as sensitive and work better in full daylight and are responsible for color distinctions. Since cats don't need to know what color their prey is, they have fewer cones than rods (25 out of 26 cells are rods compared to 5 out of 6 rods in our eyes) and it's the rods that magnify light impulses in dim light. Light doesn't automatically find the rods in cat or human eyes, but cat's eyes gets a second chance when light bounces off the tapetum lucidem increasing the chances of light hitting a rod.

Dogs, raccoons, deer, opossums and a few other animals have the same feature. Because of this double shot to their retina, a cat's eyes are able to absorb all available light and their night vision comes from utilizing all of the photons. Scientists believe cats can see clearly 6 times better than we do. In dim light, their pupils are wide open, but in direct light, you will only see a small vertical slit.

A cat's eyes are larger in relation to their body than other animals including us and the larger eyes allow more light to enter. Their lens is more curved than ours which gives them sharper focus all the way to the edge of the lens and they have a larger anterior chamber and curvature of the cornea that allows more light into their retina. A cat's eyes, like ours, has a concentration of receptor cells in the center of the eye and leads to the optic nerve, but in cats, the concentration is along a horizontal band that is broader than ours and it's that broader concentration that gives cats the ability to detect movement farther away. When they spot movement, a cat's eyes are able to calculate distance, size of the prey and all obstacles in the cat's path. Once a cat pounces on a mouse or bird, however,the prey has the advantage. A cat can't see things clearly that are right under their nose. Cats are farsighted.

If you notice one pupil larger than the other in your cat's eyes, this can indicate Horner's syndrome, Feline Leukemia Virus, an eye infection, a possible tumor or an injury to their central nervous system. Most eye problems in cats can be successfully treated and it's important for the cat's well being and vision to have any eye problem dealt with immediately.

Even though cats can't see in total darkness, they can still find prey or avoid running into the couch or coffee table after we've gone to bed. Along with their amazing eyes, cats are equipped with whiskers that act like tiny radars and are so sensitive they can feel a mouse moving around a dark room. Changes in air currents moving around objects are picked up by a cat's whiskers.

Considering how efficient a cat's eyes and whiskers are, a mouse trying to steal a piece of cat food in the middle of the night doesn't stand a chance against a predator who has everything in his corner. Unless of course, your cat is snuggled next to you in bed and sound asleep.

Karl S. Kruszelnicki, Cats Can See In The Dark, ABC Science

Kathy Wollard, How Do Cats See in the Dark?, word-detective.com

Andrew Garman, Why Do Cats Eyes Glow in the Dark?, agarman.dial.pipex.com