Why Do Cat's Eyes Glow in the Dark?


Though we might like to think that animals see the world with the same colors and shadows as human beings-although maybe from a different angle, perhaps high in the sky like an eagle, or under the sea like a shark-the truth is that animal vision is not like our own and differs greatly among animal species.

Cats and other animals that are active in the day and night have pupils shaped like vertical slits because that shape allows the pupil to change size much faster than the round pupils we humans have. The smaller the pupil, the less light comes in, so our cats are much less likely to get blinded by sudden changes in light levels than we are.

Human beings are not like tigers, or housecats for that matter, whose eyes are superbly well adapted to seeing in the dark. One reason is that cats have more rods than cones in their retinas, unlike humans, making kitty's night and motion vision superior. (Rods are the receptors that the eye uses for nighttime viewing and sudden movement; cones are used during the daytime and process color information.)

Also, cats' pupils are shaped differently than those of humans (they are elliptical rather than round), which allows for a much larger pupil size. In fact, the most notable feature of nocturnal animals is the size of their eyes. The reason for this is that large eyes can collect more ambient light.

As well, cats' eyes open and close much faster than do ours. And cats have a special membrane on the back of their eyes (called the tapetum lucidum, literally meaning "bright carpet") that increases the quantity of light caught by the retina. The tapetum collects and re-emits light back to the retina, giving the rods a second chance to absorb the image, thus maximizing their sensitivity to low light levels. As this light is reflected off the tapetum, the animal's eyes appear to glow.

The feline eye is proportionately larger than the human eye and features a layer of highly reflective cells known as the tapetum lucidum. The larger eye size and the tapetum combine to enable a cat to see movement and objects better in dim light.


The tapetum lucidum, located between the optic nerve and the retina, operates like a mirror, reflecting the light and allowing the rods and cones another opportunity to pick up the limited amount of light available at night. This anatomical feature, which proves to be an asset for animals who do their best hunting at dawn and dusk, has been passed down to the domesticated cat from his ancestors.

The eyes of these animals are geared for low-light vision, They include dogs, cats, cattle, deer, horses and ferrets. However, humans and primates do not have the tapetum lucidum, and neither do squirrels because they're more active during the day, their retinas are designed for brighter light vision.

Posted by: Lusubilo A. Mwaijengo

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