How Do Cats See In The Dark?

It’s not unusual to see a cat swipe a moth out of midair, or for pet owners to wake up to a “present” lying at the foot of their bed.

Our sweet house cats can be pretty active while we sleep — these nocturnal hunting abilities are all thanks to their excellent night vision, which “helps them hunt in the dusk and dawn,” Dr. Laura Proietto, a veterinary ophthalmologist, tells The Dodo.

Like our domestic felines’ wild ancestors, who stalk the jungle with only their glowing eyes to give them away, how cats see the world determines their behavior … and their sleep schedule.

The entire structure of cats’ beautiful and unique eyes helps enhance their ability to see in the dark — from the shape and size of their pupils to their glowing irises.

If you’ve ever wondered why a cat’s pupil can look like a vertical line during the day, but expand to saucer-sized proportions at night, it’s all to do with the amount of light the cat needs in order to see. “In the light, the cat's vertical pupil allows different amounts of light through different areas of the lens as it constricts to help them focus,” Proietto explains. “In the dark, however, their vertical pupil actually dilates to be round like ours. While this makes vision more blurry, it allows for more light to enter the eye.”

A domestic cat’s dilated pupil can be 135 to 300 times the size of its constricted state, according to a study out of the University of California, Berkeley, whereas a human’s circular pupil can only undergo a 15-fold change in area — in short, cats’ pupils can get much bigger than humans’, letting in more light.

While cats have far better night vision than humans, they still need some light to be able to see in the dark. When light enters the eye, the rays hit the retina (in both humans and cats), a layer of tissue toward the back of the eye housing the photoreceptor cells.

All retinas have two types of photoreceptors, rods and cones. Rods aid with night and peripheral vision as well as sensing motion, while cones are responsible for the perception of color and day vision. Cats and dogs have far more rods than cones in their retinas, while human eyes are skewed the opposite. This high concentration of rods allows cats to see better in dim light, using approximately one-sixth the amount of light humans need to see.

This concentration of rods helps cats hunt, despite their nearsightedness, notes Proietto. “If we are 20/20, a cat's eyesight is about 20/80 to 20/100, meaning that we can be four to five times farther away from something to see it in the same amount of detail,” Proietto explains. “Their vision is more blurry than ours, but they are very in tune with subtle motion and changes in illumination, like with a moving shadow — an adaptation for their nocturnal hunting lifestyle.”

Lastly, a reflective membrane directly behind the retina at the back of the eye called the tapetum enhances the amount of light that the rods can perceive. It is also the reason cats’ eyes glow in the dark, Proietto adds.

“Due to their tapetum, the greenish-yellow shiny part of their eye, they need less light to be able to see during the night compared to us,” Proietto notes. “Because the tapetum reflects light, the information hits the cells of the retina twice, rather than just once like us.”

“This is the yellow-green reflection you see when a light shines in the cat's eye instead of the red that you see with our eyes,” Proietto adds.

Other species, especially those who move about or hunt at night, such as deer, dogs, cattle and horses, also have a tapetum, whereas humans and some primates do not.

So next time you’re camping, and see that beautiful iridescent “eyeshine,” you might want to watch out.