Why Do Cats Have Vertical Pupils?

Cats are beautiful animals that constantly amaze us: Their hunting instincts remain intact even when they live indoors and their pouncing, running, and acrobatic sense of balance are exciting to watch. And when looking into a cat's eyes, it's a sight to behold. But look closely and you may wonder, why do they have vertical pupils? According to experts, the shape of their pupils serves an evolutionary purpose for our feline companions.

Letting in Light

"Vertical, or slit, pupils have the ability to dilate or constrict to a wide range of sizes, therefore determining how much light can enter the eye," says Dr. Gabrielle Fadl, DVM, veterinarian at Bond Vet. "The primary purpose of this in domestic cats is to allow vision in bright day light as well as dim night light."

Good vision is essential for cats in the wild and our domesticated cats still have the same abilities. That's why cats can spot a mouse scurrying in the dark or that tiny bird fluttering past the window. "As a result, the light enters the eye much faster, which is used by cats as an advantage to be able to see faster movement," explains Dr. Jesus Aramendi, senior veterinarian at Chewy. "Cats also have a special membrane located in the back of the eye behind the retina called a 'tapetum lucidum.' The tapetum allows light to reflect through the rods (cells that account for night vision) twice, further improving cats' night vision." Bonus: That tapetum membrane is the reason why cats' eye seem to glow in the dark, since light reflects off of it in the dark.

What It Means

All of the features that we think are so cute in our cats also serve to make them into magnificent hunters—even if the only prey available is a toy mouse or a feather wand. "Cats are usually very active at night, which is an inherited trait from their ancestors that were nocturnal hunters," explains Dr. Aramendi. "Equipped with exceptional night vision and other sensorial features such as very sensitive whiskers and an amazing sense of hearing, cats are able to function at night more efficiently than humans and other animals."

Cats are also considered to be ambush hunters. This is because they will crouch low and stalk their prey before jumping and pouncing on it. According to research by Banks et. al. in the August 2015 journal Science Advances, ambush predators like cats tend to have the vertical-slit pupils, which allows them to gauge the distance of their prey. Humans, in contrast, have round pupils because we are tall, upright and spend most of our time awake during daylight hours. We also have other ways of hunting and getting food.

So, while cat's beautiful eyes are mesmerizing, their eyes contribute to their superior hunting skills that are essential in the wild (or toward an unlucky mouse that creeps into the house).