why do cats have vertical pupils

It’s no coincidence cats have vertical pupils. They actually help cats hunt prey and see in low light. In fact, the shape and size of the pupil varies greatly across animals in order to fit their needs.

Why Cats Have Vertical Pupils

Animals with round pupils are “active foragers” that hunt down their food. These include taller predators such as wolves, lions, and tigers. Animals with horizontally elongated pupils are mostly plant-eating prey species with eyes located on the sides of their head; examples include deer, sheep, and horses. This shape and placement gives these animals a panoramic view so they can scan for danger while grazing or otherwise inactive.

Researchers have found that animals with vertically elongated pupils are more likely to be ambush predators. These animals need to be able to accurately judge the distance of their prey in order pounce effectively. The vertical slit has optical features that make it ideal for this purpose. Some examples of animals with vertical-slit pupils include foxes, some reptiles, and domestic cats.

Vertical Pupils Help Cats Hunt

Just like the camera’s aperture, the human pupil’s primary purpose is to control how much light enters the eye. Pupils constrict or dilate depending on circumstance–for example, when it’s dark out your pupils will constrict in order to let less light in. Humans have circular-shaped pupils while vertical-slit shaped pupils are found in other animals; these shape differences allow for different amounts of area alteration.

The difference in area between a cat’s constricted and dilated vertical slits is 135-fold, while humans have only about a 15-fold change. Researchers say that this gives cats the ability to see well in both dim light and bright sunlight.

After predators regulate the pupil for their current environment, they must accurately gauge depth to efficiently pounce on prey. The stealthy vertical slit is perfect for ambush predators because it provides two ways to gauge depth without moving: stereopsis and blur.

Stereopsis, or depth perception, happens when our brain uses information from both eyes to figure out how far away something is. You can test it by holding your finger up close to your face and taking turns closing your right eye and then your left eye. The difference in how far away your finger looks is stereopsis at work! Another way you can see stereopsis is by looking at blurry objects; objects that are further away look blurrier than those that are closer.

The best visuals come from stereopsis when shapes and contours are vertical and at a distance. Narrower pupils produce the most precise image. When focusing on horizontal contours that are close-by, blur works better. For this method, wider open pupils give optimal results. The shape that encompasses both methods is vertical-slit pupils–which just so happens to be how cat eyes naturally look.

The scientists were surprised to find that predators with slit-shaped pupils were small and close to the ground. Out of 65 frontal-eyed ambush predators in this study, 44 had vertical pupils while 36 had shoulder heights below 42 centimeters (16.5 inches).

Animals with vertical-slit pupils, like domestic cats, can see better than those with round pupils. This is because a vertical pupil helps them see more. Lions and tigers have round pupils since they don’t use their eyes as much when hunting.

Are Cat’s Nocturnal?

Your cat’s vertical-slit pupils help them see better in low light. However, this doesn’t mean they are nocturnal. Cats are actually crepuscular, meaning they’re awake mostly in the hours of dusk and dawn.

Since these hours are between the hottest and coolest parts of the day, it’s thought that this is when most of the prey are out. Therefore, it’s advantageous for cats to hunt when most prey is present.