Why do Animals Have Differently-Shaped Pupils? The Science Behind Different Types of Animal Eyes

Have you ever looked at a cat’s eyes and wondered why they have slits for pupils while we have round ones?

Different animals have differently-shaped pupils for a very specific reason — survival. The shape of a pupil dictates how much light enters the eye, and in turn, how much an animal can see. Different animals need to see differently in order for them to hunt and eat. Hence, predatory animals and prey animals have very different kinds of eyes.

Let’s have a look at how and why some animals have unique pupils.

Round pupils

Do you spend time looking at your own eye in the mirror and observing how perfectly round it is? Round pupils are common in large predators or large animals that are at the top of the food chain. Animals with round pupils, like lions, tigers, and humans tend to be daytime predators who are higher off the ground than other animals. Even large mammals like elephants that don’t necessarily hunt, still move and eat mostly in the daytime.

Round pupils don’t offer a wide view but they do give great depth perception, which means you can tell which objects are far or close in relation to other objects. Good depth perception is vital for apex predators as they need to hunt more than look out for who’s hunting them. Some animals like large cats also hunt at night, which becomes difficult with round pupils. For this, certain large cats can adjust their pupil size so that they can hunt easily without much light. Interestingly, domestic cats don’t have round pupils but most big, wild cats do.

Vertical pupils

These are the kind of pupils you’d see in small cats, alligators, crocodiles, and foxes. These are also predators but are smaller in size and don’t hunt like large predators. These animals tend to use ambushing or sneak attack techniques to get their prey. Vertical pupils come in handy with these kinds of hunting styles.

Vertical pupils help hyper-focus on prey and help in increasing the accuracy of the attack. This is important as smaller predators don’t have the luxury of size to scare their prey. They need to calculate and strike more accurately as they may not get another chance. Animals with vertical pupils can also choose to expand their pupil size depending on how much light is present.

Horizontal pupils

Prey animals tend to have horizontal pupils. If you have observed the eyes of a goat, lamb, cow, horse, or deer, you will see that they have round eyes with a dark, rectangular pupil in the middle. This lets the animals get a panoramic view of their surroundings so that it is easier for them to spot any predators around them.

Another thing to note is that these animals also have their eyes on the sides of their heads and not in the front. This position along with the horizontal pupils allows them to get a front and back view of their surroundings, without them having to turn their heads much. It also helps them keep the ground around them in focus, so that they can see where to graze as well as escape any predators quickly.

Horizontal slits

Amphibians and reptiles like frogs, lizards, snakes and octopus have pupils shaped like horizontal slits. These work similar to the horizontal pupils that prey animals have. It helps them track any vertical movements, which means predator movements. They can also expand their pupils at will to help adjust to the amount of light around them, as a lot of reptiles also tend to be nocturnal.

Crescent and W-shaped pupils

Some aquatic animals have truly unique pupils. Some fish like catfish and stingrays have crescent-shaped pupils, which decrease the light distortion that happens underwater. While scientists are still researching the other reasons behind why certain fish have half-moon pupils, some say it helps exclude any unnecessary light. It also helps the fish in spotting any predators by giving them a wide view.

The cuttlefish has an extremely unique pupil – it’s shaped like a W or a squiggly line. Some scientists say it’s a variant of the horizontal slit pupil, but we can’t be sure why exactly it’s shaped like that. The shape helps light to enter the eye from different angles and can enhance the contrast levels, so the cuttlefish can see better.

There are many more different types of pupils out there in nature. For example, the pupils of a chameleon are unique to it. The pupils are tiny, square-shaped and can move 360 degrees. On the other hand, there is also the gecko (a kind of lizard) that has pupils in the shape of a beaded string. Also, did you know that insects don’t have pupils? They have compound eyes, which eliminates the need for pupils.

What kind of pupil shape do you wish you had? Let us know in the comments. Speaking of eyes, do you want to know some interesting facts about the human eye?

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