Do All Animals Have Circular Pupils?

Though circular pupils like humans have are commonly found among animals, not all animals have them. For instance, goats, some snakes, mongooses and hippopotami have rectangular pupils, and cats, vipers and foxes have vertical slit pupils. Frogs have some of the most unusually shaped pupils, with different species of frogs having triangular, heart-shaped and star-shaped pupils, but cuttlefish are perhaps the oddest of all, with W-shaped pupils.

More facts about animals' pupils:

• Animals that hunt at night tend to have elliptically shaped pupils, which can open wider than circular pupils to take in the maximum amount of available light. They also can be contracted further than circular pupils to protect the eyes from very bright light.


• Some snakes and lizards can almost completely close their pupils, protecting the back of the eye from all but a pinpoint of bright light.


• Cats can change the amount of light hitting their retina 135-fold because of the shape of their pupils; humans can change it only tenfold.

Frequently Asked Questions

Do all animals have circular pupils?

No, not all animals have circular pupils. Pupil shapes can be circular, vertical slits, horizontal slits, or even more complex shapes like W-shaped or square. The shape of an animal's pupil is often related to their ecological niche and behavior. For example, vertical slits are common in ambush predators, aiding in depth perception and low-light vision.

What is the advantage of having vertical slit pupils?

Vertical slit pupils, often found in nocturnal predators like cats, allow for precise control of light entering the eye. They can close to a very small size in bright light and open wide in the dark, which is beneficial for animals that need to hunt at night. This shape also enhances depth perception and helps gauge distance to prey.

Why do some animals have horizontal slit pupils?

Horizontal slit pupils are typically found in grazing animals such as sheep and goats. This pupil shape offers a panoramic view of the surroundings, which is crucial for detecting predators while feeding. According to research, the horizontal orientation also helps stabilize the visual field, providing a clearer view of the ground when the animal moves its head.

Are there animals with square-shaped pupils?

Yes, some animals have square-shaped pupils. One notable example is the cuttlefish, a cephalopod known for its remarkable eye structure. The square pupil allows for a wide field of vision and helps the cuttlefish control the intensity of light entering the eye, which is essential for its underwater environment where light conditions can vary greatly.

How do pupil shapes affect an animal's vision?

Pupil shape can significantly affect an animal's vision by influencing factors like the amount of light that enters the eye, depth perception, and field of view. Circular pupils are versatile and provide a balance between sensitivity and resolution, while slit pupils can offer advantages in specific light conditions or for particular visual tasks.

Can pupil shape change in the same animal?

Yes, in many animals, pupil shape can change in response to different light conditions. For instance, domestic cats' pupils can change from vertical slits to nearly round when the light level changes. This adaptability helps animals maintain optimal vision and react to environmental changes, ensuring their survival in diverse habitats.