Have you ever noticed that big cats have round pupils while smaller cats have slit-shaped pupils?

Amber tiger has rounded pupils

All cats have light-colored eyes, allowing more light to enter the eye. This allows the animal to see better in dark conditions. Outside of the bright-colored cat eyes, what is the purpose of a round pupil vs a slit-shapped pupil?

A recent study by UC Berkeley and Durham University suggests that the eye shape of an animal is linked to the ecological niche they occupy in the wild. The correlation between ecological niche and eye shape was so specific that scientists could determine an animal’s lifestyle, including foraging habitats and the amounts an animal was active throughout the day. Large animals, like lions and tigers, have round pupils compared to small animals, like the domestic housecat, with vertical slit pupils.

The round pupils found in big cats are special adaptations for animals active both during the day and night, known as crepuscular. The round shape allows the pupil to dilate to a large size in low-light conditions, allowing more light to enter the eye and allowing the cat to see much better at night. The pupil can also shrink to be very small in size during bright-light conditions, enhancing the cat’s visibility. In addition, the round-shaped pupils help with the high depth of field needed to spot prey across various distances. 


Jake has slit shaped pupils, compared to the larger big cats that have rounded pupils

On the other hand, smaller cats and domestic house cats have slit-shaped pupils. This pupil shape is better adapted for more active animals during low-light conditions because there is more precision over the amount of light that enters the eye. Slit pupils also allow these ambush predators to judge distance more accurately through stereopsis. Stereopsis is an adaptation that enables the brain to process information from an animal’s eye using different angles while using the techniques of blur to distinguish the sharpness of objects between distances. The size and shape of the pupil have evolved to help domestic housecats hunt by stealth rather than chasing their prey actively, like lions or tigers. 

There is no doubt that lions and tigers perceive a world very differently than ours – aiding their fierceness as apex predators. These big cats have evolved and adapted as climates have changed. These predators start their lives blind, and their eyes become powerful and valuable tools to help them survive and dominate the lands they call home.

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