Why Do Cats Have Vertical Pupils?

A 2015 study by Martin Banks at UC Berkeley found that pupil shape correlates strongly with an animal ecological niche. Vertical slit pupils are common in ambush predators with eyes close to the ground (cats, snakes, crocodiles). They offer two key advantages: first, they provide an extraordinary range of light control — a cat slit pupil can change area by 135-fold (vs only 15-fold for a human round pupil), allowing hunting in both bright daylight and near-total darkness. Second, vertical slits combined with a multi-focal lens create different focal distances for horizontal and vertical contours, enabling precise depth perception (estimating pouncing distance) without moving the head. Tall predators like lions and tigers have round pupils because their eyes are far from the ground, making the slit-pupil depth trick less effective. Prey animals like goats and horses have horizontal rectangular pupils, which maximise panoramic vision to watch for predators while grazing.