A domestic cat’s eye narrows to a razor-thin vertical slit in bright sunlight, while a grazing sheep stares out through a wide horizontal bar. These are not cosmetic quirks. A 2015 study in Science ...

Pupil shapes vary widely across the animal kingdom, from the W-shaped pupils of cuttlefish to the bar-like pupils of goats.

It is commonly known that pupil size fluctuates in response to brightness and darkness during wakefulness. What is less commonly known is that pupil size is also regulated by the autonomic nervous ...