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

The size of your pupils varies throughout the day, but most people’s pupils fall within a particular size range. We’ll look at when and why your pupils change size. First, the range of “normal” pupil ...

Arousal is a fundamental part of how our brain keeps us alert, engaged, and responsive to the world around us. It is controlled by networks deep in the brainstem, like the locus coeruleus (LC), which ...

The pupillary light response helps our eyes see the world around us in various lighting conditions ranging from bright, sunny days to dark, moonlit nights. Like a camera's aperture, this adaptive ...

A team of Johns Hopkins neuroscientists has worked out how some newly discovered light sensors in the eye detect light and communicate with the brain. The report appears online this week in Nature.

Q: My elderly cat’s pupils seem to stay dilated, even in bright light. Why? A: In old cats, dilated pupils are often just a sign of a harmless condition called iris atrophy. However, if your cat has ...