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 ...

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 ...

A 23-year-old student in Germany can shrink and enlarge his pupils on demand, according to a new case report — a feat that was previously thought to be impossible. Two tiny opposing muscles in the eye ...

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.