Man can change his pupil size on command, once thought an impossible feat
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 act as puppeteers of each pupil (the dark center of the eye), dilating or enlarging them in a dark environment to let in more light and constricting them in a bright environment to limit the amount of light that flows in. This process was thought to be completely automatic; when you step into a dark room, you don't have to consciously tell your pupils to change size. Pupils can also change size in response to other factors, such as increases in arousal. It was previously known that some people can change their pupil size at will, but by using indirect methods.
