Hallux’s i-Guide: Pupil The pupil is a dark circular hole in the middle of the iris which allows light to enter the retina The size of the pupil is controlled by muscles. When more light is needed, the pupil is made larger and when less light is needed, the pupil is made smaller – just like the shutter of a camera! Next: Iris > Visit Professor Hallux’s i-Guide homepage > Download the free i-Guide podcast from iTunes More to click... Why do people go to the opticians? Hallux's i-Guide: Getting New Glasses! Hallux's i-Guide: How do we see?