The pupil is the black part of the eye and can range in size. When you look at one in the light, it is narrow and only 3 to 4 millimeters. If you stay in the dark, it will increase in size and be anywhere from 4 to 9 millimeters. Not everyone has the same size of pupil.
Pupil size varies. In the sun and some pain meds they constrict and become smaller. In the dark and other drugs the become larger. In trauma they can become unequal. Some eye suffered the round can become more squared