Final answer:
The hole in the center of the iris that regulates light entering the eye is called the pupil. The iris controls the size of the pupil based on the brightness of the light.
Step-by-step explanation:
The hole in the center of the iris that regulates how much light enters the eye is called the pupil. The iris, which is the colored part of the eye, controls the size of the pupil based on the brightness of the light. In bright light, the iris causes the pupil to narrow, and in dim light, it causes the pupil to widen.