Question

What is the structure that controls the amount of light entering the eye

Answer 1

The iris (aka the colored part of your eye that surrounds your pupil). The iris will enlarge or dilate the pupil, depending on how bright or dark the environment is.

Answer 2

The iris opens and closes to control the amount of light entering the eye through the pupil , and the pupil is the opening in the center of the iris where light enters the eye