Which part of the eye controls the amount of light entering the pupil?

The iris is the part of the eye that controls the amount of light entering the pupil. It is a thin, circular structure that has muscles allowing it to expand and contract. When the light conditions change, the iris automatically adjusts the size of the pupil, which is the opening in the center of the iris. In bright light, the iris constricts the pupil to reduce light entry, protecting the retina and helping to maintain optimal vision. In low light conditions, the iris dilates the pupil to allow more light to enter, improving visibility in dim environments.

The other parts of the eye have different functions. The sclera is the tough, outer layer that provides structural support and protection for the eye. The cornea is the transparent front part of the eye that helps to focus light but does not regulate light entry. The retina is the innermost layer that receives light and converts it into neural signals, but it does not control how much light enters the eye. Thus, the iris is the key structure for modulating light intake.