Which part of the eye constricts in bright light?

The pupil is the correct answer because it is the opening in the center of the iris that regulates the amount of light entering the eye. In bright light conditions, the muscles of the iris contract, causing the pupil to constrict, or become smaller. This physiological response helps protect the retina from excessive light, which could cause damage and allows for better vision under bright lighting conditions.

The iris, while important in this process, refers to the colored part of the eye surrounding the pupil, rather than the actual opening that adjusts in size. The cornea is the transparent front layer of the eye that helps focus light, but it does not change in size or opacity. The lens, located behind the iris and pupil, aids in focusing light onto the retina but is not responsible for changes in light intake. Thus, the pupil's constriction in response to bright light is key to proper visual function and protection of the eye.