Which part of the eye constricts in bright light?

The pupil is the opening in the center of the iris that allows light to enter the eye. When exposed to bright light, the muscles in the iris contract, causing the pupil to constrict, or become smaller. This constriction reduces the amount of light that enters the eye, helping to protect the retina from excessive brightness and improving visual acuity by reducing glare.

While the iris is involved in this process by adjusting the size of the pupil, the key function of constriction pertains specifically to the pupil itself. The cornea and lens do not change size to regulate light intake; rather, they serve different roles in focusing light onto the retina. Therefore, recognizing that the pupil is the part that actively constricts in response to bright light is crucial in understanding how the eye adapts to varying light conditions.