Which part of the eye constricts in bright light?

The iris is the part of the eye that constricts in bright light. It is a thin, circular structure located behind the cornea and in front of the lens. The primary function of the iris is to control the size of the pupil, the opening through which light enters the eye. In bright light conditions, the muscles of the iris contract, leading to a smaller pupil size. This constriction reduces the amount of light that enters the eye, helping to protect the retina from excessive light exposure and improving visual clarity.

This function is part of the eye’s reflex mechanism known as the pupillary light reflex, which is essential for adjusting vision in varying lighting conditions. The other structures mentioned do not have this role: the sclera provides structural support and protection, the cornea is primarily responsible for the initial refractive power of the eye, and the lens focuses light onto the retina but does not regulate light entry in the same way as the iris.