What is the muscle that is in the iris that keeps light from the pupil called?

The muscle in the iris that controls the amount of light entering the pupil is called the sphincter pupillae. It constricts the pupil in bright light conditions to limit the amount of light that reaches the retina. This action is part of the pupillary light reflex, which helps protect the retina from excessive brightness. In contrast, the dilator pupillae muscle works to widen the pupil in low-light conditions.