AP PSYCHOLOGY

Detailed explanation-1: -The iris sphincter muscle, also known as the pupillary sphincter or sphincter pupillae, is a muscle located in the colored part of the eye called the iris. The sphincter muscle fibers are located near the pupillary margin and are slightly anterior to the pigmented epithelium of the iris.

Detailed explanation-2: -The sphincter muscle of the iris is a circular muscle that constricts the pupil in bright light, whereas the dilator muscle of the iris expands the opening when it contracts.

Detailed explanation-3: -Last reviewed: July 19, 2022. Reading time: 6 minutes. Sphincter pupillae muscle (Musculus sphincter pupillae) Iris is a part of the eyeball that serves the regulation of the amount of light that reaches the retina, as it features an opening called the pupil through which the light can pass through.

Detailed explanation-4: -The iris dilator muscle has fibers arranged radially from the sphincter to the ciliary border, receives sympathetic innervation, and functions to cause dilation of the pupil (mydriasis).

Detailed explanation-5: -The pupil size is controlled by the iris sphincter muscle and the iris dilator muscle, which constricts and dilates the pupil, respectively (8).