pupil /pyo̅o̅″pəl/ [L, pupa, doll] , a circular opening in the iris of the eye, located slightly to the nasal side of the center of the iris. Like the iris, the pupil lies posterior to the cornea and the anterior chamber of the eye and is anterior to the lens. Its diameter changes with contraction and relaxation of the muscular fibers of the iris as the eye responds to changes in light, emotional states, and autonomic stimulation. The pupil is the window of the eye through which light passes to the lens and the retina. See also dilator pupillae, sphincter pupillae. −pupillary, adj.
