pupiller

Pupiller is a term used in several languages to denote the pupil of the eye—the circular opening in the center of the iris that allows light to reach the retina. In English, the standard term is “pupil.” The word’s roots go back to Latin pupilla, meaning a small doll or girl, reflecting historical imagery of the eye’s dark opening.

Anatomy and appearance: The pupil is an aperture bordered by the iris. Its size is controlled by two iris muscles: the sphincter pupillae, which constricts the pupil (parasympathetic control via the oculomotor nerve), and the dilator pupillae, which dilates it (sympathetic control). Pupil diameter typically ranges from about 2 to 4 millimeters in bright light and 4 to 8 millimeters in darkness, with variation due to age, medications, and individual differences.

Function and reflexes: The pupil regulates the amount of light entering the eye, contributing to image sharpness and depth of field. The pupillary light reflex involves the retina signaling to the pretectal area and Edinger–Westphal nucleus, sending parasympathetic impulses via the oculomotor nerve to the sphincter pupillae. The near response, triggered by focusing on close objects, also causes constriction. The reflex is typically consensual: shining light in one eye affects both pupils.

Clinical relevance: Abnormal pupil size or reactivity can indicate neurological or ocular problems. Anisocoria is unequal pupil size and can be benign or signify pathology depending on accompanying signs. Nonreactive or markedly unequal pupils can occur with brain injury, optic nerve disease, or certain drugs. Pupillometry—measuring pupil size and reactivity—is used in anesthesia, neurology, and ophthalmology to assess autonomic function.

See also: anisocoria, miosis, mydriasis, iris, ophthalmology.