Pupille

Pupille is the French term for the pupil of the eye, the adjustable opening in the center of the iris that regulates the amount of light reaching the retina. The pupil appears as a dark circle or oval and its size varies in response to ambient light, emotional state, and autonomic tone.

Two smooth muscle layers control diameter: the sphincter pupillae, which constricts the pupil to reduce light, and the dilator pupillae, which dilates it to allow more light. The sphincter is innervated by the parasympathetic fibers of the oculomotor nerve (cranial nerve III) via the Edinger–Westphal nucleus and ciliary ganglion; the dilator is innervated by sympathetic fibers that originate in the superior cervical ganglion and reach the iris through the long ciliary nerves.

The pupil participates in essential reflexes, notably the pupillary light reflex, which constricts the pupil in response to bright light, and constriction during accommodation for near vision. Clinically, examination of the pupils is a standard part of neurological assessment; anisocoria, or unequal pupil sizes, can indicate trauma, nerve damage, or pharmacologic effects. Pharmacologic agents used in ophthalmology, such as mydriatics, dilate the pupil for examination, while miotics constrict it.

In English-language medical literature, the corresponding term is pupil, with pupille used primarily in French. The concept remains central to vision, as the pupil governs the amount of light entering the eye and thus the quality of the retinal image.