Educational Content: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare provider for diagnosis and treatment.
Definition of Pupil
Medically reviewed by Min Clinic Staff | Updated: January 2026
Pupil: The opening of the iris. The pupil may appear to open (dilate) and close (constrict), but it is really the iris that is the prime mover; the pupil is merely the absence of iris. The pupil determines how much light is let into the eye. Both pupils are usually of equal size. If they are not, the condition is called anisocoria.