The iris is the colored part of the eye. It is located between the cornea and lens. The round, central opening of the iris is called the pupil. Very small muscles in the iris cause the pupil to get smaller and bigger to control how much light comes into the eye. This allows you to see well in lighter and darker settings.
The number of color granules in the iris determines the iris color (pigment). The amount of pigment is often related to a person's genes, skin type, and hair color.
Inflammation of the iris is called iritis. Rarely, tumors can form in the iris. When tumors do form, most often they are melanoma.
Evans M. Anatomy of the uvea. In: Yanoff M, Duker JS, eds. Ophthalmology. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 7.1.
Taber's Cyclopedic Medical Dictionary. 24th ed. F.A. Davis Company; 2021. www.tabers.com/tabersonline. Accessed April 7, 2022.
Iris - illustration
The iris is the colored portion of the eye, amembrane located between the cornea and lens that regulates the entrance of light into the eye by contracting and dilating.
Review Date: 11/4/2021
Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.