iris
Meaning of iris: The iris is the pigmented ring around the pupil that adjusts pupil size to regulate how much light enters the eye.
Definition of iris
The iris is the colored, ring shaped structure at the front of the eye that surrounds the pupil, the central opening through which light enters. It sits between the cornea in front and the lens behind, and its color comes from the amount and type of pigment present within it.
The iris contains two sets of tiny muscles that work in opposition, one that narrows the pupil in bright light and another that widens it in dim light, adjusting how much light reaches the retina at the back of the eye. This adjustment happens automatically and continuously as lighting conditions change.
Because the iris is easily examined during a routine eye exam, changes in its color, shape, or the evenness of the pupil it surrounds can provide clues to certain eye conditions or, less often, to conditions affecting the nervous system that controls its muscles.
Used in a sentence
Examination of the iris showed no abnormality on either side.
Good to know
A pupil that reacts unevenly or unequally between the two eyes can point toward a problem with the iris itself or with the nerves that control it, a distinction usually clarified through further eye examination.
Word origin
Where “iris” comes from
Formed from Greek iris, meaning rainbow, originally the name of the Greek goddess of the rainbow, later applied to the eye structure for its varied coloring.