Anisocoria

Anisocoria (say "an-eye-soh-KOR-ee-uh) is a difference in the size of your pupils. The pupil is the black area in the center of your iris. The iris is the colored part of your eye. The iris controls the pupil to let the right amount of light into the eye. In bright light, the pupil narrows (constricts) to let in less light. In dim light, the pupil widens (dilates) to let in more light.

When you have anisocoria, one of your pupils does not constrict or dilate as well as the other one. So the pupils look uneven.

A slight difference in the size of the pupils is normal for some people. But in other cases this condition is the result of a medical problem. Examples include an injury to the eye, an infection, or nerve damage.

Having different-sized pupils usually doesn't cause any symptoms. And by itself, it is rarely a cause for concern.

Anisocoria is more likely to be the sign of a serious problem if it occurs along with other symptoms, such as:

• A droopy upper eyelid.
• Eye pain.
• A severe headache.
• Vision problems, such as double vision.
• Loss of vision.

Tell your doctor right away if you have any of these symptoms.