Can the iris of one eye be larger than the other?

I want to make sure that I answer the question that you are intending to ask. When people refer to the iris they sometimes mean the pupil, and at other times they really mean the cornea, the clear window on the front of the eye that you are looking through when you see the iris. No matter what you are referring to—pupils, irises, or the cornea—each of them can be larger than the other.

Unequal pupil size may be normal or abnormal. About 20 percent of people (2 out of 10) have differently sized pupils some of the time. The difference is usually very small and the size difference does not affect their vision. At other times, unequal pupil size can be a sign of a problem. In these cases, the size difference is usually greater and there are often other signs present that suggest there is a problem. These other signs can include a droopy upper eye lid, outward deviation of an eye, and double or blurred vision.

A review of old photographs can help determine if the unequal size of the pupil is longstanding or recent. If it is a recent change or has other symptoms, evaluation by an ophthalmologist is important.

The cornea and irises of the eyes can also be of unequal size from birth or acquired due to a disease. In fact, all parts of the eyes can be of unequal size. This generally is seen in early childhood and when any parts of the eyes are of unequal size, an exam with an ophthalmologist is needed.

This question was originally answered on March 11, 2014.