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Eye and Vision Care

One dilated pupil



I`ve been noticing that frequently I`ve been having dilated pupils. Well, actually it`s just one pupil I believe that`s dilated. The first time it was noticed my friend said that one of my pupils was bigger than the other. When I went and looked it was. It wasn`t big by a huge amount but was noticable if one stared long enough. I don`t recall which pupil it was back then and this has happened about 3 times now, all of them about a month or so apart; I`m currently on my third time. Right now my left pupil is bigger than my right. I`ve been looking up causes and such for this but cannot find any. I`m a teenager and haven`t taken any pills in a while; the last I took was maybe an ibuprofen for my headache that was two weeks ago. Can you please tell me why one of my pupils keeps dilating?


You may have physiologic anisocoria which is a fancy way of saying that your pupils are unequal in size. This occurs more at times of stress, especially when there's a lack of sleep. It is thought that people who get headaches often, particularly migraines, may be more prone to this condition. Don't be concerned unless you notice that your near vision is blurred or reduced in the eye with the bigger pupil. If that occurs, see your optometrist or ophthalmologist to determine the cause.

Also, be mindful of the fact that over-the-counter eye drops that "get the red out" or some anti-allergy products do have a weak vasodilator in the formulation that can cause the pupil size to change if it's applied to the eye. Dermal patches used to treat sea sickness have a stronger version of these substances that also affect quality of near vision in addition to increasing pupil size. This effect is reversible, but just takes anywhere from a few hours to one day to wear off.

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Response by:

Cynthia Gale Heard, OD Cynthia Gale Heard, OD
Assistant Professor, Clinical Optometry
College of Optometry
The Ohio State University