This is when the pupils are of unequal size. Many people have slightly different sized pupils and this is considered normal. Large differences between the eye is not normal, however. See dilated pupil for more information.

Dr. Timothy Root is a practicing ophthalmologist and cataract surgeon in Daytona Beach, Florida. His books, video lectures, and training resources can be found at:


  1. Physiological anisocoria is when the pupils are of different sizes, but this difference is consistant in both light and dark environments. Up to 1.5 to 2 mm of difference is common. This is rarely a problem or sign of anything wrong.

    That being said, there are a couple of things that can cause a change in pupil size:

    1. Adies Pupil – harmless damage to the parasympathetic nerves

    2. Horners Syndrome – potentially dangerous damage to sympathetic nerves

    3. Chemically induced pupil changes, such as from antihistamine pills, weed killer, etc..

    4. Third Nerve Palsy – associated with double vision.

    5. Uncal Hernation – brain swelling after injury or stroke

    All new pupil abnormalities need to be evaluated by a doctor.


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