Posted on April 16, 2017
Different Sized Pupils (Anisocoria)
By: Jeffrey Colburn, MD
The pupils are the black circles in the middle of the iris, the colored part of the eye. The pupil is really just a hole in the middle of the iris that allows light to enter the eye. The iris is a flat circular disk of muscle that functions to control how much light enters the eye by controlling the pupil size. In dim light the pupil gets larger to allow more light in while in bright light the pupil gets smaller to decrease the amount of light passing through. The pupils are equal in size for most people. It is usually very noticeable if there is even a small difference in the pupil size between the eyes.
Anisocoria is the medical term for unequal pupil sizes. In a few people this could be just normal for them and not of any concern, though in these cases the difference in size is usually fairly small. Other possible causes of anisocoria in children include birth trauma to the neck or medications that can dilate the pupils. The most serious concern in young children is a type of cancer called Neuroblastoma that can happen along the spinal cord in the neck and affect one of the nerves that goes up to the face and helps control pupil size. For this reason, unequal pupil sizes should prompt a complete eye exam. Further testing may be needed if there are definite signs of concern.
As a side note, a new onset of different sized pupils in adults also warrants an eye exam as it can be a sign of neurologic issues or even a type of lung cancer in patients who are smokers.
(Photo from the American Association for Pediatric Ophthalmology & Strabismus. For more information, go here: https://aapos.org/terms/conditions/27)