Anisocoria is unequal pupil size. The pupil is the black part in the center of the eye. It gets larger in dim light and smaller in bright light.
Slight differences in pupil sizes are found in up to 1 in 5 healthy people. Most often, the diameter difference is less than 0.5 mm, but it can be up to 1 mm (0.05 inch).
Babies born with different sized pupils may not have any underlying disorder. If other family members also have similar pupils, then the pupil size difference could be genetic and is nothing to worry about.
Also, for unknown reasons, pupils may temporarily differ in size. If there are no other symptoms and if the pupils return to normal, then it is nothing to worry about.
Unequal pupil sizes of more than 1 mm that develop later in life and do NOT return to equal size may be a sign of an eye, brain, blood vessel, or nerve disease.
The use of eye drops is a common cause of a harmless change in pupil size. Other medicines that get in the eyes, including medicine from asthma inhalers, can change pupil size.
Other causes of unequal pupil sizes may include:
Treatment depends on the cause of the unequal pupil size. You should see a health care provider if you have sudden changes that result in unequal pupil size.
Contact a provider if you have persistent, unexplained, or sudden changes in pupil size. The new development of different-sized pupils may be a sign of a very serious condition.
If you have differing pupil size after an eye or head injury, get medical help immediately.
Always seek immediate medical attention if differing pupil size occurs along with:
Your provider will perform a physical exam and ask questions about your symptoms and medical history, including:
Tests that may be done include:
Treatment depends on the cause of the problem.
Reviewed By: Daniel Kantor, MD, Kantor Neurology, Coconut Creek, FL and Immediate Past President of the Florida Society of Neurology (FSN). Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.