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Anisocoria is a condition in which the pupil of one eye differs in size from the pupil of the other eye. Your pupils are the black circles in the center of your eyes, and they are usually the same size.

Anisocoria can be caused by several things. You can be born with this condition or develop it later. You might experience it on an ongoing basis or only temporarily. In some cases, your doctor might diagnose an underlying medical condition or other cause of anisocoria.

What symptoms commonly accompany anisocoria?

Depending on the underlying cause of your anisocoria, you might develop other symptoms too. For example, you might experience:

  • blurred vision
  • double vision
  • loss of vision
  • headache
  • fever
  • nausea
  • stiff neck

What causes anisocoria?

Anisocoria can result from a variety of things. For example, possible causes include:

  • direct trauma to the eye
  • concussion
  • bleeding in your skull
  • inflammation of your optic nerve
  • brain tumor
  • aneurysm
  • meningitis
  • seizure

How will your doctor diagnose the cause of anisocoria?

If you notice a difference in size between your pupils, contact your doctor right away.

During your appointment, your doctor will examine your eyes and take your vital signs. You should also discuss any other symptoms you’ve been experiencing. For example, be sure to mention if you’ve recently experienced:

  • changes to your vision
  • sensitivity to light
  • eye pain
  • headache
  • fever
  • stiff neck

Depending on your symptoms and medical history, your doctor might order one or more tests to help diagnose the underlying cause of your anisocoria. For example, these tests might include:

  • eye exams
  • complete blood count
  • blood differential
  • lumbar puncture, or spinal tap
  • CT scan
  • MRI
  • X-ray

If you experienced a head injury before your pupils changed in size, contact 911 or go to the hospital immediately. You might have a serious eye, brain, or neck injury that requires emergency treatment.

What will your treatment involve?

Your doctor’s recommended treatment plan will depend on the underlying cause of your anisocoria. For example, if an infection is to blame, your doctor might prescribe antibiotic or antiviral eye drops.

If you have an abnormal growth, such as a brain tumor, your doctor might recommend surgery to remove it. Additional options available for treating brain tumors include radiation therapy and chemotherapy to shrink the growth.

Some cases of uneven pupil size are temporary or considered to be normal and don’t require treatment.

How can you prevent anisocoria?

Some cases of anisocoria are impossible to predict or prevent. But you can take steps to reduce your risk of developing uneven pupils. For example:

  • Report any changes to your vision to your doctor immediately.
  • Wear a helmet while playing contact sports, cycling, or horseback riding.
  • Wear protective gear while using heavy machinery.
  • Wear your seatbelt while driving.

If you notice differences in the sizes of your pupils, seek medical attention immediately. Your doctor can help identify and treat the underlying cause of your condition. Following their recommended treatment plan may help improve your long-term outlook and prevent your condition from getting worse.

Content licensed from:

Written by: April Kahn
Medically reviewed on: Oct 17, 2016: Stacy R. Sampson, DO

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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