Anisocoria is a condition in which the pupil of one eye differs in size from the pupil of the other eye. Yourpupils are the black circles in the center of your eyes. 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.

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

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

If you notice a difference in size between your pupils, contact your doctor right away. If you don’t already have a provider, our Healthline FindCare tool can help you connect to physicians in your area.

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

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

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.

Your doctor’s recommended treatment plan will depend on the underlying cause of your anisocoria. For example, if an infection is the cause, 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.

In some cases, you’re not able to predict or prevent anisocoria. However, 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.