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What Is Anisocoria?

Anisocoria is a condition where the pupil of one eye differs in size from the pupil of the other. Your pupil is the black circle in the center of your eye. The pupils of your eyes are usually the same size.

Anisocoria has several causes and it is only found in a small number of people. You can be born with this condition, or it can develop over time. In some cases, there is no cause for the difference in size. In addition, some people with anisocoria experience a difference in pupil size only temporarily and then the size returns to normal without treatment.

What Causes a Difference in Pupil Size?

A difference in pupil size might be a result of a medical condition or disease, or the side effect of a drug. The most common causes for abnormal pupil size include:

  • brain tumor
  • abscess in the brain
  • meningitis
  • migraine
  • seizure
  • bleeding into the skull
  • aneurysm

Diagnosing the Cause of Uneven Pupil Size

You will normally notice an uneven pupil size yourself when you look into a mirror. Your doctor may also notice the condition during an eye examination.

You should seek medical care if the size of your pupils changes suddenly. Always contact a doctor right away if your pupils change in size following a massive headache or head injury.

During your appointment, your doctor will examine your eyes and take your vital signs. You should tell your doctor about any symptoms you have been experiencing along with the anisocoria. Be sure to mention if you recently had a headache, a change in your vision, a fever, or a stiff neck. Also notify your doctor if you have had any of the following symptoms:

  • sensitivity to light
  • eye pain
  • vision loss

Several tests can be done to find a diagnosis, depending on what your doctor suspects the cause to be. These tests include:

  • complete blood count (CBC)
  • blood differential
  • lumbar puncture, or spinal tap
  • CT (computed topography) scan
  • MRI (magnetic resonance imaging) scan
  • X-ray

What Other Symptoms May Be Present?

Uneven pupils do not usually cause symptoms on their own. However, the underlying medical condition or emergency may cause other symptoms, in addition to an uneven pupil size.

Other symptoms that may be present include:

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

Let your doctor know if you are also experiencing any of the symptoms mentioned above. This will help him or her diagnose the underlying cause of your anisocoria.

How Are Uneven Pupils Treated?

Treatment options for anisocoria can vary depending on what caused your pupils to become uneven in size.

If an infection is to blame, you may be given antibiotic or antiviral eye drops.

Abnormal growths—such as a brain tumor or a brain abscess—may be removed through surgery. If surgery is not an option, your doctor may use medical treatments to shrink the growth.

Some cases of uneven pupil size are temporary and do not need to be treated.

If you had a head injury before your pupils changed size, you should seek emergency attention immediately. Your treatment options will be discussed with doctors at the hospital.

Preventing Uneven Pupil Size

There is no way to completely prevent changes in the size of your pupils. However, you can reduce your risk of developing uneven pupils by reporting changes in sight to your doctor immediately.

You can also reduce your risk of developing this condition by wearing protective gear while playing contact sports or using heavy machinery.

Content licensed from:

Written by: April Kahn
Medically reviewed : George Krucik, MD

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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