Pupils that differ in size (Anisocoria)

Published on
October 20, 2022

Normally, our pupils are round and equal in size between both eyes, but about 20% of the population has naturally different-sized pupils. The difference is usually very small, like one millimeter. Anisocoria is a medical term that refers to pupils of different sizes. If you were born with different sized pupils that is usually not something to be concerned about. However if you suddenly notice a difference in the size of your pupils, then that can be caused by an underlying condition and should be looked at.

What can cause anisocoria?

In 20% of the population, the difference in pupil size is normal and they were born that way. However, we want to focus on the other portion of the population who have anisocoria that does not occur naturally. Among the many causes of anisocoria are:

  • Horner syndrome
  • Central nervous system issues
  • Eye injury
  • Brain tumor 
  • Aneurysm 
  • Seizure 
  • Other vascular changes

What symptoms are associated with anisocoria?

In the event that you have different-sized pupils because of underlying medical conditions, you may experience symptoms such as:

  • Blurred vision
  • Double vision
  • Loss of vision
  • Headache
  • Fever
  • Nausea
  • Stiff neck

How can anisocoria be treated?

Anisocoria does not currently have a treatment, however the underlying causes or symptoms can be addressed. The majority of the time, anisocoria does not require any treatment because it does not affect your eye health or vision. In the event that it does affect your vision, our eye doctor may be able to prescribe appropriate glasses that can help improve your vision. There may be an underlying medical condition causing the difference in pupil size, and this will be treated appropriately.

After establishing what is causing anisocoria, the eye doctor initiates appropriate treatment. When a patient has uneven pupil size due to an infection, antibiotics or antivirals are prescribed as eye drops to combat the microbes and correct the situation. In case of injury or trauma to the brain caused by abnormal growths, the doctor will refer the patient for additional tests and if needed surgery to remove the tumor and restore your normal vision and pupil size.

Pupils: what are they and how do they work?

Your pupils are the black circles at the center of the colored part of your eye. Based on what situation you're in, they let light in. If it's really bright outside, your pupils usually contract to a smaller size to prevent too much light getting in. Alternatively, if it's dark outside, they expand so that more light can be let in and you can see better. 

Schedule an eye exam in Olympia at American Family Vision Clinic

We encourage you to see our eye doctor if you notice (but were not born with) one pupil that is bigger or smaller than the other, perhaps as a result of an injury. While anisocoria isn't curable, it's important to do the workup to figure out what the underlying causes are and treat them. If you would like to schedule an eye exam, please call (360) 491-2121.


Such a nice optician. My grandson is only 4 and needs glasses. We were so sad, but he explained the issues, and we will follow up as he suggested.

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Family Vision Clinic changed our lives! My daughter was frequently car sick, and she was getting headaches every day, often painful enough that they brought her to tears. We saw a string of doctors and therapists, but we made no progress. Finally, we found Dr. Levi Zurcher and his eye therapist Rain. After ten weeks of eye therapy my daughter no longer gets headaches, and she no longer gets car sick. Daily tears are a thing of the past. I really can’t say enough about this clinic. It was fascinating to watch Dr. Zurcher work. For the first time, someone who knew what they were doing was intently studying my daughter, really trying to figure out all of her eye issues, and his therapist Rain is one of the most patient and lovely people that I’ve ever had the good fortune to meet. We’re finished with eye therapy—yay!—and I have switched to American Family Vision Clinic for all of my family’s other eye health needs.

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