Anisocoria

Go to the emergency room right away if your pupils are different sizes and you have sudden, new pain or vision loss. Even though it’s usually a temporary reaction, anisocoria can be the first sign of a life-threatening underlying condition like a stroke or aneurysm.

Overview

Anisocoria makes pupils irregularly sized
If you have anisocoria, one pupil will be noticeably larger than the other. You’ll probably be able to see the size difference.

What is anisocoria?

Anisocoria is the medical term for one of your pupils being bigger than the other.

The pupil is the black center of your eye that changes size to help you see in different amounts of light. It shrinks (contracts) in bright light and expands (dilates) in dim light.

Your pupils automatically adjust throughout the day without you noticing or controlling them. If you have anisocoria, one will be stuck noticeably larger than the other. You’ll probably be able to see the size difference in a mirror or selfie.

This might affect your vision. If one pupil can’t adjust to light like it should, you might have trouble seeing clearly, or be sensitive to light in your affected eye.

Visit an eye care specialist or go to the emergency room if you notice one of your pupils is suddenly larger than the other. Some people develop anisocoria with no long-term complications, but it can also be a sign of a life-threatening medical emergency. If you have other symptoms, like pain or noticeably worse vision, go to your nearest emergency room.

Types of anisocoria

Eye care specialists classify anisocoria as either physiological (caused by something malfunctioning inside your body) or pathological (caused by a health condition). Physiological anisocoria is more common.

This distinction isn’t as important as getting your symptoms evaluated right away. No matter what’s causing your pupils to be irregularly sized, you should see an eye care specialist as soon as possible.

How common is anisocoria?

Experts estimate that around 15% of people experience anisocoria at some point in their lives.

Some babies are born with it (congenital anisocoria), but it usually happens because of a health condition or another issue that affects your eyes.

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Symptoms and Causes

What are anisocoria symptoms?

One pupil being noticeably bigger (more dilated) than the other is the most obvious anisocoria symptom.

You might not experience other symptoms. If that’s the case, you still need to visit an eye care specialist to have the change in your eyes diagnosed.

Go to the emergency room if one pupil is bigger than the other and you experience any of the following:

Other symptoms can include:

What is the most common cause of anisocoria?

Anisocoria can be caused by lots of health conditions and injuries, and can be a side effect of some medications. It can also happen without a known cause (idiopathic anisocoria).

Some of the most common causes include:

Some serious, potentially fatal health conditions can cause anisocoria, including:

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Diagnosis and Tests

How is anisocoria diagnosed?

An eye care specialist or another healthcare provider will diagnose anisocoria with an eye exam. They’ll perform a physical exam to check for other symptoms. They might give you eye drops to make it easier to examine your eyes.

Your provider may use imaging tests to look for what’s causing anisocoria, including:

You might also need blood tests or a lumbar puncture if your provider thinks you have an infection.

Management and Treatment

How do you fix anisocoria?

Finding and treating what’s causing the anisocoria is more important than managing the irregularity in your pupils.

If you have no other symptoms — and your eye care specialist rules out any serious underlying conditions — you probably won’t need any treatment. Your pupils may return to their usual size over time.

If anisocoria is the first sign of a more serious condition, the treatment you’ll need depends on what’s causing it. Talk to your provider about what you’ll need to do next and what to expect.

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Prevention

How can I prevent anisocoria?

Because lots of conditions and injuries can cause anisocoria, there’s not one surefire way to prevent it.

Have your eyes examined regularly, and see a healthcare provider every year for a checkup. Regular eye exams and maintaining your overall health are the best ways to catch issues that might cause anisocoria before they damage your eyes and body.

Outlook / Prognosis

What can I expect if I have anisocoria?

Everyone’s outlook is different. It depends on what’s causing the anisocoria. Some issues like migraines or reactions to medications will go away on their own. If you experience something more serious like an aneurysm or stroke, your life might be changed permanently.

For most people, anisocoria is a minor part of a larger health issue, and as you treat your underlying condition, your pupils will return to their usual size.

Ask your healthcare provider or eye care specialist about your unique outlook.

Living With

When should I see my healthcare provider?

Visit an eye care specialist as soon as you notice any changes in your eyes or vision.

Go to the emergency room right away if your pupils are different sizes and you have sudden, new pain or vision loss.

What questions should I ask my healthcare provider?

You may want to ask your provider:

  • What’s causing the anisocoria?
  • Which tests will I need?
  • What’s the best treatment for me?
  • How long will recovery take?

Additional Common Questions

Which kind of doctor treats anisocoria?

Which type of healthcare provider you’ll need to see for anisocoria depends on what’s causing it and how it affects your body. You’ll probably have to visit an eye care specialist who’ll diagnose and treat issues in your eyes. You might also need to work with other specialists like a neurologist or cardiologist.

A note from Cleveland Clinic

Anisocoria is the medical name for your pupils being of different sizes. It’s usually a temporary issue, but it can be a sign that something inside your body is seriously wrong. Go to the ER if you notice anisocoria and have eye pain, vision loss or other symptoms that make you think something’s not quite right.

Even if it turns out that you’re having a short-term reaction, you should always take any changes in your eyes seriously and have them checked out by a provider right away. They’ll help you understand what’s causing the anisocoria and which treatments are best for you.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 03/11/2024.

Learn more about our editorial process.

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