Eye Miosis

“Eye miosis” is the medical term for having unusually small or constricted pupils.

The pupil is the black center of your eye. Usually, it automatically gets smaller or bigger in response to changes in light around you. Muscles in your iris (the colored part of your eye) control your pupil’s size. Your pupil gets smaller in bright light. It grows bigger in dim light.

If you have miosis, your pupils stay small even if the light changes. The muscles in your iris tighten too much. This makes your pupil much smaller than it should be. That’s why healthcare providers sometimes call this condition pinpoint pupils.

It’s the opposite of mydriasis. Mydriasis is when your pupils are bigger and more dilated than they should be.

Miosis can affect one or both of your eyes at the same time.

Visit an eye doctor or healthcare provider if you notice any changes in your eyes, especially if your vision suddenly changes.

Most common miosis causes

Miosis can affect one or both eyes. Miosis in only one eye is called anisocoria. Causes can include:

• Uveitis and/or iritis: This is inflammation in one of the layers inside your eyes. The inflammation can affect how your iris controls your pupils.
• Synechiae: Inflammation can cause your iris to stick to the lens in your eye. This can prevent your pupil from changing size as it should.
• Horner syndrome: This condition affects one side of your face. It happens because of nerve damage.
• Having eye surgery: Miosis can sometimes develop after you have eye surgery. Your pupil may react more slowly than usual or stay stuck in a small size.
• Cluster headaches: These headaches cause severe pain around your eye. They come and go, sometimes multiple times a day.

Causes of miosis in both eyes can include:

• Medication side effects: Several medicines can cause constricted pupils. Opioids, barbiturates and pilocarpine can all lead to it. Clonidine and other alpha-2 agonists can as well. Talk to your healthcare provider about potential side effects when you start or change medications.
• Traumatic brain injuries or strokes: Anything that damages your eyes, your brain or nerves can affect your pupils. Eye injuries can stop them from working correctly. A stroke, traumatic brain injury or brain bleed can also cause miosis.
• Poisoning: Ingesting poisons like organophosphates or carbamates can cause miosis. They may also lead to life-threatening complications.
• Argyll Robertson pupils: This can happen if you have untreated syphilis. In later stages, the bacteria can affect your brain and spinal cord and lead to miosis.
• Age-related miosis: Some people naturally develop miosis as they age. This can be a normal part of aging, but you should still see an eye doctor to get it checked out.

How is this symptom treated?

A healthcare provider will recommend treatments for the condition or injury that’s causing the miosis. Your provider will give you an eye exam. You may need tests, like a CT scan or MRI, or blood or urine tests.

Your provider will help you understand what you’ll need, no matter what’s causing it. For example, you might need to change or stop a medication if miosis happens as a side effect. But don’t stop taking your medicine unless your provider says you should.

Your provider may prescribe eye drops to treat conditions like uveitis or iritis, or medication for cluster headaches. You may need to visit another specialist, too.

When should this symptom be treated by a doctor or healthcare provider?

Visit a healthcare provider or eye doctor as soon as you notice any changes in your eyes or vision. Especially if your eyes hurt. The sooner a provider diagnoses what’s causing the miosis, the better.

Tell your provider if you notice constricted pupils or other side effects after starting a new or different medication. They may be able to adjust your dose or switch you to a different medicine. Don’t stop taking a prescription unless your provider says you should.