Why Are My Pupils Dilated? 5 Causes Of Dilated Pupils (Mydriasis)

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Written by Stephanie Watson, Alyson Powell KeyMedically Reviewed by Shruthi N, MD on July 01, 2024

• What Are Dilated Pupils?
• Medications That Cause Dilated Pupils
• Drug Abuse and Dilated Pupils
• Brain Injury or Disease
• Eye Injury
• Benign Episodic Unilateral Mydriasis
• Difference Between Blown Pupils and Pinpoint Pupils
• When to See Your Doctor About Dilated Pupils
• How to Manage Dilated Pupils
• Pupil Dilation Takeaways

4 min read

What Are Dilated Pupils?

You look in the mirror and notice that the dark circles in the middle of your eyes are bigger than usual. What's going on? Those dark circles are your pupils, the openings that let light enter your eye so you can see.

Muscles in the colored part of your eye, called the iris, control your pupil size. Your pupils get bigger or smaller depending on the amount of light around you. In low light, your pupils open up or dilate to let in more light. In bright light, they get smaller or constrict to let in less light.

Sometimes, pupils can dilate without any change in light. The medical term for this is mydriasis. Medicines, injuries, and diseases can all cause this eye condition. Here's a closer look at some of the causes.

Medications That Cause Dilated Pupils

Some medicines can affect the muscles that control your pupils and prevent them from getting smaller when light shines in. These meds include:

• Atropine (Atropen), which treats problems with heart rhythm, stomach issues, and some types of poisoning
• Antihistamines, such as diphenhydramine (Benadryl, Genahist, Naramin, Sominex, Unisom)
• Decongestants, such as pseudoephedrine (Afrinol, Sudafed)
• Motion sickness and anti-nausea medicines, such as dimenhydrinate (Dramamine) or a scopolamine patch
• Parkinson's medications, such as amantadine (Symmetrel) and carbidopa-levodopa (Sinemet)
• Tricyclic antidepressants , such as amitriptyline (Elavil) and desipramine (Norpramin)
• Botulinum toxin (Botox, Myobloc)
• Anti-seizure drugs, such as phenobarbital (Luminal) and topiramate (Topamax)

Drug Abuse and Dilated Pupils

Dilated pupils are one sign that someone has used illegal drugs, such as:

• Amphetamines
• Cocaine
• Ecstasy
• LSD

These drugs affect the muscle that widens the pupil, slowing how it reacts to light. So, even in a bright room, the eyes stay dilated. Withdrawal from these drugs can also make the pupils stay open wide.

Alcohol and pupils

Long-term alcohol abuse can also affect eye dilation and constriction. Talk to an eye doctor if you notice these changes.

Brain Injury or Disease

The pressure that builds inside your brain after a head injury, stroke, or tumor can damage iris muscles, which normally make your pupils open and close. One or both of your pupils can become fixed in the dilated position and can’t react to light. If that happens, you should see a doctor right away.

If you've had a head injury, your doctor or nurse might shine a light into your eye during the exam to see if your pupils get smaller.

Dilated pupils and migraines

If you get migraines and notice that your pupils are very dilated, see a doctor right away. It's a sign of a serious or life-threatening condition.

Eye Injury

An eye injury can damage nerves or the muscles in your iris that control your pupil size. That can also happen after eye surgery, such as cataract removal or corneal transplant.

Benign Episodic Unilateral Mydriasis

This condition means only one pupil is dilated. Doctors sometimes call it "benign" when it's not related to any serious conditions, but it can sometimes affect young women who get migraines. The pupil usually goes back to normal size within a few hours, but it can last several days. You should still see your doctor to rule out anything serious.

Difference Between Blown Pupils and Pinpoint Pupils

Blown or dilated pupils mean your pupils are larger than normal. Pinpoint pupils, called miosis or pupillary miosis, are when they're small or constricted, even when the light changes. The condition can happen in both eyes or just one. Common causes of pinpoint pupils include a brainstem stroke and the use of opioids, barbiturates, and other medications.

When to See Your Doctor About Dilated Pupils

See your doctor or eye specialist for an exam if your pupils are enlarged and they don't get smaller in bright light. Get emergency help if you've had a head injury and your pupils look larger -- especially if one pupil is bigger than the other.

The doctor will examine your eyes. You might also have imaging tests such as CT or MRI scans to look for an injury or other problems in your brain.

How to Manage Dilated Pupils

If a medicine causes your pupils to dilate, they should go back to normal once the drug wears off. Try to avoid the drug in the future if you can. If you need the medication for a health problem, ask your doctor if there’s a different drug you can try that won’t affect your eyes.

How to protect your eyes when the pupils are dilated

While your eyes are dilated, they will be more sensitive to light than usual. Try to avoid bright places. Wear sunglasses when you go outside. Sometimes, dilated pupils can affect your eye. Ask your eye doctor if you need to avoid driving until your pupils go back to their normal size.

Pupil Dilation Takeaways

When you notice your pupils are unusually large, it could be due to mydriasis, a condition where pupils dilate without changes in lighting. Different things can cause dilation, including certain medications and illegal drugs, conditions such as brain injuries, strokes, or tumors, and eye injuries and surgeries. If your dilated pupils are a result of medication, they typically return to normal after the drug’s effects wear off. It's best to avoid bright lights and consider protective eyewear such as sunglasses in the meantime. Always talk to a doctor if your pupils stay dilated in bright conditions or following a head injury.

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• What is Anisocoria?
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