Updated on  February 22, 2024
6 min read

What is Mydriasis (Dilated Pupils)?

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Mydriasis is when the black opening in the center of the eye (pupil) is larger than normal. Dilated pupils naturally occur in response to light and emotional events. 

In low-light environments, your pupils dilate (widen) to let more light in. However, you may have mydriasis when your pupils remain dilated for an extended period, even when there’s bright light.

People with mydriasis may experience the following symptoms:

  • Blurred vision
  • Headaches 
  • Pain around the eye 
  • Photophobia (extreme light sensitivity)
  • Red eye
  • Diplopia (double vision)
  • Transient visual obscurations (“graying out” of vision for a few seconds)

Unlike miosis, where your pupils constrict and become smaller, mydriasis refers to a continued enlargement of the pupils. Having dilated pupils can create discomfort and cause sensitivity to light or blurry vision. 

If you have mydriasis, you must consult an eye care specialist. While some mydriasis cases are harmless, others may indicate an underlying health issue, such as a brain injury. 

When to See a Doctor for Mydriasis 

Pupil dilation that’s temporary and occurs as a response to light or emotional events isn’t a cause for concern. 

Call your healthcare provider if:

  • Mydriasis comes on suddenly in one or both eyes
  • Your eyes remain dilated in bright light
  • One pupil remains bigger than the other for a long time

Seek emergency medical care if mydriasis occurs with headache, dizziness, or confusion (signs of stroke).

What Causes Mydriasis? 

Larger-than-normal pupil size may be benign or indicate an emergency problem. Seeking medical care will allow specialists to determine the cause of mydriasis and, if possible, next-step treatments.

Common causes of dilated pupils include:

Certain Medications

Different types of medications can cause mydriasis. The most common are:


Anticholinergics block specific chemicals from reaching the eyes, which can cause dilated pupils. Medications that contain anticholinergic agents include:

  • Atropine. Primarily used to treat a slow heart rate.
  • Scopolamine. Used to treat motion sickness.
  • Robinul. Used to treat excessive sweating.

Some plants, such as Jimson weed and angel’s trumpet, also contain anticholinergic agents. 

Other symptoms that may occur with anticholinergic mydriasis include dry mouth, increased heart rate, and decreased sweating. Blurry vision and dizziness are also common.


Mydriatics are medications that healthcare providers use to dilate your pupils. This allows them to examine the inside of your eye. 

Mydriatic effects usually last 4 to 8 hours. During this time, your eyes may be more sensitive to bright light.

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Other Medications

Other medications that can cause pharmacological mydriasis include:

  • Antihistamines like Benadryl
  • Drugs to treat Parkinson’s disease
  • Antidepressants
  • Drugs that treat ADHD
  • Decongestants like Sudafed
  • Botulinum toxin (Botox®)

Recreational Drugs

Many illicit drugs can cause one or both pupils to dilate, including:

  • Cocaine
  • MDMA (ecstasy)
  • Methamphetamine (crystal meth)
  • Lysergic acid diethylamide (LSD)
  • Bath salts

Other symptoms, such as tachycardia (fast heart rate), visual hallucinations, and nausea, may be present when a person uses recreational drugs. 

Traumatic Brain Injury

Injury to the brain can increase the pressure around the brain (intracranial pressure). This may lead to mydriasis.

Common causes of brain injury include:

  • Stroke
  • Tumor
  • Head trauma
  • Brain aneurysm

A traumatic brain injury can damage the nerve that controls pupillary constriction (oculomotor nerve). This can result in a condition called blown pupil, which usually causes mydriasis in only one eye.

Mydriasis that comes on suddenly and is accompanied by a head injury or headache is considered a medical emergency.

Eye Injuries

If you experience accidental eye trauma, specific eye muscles can become damaged. For example, mydriasis could lead to injury to the iris sphincter muscle (a muscle that helps with pupil constriction).

Medical Conditions

Conditions that may cause pupillary dilation include:

  • Benign episodic unilateral mydriasis (BEUM). Unilateral mydriasis is when only one pupil is dilated. BEUM can occur in response to pharmacological agents or stress.
  • Adie’s pupil. This rare neurological disorder can cause one pupil to be larger than normal. The affected pupil may react more slowly, if at all, to light stimulus.
  • Anisocoria. Unequal pupil size may be caused by anatomical abnormalities or pharmacological effects.
  • Cranial nerve neuropathy. Damage to the cranial nerves that serve the eyes can cause mydriasis in one or both eyes. This may also cause impaired vision.
  • Migraines. Ocular migraines and migraine headaches can cause pupil dilation.

Increased Oxytocin

Oxytocin is a hormone that plays a key role in emotional attachment and sexual arousal. Your body releases oxytocin during exercise and intimate physical or social interactions. This can cause temporary mild to moderate mydriasis.

How is Mydriasis Diagnosed?

Your doctor will review your symptoms and your medical and family history. You should expect to list any medications or drugs that you’re taking. If you have suffered an injury to the eye, it’s important to share that information. 

Also, your doctor will have you perform a visual acuity test. Visual acuity refers to how sharp or clear your vision is. 

Other tests may include:

  • Ocular motility test to measure eye muscle functioning
  • Blood tests
  • Brain scans

How is Mydriasis Treated?

Treatment for mydriasis will depend on the underlying cause. That’s why it’s important to see a doctor for an accurate diagnosis.

Dilated pupils often return to their normal size on their own. For more serious cases of mydriasis, treatment may include:

  • Pilocarpine. This drug is used to treat increased intraocular pressure associated with glaucoma. However, in low doses, it can also help constrict pupils. It’s not a cure, and you’ll need to follow up with an ophthalmology clinic and specialist.  
  • Wearing sunglasses. Photochromic lenses and polarized lenses can reduce sensitivity to sunlight. Your eye doctor may prescribe sunglasses or contact lenses.
  • Prosthetic contact lenses. These improve the appearance of asymmetric pupils.
  • Surgery. People who have ocular injuries or nerve damage may require surgery.

What is the Outlook for Mydriasis?

The outlook for mydriasis depends on the cause. When mydriasis is a side effect of medication or recreational drugs, pupils usually return to their normal size within hours.

More serious causes of mydriasis, such as brain injury, require immediate medical treatment. The sooner your healthcare provider can determine the cause of mydriasis, the better the outlook will be.


Mydriasis is when you have dilated pupils that don’t return to normal size in bright light. Many things can cause mydriasis, including serious problems like brain trauma. 

Less-serious causes of mydriasis include medication side effects and increased oxytocin. Mydriasis after a dilated pupil exam is temporary and not a cause for concern.

It’s important to see a doctor for mydriasis that doesn’t go away, especially if it occurs with headache, dizziness, and other signs of stroke. Your doctor will determine the underlying cause of mydriasis and recommend the best treatment.

Updated on  February 22, 2024
6 sources cited
Updated on  February 22, 2024
  1. Bensinger, RE. “Is There a Cure for Mydriasis (Dilated Pupils)?” American Academy of Ophthalmology, 2016.

  2. Jacobson, DM. “Benign Episodic Unilateral Mydriasis: Clinical Characteristics.” Ophthalmology, 1995.

  3. Ma, M, and Liao, J. “Unilateral Mydriasis: Emergent or Benign.” Proceedings of UCLA Healthcare, 2017.

  4. Roos, J. “Episodic Anisocoria and Anxiety.” Ophthalmology, 2008.

  5. Hataye, ALS. “Eye Dilation: Necessary with Every Eye Exam?” Mayo Clinic, 2022.

  6. Witten, NAK, and Di Rocco, PJ. “The ‘Blown Pupil’: Imminent Death or Harmless Contamination?” Hawai’i Journal of Health & Social Welfare, 2019.

The information provided on VisionCenter.org should not be used in place of actual information provided by a doctor or a specialist.