Dilated pupils (mydriasis) can happen for many reasons, such as a normal response to light, medication or drug use, eye exams, and medical conditions.
Dilated pupils are when the dark center of your eye is widened. This happens naturally in dim setttings. It can also happen after taking certain medications or drugs. In both of these situations, dilation is temporary.
Dilated pupils that don't turn back to their regular size, however, are not normal. Having one or two pupils that stay dilated could be a sign of a serious medical concern, such as glaucoma or a brain condition.
This article explains why pupils naturally dilate, other reasons why they can change in size, and when to see a healthcare provider.
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What Are Dilated Pupils?
Dilated pupils happen when the black circles in the colored part of your eye (iris) gets larger.Muscles in the iris control the size of your pupils. The normal pupil size for an adult varies but can be from 2 mm to 8 mm, depending on whether the eyes are being exposed to light or are in the dark.
What Is Anisocoria?
Anisocoria is when one pupil is dilated, rather than both.
Causes of Dilated Pupils
Your pupils often dilate naturally in response to the light in your environment. Other reasons they can dilate include:
- Medications or drug use
- Eye exams
- Injuries
- Medical conditions
- Emotions and focus
Natural Response to Light
Your pupils allow light to enter. Pupils constantly change in size, especially in response to light:
- Pupils normally get bigger (dilate) in low-light conditions to let more light into the eye.
- Pupils normally get smaller (constrict) in conditions with higher levels of light to minimize the amount of light that enters the eye.
How to Check Your Pupil Size
You can check the size by standing in front of a mirror, then dimming and raising the lights in the room to see how your pupils react.
This will give you a basic idea of what your pupils usually look like and how they typically react to light. This could help you notice if your pupils are not their usual size or are reacting abnormally.
Medications or Drug Use
Some medications cause dilated pupils by interfering with the function of a muscle in the iris that controls the pupil's size.
Examples of medications and drugs that can cause pupils to dilate include:
- Antihistamines, such as Benadryl (diphenhydramine)
- Muscle relaxants, such as Lioresal (baclofen)
- Decongestants, such as Sudafed (pseudoephedrine)
- Parkinson's medications, such as Symmetrel (amantadine)
- Antidepressants, such as Norpramin (desipramine)
- Illicit drugs such as cocaine and LSD
Healthcare providers can figure out whether certain medications orother drugshave caused dilated pupils.When tested, the pupils will not respond normally to light-related stimuli. Notably, they will not constrict when the eye is exposed to a large amount of light.
Dilated pupils caused by medications or drug use may come with other symptoms such as:
- Altered mental status
- Dry skin
- Fever
- Flushing
- Sudden, involuntary muscle jerks, shakes, or spasms (myoclonus)
- Seizures
- Urinary retention
If someone has overdosed on a drug, they may have other more serious symptoms such as:
- Blurred vision
- Heart palpitations
- Shortness of breath
- Constipation
- Urinary retention
- Tremulousness
- Memory difficulty
- Visual hallucinations
When Do Dilated Pupils Return to Normal After Medication Use?
Pupils will return to normal as the effect of the drug wears off. When this will happen depends on the drug and the time it takes for the amount of the active ingredient to decrease by half in your body (half-life).
Eye Exams
During acomprehensive eye exam, an optometrist or ophthalmologist may put drops in a patient's eyes to make their pupils dilate.
It takes about 20 minutes to 30 minutes for the drops to work. When they do, a provider can test the eyes for pupillary reactions, which can show if a person has a neurological problem.
The test also gives a provider insight into the health of the internal structures of the eye, including theretina, vitreous,optic nerve, blood vessels (choroid), and macula.
Ittypically takes a few hoursfor the dilating drops to wear off so you may need someone to drive you to your appointment.
Injuries
Trauma to the eye or the braincan also cause dilated pupils.
Typically, blunt closed trauma damages the iris sphincter muscle (which constricts the pupil) or one of the pathways in the brain that controls it.
It can also cause bleeding inside the skull, which can make the pupils enlarge.
Other than trauma, eye injuries can also result from:
- Intraocular surgery (cataract removalorcorneal transplant)
- Retinal procedures
Medical Conditions
Dilated pupils (in one or both eyes) can also be caused by medical conditions, including:
- Aneurysm in the brain
- Brain tumororabscess(e.g., pontine lesions)
- Excess pressure in one eye caused byglaucoma
- Brain swelling
- Intracranial hemorrhage
- Acute stroke
- Intracranial tumor
- Increased intracranial pressure
- Infection of membranes around the brain (meningitisorencephalitis)
- Migraine headache
- Seizure
- Tumor, mass, or lymph node in the upper chest or lymph node
- Horner syndrome
- Diabetic oculomotor nerve palsy
- Benign episodic unilateral mydriasis
- Holmes-Adie syndrome or Adie’s pupil
- Congenital aniridia
Emotions and Focus
Increased levels ofoxytocin(the "love" or "bonding" hormone) can lead to dilated pupils. Your pupils might get bigger when you’re feeling attraction or have an emotional response to someone or something.
A person's pupils can also dilate in situations where they are concentrating very hard, like when they’re making a decision.
Treatment for Dilated Pupils
Treating dilated pupils means figuring out what’s causing them to be dilated and addressing the underlying problem. For example, stopping a medication that is causing the pupils to enlarge or having surgery to fix an injury.
If your pupils are only temporarily dilated, such as after an eye exam, your provider might recommend wearing sunglasses to help you manage the discomfort of having eyes that are more sensitive to light. If your pupils are permanently dilated, you might be able to get special contact lenses that can make your eyes look more normal.
When to Call a Healthcare Provider
Contact your healthcare provider if you have unexplained changes in pupil size or the changes are not going away, especially if they started suddenly, are recent, or happened after an injury to the eye or your head.
Getmedical treatment immediatelyif you have dilated pupils (in one or both eyes) along with these symptoms:
- Blurred vision
- Double vision
- Eye sensitivity to light
- Fever
- Headache
- Loss of vision
- Nausea or vomiting
- Eye pain
- Stiff neck
Summary
Your pupils (the black circle in the middle of your eye) usually change size in response to light. However, it’s also possible for the pupils to dilate, or get bigger, if the eye is injured or affected by a medical condition.
Sometimes, dilated pupils are just temporary and get better without issue. However, if you have dilated pupils that are not going back to normal and other symptoms like headaches and trouble seeing, call your provider. They can figure out what’s causing your pupils to be dilated and make sure you get the right treatment.
Frequently Asked Questions
Do pupils dilate when you look at someone you love?
They can. Your pupils can dilate when you have higher levels of oxytocin. Oxytocin (the "love hormone") increases when you are emotionally aroused.
Learn MoreWhat Is Oxytocin?
Do pupils dilate when you are tired?
No, it's usually the opposite. If you are tired or sleepy, your pupils will likely be smaller than usual.
Learn MoreWhat Pupils Say About Sleep
Can stress cause dilated pupils?
Yes. Stress can cause your body to activate the sympathetic nervous system. This triggers a fight-or-flight response and can cause dilated pupils.
Learn MoreThe Body’s Stress Response
How are dilated pupils treated?
It depends on what's causing them. If medication is the cause, your doctor may recommend switching to another drug. Your doctor may suggest special contact lenses or sunglasses to reduce light sensitivity from dilated pupils.
Pupil Size and Your Health
