6 sources cited
Vision Center is funded by our readers. We may earn commissions if you purchase something via one of our links.

What is Mydriasis (Dilated Pupils)?

Mydriasis is an eye condition that relates to your pupils, the black circles in your eyes. 

Your pupils are responsible for controlling the amount of light that enters your eyes. In low-light environments, your pupils dilate (widen) to let more light in. 

However, when your pupils remain dilated for an extended period, even when there’s bright light, you may have mydriasis.

Depositphotos 55731161 XL

Unlike miosis, in which 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, it is important to consult an eye care specialist or seek clinical help. While some mydriasis cases can be harmless, other cases may indicate an underlying health issue, such as a brain injury. 

Causes of 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. 

Certain Medications

Different types of medications can cause mydriasis. Here is a list of a few of those medications:

  • Topical eye medications. These include the drops the eye doctor instills before performing a dilated eye exam. 
  • Autonomic drugs. These drugs either imitate or inhibit the normal functions of the body’s two nervous systems (parasympathetic and sympathetic).
  • Aerosolized anticholinergic drugs. Anticholinergics help inhibit the action of acetylcholine, a neurotransmitter. This chemical messenger is responsible for relaying signals between certain cells to impact how your body works.
  • Some plants with anticholinergic properties. Some plants may contain active components that cause mydriasis. For example, in Hawaii, the Angel’s trumpet plant has hyoscyamine, atropine, and scopolamine, and contact can lead to enlarged pupils.

Doctors will use light and dark exposure to determine the problematic eye. A small pupil incapable of dilating in a dark room means no sympathetic response is present. However, a large pupil incapable of constricting in a light room means there’s an abnormality in the parasympathetic nervous system. 

Drug Use

Illegal and illicit drugs like cocaine, ecstasy/MDMA, crystal methamphetamine (meth), or other amphetamines can result in mydriasis. LSD, a hallucinogenic drug, impacts the brain’s serotonin receptors and can also cause dilated pupils. 

When a person consumes or abuses drugs, other symptoms, such as tachycardia (fast heart rate) and nausea, may be present. 

Brain Disease or Injury 

Mydriasis can occur because of an underlying brain disease or traumatic brain injury. Eye diseases are not usually the cause of mydriasis. 

If you experience pupillary dilation and a headache, it is important to seek medical help immediately. While the case may be benign, doctors will need to rule out any possible serious intracranial problem. 

When there is unilateral pupil dilation, doctors may consider the following causes:

  • Stroke (inadequate blood flow to the brain) 
  • Aneurysm (bulge in a blood vessel due to a weakness in the blood vessel wall)
  • Brain herniation (increased intracranial pressure that moves the brain tissue)
  • Acute oculomotor nerve palsy (the third cranial nerve is damaged and causes a completely closed eyelid and outward/downward deviation of the eye) 

Adie’s tonic pupil is a rare neurological disorder that can cause one pupil to be larger than average and react slowly (if any reaction) to light. 

Benign Episodic Unilateral Mydriasis

In most cases, individuals with unilateral mydriasis are benign cases. These episodes may have occurred because of exposure to a topical mydriatic agent (drug).

However, benign episodic unilateral mydriasis (BEUM) may happen because of the impact caused by high levels of stress and anxiety. Evidence showing the association between these physiological responses and BEUM is growing.  

Eye Injuries

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

To determine the actual cause of mydriasis, an eye care specialist will ask for a complete history of your health and possible exposures to drugs, etc. 

Anisocoria (unequal size of the pupils) can occur in up to 18% of people in specific lighting environments. 

Symptoms of Mydriasis 

Symptoms of mydriasis can vary from one person to the next. The underlying cause of mydriasis will influence what symptoms will appear. 

Nonetheless, when a person has mydriasis, she/he may experience:

  • 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)

Possible Complications of Mydriasis

Because mydriasis could indicate a serious, underlying health problem, complications may arise. 

For example, if you experience unilateral mydriasis with a headache, doctors may suspect a brain injury like a stroke. 

However, if you do not receive proper treatment in time, you may suffer long-term consequences, including:

  • Impaired motor skills 
  • Paralysis 

Additionally, because of increased sensitivity to light, you may experience headaches or migraines more often. 

When to See a Doctor for Pupil Dilation 

You should visit your doctor or optometrist when you notice that your eyes remain dilated, often in bright settings. If you also see that one pupil is bigger than the other for an extended period, you should book an appointment. 

When you do this, your healthcare specialist can review your individual case and help determine the underlying cause of the problem. 

If you notice that your eyes frequently stay dilated even when in a bright environment, make an appointment to see your doctor or optometrist. 

It is also important to see your eye specialist if you notice that one pupil appears larger than the other for a long time. They can help you determine the underlying cause of abnormally appearing pupils.

How Mydriasis is Diagnosed

Your doctor will look over your symptoms and entire medical history. You should expect to list any medications or drugs that you’re taking. If you have suffered an injury to the eye, it’ll be 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. Furthermore, you may undergo an ocular motility test (to evaluate proper eye muscle functioning) and a blood test as well.  

Lastly, in suspected brain injury cases, your doctor may order neuroimaging scans. These images will help rule out any serious health concerns like a stroke. 

Treatment Options for Mydriasis 

Treatment for mydriasis will depend on the cause of the eye condition. 

Because the affected eye(s) will increase your sensitivity to light, your doctor may prescribe opaque contact lenses or light-sensitive sunglasses. Surgery may also be an option. 

Before proper treatment can occur, the doctor must perform the correct diagnosis. 

How to Manage Dilated Pupils

If you have dilated pupils, there are a few steps you could take to manage the condition:

  • Pilocarpine. This drug is used to treat increased intraocular pressure associated with glaucoma. However, in low doses, it can also help constrict pupils. It is not a cure, and you will need to follow up with an ophthalmology clinic and specialist.  
  • Avoid direct sunlight. You will have increased sensitivity to light. It is best to stay indoors or in the shade to prevent any possible complications, like headaches. 
  • Wear prescribed sunglasses
  • Avoid driving during the day. You may experience blurry vision because of the dilated pupils. 
  • Avoid reading books or magazines up close. This can also result in blurred vision.
6 Cited Research Articles
  1. Bensinger, Richard E. “Is There a Cure for Mydriasis (Dilated Pupils)?” American Academy of Ophthalmology, 12 Mar. 2018,
  2. Jacobson, Daniel M. “Benign Episodic Unilateral Mydriasis: Clinical Characteristics.” Ophthamology , American Academy of Ophthamology , 1 Nov. 1995,
  3. Ma, Mina, and Jessica Liao. Unilateral Mydriasis: Emergent or Benign, UCLA Healthcare, 2017,
  4. Roos, Jonathan. “Episodic Anisocoria and Anxiety.” Ophthamology - Letter to the Editor,  AAO, 1 July 2008,
  5. Softing Hataye, Alaina L. “Eye Dilation: Necessary with Every Eye Exam?” Mayo Clinic, Mayo Foundation for Medical Education and Research, 31 Dec. 2019,
  6. Witten, Nash A K, and Peter J Di Rocco. “The ‘Blown Pupil’: Imminent Death or Harmless Contamination?” Hawai'i Journal of Health & Social Welfare, University Clinical, Education & Research Associate (UCERA), Oct. 2019,
Vision Center Logo
The information provided on should not be used in place of actual information provided by a doctor or a specialist.

All about Vision Center

linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram