Symptoms & Causes of Dilated Pupils (Mydriasis)

Dilated pupils, also known as mydriasis, occur when the pupil, the black circular opening in the center of the eye, expands beyond its normal size.

This dilation is controlled by the autonomic nervous system, which responds to various stimuli, including light, stress, and certain medications. While pupil dilation is often harmless, it can also signal underlying medical conditions requiring attention.

In normal light conditions, pupils constrict to control the amount of light entering the eye. However, when exposed to low light, excitement, or during certain medical procedures, pupils naturally dilate.

Common Benign Causes of Pupil Dilation

Dilated pupils aren’t always a cause for concern. Many common causes of mydriasis are benign and resolve on their own.

Here are the most frequent triggers:

Low Light Conditions

When we are in dim or dark environments, the pupils dilate to allow more light to reach the retina, helping us see better in low-light conditions. This is a natural, temporary response that typically resolves once the lighting conditions improve.

Drug Use

Certain medications and recreational drugs can cause pupil dilation. For example:

• Antihistamines, decongestants, and medications for motion sickness are known to dilate pupils.
  
• Recreational drugs like MDMA and cocaine can cause temporary pupil dilation, whereas cannabis (marijuana) generally produces little change or even slight pupil constriction.

Stress and Excitement

During moments of excitement or stress, the body’s fight-or-flight response is triggered, releasing adrenaline. This hormone causes a range of physical changes, including dilating the pupils, to improve vision in stressful situations.

Eye Drops for Medical Purposes

Doctors often use eye drops that temporarily dilate the pupils for eye examinations. These drops, known as mydriatics, are used to give the doctor a better view of the retina and optic nerve.

Red-Flag Causes of Dilated Pupils

While most cases of dilated pupils are harmless, there are certain situations where pupil dilation can signal a serious medical condition that requires immediate attention.

If you experience any of the following symptoms along with dilated pupils, seek medical help right away.

Neurological Causes

In some cases, dilated pupils can be a result of neurological issues such as third-nerve palsy, stroke, or brain hemorrhages.

These conditions affect the nerves that control the muscles around the eye, leading to abnormal pupil dilation.

Emergency Symptoms

Certain emergency symptoms that accompany dilated pupils require immediate evaluation. These include:

• Unilateral dilation. One pupil dilates, but the other remains normal.
  
• Headaches. A sudden, severe headache, especially when combined with pupil dilation, could indicate a stroke or brain hemorrhage.
  
• Drooping eyelids (ptosis). If one eyelid droops along with pupil dilation, it could be a sign of a serious nerve issue, such as third-nerve palsy.

How Are Dilated Pupils Diagnosed?

The diagnosis of dilated pupils starts with a comprehensive eye examination and a detailed medical history. A doctor will evaluate the patient's symptoms and perform specific tests to identify the underlying cause.

Initial Examination

The doctor will conduct a visual exam of the pupils, checking for symmetry, response to light, and reaction to accommodation (focusing on objects at different distances).

If necessary, further diagnostic tests, such as imaging scans or blood tests, may be conducted to rule out more serious conditions like brain injury or neurological disorders.

Neurological Tests

If the doctor suspects a neurological cause for pupil dilation, they may recommend additional tests such as:

• MRI or CT scan of the brain
  
• Electromyography (EMG) to assess nerve function
  
• Pupillometry, a specialized test that measures pupil reactions in response to different stimuli

The diagnostic process will depend on the accompanying symptoms and medical history to determine whether the pupil dilation is due to a benign cause or something more serious.

Treatment and Management of Dilated Pupils

The approach to treating dilated pupils depends on the underlying cause. If the dilation is caused by a benign factor such as low light or drug use, treatment may not be necessary.

However, if the dilation is related to a medical or neurological condition, immediate treatment may be required to prevent further complications.

Treatment for Neurological Causes

For neurological causes of dilated pupils, immediate medical intervention may be required. The specific treatment will depend on the particular case.

For example, treatment for third-nerve palsy depends on its underlying cause. If the condition is related to a brain aneurysm, stroke, or tumor, emergency treatment will be needed and may include surgery or other therapies.

A stroke or brain hemorrhage can cause dilated pupils as part of a larger neurological emergency. Immediate treatment is crucial to improve the patient’s chances of recovery.

Treatment for stroke or hemorrhage includes:

• Ischemic stroke. Thrombolytic therapy or mechanical thrombectomy to remove clots
  
• Hemorrhagic stroke. Surgery or endovascular treatments to repair the bleeding vessels
  
• Supportive care. Intensive monitoring and rehabilitation therapy following the acute event

Other neurological conditions that may lead to dilated pupils, such as brain injuries or certain types of meningitis, will require tailored treatments.

This might involve a combination of medication, surgery, or physical therapy to manage symptoms and address the root cause.

Surgical and Non-Surgical Interventions

In some cases, when conservative treatment options do not work, surgery or non-surgical interventions may be necessary.

Here's a look at some interventions that may be used:

• Botulinum toxin injections. Botulinum toxin is not a treatment for abnormal pupil reactions; injections near the eye can actually cause unintended mydriasis (dilated pupil) as a complication rather than a cure.
  
• Eye drops. In some cases, doctors may prescribe certain eye drops to help manage symptoms related to mydriasis, especially in patients experiencing discomfort.

Surgical intervention may be necessary if an anatomical issue, such as a brain aneurysm or eye trauma, causes pupil dilation. Surgery will be aimed at addressing the root cause of the pupil dilation to restore normal function.

Preventing Pupil Dilation

Preventing pupil dilation largely depends on the cause. For instance, it’s possible to reduce your risk of stress-induced pupil dilation by practicing stress management techniques.

For drug-induced dilation, using prescription medication responsibly and avoiding recreational drugs can help.

If your dilated pupils are linked to a neurological condition, early diagnosis and treatment are key to minimizing long-term effects. Regular checkups with a healthcare provider and addressing health concerns promptly can reduce the risk of complications.

What You Can Do at Home to Alleviate Symptoms

If you’re dealing with dilated pupils due to a benign cause, there are steps you can take at home to help alleviate symptoms and discomfort:

• Wear sunglasses: Because dilated pupils let in more light, you may be sensitive to bright environments. Wearing sunglasses when outdoors can protect your eyes and reduce discomfort.
  
• Use lubricating eye drops: If dry eyes accompany pupil dilation, over-the-counter lubricating eye drops can help keep your eyes moist and relieve any irritation.
  
• Take breaks from screens: If your pupils are dilated due to stress or prolonged screen time, take regular breaks to rest your eyes and avoid eye strain.

When to See a Doctor

If you experience persistent or sudden pupil dilation, particularly when accompanied by other concerning symptoms such as severe headaches, vision changes, or weakness, seek immediate medical attention.

A timely diagnosis is crucial for identifying and treating any underlying health issues before they become more serious.