What Is Mydriasis?

Mydriasis is when pupils dilate, or widen, unnaturally—not in response to being in an environment with less light.

The pupils serve as conduits for light to enter the eyes and undergo size adjustments based on the ambient lighting conditions. In well-lit surroundings, the pupils constrict, permitting a reduced amount of light to enter. Conversely, in dimmer settings, the pupils naturally enlarge or dilate, facilitating the entry of more light. However, instances arise where the pupils dilate without corresponding changes in the light level—a phenomenon referred to as mydriasis.

Mydriasis can be triggered by a variety of factors, including the influence of certain medications, response to an ocular injury, presence of neurological disorders, or a traumatic brain injury. The underlying cause of mydriasis is pivotal in determining the appropriate course of treatment.

Symptoms

The pupils, which are the dark circular openings located at the center of the iris (the colored segment of the eye), possess a diameter that typically ranges from 2 to 4 millimeters. This dimension is contingent upon the illumination level of your surroundings. In response to varying light conditions, pupils have the ability to dilate or contract. When subjected to darkness, pupils dilate to facilitate the admission of increased light, thereby enhancing visibility. Upon re-exposure to light, the pupils constrict to their original, smaller size.

However, the occurrence of mydriasis introduces several atypical phenomena:

1. Pupils may undergo dilation without the presence of reduced light.

2. Pupils may remain dilated even when confronted with ample light.

3. Anisocoria, a condition wherein one pupil differs in size from the other, might manifest.

Depending on the root cause, additional symptoms could emerge, including:

• Headaches
• Sensitivity to light (photophobia)
• Visual disturbances, leading to blurry vision

Causes

There exist various factors that can lead to the occurrence of mydriasis in individuals.

1. Dilated Pupils During Eye Exam

The prevalent reason behind mydriasis often stems from the deliberate dilation of pupils performed by healthcare professionals during comprehensive eye examinations. In this procedure, eye drops are administered to induce pupil expansion. This dilation aids the healthcare provider in obtaining clearer visibility into the eye’s interior, facilitating the diagnosis of conditions such as glaucoma and diabetic retinopathy—a complication of diabetes that can result in vision impairment.

Following pupil dilation in an eye appointment, it is advisable for someone else to assume the role of the driver, as the process can cause temporary blurry vision. However, it’s important to note that this dilation-induced blurriness is transient, typically subsiding after a few hours, and poses no harm.

2. Medications

Mydriasis can arise due to the influence of various medications, particularly a class known as anticholinergics. These medications serve multiple purposes by impeding certain aspects of the nervous system.

Certain categories of medications, including:

• Antihistamines (used for allergies)
• Tricyclic antidepressants
• Bronchodilators
• Medications for Parkinson’s disease
• Bladder relaxants
• Antipsychotics

These substances can often trigger mydriasis. The dilation of pupils typically ceases once the medication is metabolized and exits your system. Depending on the specific medication, you might also encounter accompanying side effects, such as blurred vision and feelings of dizziness.

Additionally, drugs containing botulinum toxin A, exemplified by Botox (onabotulinumtoxinA), could also potentially contribute to mydriasis.

3. Drugs

Mydriasis can be induced by specific substances, leading to pupil dilation. Notable agents that have the potential to cause this phenomenon include:

• Marijuana
• Cocaine
• Methamphetamines
• LSD (lysergic acid diethylamide)
• Bath salts (synthetic cathinones)

Furthermore, the improper utilization or excessive consumption of opioids, prescription stimulants, such as those prescribed for attention-deficit hyperactivity disorder (ADHD), and nasal decongestants can also result in pupil dilation.

4. Injuries to the Eye

Occasionally, pupil dilation can be prompted by ocular trauma. This occurrence may be triggered by accidents involving impact, like a ball or other airborne object striking the eye. Eye injuries can also arise due to exposure to hazardous substances that come into contact with the eyes. Beyond pupil dilation, these incidents might lead to alterations in vision or, in severe cases, even blindness.

In situations involving a significant eye injury, it is crucial to promptly seek emergency medical attention.

5. Adie’s Pupil

Adie’s pupil stands as an infrequent neurological condition that gives rise to atypical pupil responses. Commonly, this disorder entails one pupil being larger than the other, and this asymmetry persists even when exposed to light. Concomitant alterations in vision might manifest, encompassing symptoms like blurred vision and heightened sensitivity to light. Activities like reading a book might become challenging due to these vision changes.

The underlying origins of Adie’s pupil remain unclear, though there is speculation of potential associations with bacterial or viral infections, as well as autoimmune disorders.

6. Microvascular Cranial Nerve Palsy

Microvascular cranial nerve palsy emerges when there is an impediment in the blood flow to the cranial nerves. In addition to pupil dilation, this condition can lead to the manifestation of other symptoms, such as double vision. It is conjectured that high blood pressure and diabetes are underlying factors contributing to the development of microvascular cranial nerve palsy. Typically, these symptoms tend to abate within a span of six to twelve weeks.

However, it’s important to note that a third nerve palsy arising from an aneurysm, albeit rare, demands urgent attention as it constitutes a critical medical situation requiring immediate evaluation.

7. Traumatic Brain Injury

Traumatic brain injuries materialize following severe head injuries. Individuals afflicted by such injuries might encounter symptoms including loss of consciousness, memory impairments, neurological disturbances, and challenges with focus and concentration. Mydriasis can also emerge as a potential symptom. Notably, this might be apparent when only one pupil becomes dilated, indicating the likelihood of a significant, unilateral injury.

8. Migraine

While not a consistent occurrence, certain forms of migraine attacks can lead to pupil dilation. Specifically, the type known as “migraine with aura” stands out. This intense migraine headache is often preceded by visual and neurological manifestations such as flashes of light and blind spots. It’s within the context of these attacks that pupil dilation might take place.

Diagnosis

Should you observe unexplained pupil dilation, it is advisable to promptly seek medical attention. Your healthcare professional will engage in a comprehensive evaluation, beginning with inquiries about your symptoms and potential medication or substance use. A thorough physical examination will be conducted, possibly involving blood tests and other relevant diagnostic procedures.

A meticulous ocular assessment will likely ensue, focusing on the reaction of your pupils to variations in light and darkness, as well as any discrepancies in size between them—referred to as anisocoria. This condition can stem from various underlying factors, some of which may have serious implications. The provider will also scrutinize your eyes and vision for any additional anomalies.

Treatment

The approach to treating mydriasis hinges upon its underlying cause. The primary objective of treatment is to restore the pupils to their customary size and address any contributing factors responsible for the deviation.

Interventions may encompass alterations in medication, as recommended by your healthcare provider. Additionally, specialized light-sensitive sunglasses or corrective contact lenses might be proposed to counteract mydriasis.

In cases where pupil dilation occurred during a standard eye examination, no therapeutic measures are required, as the pupils are expected to naturally revert to their regular size within a few hours.

When to See a Healthcare Provider

Should your pupils undergo dilation without apparent cause, it’s imperative to promptly get in touch with your healthcare provider. This becomes even more crucial if:

1. The dilation is confined to one eye.

2. You have encountered an eye injury or experienced head trauma recently.

3. You are experiencing other disconcerting symptoms, such as blurred vision, disorientation, dizziness, double vision, or a drooping eyelid.

Certain underlying conditions that trigger mydriasis, such as traumatic brain injuries, carry substantial gravity and warrant immediate attention rather than being overlooked.

A Quick Review

In general, pupils tend to dilate in response to decreased lighting conditions. However, there are instances when pupils dilate for reasons beyond just changes in light levels, a phenomenon termed mydriasis. This can be triggered by various factors, ranging from innocuous situations like pupil dilation during an eye examination, to more consequential issues like traumatic brain injuries.

Should you observe unexplained pupil dilation, it’s advisable to consult a healthcare professional. This step is crucial in order to identify the underlying cause of the change and determine whether any treatment is necessary.