Overview

Mydriasis is a medical term used to describe the abnormal dilation of the pupil, where the black center of the eye becomes enlarged and fails to constrict in response to light. Pupil size is normally regulated by the balance between the sympathetic and parasympathetic nervous systems, adapting to different lighting conditions. In mydriasis, this balance is disrupted, leading to persistently dilated pupils. This condition can be unilateral (affecting one eye) or bilateral (both eyes), and it may be temporary or permanent depending on the underlying cause.

Causes

Mydriasis can result from various causes, ranging from physiological responses to pathological conditions:

• Physiological Mydriasis: Temporary pupil dilation due to low light, emotional excitement, or stress is normal and harmless.
• Medication-Induced Mydriasis: Eye drops used during eye exams (e.g., atropine, tropicamide), as well as systemic medications like antihistamines, antidepressants, and anticholinergics, can cause pupil dilation.
• Neurological Disorders: Brain injuries, strokes, or tumors affecting the cranial nerves (especially the oculomotor nerve) can lead to mydriasis.
• Head Trauma: Concussions or traumatic brain injuries may result in dilated pupils, often indicating increased intracranial pressure.
• Drug Use: Illicit drugs such as cocaine, amphetamines, MDMA (ecstasy), or hallucinogens like LSD frequently cause mydriasis.
• Eye Injuries: Trauma to the eye can damage muscles or nerves responsible for pupil constriction.
• Adie’s Pupil (Tonic Pupil): A neurological condition where one pupil remains dilated due to damage to postganglionic fibers.
• Increased Intracranial Pressure: Conditions causing brain swelling or hemorrhage may lead to a fixed, dilated pupil, often considered a medical emergency.

Symptoms

The primary sign of mydriasis is visibly enlarged pupils. Other associated symptoms depend on the underlying cause and may include:

• Light Sensitivity (Photophobia): Difficulty tolerating bright lights due to inability of pupils to constrict properly.
• Blurry Vision: Reduced ability to focus, especially at close distances.
• Eye Pain or Discomfort: In cases where trauma or infection is involved.
• Headache: Often seen when mydriasis is associated with neurological causes.
• Visual Distortions: Seeing halos or glare, particularly at night.
• Neurological Symptoms: Depending on the cause, may include confusion, weakness, or other signs of brain dysfunction.

Diagnosis

Diagnosing mydriasis involves identifying the cause of pupil dilation through a comprehensive evaluation:

• Medical History: Review of recent trauma, medication use, recreational drug use, and any associated symptoms.
• Physical and Neurological Examination: Detailed examination of pupil size, reactivity to light, and eye movements.
• Slit-Lamp Examination: An eye doctor may use specialized equipment to closely examine the eyes and pupils.
• Pupillary Light Reflex Testing: Evaluates how pupils respond to light stimulation, helping differentiate between neurological and pharmacological causes.
• Imaging Studies: CT scans or MRIs may be ordered to rule out brain injury, stroke, or tumor if neurological causes are suspected.
• Toxicology Screening: Blood or urine tests to check for recreational drugs or toxic substances.

Treatment

Treatment of mydriasis depends on the underlying cause and whether the dilation poses any health risks:

Treatment Options

• No Treatment (Physiological Mydriasis): In cases where dilation is temporary and benign, no treatment is needed.
• Reversing Medication Effects: Stopping or changing medications that cause pupil dilation often resolves the issue.
• Treating Underlying Neurological Conditions: Addressing brain injuries, infections, or tumors through medical or surgical means if identified as the cause.
• Artificial Tears and Sunglasses: For comfort and to reduce light sensitivity, especially in long-term cases.
• Cholinergic Eye Drops: Pilocarpine drops may be used in some cases to help constrict the pupil, especially in Adie’s pupil.
• Emergency Treatment: In cases of increased intracranial pressure or serious head injury, immediate hospitalization and critical care are required.

Prognosis

The prognosis of mydriasis varies based on the cause. Physiological and medication-induced mydriasis typically resolves on its own without long-term effects. In cases linked to drug use or reversible medical conditions, full recovery is common after appropriate treatment. However, mydriasis due to neurological injury or structural damage may be permanent, particularly if the underlying cause is severe or left untreated.

Prompt diagnosis and treatment improve outcomes, especially in cases where mydriasis signals a serious underlying condition. Regular follow-up with a healthcare provider or eye specialist is recommended for persistent or unexplained pupil dilation.