Anisocoria

What is Anisocoria?

The condition where one pupil is larger than the other is referred to as anisocoria. The pupil is the black part located in the center of the eye, which expands or contracts in response to different amounts of light. In bright light, the pupil constricts to reduce light entry, and in dim light, it enlarges to enhance visibility.

The dilation and constriction of pupils are involuntary and automatically adjust according to the light conditions in the environment, a process unnoticed by people. However, in individuals with anisocoria, one pupil remains significantly larger, which can be noticeable in a mirror reflection or in photographs.

This condition can affect a person's vision. An inability of the pupil to properly adjust to the light intensity can hinder clear vision. Additionally, the affected eye may develop sensitivity to light.

If one notices a sudden change in pupil size, it is crucial to seek immediate medical attention. Some people may develop anisocoria without long-term complications; however, it can also indicate a potentially life-threatening emergency. If anisocoria is accompanied by pain and significant vision impairment, it is necessary to visit an emergency department.

Causes of Anisocoria

Anisocoria can occur due to a variety of health problems or injuries. It can also appear as a side effect of certain medications. Additionally, anisocoria can sometimes occur without any known cause, which is referred to as idiopathic anisocoria.

Common causes of anisocoria include:

• Migraine type headaches
• Side effects of surgery
• Eye drops
• Scopolamine patches
• Injuries or traumas affecting the head, eyes, or the arteries supplying them

Some serious and potentially life-threatening conditions can also cause anisocoria. These include:

• Brain aneurysms
• Strokes
• Brain tumors
• Meningitis and other infections
• Certain types of cancer

Symptoms of Anisocoria

The most distinctive sign of anisocoria is one pupil being noticeably larger than the other. Other symptoms may not be present in every individual. If this is the case, it is still important to consult an eye doctor for diagnosis.

Besides one pupil being larger, if any of the following symptoms occur, it is necessary to seek emergency medical attention:

• Eye pain
• Blurred vision
• Double vision
• Light sensitivity
• Sudden loss of vision

Other symptoms that may occur with anisocoria include:

• Fever
• Headache
• Headaches
• Nausea
• Vomiting
• Neck pain
• Stiff neck

Diagnostic Criteria for Anisocoria

Eye doctors can diagnose anisocoria through a physical examination. A physical exam is also performed to check for other symptoms. Eye drops may be given to facilitate the examination of the eyes. The physical examinations include:

• Slit lamp examination
• Fundus examination

Imaging tests may be utilized to determine the cause of the anisocoria. These imaging methods include:

• MRI
• CT
• X-ray

If an infection is suspected, blood tests or a lumbar puncture may be necessary.

Treatment Methods for Anisocoria

It is necessary to identify and treat the cause of anisocoria. These treatment methods are much more important than managing the irregularity in the pupils. If anisocoria is observed with idiopathic reasons and no other symptoms, the irregularity in the pupils usually resolves over time.

Difference Between Anisocoria and Horner's Syndrome

Horner's syndrome is classically defined by the triad of ptosis, miosis, and anhidrosis, although clinical presentations can vary. Anisocoria, on the other hand, is more pronounced in the dark due to a defect in the pupillary dilator response secondary to lesions along the sympathetic chain. Central or first-degree lesions are typically due to stroke or demyelinating diseases.