Duane syndrome

Overview

Duane syndrome, also known as Duane retraction syndrome (DRS), is a rare congenital eye movement disorder characterized by limited horizontal eye movement and abnormal functioning of the muscles that control the eye. It is one of the cranial dysinnervation disorders, meaning it results from improper nerve supply to the eye muscles. The syndrome most commonly affects one eye (usually the left), though it can be bilateral in some cases. Duane syndrome is present at birth and tends to remain stable throughout life.

Causes

Duane syndrome is caused by an abnormal development of the sixth cranial nerve (abducens nerve), which normally controls the lateral rectus muscle responsible for moving the eye outward (abduction). In individuals with Duane syndrome, this nerve is either absent or underdeveloped, and the lateral rectus muscle may instead receive innervation from the third cranial nerve (oculomotor nerve), which controls inward movement. This miswiring leads to restricted eye movement and globe retraction.

Most cases are sporadic, but some may be inherited in an autosomal dominant pattern, particularly when associated with other congenital anomalies or syndromes such as Goldenhar syndrome or Wildervanck syndrome. Mutations in the CHN1 gene have been linked to familial cases.

Symptoms

The symptoms and severity of Duane syndrome can vary but typically include:

• Limited eye movement: Especially difficulty moving the affected eye outward (abduction), inward (adduction), or both.

• Globe retraction: The eyeball pulls backward into the socket when attempting to move inward, often with narrowing of the eye opening.

• Head turn or tilt: To compensate for limited eye movement and maintain single binocular vision.

• Misalignment of the eyes (strabismus): Often esotropia (eye turns inward) or exotropia (eye turns outward).

• Reduced binocular vision: In some cases, depth perception and coordination may be affected.

Duane syndrome is typically categorized into three types:

• Type I: Limited abduction (outward movement), normal or limited adduction.

• Type II: Limited adduction, normal or limited abduction.

• Type III: Limited both in abduction and adduction.

Diagnosis

Duane syndrome is diagnosed clinically, often in infancy or early childhood, based on characteristic eye movement findings. Diagnostic steps include:

• Ophthalmic examination: Evaluation of eye movement, alignment, and the presence of globe retraction.

• Cover testing: To assess strabismus and how the eyes respond when one is covered.

• Slit-lamp and fundus examination: To rule out other structural abnormalities of the eye.

• Imaging studies (optional): MRI may be used to confirm absence or hypoplasia of the sixth cranial nerve in complex cases.

• Genetic testing: May be considered in familial cases or when Duane syndrome is associated with other syndromes.

Treatment

There is no cure for Duane syndrome, and treatment is tailored to the individual’s symptoms and visual needs. Many people with mild forms do not require intervention. Management options include:

• Observation: For cases with minimal symptoms and good head posture.

• Glasses: To correct any associated refractive errors or accommodative esotropia.

• Prism lenses: May help alleviate mild eye misalignment or reduce head turn.

• Surgery: Considered for patients with significant head posture, large misalignment, or abnormal eye movements. Procedures may include recession or resection of eye muscles to improve alignment and reduce globe retraction.

Surgery can improve function and appearance but typically does not restore normal eye movement.

Prognosis

The long-term outlook for individuals with Duane syndrome is generally favorable. While the condition is lifelong, many people adapt well and maintain functional vision with or without treatment. Early diagnosis and monitoring are important to address any complications such as amblyopia (lazy eye), misalignment, or social concerns related to appearance. In most cases, Duane syndrome does not worsen over time, and with appropriate care, individuals can lead normal, active lives.