Overview

Duane syndrome is a rare congenital eye movement disorder characterized by limited horizontal eye movement, particularly difficulty moving the eye outward (abduction), inward (adduction), or both. It is caused by improper development of the sixth cranial nerve (abducens nerve), which controls the lateral rectus muscle responsible for outward eye movement. As a result, the affected eye often shows retraction (pulling back) into the socket when attempting to move, and the eyelid may narrow or widen abnormally. Duane syndrome usually affects only one eye, most commonly the left, and is present from birth. It is considered a non-progressive condition, meaning it does not worsen over time, but it can impact visual function and appearance.

Causes

The exact cause of Duane syndrome is linked to developmental abnormalities of the sixth cranial nerve. This nerve either fails to develop properly or is absent, causing the eye muscles to receive misdirected nerve signals. The lateral rectus muscle does not function normally, and in some cases, other muscles receive abnormal innervation, causing the eye to retract. The majority of cases are isolated and occur sporadically, but there are some known factors:

• Congenital factors: Duane syndrome occurs during early fetal development, likely between the fourth and eighth week of gestation.
• Genetic mutations: Although most cases are not inherited, mutations in genes like CHN1 have been associated with familial forms of Duane syndrome.
• Sporadic occurrence: Most individuals with Duane syndrome have no family history or identifiable genetic cause.
• Syndromic associations: In rare cases, Duane syndrome may be part of a broader syndrome, such as Goldenhar syndrome, Holt-Oram syndrome, or Okihiro syndrome.

Symptoms

The symptoms of Duane syndrome vary in severity and are mainly related to restricted eye movement. Common symptoms include:

• Limited horizontal eye movement: Difficulty moving the affected eye outward (abduction), inward (adduction), or both.
• Globe retraction: The eyeball retracts or sinks backward into the orbit when attempting certain eye movements, causing a narrowing of the eye opening (palpebral fissure).
• Head posture: People with Duane syndrome often adopt an abnormal head position (head turn or tilt) to compensate for limited eye movement and maintain binocular vision.
• Misalignment of the eyes (strabismus): The affected eye may appear crossed inward (esotropia) or outward (exotropia) in certain gaze positions.
• Reduced binocular vision: In some cases, depth perception may be affected, especially if double vision (diplopia) is present.
• No progression: The condition is present from birth and typically does not worsen over time.

Diagnosis

Duane syndrome is diagnosed based on clinical signs and eye movement patterns. The diagnostic process usually involves:

• Clinical examination: A detailed eye examination by an ophthalmologist or pediatric ophthalmologist to assess eye alignment, movements, and globe retraction.
• Ocular motility tests: Tests to determine the extent of restricted eye movements and compensatory head posture.
• Strabismus assessment: Measuring the degree of eye misalignment in different gaze directions.
• Vision testing: Evaluating binocular vision, depth perception, and the presence of amblyopia (lazy eye).
• Imaging studies: MRI or CT scans are rarely needed but may be used in atypical cases or when associated with other neurological findings.
• Genetic testing: Considered in familial cases or when Duane syndrome is suspected to be part of a broader genetic syndrome.

Treatment

Treatment for Duane syndrome is tailored to the individual, depending on the severity of symptoms and functional impact. Common management approaches include:

• Observation: Many cases are mild and do not require treatment, especially if there is minimal eye misalignment and no abnormal head posture.
• Glasses: Refractive errors such as farsightedness or nearsightedness can be corrected with glasses, which may improve overall visual comfort.
• Prism lenses: In some cases, prism lenses can help reduce double vision or minor misalignment.
• Surgical intervention: Eye muscle surgery may be recommended to improve eye alignment, reduce abnormal head posture, or minimize globe retraction. Surgery aims to reposition or weaken certain eye muscles but does not restore normal eye movement.
• Treatment of amblyopia: If lazy eye is present, patching the stronger eye or using atropine drops can help improve vision in the weaker eye.

Prognosis

The prognosis for individuals with Duane syndrome is generally favorable, especially when the condition is properly managed. Most people with Duane syndrome adapt well, maintaining good vision in at least one eye and achieving normal daily functioning. The condition is stable and non-progressive, meaning it does not worsen with age. With proper treatment, issues such as abnormal head posture, significant eye misalignment, or amblyopia can be effectively addressed. However, normal full range of horizontal eye movement is usually not fully restored. Overall, with timely diagnosis and appropriate care, individuals with Duane syndrome can lead healthy and productive lives.