Duane syndrome

Presentation

The syndrome features limitation of abduction of the affected eye, with less marked limitation of adduction. On adduction, the eyeball retracts into the socket and the palpebral fissure narrows; on attempted abduction the fissure widens.

Poor convergence is present. A head turn toward the affected side compensates for movement limitations and maintains binocular vision. Although usually isolated to the eye, Duane syndrome can be associated with cervical spine abnormalities, Klippel–Feil syndrome, Goldenhar syndrome, heterochromia, and congenital deafness.

Causes

Duane syndrome is thought to be caused by incorrect wiring of the eye muscles, leading some muscles to contract at the wrong time and others to fail to contract when needed. In many cases, the sixth cranial nerve and its nucleus are missing or underdeveloped, and the lateral rectus muscle receives signals from a branch of the third cranial nerve instead. This misrouting means opposing muscles are controlled by the same nerve, so when the eye tries to move outward, both the lateral and medial rectus muscles contract together.

This co-contraction restricts eye movement and pulls the eye back into the socket. Additional mechanical issues, such as fibrous bands tethering the horizontal muscles to the orbital walls and scarring of the lateral rectus, are considered secondary effects. The tight lateral rectus can act like a leash, and co-contraction may cause the eye to slide upward or downward, creating the condition’s distinctive vertical movements.

Diagnosis

Duane syndrome has three variants: Type I with limited abduction with or without esotropia; Type II with limited adduction with or without exotropia; and Type III with limitation of both abduction and adduction and any form of horizontal strabismus. Brown classified the syndrome by movement limitation: Type A with limited abduction and less-marked limitation of adduction; Type B with limited abduction but normal adduction; and Type C where adduction limitation exceeds abduction limitation, with exotropic deviation and a compensatory head turn.

Type A accounts for 85% of cases. Differential diagnosis is difficult at very early ages; the clinician must examine abduction and adduction, and look for palpebral fissure changes or head postures, to distinguish Duane syndrome from common childhood squint or abducens nerve palsy. Acquired Duane syndrome is rare and occurs after peripheral nerve palsy.

Treatment

Most patients remain symptom free and maintain binocularity with only a slight face turn. Amblyopia is uncommon and, when present, rarely dense; it can be treated with occlusion, and refractive errors can be corrected. Duane syndrome cannot be cured because the missing cranial nerve cannot be replaced, and surgery is not expected to increase eye movement range. Surgical intervention is recommended only when the patient cannot maintain binocularity, experiences symptoms, or adopts a cosmetically unsightly or uncomfortable head posture.

The aims are to place the eye more centrally and reduce the need for abnormal head posture. Surgery may become appropriate later in life due to progressive muscle contracture. Approaches include medial rectus recession in one or both eyes; modest unilateral medial rectus recession with lateral rectus resection in selected patients; lateral transposition of the vertical muscles; and orbital wall fixation of the lateral rectus muscle to inactivate it in cases of marked anomalous innervation and severe cocontraction.

Did You Know?

• Two known genetic associations are with variants in the Chimerin 1 gene and the Transcription factor MafB gene.
• Duane syndrome has no particular race predilection.