Electrophysiology and Pathology of Duane Retraction Syndrome

Duane's retraction syndrome is a congenital condition that is characterized clinically by abnormalities of abduction, adduction, or both. In the most common form of this condition, there is mild limitation of adduction associated with narrowing of the lid fissure and retraction of the globe, and moderate to severe limitation of abduction with widening of the lid fissure. Although it was once thought that the condition was caused by primary fibrosis of the lateral rectus muscle, electromyographic and pathologic studies have shown that the condition is caused by anomalous innervation of the horizontal rectus muscles such that in most cases, there are no abducens motoneurons in the region normally occupied by the abducens nucleus, there is no abducens nerve, and the affected lateral rectus muscle is innervated by a branch of the oculomotor nerve. The areas of fibrosis within the lateral rectus muscle are areas that lack innervation. Patients with Duane retraction syndrome are able to make conjugate eye movements because of preservation of the internuclear neurons that receive input from both vestibular neurons and neurons subserving voluntary horizontal gaze originating in the cerebral cortex and that ascend via the medial longitudinal fasciculus to the sub-nucleus of the contralateral medial rectus muscle.