Synergistic Convergence in Congenital Extraocular Muscle Misinnervation

S ynergistic divergence is a well-established clinical condition in which abduction arises on attempted adduction, leading to simultaneous abduction of both eyes on lateral gaze. Synergistic divergence can occur as an extreme form of Duane syndrome, where most if not all oculomotor nerve branch fibers originally directed to the medial rectus muscle innervate the lateral rectus muscle. Synergistic convergence is an extremely rare form of ocular motor synkinesis characterized by simultaneous adduction on lateral gaze. It has only been described once in a case of congenital fibrosis of the extraocular muscles. Here we describe a girl with isolated congenital synergistic convergence and discuss its probable pathophysiology.