Congenital adduction palsy and synergistic divergence.

Electromyography of the medial and lateral recti muscles in the right eye of a 7-year-old boy with congenital variable exotropia demonstrated cocontraction. This explained the observed simultaneous abduction on attempted levoversion. Abduction of the right eye increased intraocular pressure to 25 mm Hg from 15 mm Hg. This synergistic divergence should be considered a variant of Duane's syndrome, and, like Duane's syndrome, may occur as the result of anomalies of the peripheral oculomotor nerves or of central synaptic alterations, or of a combined central and peripheral mechanism.