Motility Disturbances

This 5-year-old child presented with a 70 PD exotropia OS and a right face turn. She had a CT scan of the head at age 4 months that was normal , and she was felt to have an isolated left medial rectus paresis. Her acuity was 20/20 OU. She could fuse with a large face turn, and was orthomorphic is extreme left gaze. On attempted right gaze, there was no adduction OS, and both eyes were seen to have paradoxical simultaneous abduction. The left eye would be seen to abduct as soon as the right eye abducted past the midline. In left gaze, the right eye would fully adduct and the left eye would go left, but would not abduct as fully as it would in right gaze. The diagnosis is synergistic divergence, a variant of Duane's syndrome, type II. The patient did not have fissure changes or retraction of the globe. it was felt that there was a paradoxical innervation here, with increased right lateral rectus firing on left gaze. Innervation of the right medial rectus, in the one such case recorded by EMG, was essentially normal. In Duane's syndrome, type II, the lateral rectus is fired both in abduction and adduction. The major difference between this and synergistic divergence is the marked firing of the involved lateral rectus on attempted adduction.