Synergistic divergence: saccadic velocity analysis and surgical results.

The clinical findings are described in four patients with synergistic divergence (SD), an ocular motility disorder which is considered to be a variant of Duane retraction syndrome (DRS). Saccadic velocity studies in three patients demonstrated preserved abducting saccades in the affected eye with equally reduced amplitudes on both attempted abduction and adduction. The preserved saccades on attempted abduction of the affected eye, coupled with electromyographic evidence that shows maintenance of normal reciprocal innervation with respect to gaze on attempted abduction as dictated by Sherrington's law, strongly suggest that the abducens nerve is not necessarily absent or severely hypoplastic in this condition. One patient showed typical DRS in the contralateral eye and had a son with bilateral DRS, attesting to a possible genetic and etiologic relationship between SD and DRS. Three patients underwent strabismus surgery. Review of our surgical results and an analysis of the literature indicate that a crippling procedure to the ipsilateral lateral rectus muscle, such as extirpation, may be necessary to eliminate simultaneous abduction. Overcorrection did not occur following lateral rectus extirpation.