Type 4 Duane syndrome

PurposeTo identify cases of synergistic divergence whose characteristics suggest that this entity is a form of Duane syndrome.MethodsThe records of all patients with a Duane syndrome diagnosis, including standardized eye position photographs, from the E-Consultation program of Cybersight, Orbis International were analyzed.ResultsA total of 350 Duane syndrome cases were identified. Of these, 19 (5%) had features consistent with synergistic divergence, or type 4 Duane syndrome. Of the 19, 16 (84%) were male, 15 (79%) had palpebral fissure narrowing, all had anomalous head posture, and 18 (95%) were exotropic. Only 9 (47%) patients were reported to have undergone surgery.ConclusionsSynergistic divergence is a rare entity with features similar to those of Duane syndrome. We suggest that this entity be classified as type 4 Duane syndrome, because it has unique findings and an innervation pattern that differs from the other 3 recognized types.