Hyperdeviation associated with isolated unilateral abducens palsy.

Sixteen patients with isolated unilateral abducens palsy were found to have an associated hyperdeviation (HD) in peripheral gaze on Maddox rod examination. In four patients, the chief complaint was vertical as well as horizontal diplopia. Vertical ductions were normal in each case and the maximal HD ranged from 8 to 16 prism diopters (PD) in 10 of 16 patients (62.5%) and from 4 to 7 PD in 6 of 16 patients (37.5%). In ten cases, an HD in primary as well as peripheral gaze was detected. The magnitude of HD did not correlate with the degree of abduction defect, and the HD was maximal to the side of the paretic lateral rectus muscle in 14 of 16 cases, with 2 cases greatest on direct lateral gaze; 6 cases, lateral upgaze; and 6 cases, lateral downgaze. The Bielschowsky head tilt test was positive in 1 of 14 cases, and the double Maddox rod test showed the absence of cyclodeviation in 10 of 12 cases tested. A variable HD was present in six cases. In two cases, up and downshooting of the paretic eye, respectively, was noted on attempted abduction. The HD diminished in synchrony with abduction improvement. Mechanical factors and vertical substitution movements may explain the HD.