Eye deviation in patients with one-and-a-half syndrome

To understand malalignments of the visual axes in one-and-a-half syndrome, we measured eye positions in 4 patients with this syndrome under two condit ions: with Frenzel goggles to prevent eye fixation and without Frenzel gogg les. When fixation was prevented with the Frenzel goggles, all patients sho wed mild outward deviation in both eyes. Removal of the Frenzel goggles eli cited adduction of the eye ipsilateral to the side of the lesion for fixati on, with greater outward deviation of the contralateral eye (acute stage), or adduction of both eyes to midposition for biocular fixation (convalescen t stage). In 3 patients whose outward eye deviation with Frenzel goggles wa s greater on the ipsilateral side, a transition from one-and-a-half syndrom e to ipsilateral internuclear ophthatmoplegia was noted, whereas a transiti on to ipsilateral gaze palsy was seen in the one patient whose deviation wa s greater on the contralateral side. These findings suggest that in one-and -a-half syndrome patients, the eyes tend to be in divergent positions when fixation is prevented; ipsilateral eye deviation may result from medial lon gitudinal fasciculus involvement, and contralateral eye deviation may resul t from paramedian pontine reticular formation involvement. Viewing a target may lead to a secondary deviation or adaptation of eye positions for fixat ion. Copyright (C) 2000 S. Karger AG, Basel.