Disconjugate adaptation of vertical saccades in superior oblique palsy

Abstract

Vertical eye movements along the midline were recorded in a patient with recent (1 month) right eye superior oblique muscle palsy. The patient showed severe right eye hypertropia and impairment of the yoking of the eyes during and after vertical saccades, particularly downward saccades. One month later, the right eye hypertropia was spontaneously reduced. Yoking of vertical saccades was also improved. To test whether a central adaptive mechanism could be responsible for the improvement of the yoking of vertical saccades, we tested the ability of the patient to adapt to optical aniseikonia, image size inequality. Vertical saccades developed disconjugacy that reduced the disparity of the aniseikonic images. Disconjugacy persisted for upward saccades, even under subsequent monocular viewing. This suggests a capacity for visually driven adaptation of saccade yoking that could be used to reduce the deficits caused by the paresis. Importantly, the disparity reducing oculomotor learning mechanism can function even when no bifoveal fusion can be obtained.