Dysfunction of pontine omnipause neurons causes impaired fixation: macrosaccadic oscillations with a unilateral pontine lesion

Macrosaccadic oscillations of eyes (MSO) are regarded as a form of saccadic dysmetria secondary to cerebellar dysfunction. They are usually conjugate, horizontal, and symmetric in both directions of gaze. Using magnetic search coils, we studied a patient with MSO that developed five years following head injury and involved synchronously horizontal, vertical, and torsional planes. The MSO were characterized by directional preponderance and were associated with ipsilateral pontine lesion. We propose a disturbance of fixation mechanisms due to unilateral disinhibition of saccadic burst neurons in three planes. This could arise from either primary or secondary dysfunction of omnipause neurons, due to impaired input from the contralateral superior colliculus. The delayed onset is suggestive of denervation supersensitivity as the underlying pathophysiology.