Transient monocular abduction on upgaze with impaired downward pursuit in downgaze – a new pattern of misdirection?

Abstract

A patient with a long history of diplopia on upgaze was examined clinically and electro-oculographically. Upward saccades were normal in the right eye, whilst the left eye made a diagonal saccade up and to the left, coming back to midline with a slow movement. Only minor underaction of her left lateral rectus was observed on examination and both adducting and abducting saccades were of normal velocity. Upward smooth pursuit was largely smooth, albeit with occasional saccadic intrusions; downward pursuit was smooth from upgaze to the horizontal and saccadic from there to downgaze. The saccadic defect could arise from a misdirected axonal projection from the third nerve nucleus to the left lateral rectus; the pursuit deficit could arise from a proposed misrouting of vertical smooth pursuit signals.