 Upbeat nystagmus is a vertical jerk nystagmus whose fast phases are in the upward direction. This patient exhibited upbeat nystagmus in primary gaze. Note how in this example they were diminished in up gaze and increased in down gaze. Sometimes just the opposite can be observed. Upbeat nystagmus localized to the brainstem. It can be seen in strokes, demyelination, or even tumors.