Fig. 3 A typical downbeat nystagmus that is maximum in frequency and amplitude on eccentric and downward gaze. The nystagmus is absent during up and left gaze and up and right gaze; it is minimal during straight up or straight down gaze. In primary position the down-beating nystagmus is moderate in amplitude and slow in frequency. The frequency but not the amplitude increases on gaze right and left. On oblique downward gaze both amplitude and frequency increase, and on down and left gaze the eyes have a mixed pattern combining vertical and rotary components.