Figure 2a: The three planes of operation of the vestibuloocular reflex (VOR). Sagittal pitch plane (green), frontal roll plane (gray), horizontal yaw plane (green) [23].
Figure 2b: Nystagmus in defined disorders in the three planes of operation of the VOR. Tonus imbalance in the pitch plane leads to a vertical nystagmus (upbeat or downbeat nystagmus). Disorders in the roll plane cause a torsional nystagmus while disorders of the VOR in the yaw plane cause a horizontal nystagmus.