Tilt the head of the patient forward 30 degrees and shake the head in the horizontal plane at 2 Hz for 20 seconds. Observe for post-headshake nystagmus and note direction and any reversal. Fresnel lenses are preferred to avoid fixation. The maneuver may be repeated in the vertical direction.
Peripheral - a few beats of increased horizontal nystagmus
Central - Prolonged nystagmus, vertical nystagmus, and disconjugate nystagmus