Nystagmus of paroxysmal positional vertigo

During attacks of paroxysmal positional vertigo in 12 patients, nystagmus in different gaze positions was observed visually and recorded by electronystagraphy (eyes open, fixating). Visually observed eye movement was similar in all cases, with oblique (upward and horizontal) and rotatory (clockwise during leftward movement) components in fast phase; rotation dominated on ipsilateral gaze (toward the lower ear) and oblique movement dominated on contralateral gaze. However, ENG recordings showed greater variability and were often inconsistent with visual observation; the horizontal component often reversed with change in gaze position, and dissociated eye movements, as well as down-beating nystagmus, were sometimes seen. More sophisticated measurement and strict attention to gaze position is required to resolve these discrepancies.