Periodic Alternating Nystagmus

ABSTRACT

Periodic alternating nystagmus is a horizontal jerk nystagmus that periodically changes in amplitude and directions every 3 or 4 minutes. Usually the eyes beat in one direction for approximately 90 seconds and then go into a null phase for 10 to 20 seconds before beginning to move in the opposite direction and continued about 90 seconds. The exact mechanism is unknown but the rhythmic alteration of the null zone of horizontal jerk nystagmus is taken as a possible mechanism. These patients periodically show alternating head turning. The authors report 6 cases of congenital periodic alternating nystagmus which show horizontal jerk nystagmus of rhythmic direction change and confirmed by electro-oculogram.