The eye movements of syncope.

We videotaped the eye movements of syncope in 25 healthy volunteers who induced fainting by hyperventilation and Valsalva maneuver on a tilt table. In an additional three subjects, syncope was similarly induced during horizontal sinusoidal oscillation on a rotating chair while eye movements were recorded by electro-oculogram. Fourteen of 25 subjects experienced syncope on the tilt table. Six had downbeat nystagmus (DBN) at the onset that evolved into upward eye deviation, whereas seven showed isolated tonic upward deviation. In one subject the eyes remained in primary position. The gain of the vestibulo-ocular reflex (VOR) increased by 65% on average during syncope with concurrent vestibular stimulation. DBN, upward eye deviation, and increased VOR gain may all be caused by vestibular disinhibition caused by cerebellar hypoperfusion.