Positional nystagmus in asymptomatic human subjects.

Nystagmus produced by static placement of the head in different orientations is termed positional nystagmus and is known to occur in human subjects who are free of vestibular symptoms. This study provides quantitative data for horizontal positional nystagmus occurrence in 49 normal human subjects, in whom the number of nystagmus beats, the slow-phase velocity of each beat, and distribution statistics were determined. A metric for the possible differentiation of physiologic positional nystagmus from pathologic nystagmus is described.