Physiologic nystagmus is a natural reflexive movement to reset eye position when body orientation changes. In contrast, pathologic nystagmus (hereafter referred to simply as nystagmus) is an abnormal involuntary rhythmic oscillation of the eyes that is usually horizontal in direction, but may be vertical, torsional (i.e., twisting), or a combination of the three. Nystagmus may be associated with significant impairment of vision and social function.