Optokinetic Nystagmus: Sensitivity and Specificity

Introduction: Vestibular nystagmus may be central or peripheral. Important differentiating features between central and peripheral nystagmus include the following: peripheral nystagmus is unidirectional with the fast phase opposite the lesion; central nystagmus may be unidirectional or bidirectional; purely vertical or torsional nystagmus suggests a central location; central vestibular nystagmus is not dampened or inhibited by visual fixation; tinnitus or deafness often is present in peripheral vestibular nystagmus, but it usually is absent in central vestibular nystagmus. According to Alexander's law, the nystagmus associated with peripheral lesions becomes more pronounced with gaze toward the side of the fast-beating component; with central nystagmus, the direction of the fast component is directed toward the side of gaze (eg, left-beating in left gaze, right-beating in right gaze, up-beating in upgaze).

http://emedicine.medscape.com/article/1199177-overview