Localization of static positional nystagmus with the ocular fixation test.

OBJECTIVE

Characteristics of static positional nystagmus (SPN) (i.e., persistency, direction fixed, direction changing) are observed in both peripheral and central disturbances and possess no localizing value for vestibular lesions. Our objective was to investigate whether the ocular fixation test as applied to SPN could assist in localizing vestibular lesions.

STUDY DESIGN

A 3-year prospective study that included 43 patients with SPN.

METHODS

All patients underwent a standard vestibular test battery and cerebral imaging (7, computed tomography scan; 36, magnetic resonance imaging). The ocular fixation index (OFI) was calculated by the ratio of the mean slow component velocity of SPN (measured with red light-emitting diode fixation) to that measured in darkness, multiplied by 100. An OFI less than 50 was considered normal.

RESULTS

In 33 of 35 patients whose OFI was less than 50, the cerebral imaging was normal and a peripheral vestibular lesion was diagnosed (two benign tumors of the fourth ventricle were missed). In all eight patients whose OFI was greater than 50, the cerebral imaging was abnormal and a central vestibular lesion was noted.

CONCLUSIONS

These results indicate that the visual suppression of SPN does, indeed, permit the localization of vestibular lesions. The predictive value of the ocular fixation test on the origin of SPN is greater than 94% for peripheral lesions and 100% for central disorders.