Ocular torsion responses to electrical vestibular stimulation in Vestibular Schwannoma

Objectives: We determined if eye movements evoked by Electrical Vestibular Stimulation (EVS) can be used to detect vestibular dysfunction in patients with unilateral vestibular schwannoma (VS).

Methods: Ocular torsion responses to monaural sinusoidal EVS currents (± 2mA, 2Hz) were measured in 25 patients with tumours ranging in size from Koos grade 1 to 3. For comparative purposes we also measured postural sway response to EVS, and additionally assessed vestibular function with the lateral Head Impulse Test (HIT). Patient responses were compared to age-matched healthy control subjects.

Results: Patients exhibited smaller ocular responses to ipsilesional versus contralesional EVS, and showed a larger asymmetry ratio (AR) than control subjects (19.4 vs. 3.3%, p<0.05). EVS-evoked sway responses were also smaller in ipsilesional ear, but exhibited slightly more variability than the eye movement response, along with marginally lower discriminatory power (patients vs. controls: AR=16.6 vs 2.6%, p<0.05). The HIT test exhibited no significant difference between groups.

Conclusions: These results demonstrate significant deficits in the ocular torsion response to EVS in VS patients.Significance: The fast, convenient and non-invasive nature of the test are well suited to clinical use.