Ocular torsion responses to electrical vestibular stimulation in Meniere’s disease and vestibular schwannoma

Introduction: Electrical vestibular stimulation (EVS) induces torsional eye movements which can be used to detect vestibular deficits (Mackenzie et al., 2018, 2019; Mackenzie & Reynolds, 2018). Prior work suggests elevated EVS responses in Meniere’s disease (MD) which may help differential diagnosis (Aw et al., 2013). To investigate this, we assessed responses to EVS in patients with unilateral MD or Vestibular Schwannoma (VS) and compared them to caloric irrigation and video head impulse test (vHIT) responses.Methods: We measured EVS, Caloric, and vHIT responses in 62 unilateral MD (mean age ± SD: 61 ± 13 yrs, 34 male), 30 unilateral VS patients (60 ± 13 yrs; 12 male) and 52 healthy controls (HC; 55 ± 21 yrs; 30 male). All MD patients received a definitive diagnosis according to the Barany criteria, while VS was confirmed by MRI. A Digitimer DS5 was used to apply sinusoidal EVS current (0.5 Hz, 4 mA, 30 s) to each ear separately using gel-covered carbon rubber electrodes. The stimulating and return electrodes were placed over the mastoid process and C7, respectively. Ocular torsion responses were tracked using Interacoustic’s VisualEyes system (Hamel et al., 2025). Participants fixated on a green LED against a background of darkness. Bi-thermal caloric irrigation was delivered using an AquaStim water irrigator according to BSA guidelines and vHIT was measured using the EyeSeeCam system. Ocular torsion responses to EVS were quantified as the peak FFT magnitude at 0.5 Hz. Percentage asymmetry between affected and healthy ears was then calculated. Caloric asymmetry was calculated using the Jongkees formula. For vHIT, percentage asymmetry for Lateral, RALP and LARP canal pairings was first calculated before averaging across canal pairs. ANOVA and Tukey post-hoc comparisons were performed using Jamovi to compare differences between patient groups for each test.Results: ANOVA revealed a significant effect of patient cohort for all three tests (F ≥ 18.4, p ≤ 0.001). Healthy controls exhibited no significant asymmetry for EVS (-2.1 ± 15 %; mean ± SD). However, MD patients exhibited a larger EVS response in their affected versus contralateral ear, resulting in a 10.6 ± 16 % asymmetry. In contrast, VS patients exhibited a -16.7 ± 28 % asymmetry. Unlike EVS, both Caloric and vHIT responses displayed a negative asymmetry for both patient groups. Furthermore, unlike EVS, post-hoc comparisons did not statistically differentiate all three groups.Conclusions: Ocular torsion responses to EVS are elevated in the affected ear of unilateral MD patients and suppressed in the affected ear of VS patients. In contrast, both groups showed reduced responses in the affected ears when tested with either Caloric or vHIT. EVS was the only test to statistically distinguish all three groups based upon asymmetry. These results suggest that EVS is a promising test of vestibular asymmetry, with a potential contribution to differential diagnosis of Meniere’s disease.Acknowledgements: This work was supported by a grant from the UK Medical Research Council to Reynolds and Irving (MR/X013944/1).