Ocular torsional responses to electrical vestibular stimulation in children: A tolerability and feasibility study

Introduction: Electrical Vestibular Stimulation (EVS) evokes eye movements which can be used to assess peripheral vestibular function (Mackenzie et al., 2019). The ocular response is mainly torsional (Mackenzie et al., 2018). Previously, this could only be recorded using invasive techniques such as scleral coils, or directly marking the sclera (Houben et al., 2006). This limited the practical use of EVS due to tolerability concerns. In recent years higher resolution cameras and software solutions have been developed for non-invasive ocular torsion tracking using iris striations (Mackenzie et al., 2019). Our research has successfully used this technique to assess vestibular dysfunction. We have also demonstrated good patient tolerability in adults compared to conventional vestibular diagnostics using currents up to 4 mA (Hamel et al., 2025; Mackenzie et al., 2018, 2019). However, EVS has not previously been used to assess pediatric vestibular function. Both the anatomy and physiology of children differ compared to adults. The primary aim of the current study was to assess the tolerability of EVS in healthy children. A secondary aim was to determine the quality of the ocular tracking data to establish whether meaningful assessment of peripheral vestibular function in children is feasible.Methods: 28 children aged between 8-16 years received EVS while accompanied by a parent (15 boys; 13 girls, mean age 11 ± 2.5 years). Informed written consent was obtained from both parent and child, and children were given a £20 Amazon voucher for participation. Both children and parents were clearly informed that the voucher would be given regardless of their EVS tolerance and were not coerced in any way. A stimulating electrode was placed over the mastoid process, with a reference electrode at C7, allowing each ear to be assessed separately. Sinusoidally-varying current at 0.5 Hz was applied for 15 s while children sat in a darkened booth fixating an LED placed 85 cm directly ahead. A starting current of 0.5 mA was applied and, if tolerated, was systematically increased to 1, 2, 3 and 4 mA. Tolerability was assessed after each test, including a non-stimulation recording to provide a baseline assessment. Participants were asked to give feedback on pain/discomfort using a numeric rating scale from 0-10 in the following domains: Difficulty keeping eyes open (E), vestibular/sway sensation (V), sensation of electricity on the skin (S), which we term the ‘E’ ‘V’ & ‘S’ scores. Ocular torsion data was recorded using Interacoustics VisualEyes goggles (Middlefahrt, Denmark). Torsional amplitude was quantified as the peak Fast Fourier Transform (FFT) value at 0.5 Hz when data quality permitted.Results: 71 % of children (i.e., 20 of 28) were able to tolerate the maximum 4mA current. 89 % achieved 2 mA (25 of 28). Discomfort ratings at 4 mA were (eyes: 1.7, vestibular: 3.2, skin: 3.5). As expected, discomfort scores systematically increased with increasing current for eyes, vestibular and skin (F(5,90) ≥ 3.3, p ≤ 0.009). Preliminary analysis of ocular torsion signals suggests ~50 % of children had usable eye tracking data at 4 mA, allowing for FFT-based asymmetry assessment. The issues encountered which prevented usable data included frequent blinking, distraction and losing eye tracking due to a large pupil diameter relative to palpebral fissure height which are larger in children than adults (Diamond, 2001). Changes in goggle design along with increased ambient light may help to improve ocular tracking.Conclusions: EVS is well tolerated in children at current intensities previously used in adult populations and has potential as a quick assessment of peripheral vestibular function. Fine tuning of test parameters in future research with children is required to establish the optimal stimulus and lighting conditions for reliable assessment of vestibular asymmetry.Acknowledgements: This work was supported by grants from the Birmingham Women’s and Children’s Hospital Charity and the UK Medical Research Council (MR/X013944/1).