Unilateral (UV) and bilateral vestibulopathy (BV) are chronic disorders caused by partial or complete loss of vestibular function in one or both ears, respectively. These disorders disrupt reflexes such as the vestibulo-ocular (VOR), vestibulo-spinal (VSR), and vestibulo-colic (VCR) reflexes, leading to symptoms of oscillopsia and postural instability. Vestibulopathy transforms automatically executed tasks into conscious, tiring efforts, hence dramatically affecting daily functioning and the quality of life. Given the lack of effective treatments, the vestibulo-cochlear implant (VCI) was developed as a rehabilitative tool to restore balance and hearing. Currently, there is a growing need for objective outcome measures that can capture functional vestibular deficits and link them to patient symptoms. The quantification of such deficits is important for evaluating the efficacy of new rehabilitative methods, such as the VCI.
This study aimed to investigate whether eye movement metrics could serve as valid biomarkers of functional impairment in patients with vestibulopathy. 53 participants in three groups (BV, UV, and healthy controls: HC) performed 13 standardized, real-life tasks while equipped with the wearable eye-tracker. Eye movement and head movement data (gyroscope data) was obtained from the eye-tracker, which were primarily filtered and analyzed on the Tobii Pro Lab software and MATLAB, respectively. The extracted metrics were grouped into four categories: eye movement metrics, temporal metrics, Area of Interest (AOI) metrics and gyroscope metrics. Group comparisons were conducted using appropriate statistical tests, and metric correlations with Dizziness Handicap Inventory (DHI) scores of the BV and UV participants were examined. Lastly, to objectively assess the utility of these proposed biomarkers, we utilized the COSMIN framework to test their validity (discriminant and convergent).
We found no clear evidence of differences in eye movement characteristics between the patient groups and healthy controls. Similarly, no consistent patterns emerged from the AOI and gyroscope metrics. Task completion time was the only metric that consistently differed between groups, with BV patients taking significantly longer than both HC and UV participants to complete the tasks. Notably, it was also the only metric to meet the COSMIN criteria for both discriminant and convergent validity. These findings suggest that functional performance, rather than eye movement behavior, may serve as a more reliable indicator of vestibular impairment. This study contributes to the investigation into objective outcome measures that reflect real-life functional deficits in vestibular disorders. Nonetheless, several limitations, such as small sample size, task complexity, and the limited sensitivity of head-mounted eye-tracking equipment, may have influenced the results and should be addressed in future research.
