Concussed patients with visually induced dizziness exhibit increased ocular torsion and vertical vergence during optokinetic gaze-stabilization

Abstract

Visually Induced Dizziness (VID) is a common post-concussion sequalae that remains poorly understood and difficult to quantify. The present study aims to identify biomarkers for VID in the form of gaze-stabilizing eye movements. Nine patients with post-commotio VID and nine age-matched healthy controls were recruited by physiotherapists at a local neurorehabilitation centre. Torsional and vergence eye movements were recorded while participants viewed a series of optokinetic rotations where the central- and peripheral regions moved coherently, incoherently, or semi-randomly. Results showed that vergence and torsional velocities were increased in VID patients, reflecting increased oculomotor gain to visual motion, and that responses correlated with symptom severity. Coherent stimulation produced fastest torsional slow-phases across all participants; when faced with confliction directional information, eye movements tended to follow the direction of the central visual field, albeit at slower velocities than during coherent motion, meaning that while torsion was sensitive to visual content of the entire visual field it expressed directional preference to the central stimulation. In conclusion, post-commotio VID was associated with faster slow-phases during optokinetic gaze-stabilization, with both vergence and torsion being correlated to symptom intensity. As torsional tracking remains inaccessible using commercial eye-trackers, vertical vergence may prove particularly accessible for clinical utility.

Temporal dynamics of ocular torsion and vertical vergence during visual, vestibular, and visuovestibular rotations

“…VV is also increased during monocular viewing compared to binocular conditions, meaning that it likely serves a fusional purpose as it is supressed during binocular viewing (Wibble and Pansell 2020 ). We have also described how visually induced VV is affected in concussed patients suffering from vestibular symptoms of vertigo or dizziness to visual motion (Wibble et al 2023 ; Frattini et al 2024 ). The relationship between torsion and vergence during vestibular movements appears to remain relatively constant by comparison (Wibble and Pansell 2019 ; Wibble et al 2020a ).…”

“…This response can also be altered depending on the visual content; increased visual clutter will increase the relative gain of torsion over vergence (Wibble and Pansell 2019 ), while heightened accelerations will lead to an inverse shift (Wibble et al 2020a ). These eye movement responses are also affected by cognitive states such as alertness or attention (Frattini and Wibble 2021 ; Magnusson et al 1985 ), and they have been shown to act as promising biomarkers for visual processing disorders following concussion (Wibble et al 2023 ; Bertolini et al 2020 ).…”

A Proposed Mechanism for Visual Vertigo: Post-Concussion Patients Have Higher Gain From Visual Input Into Subcortical Gaze Stabilization

“… 16 Concussion has been shown to alter the visual information pathways across the brain, ranging from the basal ganglia to several cortical areas. 17 , 18 It is also known that concussion can lead to maladaptive gaze control, influencing both voluntary gaze shifts 19 and optokinetic gaze stabilization, 9 , 20 indicating a mechanism of injury that can influence both fundamental subcortical motion integration as well as higher level sensory processing. It has been proposed that this increased responsiveness to visual cues leads to sensory reweighing, where visual motion gains in relevance compared to the mismatched vestibular input.…”