Aging Delays Completion of Head Rotation Cycles in Continuous Gaze Stabilization Exercises despite Putative Healthy Vestibular Function.

INTRODUCTION: Aging is associated with loss of balance, with falls being one of the leading causes of death among the elderly in the USA. Gaze stabilization exercises (GSE) improve balance control in vestibular populations and could be useful to prevent falls in healthy individuals. However, the extent to which aging affects head kinematics in GSE is unknown. METHODS: Forty-eight younger (n = 25, 24 ± 6 years, 60% female) and older (n = 23, 66 ± 5 years, 56% female) adults completed six 30-s GSE. Participants were asked to maintain gaze fixation on a stationary target while continuously performing head movements in pitch (e.g., vertical) and yaw (e.g., horizontal) directions. The visual target was placed on the wall 1 m or 2 m away or handheld at arm's length. Head kinematics were recorded with an inertial measurement unit placed on the back of the participants' head. RESULTS: Older adults took significantly more time (e.g., delay) to complete cycles of head rotation in both pitch and yaw compared to younger participants across all GSE. Such delay was further increased during yaw head rotation while fixating gaze of the 1 m target. The average peak velocity (APV) and average angular displacement (AAD), however, were equivalent between groups in all GSE. CONCLUSION: Aging leads to the maintenance of head rotation APV and AAD at the expense of delayed cycles of head rotation, suggesting an age-dependent prioritization strategy (e.g., adapt duration first, range second) during continuous head movements. The distance of the visual target and head movement direction influenced elderly performance and should be considered when prescribing GSE to older populations.

Visual scale to document acute dizziness in the hospital.

BACKGROUND: Managing acute vertigo/dizziness for inpatients requires valid communication between the various healthcare professionals that triage such life-threatening presentations, yet there are no current scaling methods for managing such acute vertigo symptoms for inpatients. OBJECTIVE: To describe the development and validation of the Krems Acute Vertigo/Dizziness Scale (KAVEDIS), a new instrument for tracking subjective symptoms (vertigo, dizziness) and gait impairment across four unique vestibular diagnoses (Menière's disease, benign paroxysmal positional vertigo, peripheral vestibular hypofunction, and vestibular migraine) over a one-year period after inpatient hospital admission. METHODS: Retrospective data collection study from KAVEDIS scale and chart documentation. RESULTS: The KAVEDIS scale can significantly distinguish scores from admission to discharge in three of four vestibular diagnoses. The documented course of subjective vestibular symptoms and gait disturbances were correlated in all four groups. CONCLUSION: We suggest that KAVEDIS documentation among inpatients admitted with acute vertigo/dizziness may improve communication between the various intervening clinicians and help to raise concern in cases of symptomprogression.

Molecular and physiological changes in the SpaceX Inspiration4 civilian crew.

Human spaceflight has historically been managed by government agencies, such as in the NASA Twins Study1, but new commercial spaceflight opportunities have opened spaceflight to a broader population. In 2021, the SpaceX Inspiration4 mission launched the first all-civilian crew to low Earth orbit, which included the youngest American astronaut (aged 29), new in-flight experimental technologies (handheld ultrasound imaging, smartwatch wearables and immune profiling), ocular alignment measurements and new protocols for in-depth, multi-omic molecular and cellular profiling. Here we report the primary findings from the 3-day spaceflight mission, which induced a broad range of physiological and stress responses, neurovestibular changes indexed by ocular misalignment, and altered neurocognitive functioning, some of which match those of long-term spaceflight2, but almost all of which did not differ from baseline (pre-flight) after return to Earth. Overall, these preliminary civilian spaceflight data suggest that short-duration missions do not pose a significant health risk, and moreover present a rich opportunity to measure the earliest phases of adaptation to spaceflight in the human body at anatomical, cellular, physiological and cognitive levels. Finally, these methods and results lay the foundation for an open, rapidly expanding biomedical database for astronauts3, which can inform countermeasure development for both private and government-sponsored space missions.

Evidence for the differential efficacy of yaw and pitch gaze stabilization mechanisms in people with multiple sclerosis.

People with multiple sclerosis (PwMS) who report dizziness often have gaze instability due to vestibulo-ocular reflex (VOR) deficiencies and compensatory saccade (CS) abnormalities. Herein, we aimed to describe and compare the gaze stabilization mechanisms for yaw and pitch head movements in PwMS. Thirty-seven PwMS (27 female, mean ± SD age = 53.4 ± 12.4 years old, median [IQR] Expanded Disability Status Scale Score = 3.5, [1.0]. We analyzed video head impulse test results for VOR gain, CS frequency, CS latency, gaze position error (GPE) at impulse end, and GPE at 400 ms after impulse start. Discrepancies were found for median [IQR] VOR gain in yaw (0.92 [0.14]) versus pitch-up (0.71 [0.44], p < 0.001) and pitch-down (0.81 [0.44], p = 0.014]), CS latency in yaw (258.13 [76.8]) ms versus pitch-up (208.78 [65.97]) ms, p = 0.001] and pitch-down (132.17 [97.56] ms, p = 0.006), GPE at impulse end in yaw (1.15 [1.85] degs versus pitch-up (2.71 [3.9] degs, p < 0.001), and GPE at 400 ms in yaw (-0.25 [0.98] degs) versus pitch-up (1.53 [1.07] degs, p < 0.001) and pitch-down (1.12 [1.82] degs, p = 0.001). Compared with yaw (0.91 [0.75]), CS frequency was similar for pitch-up (1.03 [0.93], p = 0.999) but lower for pitch-down (0.65 [0.64], p = 0.023). GPE at 400 ms was similar for yaw and pitch-down (1.88 [2.76] degs, p = 0.400). We postulate that MS may have preferentially damaged the vertical VOR and saccade pathways in this cohort.

Remote assessment and management of patients with dizziness: development, validation, and feasibility of a gamified vestibular rehabilitation therapy platform.

Introduction: Dizziness is a growing public health concern with as many as 95 million adults in Europe and the United States experiencing vestibular hypofunction, which is associated with reduced quality of life, poorer health, and falls. Vestibular rehabilitation therapy (VRT) is effective in reducing symptoms and improving balance; however, limited access to qualified clinicians and poor patient adherence impedes optimal delivery. The goal of this study was to develop and evaluate the feasibility of a remote therapeutic monitoring VRT Platform application (APP) for the assessment and treatment of vestibular dysfunction. Methods: User-centered iterative design process was used to gather and integrate the needs of users (clinicians and patients) into the design at each stage of development. Commonly used vestibular patient-reported outcome measures (PROs) were integrated into the APP and adults with chronic dizziness were enrolled to evaluate validity and reliability of the APP compared to standard clinical measures (CLIN). Gaze stabilization exercises were gamified to provide an engaging experience and an off-the-shelf sensor captured eye and head movement to provide feedback on accuracy of performance. A prospective, pilot study design with pre-and post-treatment assessment assessed feasibility of the APP compared to standard VRT (CLIN). Results: Participants with dizziness wanted a summary rehabilitation report shared with their clinicians, felt that an app could help with accountability, and believed that a gaming format might help with exercise adherence. Clinicians felt that the app should include features to record and track eye and head movement, monitor symptoms, score accuracy of task performance, and measure adherence. Validity and reliability of the digital PROs (APP) were compared to scores from CLIN across two sessions and found to have good validity, good to excellent test-retest reliability, and excellent usability (≥88%ile). The pilot study demonstrated feasibility for use of the APP compared to CLIN for treatment of vestibular hypofunction. The mean standard system usability score of the APP was 82.5 indicating excellent usability. Discussion: Both adult patients with chronic dizziness and VRT clinicians were receptive to the use of technology for VRT. The HiM-V APP is a feasible alternative to clinical management of adults with chronic peripheral vestibular hypofunction.

Development of a ground-based sensorimotor disorientation analog to replicate astronaut postflight experience.

The perceptual and motor coordination problems experienced following return from spaceflight reflect the sensory adaptation to altered gravity. The purpose of this study was to develop a ground-based analog that replicates similar sensorimotor impairment using a standard measures test battery and subjective feedback from experienced crewmembers. This Sensorimotor Disorientation Analog (SDA) included varying levels of sensorimotor disorientation through combined vestibular, visual, and proprioceptive disruptions. The SDA was evaluated on five previously flown astronauts to compare with their postflight experience and functional motor performance immediately (Return (R)+0 days) and +24 h (R+1) after landing. The SDA consisted of galvanic vestibular stimulation (GVS), visual disruption goggles, and a weighted suit to alter proprioceptive feedback and replicate perceived heaviness postflight. Astronauts reported that GVS alone replicated ∼50-90% of their postflight performance with the weighted suit fine-tuning the experience to replicate an additional 10%-40% of their experience. Astronauts did not report feeling that the disruption goggles represented either the visual disruptions or illusory sensations that they experienced, nor did they impact motor performance in postflight tasks similarly. Based on these results, we recommend an SDA including the GVS and the weighted suit. These results provide a more realistic and portable SDA framework to provide transient spaceflight-relevant sensorimotor disruptions for use in countermeasure testing and as a pre-flight training tool.

Epidemiology and Comorbidities of Vestibular Disorders: Preliminary Findings of the AVOCADO Study.

INTRODUCTION: Studies on incidence and prevalence of vestibular disorders tend to focus on small pockets of patients recruited from specialized clinics and often exclude measures of vestibular function. The objectives of the study were to characterize patients with common vestibular disorders, estimate the prevalence of common vestibular disorders, and ascertain whether patients with vestibular disorders experience increased risks of falls and morbidity. MATERIALS AND METHODS: This retrospective cohort study includes both inpatient and outpatient routine clinical care data culled from a nationally representative, population-based sample. Patients were included if their record in the TriNetX Diamond Cohort comprised at least one vestibular function test or vestibular diagnosis. The main outcome measures were diagnosis with a vestibular disorder, a fall, or a common medical comorbidity (e.g., diabetes, cerebrovascular disease). RESULTS: The cohort includes n = 4,575,724 patients, of which 55% (n = 2,497,136) had a minimum of one vestibular diagnosis. Patients with vestibular diagnoses were 61.3 ± 16.6 years old (mean ± standard deviation), 67% women, 28% White race (69% unknown race), and 30% of non-Hispanic or Latino ethnicity (66% unknown ethnicity). The prevalence of vestibular disorders was estimated at 2.98% (95% confidence interval [CI]: 2.98-2.98%). Patients with vestibular diagnoses experienced a significantly greater odds of falls (odds ratio [OR] = 1.04; 95% CI: 1.02-1.05), cerebrovascular disease (OR = 1.42; 95% CI: 1.40-1.43), ischemic heart disease (OR = 1.17; 95% CI: 1.16-1.19), and diabetes (OR = 1.14; 95% CI: 1.13-1.15), among others. DISCUSSION: Vestibular disorders affect an estimated 3% of the U.S. population, after weighting. Patients with these disorders are at greater risk for many common, consequential medical conditions.

Visual vertigo and motion sickness is different between persistent postural-perceptual dizziness and vestibular migraine.

INTRODUCTION: Persistent postural-perceptual dizziness (PPPD) and vestibular migraine (VM) share symptoms of visual vertigo and motion sickness that can be confusing for clinicians to distinguish. We compare the severity of these symptoms and dynamic subjective visual vertical (dSVV) in these two common vestibular conditions. METHOD: Twenty-nine patients with PPPD, 37 with VM, and 29 controls were surveyed for subjective symptoms using the visual vertigo analogue scale (VVAS) and motion sickness susceptibility questionnaire during childhood (MSA) and the past 10 years (MSB). dSVV is a measure of visual dependence measures perception of verticality against a rotating background (5 deg./s). RESULTS: VVAS revealed contextual differences for dizziness between those with PPPD and VM. Ratings of visual vertigo were most severe in PPPD, less in VM, and mild in controls (VVAS PPPD 27.1, VM 11.2, control 4.6, p < 0.001). MSA was more severe in VM than in PPPD or control (12.8 vs 7.6 vs 8.5, p = 0.01). MSB was more severe in VM than controls (MSB score 12.9 VS 8.1 p = 0.009) but was not different than PPPD (MSB score 10.0, p = 0.10). dSVV alignment was similar among the three groups (p = 0.83). Both VM and PPPD groups had greater simulator sickness than controls after completing the dSVV. CONCLUSIONS: Patients with PPPD report more visual vertigo than those with VM, but a history of motion sickness as a child is more common in VM. Additionally, the environmental context that induces visual vertigo is different between PPPD and VM.

Case Report: Keep your eyes open! Nystagmus guides atypical BPPV.

The clinical diagnosis of benign paroxysmal positional vertigo (BPPV) is confirmed from observing the direction, intensity, and duration of nystagmus from unique head positions that advantage gravity to overcome the inertia of otoconia displaced inside the semicircular canals. This case series highlights BPPV with atypical nystagmus presentations relative to the head position. Clinicians should carefully observe symptoms and nystagmus presentations regardless of the testing position and utilize technology and rules of vestibular physiology to enhance their diagnostic acumen.

Effect of vestibular loss on head-on-trunk stability in individuals with vestibular schwannoma.

The vestibulo-collic reflex generates neck motor commands to produce head-on-trunk movements that are essential for stabilizing the head relative to space. Here we examined the effects of vestibular loss on head-on-trunk kinematics during voluntary behavior. Head and trunk movements were measured in individuals with vestibular schwannoma before and then 6 weeks after unilateral vestibular deafferentation via surgical resection of the tumor. Movements were recorded in 6 dimensions (i.e., 3 axes of rotation and 3 axes of translation) using small light-weight inertial measurement units while participants performed balance and gait tasks. Kinematic measures differed between individuals with vestibular schwannoma (at both time points) and healthy controls for the more challenging exercises, namely those performed in tandem position or on an unstable surface without visual input. Quantitative assessment of the vestibulo-ocular reflex (VOR) revealed a reduction in VOR gain for individuals with vestibular schwannoma compared to control subjects, that was further reduced following surgery. These findings indicated that the impairment caused by either the tumor or subsequent surgical tumor resection altered head-on-trunk kinematics in a manner that is not normalized by central compensation. In contrast, we further found that head-on-trunk kinematics in individuals with vestibular schwannoma were actually comparable before and after surgery. Thus, taken together, our results indicate that vestibular loss impacts head-on-trunk kinematics during voluntary balance and gait behaviors, and suggest that the neural mechanisms mediating adaptation alter the motion strategies even before surgery in a manner that may be maladaptive for long-term compensation.

Risk of Cervical Dizziness in Patients With Cervical Spondylosis.

Importance: The dizziness associated with cervical spondylosis is a controversial topic given that many experts believe that cervical spondylosis is a common cause of dizziness, whereas others do not believe it exists. Objective: To compare the risk of dizziness between patients with cervical spondylosis and matched controls (ie, patients with lumbar spondylosis after propensity score matching [PSM]). Design, Setting, and Participants: This cohort study used medical claims data from the National Health Insurance Research Database of Taiwan for patients 60 years or older with cervical or lumbar spondylosis newly diagnosed in any outpatient department between January 1, 2010, and December 31, 2015. Patients diagnosed with cervical spondylosis were included as the study cohort, and those diagnosed with lumbar spondylosis who were matched to the study cohort via PSM were selected as the control cohort. Both cohorts were followed up for 1 year unless they were diagnosed with dizziness, censored by death, or withdrew from the health insurance program. Data analysis was performed from August 9 to September 20, 2022. Main Outcomes and Measures: The main outcome was the date of outpatient diagnosis of dizziness. The risks of dizziness were compared between groups. The relative risk and incidence rate difference were calculated. Results: A total of 3638 patients with cervical spondylosis (mean [SD] age, 67.9 [7.1] years; 2024 [55.6%] male) and 3638 patients with lumbar spondylosis (mean [SD] age, 68.0 [7.1] years; 2024 [55.6%] male) after PSM were selected as the study and control cohorts, respectively. The patients with cervical spondylosis had higher risk of dizziness than matched controls, with a 1-year relative risk of 1.20 (95% CI, 1.03-1.39). The 1-year incidence of dizziness was 10.2% (95% CI, 9.2%-11.2%) in patients with cervical spondylosis and 8.6% (95% CI, 7.7%-9.5%) in the matched group of lumbar spondylosis. The incidence rate difference between the groups was 1.6% (95% CI, 0.3%-3.0%). Conclusions and Relevance: These data support the association between dizziness and cervical spondylosis, but the small difference between groups reveals that dizziness associated with cervical spondylosis is uncommon. Clinicians should be wary of diagnosing a cervical cause for dizziness based on an actual history of cervical spondylosis.

Head movement kinematics are differentially altered for extended versus short duration gait exercises in individuals with vestibular loss.

Head kinematics are altered in individuals with vestibular schwannoma (VS) during short duration gait tasks [i.e., Functional Gait Assessment (FGA)], both before and after surgery, yet whether these differences extend to longer duration gait exercises is currently unknown. Here we examined the effects of vestibular loss and subsequent compensation on head kinematics in individuals with VS during gait exercises of relatively extended versus short duration (< 10 versus 30 s), compared to age-matched controls. Six-dimensional head movements were recorded during extended and short duration gait exercises before and then 6 weeks after sectioning of the involved vestibular nerve (vestibular neurectomy). Standard functional, physiological, and subjective clinical assessments were also performed at each time point. Kinematics were differentially altered in individuals with vestibular loss at both time points during extended versus short duration exercises. Range of motion was significantly reduced in extended tasks. In contrast, movement variability predominately differed for the short duration exercises. Overall, our results indicate that quantifying head kinematics during longer duration gait tasks can provide novel information about how VS individuals compensate for vestibular loss, and suggest that measurements of range of motion versus variability can provide information regarding the different strategies deployed to maintain functional locomotion.

Resolution of atypical posterior semicircular canal BPPV: evidence for putative short-arm location.

This case demonstrates the successful identification and treatment of atypical posterior semicircular canal benign paroxysmal positional vertigo (BPPV) based on a unique presentation of positional nystagmus, the resultant nystagmus from repositioning manoeuvers, and restored function of the affected semicircular canal. This case illustrates the importance of completing a comprehensive clinical examination and the value for incorporating the video head impulse test as well as adjusting treatment based on testing and patient response when managing variant cases of BPPV.

Video Ocular Counter-Roll (vOCR): Otolith-Ocular Function and Compensatory Effect of the Neck Following Vestibular Loss.

OBJECTIVE: Assessment of recovery following vestibular loss has been limited by the lack of bedside measures in clinical settings. Here, we used the video ocular counter-roll (vOCR) test to study otolith-ocular function and compensatory effect of neck proprioception in patients at different stages of vestibular loss. STUDY DESIGN: Case-control study. SETTING: Tertiary care center. METHODS: Fifty-six subjects were recruited including patients with acute (9 ± 2 days [mean ± standard error of mean]), subacute (61 ± 11 days), and chronic (1009 ± 266 days) unilateral loss of vestibular function, as well as a group of healthy controls. We used a video-oculography method based on tracking the iris for vOCR measurement. To examine the effect of neck inputs, vOCR was recorded during two simple tilt maneuvers in all subjects while seated: 30° head-on-body tilt and 30° head-and-body tilt. RESULTS: The vOCR responses evolved at different stages following vestibular loss with improvement of the gains in the chronic stage. The deficit was more pronounced when the whole body was tilted (acute: 0.08 ± 0.01, subacute: 0.11 ± 0.01, chronic: 0.13 ± 0.02, healthy control: 0.18 ± 0.01), and the gain of vOCR improved when the head was tilted on the body (acute: 0.11 ± 0.01, subacute: 0.14 ± 0.01, chronic: 0.13 ± 0.02, healthy control: 0.17 ± 0.01). The time course of vOCR response was affected as well with reduced amplitude and slower response in the acute stage of vestibular loss. CONCLUSION: The vOCR test can be valuable as a clinical marker to measure vestibular recovery and compensatory effect of neck proprioception in patients at different stages following loss of vestibular function.

The minimal clinically important difference for gait speed in significant unilateral vestibular hypofunction after vestibular rehabilitation.

Gait speed is a valid measure of both physical function and vestibular health. Vestibular rehabilitation is useful to improve gait speed for patients with vestibular hypofunction, yet there is little data to indicate how changes in gait speed reflect changes in patient-reported health outcomes. We determined the minimal clinically important difference in the gait speed of patients with unilateral vestibular hypofunction, mostly due to deafferentation surgery, as anchored to the Dizziness Handicap Index and the Activities Balance Confidence scale, validated using regression analysis, change difference, receiver-operator characteristic curve, and average change methods. After six weeks of vestibular rehabilitation, a change in gait speed from 0.20 to 0.34 m/s with 95% confidence was required for the patients to perceive a significant reduction in perception of dizziness and improved balance confidence.

Comparison of Asymmetry between Perceptual, Ocular, and Postural Vestibular Screening Tests.

BACKGROUND: A better understanding of how vestibular asymmetry manifests across tests is important due to its potential implications for balance dysfunction, motion sickness susceptibility, and adaptation to new environments. OBJECTIVE: We report the results of multiple tests for vestibular asymmetry in 32 healthy participants. METHODS: Asymmetry was measured using perceptual reports during unilateral centrifugation, oculomotor responses during visual alignment tasks, vestibulo-ocular reflex gain during head impulse tests, and body rotation during stepping tests. RESULTS: A significant correlation was observed between asymmetries of subjective visual vertical and verbal report during unilateral centrifugation. Another significant correlation was observed between the asymmetries of ocular alignment, vestibulo-ocular reflex gain, and body rotation. CONCLUSIONS: These data suggest that there are underlying vestibular asymmetries in healthy individuals that are consistent across various vestibular challenges. In addition, these findings have value in guiding test selection during experimental design for assessing vestibular asymmetry in healthy adults.

When, where, and why should we look for vestibular dysfunction in people with diabetes mellitus?

The biochemistry of diabetes mellitus results in multi-system tissue compromise that reduces functional mobility and interferes with disease management. Sensory system compromise, such as peripheral neuropathy and retinopathy, are specific examples of tissue compromise detrimental to functional mobility. There is lack of clarity regarding if, when, and where parallel changes in the peripheral vestibular system, an additional essential sensory system for functional mobility, occur as a result of diabetes. Given the systemic nature of diabetes and the plasticity of the vestibular system, there is even less clarity regarding if potential vestibular system changes impact functional mobility in a meaningful fashion. This commentary will provide insight as to when we should employ diagnostic vestibular function tests in people with diabetes, where in the periphery we should look, and why testing may or may not matter. The commentary concludes with recommendations for future research and clinical care.

Head movement kinematics are altered during balance stability exercises in individuals with vestibular schwannoma.

BACKGROUND: Balance stabilization exercises are often prescribed to facilitate compensation in individuals with vestibular schwannoma (VS). However, both the assessment and prescription of these exercises are reliant on clinical observations and expert opinion rather than on quantitative evidence. The aim of this study was to quantify head motion kinematics in individuals with vestibular loss while they performed commonly prescribed balance stability exercises. METHODS: Using inertial measurement units, head movements of individuals with vestibular schwannoma were measured before and after surgical deafferentation and compared with age-matched controls. RESULTS: We found that individuals with vestibular schwannoma experienced more variable head motion compared to healthy controls both pre- and postoperatively, particularly in absence of visual input, but that there was little difference between preoperative and postoperative kinematic measurements for our vestibular schwannoma group. We further found correlations between head motion kinematic measures during balance exercises, performed in the absence of visual input, and multiple clinical measurements for preoperative VS subjects. Subjects with higher head motion variability also had worse DVA scores, moved more slowly during the Timed up and Go and gait speed tests, and had lower scores on the functional gait assessment. In contrast, we did not find strong correlations between clinical measures and postoperative head kinematics for the same VS subjects. CONCLUSIONS: Our data suggest that further development of such metrics based on the quantification of head motion has merit for the assessment and prescription of balance exercises, as demonstrated by the calculation of a "kinematic score" for identifying the most informative balance exercise (i.e., "Standing on foam eyes closed").

Greater Disability Is Associated with Worse Vestibular and Compensatory Oculomotor Functions in People Living with Multiple Sclerosis.

Globally, there are nearly three million people living with multiple sclerosis (PLW-MS). Many PLW-MS experience vertigo and have signs of vestibular dysfunction, e.g., low vestibulo-ocular reflex (VOR) gains or the presence of compensatory saccades (CSs), on video head impulse testing (vHIT). We examined whether the vestibular function and compensatory oculomotor behaviors in PLW-MS differed based on the level of MS-related disability. The VOR gain, CS frequency and latency, and gaze position error (GPE) were calculated from the individual traces obtained during six-canal vHIT for 37 PLW-MS (mean age 53.4 ± 12.4 years-old, 28 females) with vertigo and/or an imbalance. The subjects were grouped by their Expanded Disability Status Scale (EDSS) scores: PLW-min-MS (EDSS = 1.0-2.5, n = 8), PLW-mild-MS (EDSS = 3.0-4.5, n = 23), and PLW-moderate-MS (EDSS = 5.0-6.0, n = 6). The between-group differences were assessed with Kruskal-Wallis tests. The VOR gains for most of the canals were higher for PLW-min-MS compared to PLW-mild- and mod-MS, respectively. CS occurred less often in PLW-min-MS versus PLW-mild- and mod-MS, respectively. No clear trend in CS latency was found. The GPE was often lower for PLW-min-MS compared to PLW-mild- and mod-MS, respectively. Thus, our data demonstrate that worse VOR and compensatory oculomotor functions are associated with a greater MS-related disability. PLW-MS may benefit from personalized vestibular physical therapy.

Unique compensatory oculomotor behavior in people living with multiple sclerosis.

INTRODUCTION: Globally, there are 3 million people living with multiple sclerosis (PLW-MS). A large proportion of PLW-MS have abnormal vestibular function tests that suggest central vestibular lesions. Yet, data regarding vestibular-ocular control in PLW-MS is limited. Thus, we aimed to further characterize compensatory saccade (CS) behavior in PLW-MS. METHODS: We analyzed video head impulse data from four groups of six age- and sex-matched adults: people living with mild MS (PLW-mild-MS, people living with moderate MS (PLW-moderate-MS), people living with unilateral vestibular deafferentation (PLW-UVD), and healthy controls (HC). RESULTS: PLW-moderate-MS had lower lateral canal vestibulo-ocular reflex (VOR) gain bilaterally compared to PLW-mild MS (p < 0.001), HC (p < 0.001), and PLW-UVD (p < 0.001). CS frequency was higher for impulses towards the less affected side in PLW-moderate-MS versus the more (p = 0.01) and less (p < 0.001) affected sides in PLW-mild-MS. CS latency was shorter (p < 0.001) and CS peak velocity was lower (p < 0.001) with impulses towards the more affected side versus the less affected side in PLW-moderate-MS. However, CS peak velocity with impulses towards each side was similar in PLW-mild-MS (p = 0.12). Gaze position error (GPE) was larger after impulses towards the more affected side versus the less affected side in PLW-moderate-MS (p < 0.001) and PLW-mild-MS (p < 0.001). MS-related disability was moderately associated with VOR gain (p < 0.001) and GPE (p < 0.001). Additionally, we identified micro-saccades and position correcting saccades that were uniquely employed by PLW-MS as compensatory gaze stabilizing strategies. CONCLUSIONS: In PLW-MS, the characteristics of compensatory oculomotor behavior depend on the extent of residual VOR gain.