Modification of compensatory saccades after aVOR gain recovery

Vestibular Decompensation Following COVID-19 Infection in a Person With Compensated Unilateral Vestibular Loss: A Rehabilitation Case Study

BACKGROUND AND PURPOSE

Surgical removal of a vestibular schwannoma (vestibular schwannoma resection; VSR) results in a unilateral vestibular hypofunction with complaints of dizziness and imbalance. Although the anatomic lesion is permanent, recovery of balance and diminution of dizziness occurs through central neurophysiologic compensation. Compensation of the system is maintained through daily activity. Unfortunately, interruption of stimulus, such as decreased activities due to illness, can cause decompensation. Decompensation is described as the return of symptoms consistent with that experienced during the initial insult/injury (eg, dizziness, oscillopsia, balance difficulty). This case study describes a reoccurrence of vestibular dysfunction in a person with a history of VSR following hospitalization and protracted recovery from a COVID-19 infection. It further documents her recovery that may be a result of vestibular rehabilitation.

CASE DESCRIPTION

A 49-year-old woman (M.W.) with a surgical history of VSR (10 years prior) and a medical history of significant COVID-19 infection, resulting in an intensive care unit stay and prolonged use of supplemental oxygen, presented to physical therapy with persistent dizziness and imbalance. The video head impulse test confirmed unilateral vestibular hypofunction.

INTERVENTION

M.W. attended biweekly vestibular rehabilitation for 6 weeks and completed daily home exercises.

OUTCOMES

At discharge, M.W. demonstrated improvements in patient-reported outcomes (Dizziness Handicap Inventory), functional testing (MiniBEST, 2-Minute Walk Test), and gaze stability measures (video head impulse testing, dynamic visual acuity).

DISCUSSION

Vestibular decompensation preluded by a COVID-19 infection caused a significant decrease in functional mobility. Vestibular rehabilitation targeted at gaze and postural stability effectively reduced symptoms and facilitated recovery to M.W.'s pre-COVID-19 level of function. Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1 available at: http://links.lww.com/JNPT/A458 ).

[Rehabilitation in bilateral vestibulopathy: trends and perspectives]

A review of the literature on rehabilitation methods for bilateral vestibulopathy is presented using RSCI, Scopus and PubMed databases. The principles and effectiveness of physical vestibular rehabilitation, vestibular implants, galvanic vestibular stimulation, and biofeedback-based sensory substitution and augmentation systems are described. The advantages and disadvantages of each method and perspectives for their improvement are presented.

The relationship between functional head impulse test and age in healthy individuals

BACKGROUND

fHIT is an easily applicable test battery that indirectly evaluates the vestibulo-ocular reflex (VOR) from a functional perspective.

AIMS/OBJECTIVES

The aim of this study was to Individuals determine the correlation between age and the percentage of correct answers (% CA) obtained in the functional head impulse test (fHIT) in healthy individuals.

MATERIAL AND METHODS

A total of 105 volunteers, 50 males and 55 females, between the ages of 18 and 70 years, participated in the study. A Beon Solution fHIT system (Zero Branco (TV), Italy) was used in the study.

RESULTS

In our study, a decrease in the mean % CA was observed in all semicircular canals (SCCs) with increasing age. Between age and mean % CA, a significant negative moderate (-0.311) correlation was observed in lateral SCCs, and a significant negative low (-0.257) correlation was observed in posterior SCCs (p <  0.05). In anterior SCCs, there was no statistically significant relationship between age and mean % CA (p >  0.05).

CONCLUSIONS

The present study performed in a healthy population will be helpful in terms of making comparisons in studies to be conducted in various vestibular diseases. It will also be a guide for identifying pathological consequences in vestibular diseases.

Detection of VOR dysfunction during the gaze stabilization test: Does target size matter?

BACKGROUND

The Gaze Stabilization Test (GST) identifies vestibulo-ocular reflex (VOR) dysfunction using a decline in target recognition with increasing head velocity, but there is no consensus on target (optotype) size above static visual acuity.

OBJECTIVE

To determine the optimal initial optotype size above static visual acuity to be used during the GST in subjects with unilateral vestibular dysfunction and healthy individuals.

METHODS

Eight subjects with unilateral vestibular dysfunction (UVD) and 19 age-matched, healthy control subjects were studied with the standard GST protocol using two optotype sizes, 0.2 and 0.3 logMAR above static visual acuity (ΔlogMAR). Maximal head velocity achieved while maintaining fixation on both optotypes was measured. Sensitivity, specificity and receiver-operator characteristic area under the curve (ROC AUC) analyses were performed to determine the optimal head velocity cut off point for each optotype, based on ability to identify the lesioned side of the UVD group from the control group.

RESULTS

There was a significant difference in maximal head velocity between the UVD group and control group using 0.2 ΔlogMAR (p = 0.032) but not 0.3 ΔlogMAR (p = 0.061). While both targets produced similar specificities (90%) for distinguishing normal from subjects with UVD, 0.2 ΔlogMAR targets yielded higher sensitivity (75%) than 0.3 logMAR (63%) and accuracy (86% vs 80%, respectively) in detecting the lesioned side in subjects with UVD versus controls with maximal head velocities≤105 deg/s (p = 0.017). Furthermore, positive likelihood ratios were nearly twice as high when using 0.2 ΔlogMAR targets (+ LR 10) compared to 0.3 ΔlogMAR (+ LR 6.3).

CONCLUSION

The 0.2 ΔlogMAR optotype demonstrated significantly superior identification of subjects with UVD, better sensitivity and positive likelihood ratios than 0.3 ΔlogMAR for detection of VOR dysfunction. Using a target size 0.2logMAR above static visual acuity (ΔlogMAR) during GST may yield better detection of VOR dysfunction to serve as a baseline for gaze stabilization rehabilitation therapy.

Association of the Video Head Impulse Test With Improvement of Dynamic Balance and Fall Risk in Patients With Dizziness

Importance

It is important to know whether recovery of the vestibuloocular reflex (VOR) as measured by the video head impulse test (vHIT) is associated with the recovery of dynamic balance. It is also critical to know how much change in VOR gain is clinically relevant for establishing the recovery of dynamic balance.

Objectives

To investigate the association between improved VOR gain as measured by the vHIT and improved dynamic balance (reduced fall risk) as measured by the dynamic gait index (DGI) and to calculate the minimal clinically important difference of VOR gain.

Design, Setting, and Participants

This retrospective case series study was performed at a tertiary referral center at the Johns Hopkins University School of Medicine. Thirty-eight consecutive patients with subacute or chronic dizziness from January 1, 2014, through May 31, 2017, who visited the vestibular physical therapy clinic were included in the study.

Interventions

Each patient was evaluated with room light and video-infrared oculomotor examination, vHIT, and balance testing before and after vestibular physical therapy.

Main Outcomes and Measures

Gain of the lesioned VOR and score on the DGI.

Results

Among the 38 patients (25 women [66%]; mean [SD] age, 65 [14] years), the mean (SD) initial lesioned VOR gain was 0.66 (0.23) and initial DGI score was 16 (3). No correlation was found between initial VOR gain and initial DGI score (r = -0.04; 95% CI, -0.35 to 0.28). At follow-up, 15 patients (39%) had an improved VOR gain and 30 (79%) had an improved DGI score, which was correlated (r = 0.49; 95% CI, 0.20-0.69). In those 15 patients with improved VOR gain, 14 (93%) had improvement of DGI score. In the 23 patients without improvement of VOR gain, 16 (70%) still showed improvement in their DGI score. When using VOR gain to estimate improvement of DGI, the minimal clinically important difference of VOR gain was -0.06.

Conclusions and Relevance

The change of VOR gain in the vHIT was moderately associated with the change of DGI score. Improved VOR gain was associated with a high probability of improved dynamic balance. However, in most of the patients whose VOR gains did not improve, balance improvement occurred putatively through sensory reweighting strategies.

VOR adaptation training and retention in a patient with profound bilateral vestibular hypofunction

A novel training method known as incremental VOR adaptation (IVA) can improve the vestibulo-ocular reflex (VOR) gain for both active and passive head rotation by coupling active head rotations with a laser-projected target that moves in the opposite direction of the head at a fraction of the head velocity. A 51-year-old male with bilateral vestibular hypofunction participated in a research protocol using a portable IVA device for 645 days. Passive VOR gains improved 179% to 600%; standing posture and gait also improved. Motor learning within the vestibular system using the IVA method is possible after severe vestibular pathology. Laryngoscope, 129:2568-2573, 2019.

Optimal Human Passive Vestibulo-Ocular Reflex Adaptation Does Not Rely on Passive Training

The vestibulo-ocular reflex (VOR) is the main vision-stabilising system during rapid head movements in humans. A visual-vestibular mismatch stimulus can be used to train or adapt the VOR response because it induces a retinal image slip error signal that drives VOR motor learning. The training context has been shown to affect VOR adaptation. We sought to determine whether active (self-generated) versus passive (externally imposed) head rotation vestibular training would differentially affect adaptation and short-term retention of the active and passive VOR responses. Ten subjects were tested, each over six separate 1.5-h sessions. We compared active versus passive head impulse (transient, rapid head rotations with peak velocity ~ 150 °/s) VOR adaptation training lasting 15 min with the VOR gain challenged to increment, starting at unity, by 0.1 every 90 s towards one side only (this adapting side was randomised to be either left or right). The VOR response was tested/measured in darkness at 10-min intervals, 20-min intervals, and two single 60-min interval sessions for 1 h post-training. The training was active or passive for the 10- and 20-min interval sessions, but only active for the two single 60-min interval sessions. The mean VOR response increase due to training was ~ 10 % towards the adapting side versus ~2 % towards the non-adapting side. There was no difference in VOR adaptation and retention between active and passive VOR training. The only factor to affect retention was exposure to a de-adaptation stimulus. These data suggest that active VOR adaptation training can be used to optimally adapt the passive VOR and that adaptation is completely retained over 1 h as long as there is no visual feedback signal driving de-adaptation.

Stability of the aVOR to Repeat Head Impulse Testing

OBJECTIVE

The angular vestibulo-ocular reflex (aVOR) is known to be influenced by factors such as arousal and cognition during traditional vestibular function testing. However, the inherent variability of the aVOR to head impulse testing has not been explicitly examined. The purpose of this study was to determine the variability of the aVOR to active and passive head impulses using the gold standard scleral search coil method to record head and eye rotation.

STUDY DESIGN

Descriptive.

SETTING

Tertiary referral center.

PATIENTS

Twenty six healthy control subjects agreed to active and passive horizontal head impulse testing on at least two separate sessions from two unique institutions. An additional 27 individuals with cochlear implantation (CI) underwent passive horizontal and vertical semicircular canal plane head impulse testing. Test sessions were separated from 3 to 210 days in the normal subjects and from 49 to 537 days in the subjects with CI.

MAIN OUTCOME MEASURE(S)

Reliability of the angular VOR gain (eye velocity/head velocity) over time.

RESULTS

In the healthy control subjects, there was no difference in aVOR gain between right and left ears, between session one and session two, or between active (self-generated, 0.99 ± 0.08) or passive (imposed, 1.0 ± 0.08) head impulses. In the patients, we also found the aVOR gain very stable over time. However, the aVOR gains of the patients were different across the semicircular canal planes tested (p < 0.001) with the four vertical semicircular canals having lower aVOR gains than the two horizontal canals.

CONCLUSIONS

Our data suggest the aVOR gain is quite stable when tested across unique days in healthy controls and patients with auditory-only inner ear pathology.

Eye Movements Are Correctly Timed During Walking Despite Bilateral Vestibular Hypofunction

Individuals with bilateral vestibular hypofunction (BVH) often report symptoms of oscillopsia (the perception that the world is bouncing or unstable) during walking. Efference copy/proprioception contributes to locomotion gaze stability in animals, sometimes inhibiting the vestibulo-ocular reflex (VOR). Gaze stability requires both adequate eye velocity and appropriate timing of eye movements. It is unknown whether eye velocity (VOR gain), timing (phase), or both are impaired for individuals with BVH during walking. Identifying the specific mechanism of impaired gaze stability can better inform rehabilitation options. Gaze stability was measured for eight individuals with severe BVH and eight healthy age- and gender-matched controls while performing a gaze fixation task during treadmill walking. Frequency response functions (FRF) were calculated from pitch eye and head velocity. A one-way ANOVA was conducted to determine group differences for each frequency bin of the FRF. Pearson correlation coefficients were calculated to determine the relationship between the real and imaginary parts of the FRF and the Oscillopsia Visual Analog Scale (oVAS) scores. Individuals with BVH demonstrated significantly lower gains than healthy controls above 0.5 Hz, but their phase was ideally compensatory for frequencies below 3 Hz. Higher oVAS scores were correlated with lower gain. Individuals with BVH demonstrated ideal timing for vertical eye movements while walking despite slower than ideal eye velocity when compared to healthy controls. Rehabilitation interventions focusing on enhancing VOR gain during walking should be developed to take advantage of the intact timing reported here. Specifically, training VOR gain while walking may reduce oscillopsia severity and improve quality of life.

Refixation Saccades with Normal Gain Values: A Diagnostic Problem in the Video Head Impulse Test: A Case Report

Refixation saccades with normal gain value occur more frequently with increasing age. The phenomenon has also been observed in different vestibular disorders. In this case, we present a young male with normal gain value and refixation saccades tested with the video head impulse test (vHIT) the day after his cochlear implantation. One month after surgery, refixation saccades were no longer present. This suggests that refixation saccades can occur as a result of temporary pathology such as surgery. Refixation saccades with normal gain values might reflect a partial deficit in the vestibulo-ocular reflex. However, this partial deficit is in conflict with the current way of interpreting vHIT results in which the vestibular function is classified as either normal or pathological based only on the gain value. Refixation saccades, which are evident signs of vestibulopathy, are not considered in the evaluation. A new way of interpreting the vHIT based on the saccades must be considered.

Compensatory Saccades Are Associated With Physical Performance in Older Adults: Data From the Baltimore Longitudinal Study of Aging

OBJECTIVE

To determine whether compensatory saccade metrics observed in the video head impulse test, specifically saccade amplitude and latency, predict physical performance.

STUDY DESIGN

Cross-sectional analysis of the Baltimore Longitudinal Study of Aging, a prospective cohort study.

SETTING

National Institute on Aging Intramural Research Program Clinical Research Unit in Baltimore, Maryland.

PATIENTS

Community-dwelling older adults.

INTERVENTION(S)

Video head impulse testing was performed, and compensatory saccades and horizontal vestibulo-ocular reflex (VOR) gain were measured. Physical performance was assessed using the Short Physical Performance Battery (SPPB), which included the feet side-by-side, semitandem, tandem, and single-leg stance; repeated chair stands; and usual gait speed measurements.

MAIN OUTCOME MEASURE(S)

Compensatory saccade amplitude and latency, VOR gain, and SPPB performance.

RESULTS

In 183 participants who underwent vestibular and SPPB testing (mean age 71.8 yr; 53% females), both higher mean saccade amplitude (odds ratio [OR] =1.62, p = 0.010) and shorter mean saccade latency (OR = 0.88, p = 0.004) were associated with a higher odds of failing the tandem stand task. In contrast, VOR gain was not associated with any physical performance measure.

CONCLUSION

We observed in a cohort of healthy older adults that compensatory saccade amplitude and latency were associated with tandem stance performance. Compensatory saccade metrics may provide insights into capturing the impact of vestibular loss on physical function in older adults.

VOR Gain Is Related to Compensatory Saccades in Healthy Older Adults

Objective: Vestibulo-ocular reflex (VOR) gain is well-suited for identifying rotational vestibular dysfunction, but may miss partial progressive decline in age-related vestibular function. Since compensatory saccades might provide an alternative method for identifying subtle vestibular decline, we describe the relationship between VOR gain and compensatory saccades in healthy older adults.

Methods: Horizontal VOR gain was measured in 243 subjects age 60 and older from the Baltimore Longitudinal Study of Aging using video head impulse testing (HIT). Saccades in each HIT were identified as either “compensatory” or “compensatory back-up,” i.e., same or opposite direction as the VOR response respectively. Saccades were also classified as “covert” (occurring during head movement) and “overt” (occurring after head movement). The relationship between VOR gain and percentage of HITs with saccades, as well as the relationship between VOR gain and saccade latency and amplitude, were evaluated using regression analyses adjusting for age, gender, and race.

Results: In adjusted analyses, the percentage of HITs with compensatory saccades increased 4.5% for every 0.1 decrease in VOR gain (p < 0.0001). Overt compensatory saccade amplitude decreased 0.6° (p < 0.005) and latency increased 90 ms (p < 0.001) for every 0.1 increase in VOR gain. Covert back-up compensatory saccade amplitude increased 0.4° for every 0.1 increase in VOR gain.

Conclusion: We observed significant relationships between VOR gain and compensatory saccades in healthy older adults. Lower VOR gain was associated with larger amplitude, shorter latency compensatory saccades. Compensatory saccades reflect underlying rotational vestibular hypofunction, and may be particularly useful at identifying partial vestibular deficits as occur in aging adults.

Comparison of the gaze stabilization test and the dynamic visual acuity test in unilateral vestibular loss patients and controls

OBJECTIVE

Compare the dynamic visual acuity test (DVAT) and gaze stabilization test (GST) in patients with unilateral vestibular loss (UVL) and healthy control subjects using a novel computerized testing system prototype.

STUDY DESIGN

Cross-sectional study.

SETTING

Tertiary academic referral laboratory.

PATIENTS

Seventeen UVL patients (median age 62 yr) with bithermal caloric asymmetry (≥49%) or ablative surgery and 17 control subjects (median age 57 yr).

INTERVENTION(S)

Diagnostic.

MAIN OUTCOME MEASURE(S)

Comparison of DVAT and GST results during self-generated sinusoidal head movements using transient unpredictable target presentations less than 95 milliseconds in duration.

RESULTS

UVL patients had significantly higher DVAT scores toward the lesioned side compared with controls (p = 0.001) and the non-lesioned side (p = 0.003), but the non-lesioned side was not significantly different from controls (p = 0.157). When comparing GST scores, UVL patients required a slower head velocity to maintain visual acuity with movement toward the lesioned side compared with controls (p < 0.001) and the non-lesioned side (p = 0.004). In addition, UVL patients had significantly lower scores toward the non-lesioned side (p = 0.002) compared to controls. ROC curve analysis identified optimal thresholds for abnormal test results to discriminate the lesioned side from controls. A DVAT score greater than or equal to 0.3 ΔlogMAR provided 65% sensitivity and 88% specificity while a GST score less than or equal to 95 degrees/s provided 71% sensitivity and 100% specificity. When GST results were normal, adding DVAT increased overall sensitivity to 88% with 88% specificity.

CONCLUSIONS

Both GST and DVAT demonstrated reduced gaze stabilization toward the lesioned side in the patient group compared with normal controls. Performing GST first and utilizing DVAT when GST was normal provides optimal identification of patients with vestibular dysfunction.

Pilot study of a new rehabilitation tool: improved unilateral short-term adaptation of the human angular vestibulo-ocular reflex

HYPOTHESIS

Unilateral vestibulo-ocular reflex (VOR) short-term adaptation training causes some increase toward the nonadapting side (~30% of increase on adapting side). We conducted a pilot study to determine if the increase could be reduced by providing a visual stimulus during rotations to the nonadapting side.

BACKGROUND

Unilateral vestibular short-term adaptation is a technique that could increase the ipsilesional VOR response of vestibular patients with unilateral hypofunction. However, this technique results in the VOR response increasing for rotations toward the nonadapting (normal) side, which is undesirable because the VOR will be overcompensatory (causing nonstable vision) during head rotations toward the normal side.

METHODS

We built a portable helmet device that sensed horizontal angular head velocity to generate a visual target that required a preset VOR gain (eye velocity/head velocity) for optimal image stabilization that could be set differently for leftward and rightward head rotations. We tested 10 subjects (six controls and four patients with vestibular hypofunction). We measured the active and passive VOR gain during high-peak-acceleration, unilateral, transient head rotations (head impulses) before and after unilateral VOR adaptation training.

RESULTS

In control subjects, for rotations toward the adapting side (target gain = 1.5), the VOR gain increased because of training by 26.1% ± 23.4% during active head impulses and by 14.6% ± 13.0% during passive head impulses. In contrast, for rotations toward the nonadapting side, there were no statistically significant increases.

CONCLUSION

A visual stimulus driving the VOR gain to unity toward the nonadapting side aids unilateral adaptation more so than no visual stimulus.

Compensatory saccade differences between outward versus inward head impulses in chronic unilateral vestibular hypofunction

The horizontal head impulse test (HIT) is a valuable clinical tool that can help identify peripheral vestibular hypofunction by the refixation (compensatory) saccade that returns the eyes to the target of interest after the head has stopped. We asked if there were differences in the compensatory saccade responses during the HIT when the head was rotated away or toward straight ahead (outward versus inward). We also investigated the influence of a fixation target. Using scleral search-coils, we tested five patients with chronic unilateral vestibular hypofunction (UVH) and three healthy control subjects. In UVH patients, the latencies of both overt and covert saccades were longer when the head was rotated inward from an initially eccentric position, regardless of a visual target. The proportion of HIT with covert saccades was independent of a visual target. In control subjects no compensatory saccades were observed and there were no differences in either angular vestibulo-ocular reflex gain or latency between inward and outward HIT. Our data suggest that inward applied HIT in chronic UVH is more likely to include an overt compensatory saccade based on its lengthened latency. Neither latency nor the occurrence of covert compensatory saccades during HIT depended on a visual target, suggesting they have become a learned behavior in response to chronic UVH.

Interactive wiimote gaze stabilization exercise training system for patients with vestibular hypofunction

BACKGROUND

Peripheral vestibular hypofunction is a major cause of dizziness. When complicated with postural imbalance, this condition can lead to an increased incidence of falls. In traditional clinical practice, gaze stabilization exercise is commonly used to rehabilitate patients. In this study, we established a computer-aided vestibular rehabilitation system by coupling infrared LEDs to an infrared receiver. This system enabled the subjects' head-turning actions to be quantified, and the training was performed using vestibular exercise combined with computer games and interactive video games that simulate daily life activities.

METHODS

Three unilateral and one bilateral vestibular hypofunction patients volunteered to participate in this study. The participants received 30 minutes of computer-aided vestibular rehabilitation training 2 days per week for 6 weeks. Pre-training and post-training assessments were completed, and a follow-up assessment was completed 1 month after the end of the training period.

RESULTS

After 6 weeks of training, significant improvements in balance and dynamic visual acuity (DVA) were observed in the four participants. Self-reports of dizziness, anxiety and depressed mood all decreased significantly. Significant improvements in self-confidence and physical performance were also observed. The effectiveness of this training was maintained for at least 1 month after the end of the training period.

CONCLUSION

Real-time monitoring of training performance can be achieved using this rehabilitation platform. Patients demonstrated a reduction in dizziness symptoms after 6 weeks of training with this short-term interactive game approach. This treatment paradigm also improved the patients' balance function. This system could provide a convenient, safe and affordable treatment option for clinical practitioners.