Innovative vestibular testing

Dizziness and vertigo are common complaints in the general population, affecting yearly 15-20% of adults and 5-25% of children of school age and having considerable impact on everyday life. As the assessment of peripheral vestibular deficits is challenging, it is crucial to dispose of techniques to provide clinicians support for the correct diagnosis. The aim of this dissertation is therefore to apply in the clinical context cutting-edge diagnostic tools for the easy, quick and reliable assessment of peripheral vestibular impairments and the related functionality. Traditional techniques for the evaluation of semicircular canals, such as the caloric test, the rotational test or the search-coil Head Impulse Test, present several disadvantages, being unpleasant, expensive, time-consuming, not always available at the bedside or appropriate for any group of patients. Additionally, testing the vestibular system at low frequencies, such as in the caloric test, does not cover the physiologically relevant range. The video Head Impulse Test (vHIT) represents an alternative to indirectly evaluate semicircular canals’ function, stimulating the vestibulo-ocular reflex (VOR) with high-frequency head rotations and measuring the resulting eye and head movements. The first study reported in this dissertation extends the potentiality of the vHIT, assessing its feasibility in a group of healthy children and validating its use as a simple and well-tolerated bedside test for the vestibular screening of the pediatric population. The quantitative outcomes of the vHIT, however, do not always reflect functionality, i.e., how efficient is the VOR in stabilizing the visual scene during head perturbations. This represents the starting point for the development of tests whose aim is to assess the subjective perception of this ability. Among the most recently introduced techniques, the Head Impulse Testing Device (HITD) quantifies, without recording eye movements, patient’s reading abilities while performing high-frequency passive head rotations during equally challenging visual stimuli. The second section introduces and validates a new diagnostic tool, the Head Impulse Testing Device-Functional Testing (HITD-FT), which combines the HITD with eye movements recording. The HITD-FT is tested on healthy participants, whose vestibular functionality is transiently impaired by opioid administration. The work assesses the combined effect of VOR and re-fixation saccades on gaze stabilization during high-frequency passive head rotations. Moreover, it describes the role of covert re-fixation saccades on image stabilization and in enhancing overall dynamic vision. The HIDT-FT is furthermore exploited within the context of this dissertation to monitor the overall dynamic visual performance of vestibular patients during rehabilitation. The same experimental set-up, with healthy subjects undergoing opioid administration, is lately also exploited to explore the causes underlying post-operative nausea and vomiting, whose mechanism is still not completely understood. Preliminary studies suggest that opioids, acting on semicircular canals, generate a mismatch between the altered canals’ inputs and other non-consistently altered sensory inputs, triggering nausea and vomiting. The here reported study investigates whether the mismatch between semicircular canals’ inputs and other vestibular sensory inputs, or the mismatch between vestibular and visual inputs, are clinically relevant. A better understanding of this mechanism, i.e. that intra-vestibular mismatches have a particular importance, can help reducing the unpleasant side effects and improve pain management with opioids.Schwindelsyndrome sind häufig. Sie betreffen jährlich 15-20% der Erwachsenen und 5- 25% der Schulkinder und haben erhebliche Auswirkungen auf den Alltag. Die Beurteilung peripherer vestibulärer Defizite ist eine Herausforderung. Daher ist es entscheidend, Meth- oden zur Verfügung zu haben um Mediziner bei der Diagnosestellung zu unterstützen. Ziel dieser Doktorarbeit ist es, innovative Diagnose-Tools zur einfachen, schnellen und zuverlässigen Beurteilung der Funktion des vestibulären Systems in die Klinik zu übertragen. Traditionelle Methoden zur Evaluation der Bogengänge wie Kalorik, Drehstuhltest oder der Search-Coil-Kopfimpulstest haben mehrere Nachteile: sie sind unangenehm, teuer, zeitaufwändig, nicht am Krankenbett verfügbar oder eignen sich nicht für jede Patientengruppe. Die Untersuchung des vestibulären Systems im Niederfrequenzbereich wie bei der Kalorik deckt zudem nicht den physiologisch relevanten Bereich ab. Der videobasierte Kopfimpuls-Test (vHIT) ist dafür eine Alternative. Durch Stimulation des vestibulo- okulären Reflexes (VOR) mit Hochfrequenz-Kopfdrehungen und Messung von Auge- und Kopfbewegung wird dabei indirekt die Funktion der Bogengänge untersucht. Die erste Studie dieser Doktorarbeit erweitert die Anwendung des vHITs; seine Durchführbarkeit wird bei gesunden Kindern geprüft. Er stellt sich als einfacher und gut verträglicher „Bed- side Test“ für das vestibuläre Screening bei Kindern heraus. Die quantitativen vHIT Ergebnisse alleine spiegeln nicht immer wider, wie gut das Se- hen während Kopfbewegung stabil gehalten wird. Dies war Ausgangspunkt für die Entwicklung von Tests zur subjektiven Wahrnehmung dieser Funktion. Eine neue Methode auf diesem Gebiet, der Head Impulse Testing Device (HITD), untersucht - ohne Mes- sung der Augenbewegungen - die Lesefähigkeit anspruchsvoller visueller Stimuli während passiven Hochfrequenz-Kopfimpulsen. Im zweiten Teil der Doktorarbeit wird ein innovatives Diagnose-Tool – Head Impulse Testing Device – Functional Testing (HIDT-FT)– eingeführt und validiert. Der Test kombiniert HIDT mit Augenbewegungsmessung. Der HITD-FT wird an gesunden Probanden geprüft, deren vestibuläre Funktion mit Opi- oiden vorübergehend beeinträchtig ist. Die Studie untersucht den kombinierten Effekt von VOR und Re-Fixationsakkaden auf die Blickstabilisierung während passiver Hochfrequenz- Kopfimpulsen. Außerdem wird die Rolle sogenannter verdeckter (covert) Re-Fixationsakkaden bei der Bildstabilisierung und beim dynamischen Sehen geprüft. Der HITD-FT wird im Rahmen der Doktorarbeit zudem erfolgreich zur Dokumentation des dynamischen Sehens bei der Rehabilitation vestibulärer Patienten eingesetzt. Zum Schluss wird ein ähnlicher Versuchsaufbau mit Gabe von Opioiden bei Gesunden benutzt, um der Ursache von postoperativer Übelkeit und Erbrechen näher zu kommen, deren Mechanismus bisher nicht gut verstanden ist. Vorarbeiten legen nahe, dass Opiate eine Wirkung auf die Bogengänge haben und dass so eine Inkongruenz zwischen geänderten Bogengangs-Eingängen und nicht konsistenten geänderten anderen sensorische In- puts entsteht, die zu Übelkeit und Erbrechen führt. Die hier vorgelegte Arbeit untersucht, ob die Inkongruenz zwischen Bogengangsinformation und anderen vestibulären Sensoren oder die zwischen vestibulärem und visuellem Eingang klinisch relevant ist. Das Verständnis, dass intra-vestibuläre Inkongruenzen vor allem von Bedeutung sind, kann helfen diese unangenehmen Nebenwirkungen zu reduzieren und die Schmerzbehandlung mit Opiate zu verbessern

Innovative vestibular testing

Dizziness and vertigo are common complaints in the general population, affecting yearly 15-20% of adults and 5-25% of children of school age and having considerable impact on everyday life. As the assessment of peripheral vestibular deficits is challenging, it is crucial to dispose of techniques to provide clinicians support for the correct diagnosis. The aim of this dissertation is therefore to apply in the clinical context cutting-edge diagnostic tools for the easy, quick and reliable assessment of peripheral vestibular impairments and the related functionality. Traditional techniques for the evaluation of semicircular canals, such as the caloric test, the rotational test or the search-coil Head Impulse Test, present several disadvantages, being unpleasant, expensive, time-consuming, not always available at the bedside or appropriate for any group of patients. Additionally, testing the vestibular system at low frequencies, such as in the caloric test, does not cover the physiologically relevant range. The video Head Impulse Test (vHIT) represents an alternative to indirectly evaluate semicircular canals’ function, stimulating the vestibulo-ocular reflex (VOR) with high-frequency head rotations and measuring the resulting eye and head movements. The first study reported in this dissertation extends the potentiality of the vHIT, assessing its feasibility in a group of healthy children and validating its use as a simple and well-tolerated bedside test for the vestibular screening of the pediatric population. The quantitative outcomes of the vHIT, however, do not always reflect functionality, i.e., how efficient is the VOR in stabilizing the visual scene during head perturbations. This represents the starting point for the development of tests whose aim is to assess the subjective perception of this ability. Among the most recently introduced techniques, the Head Impulse Testing Device (HITD) quantifies, without recording eye movements, patient’s reading abilities while performing high-frequency passive head rotations during equally challenging visual stimuli. The second section introduces and validates a new diagnostic tool, the Head Impulse Testing Device-Functional Testing (HITD-FT), which combines the HITD with eye movements recording. The HITD-FT is tested on healthy participants, whose vestibular functionality is transiently impaired by opioid administration. The work assesses the combined effect of VOR and re-fixation saccades on gaze stabilization during high-frequency passive head rotations. Moreover, it describes the role of covert re-fixation saccades on image stabilization and in enhancing overall dynamic vision. The HIDT-FT is furthermore exploited within the context of this dissertation to monitor the overall dynamic visual performance of vestibular patients during rehabilitation. The same experimental set-up, with healthy subjects undergoing opioid administration, is lately also exploited to explore the causes underlying post-operative nausea and vomiting, whose mechanism is still not completely understood. Preliminary studies suggest that opioids, acting on semicircular canals, generate a mismatch between the altered canals’ inputs and other non-consistently altered sensory inputs, triggering nausea and vomiting. The here reported study investigates whether the mismatch between semicircular canals’ inputs and other vestibular sensory inputs, or the mismatch between vestibular and visual inputs, are clinically relevant. A better understanding of this mechanism, i.e. that intra-vestibular mismatches have a particular importance, can help reducing the unpleasant side effects and improve pain management with opioids.Schwindelsyndrome sind häufig. Sie betreffen jährlich 15-20% der Erwachsenen und 5- 25% der Schulkinder und haben erhebliche Auswirkungen auf den Alltag. Die Beurteilung peripherer vestibulärer Defizite ist eine Herausforderung. Daher ist es entscheidend, Meth- oden zur Verfügung zu haben um Mediziner bei der Diagnosestellung zu unterstützen. Ziel dieser Doktorarbeit ist es, innovative Diagnose-Tools zur einfachen, schnellen und zuverlässigen Beurteilung der Funktion des vestibulären Systems in die Klinik zu übertragen. Traditionelle Methoden zur Evaluation der Bogengänge wie Kalorik, Drehstuhltest oder der Search-Coil-Kopfimpulstest haben mehrere Nachteile: sie sind unangenehm, teuer, zeitaufwändig, nicht am Krankenbett verfügbar oder eignen sich nicht für jede Patientengruppe. Die Untersuchung des vestibulären Systems im Niederfrequenzbereich wie bei der Kalorik deckt zudem nicht den physiologisch relevanten Bereich ab. Der videobasierte Kopfimpuls-Test (vHIT) ist dafür eine Alternative. Durch Stimulation des vestibulo- okulären Reflexes (VOR) mit Hochfrequenz-Kopfdrehungen und Messung von Auge- und Kopfbewegung wird dabei indirekt die Funktion der Bogengänge untersucht. Die erste Studie dieser Doktorarbeit erweitert die Anwendung des vHITs; seine Durchführbarkeit wird bei gesunden Kindern geprüft. Er stellt sich als einfacher und gut verträglicher „Bed- side Test“ für das vestibuläre Screening bei Kindern heraus. Die quantitativen vHIT Ergebnisse alleine spiegeln nicht immer wider, wie gut das Se- hen während Kopfbewegung stabil gehalten wird. Dies war Ausgangspunkt für die Entwicklung von Tests zur subjektiven Wahrnehmung dieser Funktion. Eine neue Methode auf diesem Gebiet, der Head Impulse Testing Device (HITD), untersucht - ohne Mes- sung der Augenbewegungen - die Lesefähigkeit anspruchsvoller visueller Stimuli während passiven Hochfrequenz-Kopfimpulsen. Im zweiten Teil der Doktorarbeit wird ein innovatives Diagnose-Tool – Head Impulse Testing Device – Functional Testing (HIDT-FT)– eingeführt und validiert. Der Test kombiniert HIDT mit Augenbewegungsmessung. Der HITD-FT wird an gesunden Probanden geprüft, deren vestibuläre Funktion mit Opi- oiden vorübergehend beeinträchtig ist. Die Studie untersucht den kombinierten Effekt von VOR und Re-Fixationsakkaden auf die Blickstabilisierung während passiver Hochfrequenz- Kopfimpulsen. Außerdem wird die Rolle sogenannter verdeckter (covert) Re-Fixationsakkaden bei der Bildstabilisierung und beim dynamischen Sehen geprüft. Der HITD-FT wird im Rahmen der Doktorarbeit zudem erfolgreich zur Dokumentation des dynamischen Sehens bei der Rehabilitation vestibulärer Patienten eingesetzt. Zum Schluss wird ein ähnlicher Versuchsaufbau mit Gabe von Opioiden bei Gesunden benutzt, um der Ursache von postoperativer Übelkeit und Erbrechen näher zu kommen, deren Mechanismus bisher nicht gut verstanden ist. Vorarbeiten legen nahe, dass Opiate eine Wirkung auf die Bogengänge haben und dass so eine Inkongruenz zwischen geänderten Bogengangs-Eingängen und nicht konsistenten geänderten anderen sensorische In- puts entsteht, die zu Übelkeit und Erbrechen führt. Die hier vorgelegte Arbeit untersucht, ob die Inkongruenz zwischen Bogengangsinformation und anderen vestibulären Sensoren oder die zwischen vestibulärem und visuellem Eingang klinisch relevant ist. Das Verständnis, dass intra-vestibuläre Inkongruenzen vor allem von Bedeutung sind, kann helfen diese unangenehmen Nebenwirkungen zu reduzieren und die Schmerzbehandlung mit Opiate zu verbessern

Vestibulo-Ocular Responses and Dynamic Visual Acuity During Horizontal Rotation and Translation

Dynamic visual acuity (DVA) provides an overall functional measure of visual stabilization performance that depends on the vestibulo-ocular reflex (VOR), but also on other processes, including catch-up saccades and likely visual motion processing. Capturing the efficiency of gaze stabilization against head movement as a whole, it is potentially valuable in the clinical context where assessment of overall patient performance provides an important indication of factors impacting patient participation and quality of life. DVA during head rotation (rDVA) has been assessed previously, but to our knowledge, DVA during horizontal translation (tDVA) has not been measured. tDVA can provide a valuable measure of how otolith, rather than canal, function impacts visual acuity. In addition, comparison of DVA during rotation and translation can shed light on whether common factors are limiting DVA performance in both cases. We therefore measured and compared DVA during both passive head rotations (head impulse test) and translations in the same set of healthy subjects (n = 7). In addition to DVA, we computed average VOR gain and retinal slip within and across subjects. We observed that during translation, VOR gain was reduced (VOR during rotation, mean ± SD: position gain = 1.05 ± 0.04, velocity gain = 0.97 ± 0.07; VOR during translation, mean ± SD: position gain = 0.21 ± 0.08, velocity gain = 0.51 ± 0.16), retinal slip was increased, and tDVA was worse than during rotation (average rDVA = 0.32 ± 0.15 logMAR; average tDVA = 0.56 ± 0.09 logMAR, p = 0.02). This suggests that reduced VOR gain leads to worse tDVA, as expected. We conclude with speculation about non-oculomotor factors that could vary across individuals and affect performance similarly during both rotation and translation

The Effect of Vestibulo-Ocular Reflex Deficits and Covert Saccades on Dynamic Vision in Opioid-Induced Vestibular Dysfunction

Patients with bilateral vestibular dysfunction cannot fully compensate passive head rotations with eye movements, and experience disturbing oscillopsia. To compensate for the deficient vestibulo-ocular reflex (VOR), they have to rely on refixation saccades. Some can trigger "covert'' saccades while the head still moves; others only initiate saccades afterwards. Due to their shorter latency, it has been hypothesized that covert saccades are particularly beneficial to improve dynamic visual acuity, reducing oscillopsia. Here, we investigate the combined effect of covert saccades and the VOR on clear vision, using the Head Impulse Testing Device - Functional Test (HITD-FT), which quantifies reading ability during passive high-acceleration head movements. To reversibly decrease VOR function, fourteen healthy men (median age 26 years, range 2131) were continuously administrated the opioid remifentanil intravenously (0.15 mu g/kg/min). VOR gain was assessed with the video head-impulse test, functional performance (i.e. reading) with the HITD-FT. Before opioid application, VOR and dynamic reading were intact (head-impulse gain: 0.87 +/- 0.08, mean +/- SD;HITD-FT rate of correct answers: 90 +/- 9%). Remifentanil induced impairment in dynamic reading (HITD-FT 26 +/- 15%) in 12/14 subjects, with transient bilateral vestibular dysfunction (head-impulse gain 0.63 +/- 0.19). HITD-FT score correlated with head-impulse gain (R = 0.63, p = 0.03) and with gain difference (before/with remifentanil, R = -0.64, p = 0.02). One subject had a non-pathological head-impulse gain (0.82 +/- 0.03) and a high HITD-FT score (92%). One subject triggered covert saccades in 60% of the head movements and could read during passive head movements (HITD-FT 93%) despite a pathological head-impulse gain (0.59 +/- 0.03) whereas none of the 12 subjects without covert saccades reached such high performance. In summary, early catch-up saccades may improve dynamic visual function. HITD-FT is an appropriate method to assess the combined gaze stabilization effect of both VOR and covert saccades (overall dynamic vision), e.g., to document performance and progress during vestibular rehabilitation

Unstable Gaze in Functional Dizziness: A Contribution to Understanding the Pathophysiology of Functional Disorders

Objective: We are still lacking a pathophysiological mechanism for functional disorders explaining the emergence and manifestation of characteristic, severely impairing bodily symptoms like chest pain or dizziness. A recent hypothesis based on the predictive coding theory of brain function suggests that in functional disorders, internal expectations do not match the actual sensory body states, leading to perceptual dysregulation and symptom perception. To test this hypothesis, we investigated the account of internal expectations and sensory input on gaze stabilization, a physiologically relevant parameter of gaze shifts, in functional dizziness. Methods: We assessed gaze stabilization in eight functional dizziness patients and 11 healthy controls during two distinct epochs of large gaze shifts: during a counter-rotation epoch (CR epoch), where the brain can use internal models, motor planning, and resulting internal expectations to achieve internally driven gaze stabilization; and during an oscillation epoch (OSC epoch), where, due to terminated motor planning, no movement expectations are present, and gaze is stabilized by sensory input alone. Results: Gaze stabilization differed between functional patients and healthy controls only when internal movement expectations were involved [F(1,17) = 14.63, p = 0.001, and partial η(2) = 0.463]: functional dizziness patients showed reduced gaze stabilization during the CR (p = 0.036) but not OSC epoch (p = 0.26). Conclusion: While sensory-driven gaze stabilization is intact, there are marked, well-measurable deficits in internally-driven gaze stabilization in functional dizziness pointing at internal expectations that do not match actual body states. This experimental evidence supports the perceptual dysregulation hypothesis of functional disorders and is an important step toward understanding the underlying pathophysiology

Usability of the Video Head Impulse Test: Lessons From the Population-Based Prospective KORA Study

Objective: The video head impulse test (vHIT) has become a common examination in the work-up for dizziness and vertigo. However, recent studies suggest a number of pitfalls, which seem to reduce vHIT usability. Within the framework of a population-based prospective study with naïve examiners, we investigated the relevance of previously described technical mistakes in vHIT testing, and the effect of experience and training.Methods: Data originates from the KORA (Cooperative Health Research in the Region of Augsburg) FF4 study, the second follow-up of the KORA S4 population-based health survey. 681 participants were selected in a case-control design. Three examiners without any prior experience were trained in video head impulse testing. VHIT quality was assessed weekly by an experienced neuro-otologist. Restrictive mistakes (insufficient technical quality restricting interpretation) were noted. Based on these results, examiners received further individual training.Results: Twenty-two of the 681 vHITs (3.2%) were not interpretable due to restrictive mistakes. Restrictive mistakes could be grouped into four categories: slippage, i.e., goggle movement relative to the head (63.6%), calibration problems (18.2%), noise (13.6%), and low velocity of the head impulse (4.6%). The overall rate of restrictive mistakes decreased significantly during the study (12% / examiner within the first 25 tested participants and 2.1% during the rest of the examinations, p < 0.0001).Conclusion: Few categories suffice to explain restrictive mistakes in vHIT testing. With slippage being most important, trainers should emphasize the importance of tight goggles. Experience and training seem to be effective in improving vHIT quality, leading to high usability

Preventing opioid-induced nausea and vomiting: Rest your head and close your eyes?

Although opioid-induced nausea and vomiting (OINV) is common and debilitating, its mechanism is still unclear. Recently, we suggested that opioids affect semicircular canal function and that this leads to a mismatch between canal input and other sensory information during head motion, which triggers OINV. Here, we assess if visual input is relevant for this mismatch. In a randomized-controlled crossover study 14 healthy men (26.9 +/- 3.4 years, mean +/- SD) were tested twice, once blindfolded and once with eyes open, with at least one-day washout. The opioid remifentanil was administered intravenously (0.15 mu g/kg/min) for 60 minutes. After a thirty-minutes resting period, subjects' head and trunk were passively moved. Nausea was rated before remifentanil start (T-0), before the movement intervention (T-30) and after 60 minutes (T-60) of administration. At rest (T-0, T-30), median nausea ratings were zero whether subjects were blindfolded or not. Movement triggered nausea independently of visual input (nausea rating 1.5/3.0 (median/interquartile range) in the blindfolded, 2.5/6 in the eyes-open condition, chi(2) (1) = 1.3, p = 0.25). As movement exacerbates OINV independently of visual input, a clash between visual and semicircular canal information is not the relevant trigger for OINV. To prevent OINV, emphasis should be put on head-rest, eye-closure is less important

Vestibulo-Ocular Responses and Dynamic Visual Acuity During Horizontal Rotation and Translation

Dynamic visual acuity (DVA) provides an overall functional measure of visual stabilization performance that depends on the vestibulo-ocular reflex (VOR), but also on other processes, including catch-up saccades and likely visual motion processing. Capturing the efficiency of gaze stabilization against head movement as a whole, it is potentially valuable in the clinical context where assessment of overall patient performance provides an important indication of factors impacting patient participation and quality of life. DVA during head rotation (rDVA) has been assessed previously, but to our knowledge, DVA during horizontal translation (tDVA) has not been measured. tDVA can provide a valuable measure of how otolith, rather than canal, function impacts visual acuity. In addition, comparison of DVA during rotation and translation can shed light on whether common factors are limiting DVA performance in both cases. We therefore measured and compared DVA during both passive head rotations (head impulse test) and translations in the same set of healthy subjects (n = 7). In addition to DVA, we computed average VOR gain and retinal slip within and across subjects. We observed that during translation, VOR gain was reduced (VOR during rotation, mean +/- SD: position gain = 1.05 +/- 0.04, velocity gain = 0.97 +/- 0.07VOR during translation, mean +/- SD: position gain = 0.21 +/- 0.08, velocity gain = 0.51 +/- 0.16), retinal slip was increased, and tDVA was worse than during rotation (average rDVA = 0.32 +/- 0.15 logMARaverage tDVA = 0.56 +/- 0.09 IogMAR, p = 0.02). This suggests that reduced VOR gain leads to worse tDVA, as expected. We conclude with speculation about non-oculomotor factors that could vary across individuals and affect performance similarly during both rotation and translation

The effect of vestibulo-ocular reflex deficits and covert saccades on dynamic vision in opioid-induced vestibular dysfunction.

Patients with bilateral vestibular dysfunction cannot fully compensate passive head rotations with eye movements, and experience disturbing oscillopsia. To compensate for the deficient vestibulo-ocular reflex (VOR), they have to rely on re-fixation saccades. Some can trigger "covert" saccades while the head still moves; others only initiate saccades afterwards. Due to their shorter latency, it has been hypothesized that covert saccades are particularly beneficial to improve dynamic visual acuity, reducing oscillopsia. Here, we investigate the combined effect of covert saccades and the VOR on clear vision, using the Head Impulse Testing Device-Functional Test (HITD-FT), which quantifies reading ability during passive high-acceleration head movements. To reversibly decrease VOR function, fourteen healthy men (median age 26 years, range 21-31) were continuously administrated the opioid remifentanil intravenously (0.15 µg/kg/min). VOR gain was assessed with the video head-impulse test, functional performance (i.e. reading) with the HITD-FT. Before opioid application, VOR and dynamic reading were intact (head-impulse gain: 0.87±0.08, mean±SD; HITD-FT rate of correct answers: 90±9%). Remifentanil induced impairment in dynamic reading (HITD-FT 26±15%) in 12/14 subjects, with transient bilateral vestibular dysfunction (head-impulse gain 0.63±0.19). HITD-FT score correlated with head-impulse gain (R = 0.63, p = 0.03) and with gain difference (before/with remifentanil, R = -0.64, p = 0.02). One subject had a non-pathological head-impulse gain (0.82±0.03) and a high HITD-FT score (92%). One subject triggered covert saccades in 60% of the head movements and could read during passive head movements (HITD-FT 93%) despite a pathological head-impulse gain (0.59±0.03) whereas none of the 12 subjects without covert saccades reached such high performance. In summary, early catch-up saccades may improve dynamic visual function. HITD-FT is an appropriate method to assess the combined gaze stabilization effect of both VOR and covert saccades (overall dynamic vision), e.g., to document performance and progress during vestibular rehabilitation

Head-Movement-Emphasized Rehabilitation in Bilateral Vestibulopathy

Objective: Although there is evidence that vestibular rehabilitation is useful for treating chronic bilateral vestibular hypofunction (BVH), the mechanisms for improvement, and the reasons why only some patients improve are still unclear. Clinical rehabilitation results and evidence from eye-head control in vestibular deficiency suggest that head movement is a crucial element of vestibular rehabilitation. In this study, we assess the effects of a specifically designed head-movement-based rehabilitation program on dynamic vision, and explore underlying mechanisms. Methods: Two adult patients (patients 1 and 2) with chronic BVH underwent two 4-week interventions: (1) head-movement-emphasized rehabilitation (HME) with exercises based on active head movements, and (2) eye-movement-only rehabilitation (EMO), a control intervention with sham exercises without head movement. In a double-blind crossover design, the patients were randomized to first undergo EMO (patient 1) and-after a 4-week washout- HME, and vice-versa (patient 2). Before each intervention and after a 4-week follow-up patients' dynamic vision, vestibulo-ocular reflex (VOR) gain, as well as re-fixation saccade behavior during passive head motion were assessed with the head impulse testing device-functional test (HITD-FT). Results: HME, not EMO, markedly improved perception with dynamic vision during passive head motion (HITD-FT score) increasing from 0 to 60% (patient 1) and 75% (patient 2). There was a combination of enhanced VOR, as well as improved saccadic compensation. Conclusion: Head movement seems to be an important element of rehabilitation for BVH. It improves dynamic vision with a combined VOR and compensatory saccade enhancement