Visual dependence and BPPV

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

Purpose

Post-concussion syndrome (PCS) is commonly associated with dizziness and visual motion sensitivity. This case-control study set out to explore altered motion processing in PCS by measuring gaze stabilization as a reflection of the capacity of the brain to integrate motion, and it aimed to uncover mechanisms of injury where invasive subcortical recordings are not feasible.

Methods

A total of 554 eye movements were analyzed in 10 PCS patients and nine healthy controls across 171 trials. Optokinetic and vestibulo-ocular reflexes were recorded using a head-mounted eye tracker while participants were exposed to visual, vestibular, and visuo-vestibular motion stimulations in the roll plane. Torsional and vergence eye movements were analyzed in terms of slow-phase velocities, gain, nystagmus frequency, and sensory-specific contributions toward gaze stabilization.

Results

Participants expressed eye-movement responses consistent with expected gaze stabilization; slow phases were fastest for visuo-vestibular trials and slowest for visual stimulations (P < 0.001) and increased with stimulus acceleration (P < 0.001). Concussed patients demonstrated increased gain from visual input to gaze stabilization (P = 0.005), faster slow phases (P = 0.013), earlier nystagmus beats (P = 0.003), and higher relative visual influence over the gaze-stabilizing response (P = 0.001), presenting robust effect sizes despite the limited population size.

Conclusions

The enhanced neural responsiveness to visual motion in PCS, combined with semi-intact visuo-vestibular integration, presented a subcortical hierarchy for altered gaze stabilization. Drawing on comparable animal trials, findings suggest that concussed patients may suffer from diffuse injuries to inhibiting pathways for optokinetic information, likely early in the visuo-vestibular hierarchy of sensorimotor integration. These findings offer context for common but elusive symptoms, presenting a neurological explanation for motion sensitivity and visual vertigo in PCS.

Clinical characteristics of visual motion hypersensitivity: a systematic review

This qualitative systematic review presents an overview of the state of the research relating to visual motion hypersensitivity (VMH) and offers a reference tool for future studies in the field. The study set out to identify and collate articles investigating risk groups with aberrant responses to visual motion as compared to healthy control groups, presenting evidence for risk factors associated with visual motion hypersensitivity. Data were synthesized into the state of the research and analyzed in the context of the clinical characteristics of each risk factor. Literature searches were performed on Medline Ovid, EMBASE, Web of Science, and Cinahl, identifying a total of 586 studies of which 54 were finally included. Original articles published between the dates of commencement for each database and 19th January 2021 were included. JBI critical appraisal tools were implemented for each corresponding article type. In total, the following number of studies was identified for each respective risk factor: age (n = 6), migraines (n = 8), concussions (n = 8), vestibular disorders (n = 13), psychiatric conditions (n = 5), and Parkinson's disease (n = 5). Several studies described VMH as the primary concern (n = 6), though these primarily included patients with vestibulopathies. There were considerable differences in the nomenclature employed to describe VMH, depending largely on the investigating group. An overview of investigated risk factors and their evaluation methods was presented in a Sankey diagram. Posturography was the most implemented methodology but due to diverse measurements meta-analyses were not possible. One may however note that while the easily implemented Vestibular Ocular Motor Screening (VOMS) was designed for concussed patients, it may prove useful for other risk groups.

Factors influencing clinical outcome in vestibular neuritis - A focussed review and reanalysis of prospective data

Following vestibular neuritis (VN), long term prognosis is not dependent on the magnitude of the residual peripheral function as measured with either caloric or the video head-impulse test. Rather, recovery is determined by a combination of visuo-vestibular (visual dependence), psychological (anxiety) and vestibular perceptual factors. Our recent research in healthy individuals has also revealed a strong association between the degree of lateralisation of vestibulo-cortical processing and gating of vestibular signals, anxiety and visual dependence. In the context of several functional brain changes occurring in the interaction between visual, vestibular and emotional cortices, which underpin the aforementioned psycho-physiological features in patients with VN, we re-examined our previously published findings focusing on additional factors impacting long term clinical outcome and function. These included: (i) the role of concomitant neuro-otological dysfunction (i.e. migraine and benign paroxysmal positional vertigo (BPPV)) and (ii) the degree to which brain lateralisation of vestibulo-cortical processing influences gating of vestibular function in the acute stage. We found that migraine and BPPV interfere with symptomatic recovery following VN. That is, dizziness handicap at short-term recovery stage was significantly predicted by migraine (r = 0.523, n = 28, p = .002), BPPV (r = 0.658, n = 31, p < .001) and acute visual dependency (r = 0.504, n = 28, p = .003). Moreover, dizziness handicap in the long-term recovery stage continued to be predicted by migraine (r = 0.640, n = 22, p = .001), BPPV (r = 0.626, n = 24, p = .001) and acute visual dependency (r = 0.667, n = 22, p < .001). Furthermore, surrogate measures of vestibulo-cortical lateralisation were predictive of the amount of cortical suppression exerted over vestibular thresholds. That is, in right-sided VN patients, we observed a positive correlation between visual dependence and acute ipsilesional oculomotor thresholds (R² 0.497; p < .001), but not contralateral thresholds (R² 0.017: p > .05). In left-sided VN patients, we observed a negative correlation between visual dependence and ipsilesional oculomotor thresholds (R² 0.459; p < .001), but not for contralateral thresholds (R² 0.013; p > .05). To surmise, our findings illustrate that in VN, neuro-otological co-morbidities retard recovery, and that measures of the peripheral vestibular system are an aggregate of residual function and cortically mediated gating of vestibular input.

Clinical characteristics and diagnostic aspects of cervicogenic dizziness in patients with chronic dizziness: A cross-sectional study

BACKGROUND AND OBJECTIVES

Chronic dizziness can significantly affect quality of life, but identifying the underlying cause remains challenging. This study focuses on proprioceptive cervicogenic dizziness (CGD) and aims: (1) to compare clinical test results between patients with CGD, dizzy patients without CGD, and healthy controls; and (2) to evaluate the diagnostic value of the clinical tests for CGD in patients with chronic dizziness.

METHODS

Sixty patients with chronic dizziness (18 with CGD and 42 without CGD), and 43 healthy controls underwent clinical tests evaluating neck function (mobility, proprioception, muscle function and disability), balance control, and the presence of visually induced dizziness. Data were analysed through one-way ANOVA, chi-square, independent samples t-test, and logistic regression analyses.

RESULTS

Patients with CGD had significantly more neck pain-related disability (Neck Bournemouth questionnaire (NBQ), p = 0.006), but better static (Static Balance, p = 0.001) and dynamic balance (Tandem Gait, p = 0.049), compared to dizzy patients without CGD. Univariable analyses revealed that increased NBQ (OR 1.05 [1.01; 1.09], p = 0.017), Joint Position Error (JPE) _{after extension} (OR 1.52 [1.00; 2.32], p = 0.050), and Tandem Gait scores (OR 1.09 [1.01; 1.18], p = 0.046) were individually associated with higher odds of having CGD. Their optimal cut-off level (based on the maximum Youden index) had high sensitivity but low specificity for CGD. The multivariable model, including NBQ and Tandem Gait, had fair discriminative ability (AUC = 0.74, 95% CI [0.61; 0.87]).

CONCLUSION

The combined use of the NBQ and Tandem Gait tests had the highest discriminative ability to detect CGD in patients with chronic dizziness.

Comparison of Clinical Balance and Visual Dependence Tests in Patients With Chronic Dizziness With and Without Persistent Postural-Perceptual Dizziness: A Cross-Sectional Study

Background

The diagnosis of persistent postural-perceptual dizziness (PPPD) is primarily based on medical history taking. Research on the value of clinical balance and visual dependence tests in identifying PPPD is scarce.

Objectives

(1) to contrast clinical balance and visual dependence tests between PPPD patients, dizzy non-PPPD patients, and healthy persons; and (2) to evaluate whether these clinical tests can help to identify PPPD in patients with chronic dizziness.

Methods

Consecutive patients with chronic dizziness (38 PPPD and 21 non-PPPD) and 69 healthy persons underwent Static Balance tests, the Timed Up and Go test, the Tandem Gait test, and the Functional Gait Assessment (FGA). Visual dependence tests included the Visual Vertigo Analog Scale (VVAS), the Rod-and-Disc test (RDT), and postural sway while facing rotating dots. Groups were compared using ANOVA with post-hoc Tukey, or independent samples t-tests. The value of the clinical tests for PPPD identification was evaluated through logistic regression and Partial Least Squares Discriminant (PLS-DA) analyses.

Results

PPPD patients had significantly higher VVAS scores than dizzy non-PPPD patients (p = 0.006). Facing rotating dots, PPPD and dizzy non-PPPD patients had increased postural sway compared to healthy persons (PPPD vs. healthy: center of pressure (COP) velocity p &lt; 0.001, and COP area p &lt; 0.001; but non-PPPD vs. healthy: COP velocity p = 0.116 and COP area p = 0.207). PPPD patients had no significantly increased postural sway compared to dizzy non-PPPD patients. PPPD and dizzy non-PPPD patients also scored significantly worse on balance tests compared to healthy persons (PPPD vs. healthy: for all balance tests p &lt; 0.001; non-PPPD vs. healthy: FGA p &lt; 0.001, for all other tests p &lt; 0.05). Differences were insignificant in balance scores between PPPD and dizzy non-PPPD patients, or in RDT scores between the three study groups. In patients with chronic dizziness, a higher VVAS score was most associated with PPPD [odds ratio 1.04; 95% CI (1.01; 1.07); p = 0.010]. The cross-validated (CV) PLS-DA model with all clinical tests included, had fair discriminative ability (CVerror = 47%).

Conclusion

PPPD patients were more visually dependent, but did not have worse postural balance compared to dizzy non-PPPD patients. Elevated VVAS scores characterized PPPD most in patients with chronic dizziness.

The Role of the Functional Head Impulse Test with and without Optokinetic Stimuli in Vestibular Migraine and Acute Unilateral Vestibulopathy: Discovering a Dynamic Visual Dependence

(1) Background: Visually induced vertigo (i.e., vertigo provoked by moving visual scenes) can be considered a noticeable feature of vestibular migraines (VM) and can be present in patients suffering from acute unilateral vestibulopathy (AUV). Hypersensitivity to moving or conflicting visual stimulation is named visual dependence. (2) Methods: Visuo-vestibular interactions were analyzed via the functional Head Impulse Test (fHIT) with and without optokinetic stimulation (o-fHIT) in 25 patients with VM, in 20 subjects affected by AUV, and in 20 healthy subjects. We calculated the percentage of correct answers (%CA) without and with the addition of the optokinetic background (OB). (3) In VM groups, the %CA on the fHIT was 92.07% without OB and 73.66% with OB. A significant difference was found between %CA on the deficit side and that on the normal side in AUV, both without OB and with OB. (4) Conclusions: The fHIT results in terms of %CA with and without OB could be useful to identify the presence of a dynamic visual dependence, especially in patients suffering from VM. The difference in %CA with and without OB could provide instrumental support to help correctly identify subjects suffering from VM. We propose the use of the fHIT in clinical practice whenever there is a need to highlight a condition of dynamic visual dependence.

Persistent postural perceptual dizziness following paroxysmal positional vertigo in migraine

Objective

This prospective study aimed to investigate the role of migraine in favouring the onset of persistent postural perceptual dizziness (PPPD) following paroxysmal positional vertigo (PPV).

Methods

A group of patients who came to our attention suffering of PPV with or without migraine and/or vestibular migraine (VM) was examined. Three months after the resolution, an anamnestic research was conducted aimed at establishing whether any patient-related dizziness could meet the diagnostic criteria for PPPD.

Results

12 of the 240 patients recruited met the diagnostic criteria for PPPD for an overall incidence of 5%, with 3 (1.85%) belonging to the non-migraine group and 9 (11.5%) to the migraine group. In the latter, 6 (28.6%) patients with VM and 3 (5.26%) without VM were affected.

Conclusions

The study shows a significant increase of PPPD diagnosis in migraine compared to patients without migraine (p = 0.003). Within migraine there was a significant increase in those with VM compared to patients without VM (p = 0.0016). No difference emerged between patients without migraine and migraine patients without VM (p > 0.05). The presence of VM in patient’s history, but not migraine without VM, appears to significantly increase the incidence of PPPD in patients with PPV.

Visuo-postural dependency index (VPDI) in human postural control

Background

Computerized stabilometry has been utilized to investigate the effect of vision on the neuromechanisms of human postural control. However, this approach lacks operational methods to quantify visual dependency during upright stance. This study had three goals: (1) To introduce the concept of visuo-postural dependency indices (VPDI) representing balance sway characteristics in multiple analytical domains (spatial, temporal, frequency, and structural), (2) To investigate the age and gender effects on VPDIs, and (3) To investigate the degree of relationships between VPDI and both subjective visual vertical and horizontal perception (SVV and SVH, respectively).

Methods

102 participants (16 to 80 years old) performed bipedal stances on a force platform with eyes open and closed. Response variables included the VPDIs computed for each postural index. In addition, 29 participants also performed SVV and SVH assessments.

Results

Fifteen VPDIs showed to be robust indicators of visual input modulation, and the variation across their magnitudes of modulation revealed a non-homogeneous response to changes in visual stimuli. Gender and age were not found to be a significant factor to VPDI modulation.

Conclusions

VPDIs revealed to be potential measures capable to quantitatively assess visuo-postural dependency and aid the assessment of fall risks and balance impairments.

A novel method for reducing motion sickness susceptibility through training visuospatial ability - A two-part study

Everyone can be susceptible to motion sickness (except those with complete loss of labyrinth function) and around one in three are known to be servery susceptible. Motion sickness can be experienced in many domains, including car travel, on a boat, using virtual reality headsets and simulator use amongst others. It is expected that due to potential designs and use cases, self-driving cars will increase motion sickness onset likelihood and severity for many car travellers. Besides medication, there are limited methods through which one can actively reduce their motion sickness susceptibility. This research develops a novel visuospatial training tool and explores the effect of visuospatial training on motion sickness. With a combined sample of 42 participants split between driving simulator trials (n = 20), and on-road trials (n = 22) baseline visuospatial skills and motion sickness were first measured. After a 14-day training period where participates completed 15-min of pen and paper tasks per day, it was found that visuospatial skills improved by 40%. This increase in visuospatial ability was shown to be directly responsible for a reduction in motion sickness by 51% in the simulator (with a 60% reduction in participant dropouts) and a 58% reduction in the on-road trial. This research has successfully identified a new method to reduce motion sickness susceptibility and the impact of these findings have wide reaching implications for motion sickness research, especially in the field of self-driving vehicles.

Visual Fixations and Motion Sensitivity: Protocol for an Exploratory Study

Background

Motion sensitivity after vestibular disorders is associated with symptoms of nausea, dizziness, and imbalance in busy environments. Dizziness and imbalance are reported in places such as supermarkets and shopping malls which have unstable visual backgrounds; however, the mechanism of motion sensitivity is poorly understood.

Objective

The main aim of this exploratory observational study is to investigate visual fixations and postural sway in response to increasingly complex visual environments in healthy adults and adults with motion sensitivity.

Methods

A total of 20 healthy adults and 20 adults with motion sensitivity will be recruited for this study. Visual fixations, postural sway, and body kinematics will be measured with a mobile eye tracker device, force plate, and 3D motion capture system, respectively. Participants will be exposed to experimental tasks requiring visual fixation on letters, projected on a range of backgrounds on a large screen during quiet stance. Descriptive statistics (mean and standard deviation) will be calculated for each of the variables. One-way independent-measures analyses of variance will be performed to investigate the differences between groups for all variables.

Results

Data collection was started in May 2019 and was completed by February 2020. It was approved by Health and Disability Ethics Committees, Ministry of Health, New Zealand on November 2, 2018 (Ethics ref: 18/CEN/193). We are currently processing the data and will begin data analysis in July 2020. We expect the results to be available for publication by the end of 2020. The trial was funded by the Neurology Special Interest Group, Physiotherapy New Zealand, and the Eisdell Moore Centre in November 2018.

Conclusions

This study will provide a detailed investigation of visual fixations in response to increasingly complex visual environments. Investigating characteristics of visual fixations in healthy adults and those with motion sensitivity will provide insight into this disabling condition and may inform the development of new intervention strategies which explicitly cater to the needs of this population.

Trial Registration

Australian New Zealand Clinical Trials Registry, ACTRN12619000254190; https://tinyurl.com/yxbn7nks

International Registered Report Identifier (IRRID)

PRR1-10.2196/16805

Abnormal visuo-vestibular interactions in vestibular migraine: a cross sectional study

Vestibular migraine is among the commonest causes of episodic vertigo. Chronically, patients with vestibular migraine develop abnormal responsiveness to both vestibular and visual stimuli characterized by heightened self-motion sensitivity and visually-induced dizziness. Yet, the neural mechanisms mediating such symptoms remain unknown. We postulate that such symptoms are attributable to impaired visuo-vestibular cortical interactions, which in turn disrupts normal vestibular function. To assess this, we investigated whether prolonged, full-field visual motion exposure, which has been previously shown to modulate visual cortical excitability in both healthy individuals and avestibular patients, could disrupt vestibular ocular reflex and vestibular-perceptual thresholds of self-motion during rotations. Our findings reveal that vestibular migraine patients exhibited abnormally elevated reflexive and perceptual vestibular thresholds at baseline. Following visual motion exposure, both reflex and perceptual thresholds were significantly further increased in vestibular migraine patients relative to healthy controls, migraineurs without vestibular symptoms and patients with episodic vertigo due to a peripheral inner-ear disorder. Our results provide support for the notion of altered visuo-vestibular cortical interactions in vestibular migraine, as evidenced by vestibular threshold elevation following visual motion exposure.

Use of Commercial Virtual Reality Technology to Assess Verticality Perception in Static and Dynamic Visual Backgrounds

OBJECTIVES

The Subjective Visual Vertical (SVV) test and the closely related Rod and Disk Test (RDT) are measures of perceived verticality measured in static and dynamic visual backgrounds. However, the equipment used for these tests is variable across clinics and is often too expensive or too primitive to be appropriate for widespread use. Commercial virtual reality technology, which is now widely available, may provide a more suitable alternative for collecting these measures in clinical populations. This study was designed to investigate verticality perception in symptomatic patients using a modified RDT paradigm administered through a head-mounted display (HMD).

DESIGN

A group of adult patients referred by a physician for vestibular testing based on the presence of dizziness symptoms and a group of healthy adults without dizziness symptoms were included. We investigated degree of visual dependence in both groups by measuring SVV as a function of kinematic changes to the visual background.

RESULTS

When a dynamic background was introduced into the HMD to simulate the RDT, significantly greater shifts in SVV were found for the patient population than for the control population. In patients referred for vestibular testing, the SVV measured with the HMD was significantly correlated with traditional measures of SVV collected in a rotary chair when accounting for head tilt.

CONCLUSIONS

This study provides initial proof of concept evidence that reliable SVV measures in static and dynamic visual backgrounds can be obtained using a low-cost commercial HMD system. This initial evidence also suggests that this tool can distinguish individuals with dizziness symptomatology based on SVV performance in dynamic visual backgrounds.

Influence of Visual Dependence on Inter-Segmental Coordination during Upright Stance in Cerebral Palsy

The presence of visual dependence as an influential factor on the development of functional stability in ambulatory individuals with cerebral palsy (CP) was studied in 22 adults with spastic bilateral CP, 11 of whom were considered visually dependent, and 18 healthy adults. Participants stood upright during pitch plane disturbances of the visual field and support surface. Intersegmental coordination behaviors were assessed by fitting trajectories of adjacent body segments to an ellipse. Mixed-model repeated measures ANOVAs were performed on ellipse orientation angle and area. Dissimilar stabilizing strategies adopted by the two groups with CP imply that visual dependence impacts postural control. Postural reorganization in response to visual flow in all groups indicates that we cannot ignore perceptual aspects of postural control when designing therapeutic interventions.

Visual dependence and spatial orientation in benign paroxysmal positional vertigo

People with benign paroxysmal positional vertigo (BPPV) probably have otoconial particles displaced from the utricle into the posterior semicircular canal. This unilateral change in the inertial load distributions of the labyrinth may result in visual dependence and may affect balance control. The goal of this study was to explore the interaction between visual dependence and balance control. We compared 23 healthy controls to 17 people with unilateral BPPV on the Clinical Test of Sensory Interaction and Balance on compliant foam with feet together, the Rod-and-Frame Test and a Mental Rotation Test. In controls, but not BPPV subjects, subjects with poor balance scores had significantly greater visual dependence, indicating that reliance on visual cues can affect balance control. BPPV and control subjects did not differ on the mental rotation task overall but BPPV reaction time was greater at greater orietantions, suggesting that this cognitive function was affected by BPPV. The side of impairment was strongly related to the side of perceived bias in the Earth vertical determined by BPPV subjects, indicating the relationship between the effect of asymmetric otolith unloading with simultaneous canal loading on spatial orientation perception.

Acetazolamide: A New Treatment for Visual Vertigo

Visual vertigo is a disorder characterised by symptoms of dizziness, vertigo, unsteadiness, disorientation, and general discomfort induced by visual triggers. It is currently treated with vestibular rehabilitation therapy, with no effective pharmacotherapy available for treatment-resistant cases. The objective of this study was to evaluate the efficacy of oral acetazolamide in improving symptoms of visual vertigo. A comparative case series of adult patients clinically diagnosed with visual vertigo was conducted from January 1992 to May 2015. Patients without a full neurologic or otorhinolaryngologic work-up, negative magnetic resonance imaging (MRI), and an organic cause for their symptoms were excluded. The identified patients were then contacted by phone to complete a voluntary symptom survey. Main outcome was the subjective reported percentage in symptom improvement. Secondary outcomes were subjective improvement by symptom triggers. The participants were retrospectively divided into three groups based on their treatment with acetazolamide: currently on acetazolamide, terminated acetazolamide, or never initiated acetazolamide. Fifty-seven patients met the inclusion criteria and were willing to complete the phone survey (19 currently on acetazolamide, 27 terminated acetazolamide, and 11 never initiated therapy). Overall symptomatic improvement was reported by 18 (94.7%) patients currently on acetazolamide, 18 (66.7 %) who terminated acetazolamide, and 5 (45.5%) who never initiated therapy, varying significantly by group (p = 0.0061). Greatest improvement was reported in symptoms triggered by being a passenger in a car. These results show that acetazolamide has a positive association with improvement of symptoms of visual vertigo.

Tandem walking as a quick screening test for vestibular disorders

OBJECTIVES/HYPOTHESIS

Although many screening tests of balance are available, few of them have been well validated for clinical or research uses. The goal of this study was to test an updated version of an old test, Tandem Walking, to determine how useful it is for screening patients with vestibular disorders.

STUDY DESIGN

Case-control study.

METHODS

Subjects were 90 adult patients with vestibular disorders and 292 healthy adult controls. They were tested on the number of correct tandem steps they could perform with arms crossed and eyes closed in a series of 10 steps. Correct steps could be nonconsecutive. Subjects were given one practice trial with eyes open and three experimental trials with eyes closed.

RESULTS

Receiver operating characteristic (ROC), and sensitivity and specificity were calculated. ROC values, sensitivity, and specificity were, at best, only moderate, no matter how the age range was cut. Even for subjects in the age group with the highest ROC value (i.e., age less than 50 years), ROC = 0.8, sensitivity = 0.77, and specificity = 0.72.

CONCLUSIONS

These results indicate that 23% of patients will not be identified. Therefore, we recommend that if this test is used for screening patients in the clinic or healthy volunteers, the result should be interpreted with care.

LEVEL OF EVIDENCE

3b. Laryngoscope, 128:1687-1691, 2018.

Framing visual roll-motion affects postural sway and the subjective visual vertical

Effects of visual roll-motion on postural sway and the subjective visual vertical (SVV) often is studied using mechanical devices, whereas electronic displays offer cheaper and more flexible alternatives. These devices typically emit and reflect light scattered by the edges of the screen, providing Earth-fixed cues of verticality. These cues may decrease the effects of rotating stimuli, a possibility that has not been studied explicitly before in one experimental design. We exposed 16 participants to a visual dot pattern, either stationary, or rotating in roll, that was or was not surrounded by a visible Earth-fixed reference frame. To eliminate unintended visual cues, the experiment was performed in complete darkness and participants wore neutral density goggles passing only 1% of light. Postural sway was measured using a force platform. SVV measurements were obtained from a visible rod. To monitor the participants, motion sickness severity was obtained with an 11-point rating scale. Results showed that the presence of an Earth-fixed frame significantly decreased the effect of the rotating pattern on postural sway and SVV deviations. Therefore, when studying subjective verticality related effects of visual stimuli, it is imperative that all visual Earth-fixed cues are not just minimized but completely eliminated. The observation that an Earth-fixed frame significantly decreased the effect of the rotating pattern on both postural sway and the SVV points towards a common neural origin, possibly involving a neural representation of verticality. Finally, we showed that an electronic screen can yield similar effect sizes as those taken from the literature using mechanical devices.

Practice Guidelines for the Diagnosis and Management of Benign Paroxysmal Positional Vertigo Otoneurology Committee of Spanish Otorhinolaryngology and Head and Neck Surgery Consensus Document

Benign Paroxysmal Positional Vertigo is the most frequent episodic vestibular disorder. The purpose of this guide, requested by the committee on otoneurology of the Spanish Society of Otolaryngology and Head and Neck Surgery, is to supply a consensus document providing practical guidance for the management of BPPV. It is based on the Barany Society criteria for the diagnosis of BPPV. This guideline provides recommendations on each variant of BPPV, with a description of the different diagnostic tests and the therapeutic manoeuvres. For this purpose, we have selected the tests and manoeuvres supported by evidence-based studies or extensive series. Finally, we have also included a chapter on differential diagnosis and a section relating to general aspects in the management of BPPV.

Vestibular and oculomotor influences on visual dependency

Participants made verticality judgments using the rod-and-disk test, a test of visual dependence, and then repeated after caloric irrigation. If the combination of rotating disk and caloric increased the slow-phase velocity of the torsional nystagmus the tilt in subjective verticality increased, whereas reductions in eye velocity were associated with reduced tilt. Thus visual dependency measures are not only modulated by perceptual style but can also reflect local vestibulo-ocular function, specifically torsional eye movements.

The degree to which a person relies on visual stimuli for spatial orientation is termed visual dependency (VD). VD is considered a perceptual trait or cognitive style influenced by psychological factors and mediated by central reweighting of the sensory inputs involved in spatial orientation. VD is often measured with the rod-and-disk test, in which participants align a central rod to the subjective visual vertical (SVV) in the presence of a background that is either stationary or rotating around the line of sight—dynamic SVV. Although this task has been employed to assess VD in health and vestibular disease, what effect torsional nystagmic eye movements may have on individual performance is unknown. Using caloric ear irrigation, 3D video-oculography, and the rod-and-disk test, we show that caloric torsional nystagmus modulates measures of VD and demonstrate that increases in tilt after irrigation are positively correlated with changes in ocular torsional eye movements. When the direction of the slow phase of the torsional eye movement induced by the caloric is congruent with that induced by the rotating visual stimulus, there is a significant increase in tilt. When these two torsional components are in opposition, there is a decrease. These findings show that measures of VD can be influenced by oculomotor responses induced by caloric stimulation. The findings are of significance for clinical studies, as they indicate that VD, which often increases in vestibular disorders, is modulated not only by changes in cognitive style but also by eye movements, in particular nystagmus.

Multisensory integration in balance control

This chapter provides an introduction to the topic of multisensory integration in balance control in, both, health and disease. One of the best-studied examples is that of visuo-vestibular interaction, which is the ability of the visual system to enhance or suppress the vestibulo-ocular reflex (VOR suppression). Of clinical relevance, examination of VOR suppression is clinically useful because only central, not peripheral, lesions impair VOR suppression. Visual, somatosensory (proprioceptive), and vestibular inputs interact strongly and continuously in the control of upright balance. Experiments with visual motion stimuli show that the visual system generates visually-evoked postural responses that, at least initially, can override vestibular and proprioceptive signals. This paradigm has been useful for the study of the syndrome of visual vertigo or vision-induced dizziness, which can appear after vestibular disease. These patients typically report dizziness when exposed to optokinetic stimuli or visually charged environments, such as supermarkets. The principles of the rehabilitation treatment of these patients, which use repeated exposure to visual motion, are presented. Finally, we offer a diagnostic algorithm in approaching the patient reporting oscillopsia - the illusion of oscillation of the visual environment, which should not be confused with the syndrome mentioned earlier of visual vertigo.

Benign paroxysmal positional vertigo--toward new definitions

OBJECTIVE

To review new clinical data and theories concerning atypical positional nystagmus in vertical canal benign paroxysmal positional vertigo (BPPV).

DATA SOURCES

Peer reviewed, clinical papers describing nystagmus provoked by positioning in cases with BPPV.

STUDY SELECTION

Basic scientific articles detailing 3D anatomical reconstructions of the inner ear.

CONCLUSION

In BPPV, it is hypothetically possible that otoconia become dislocated but do not fall into the common crus of the vertical canals or into the horizontal canal; in these cases, they may gravitate toward the most inferior part of the utriculus, the ampulla of the inferior canal. It is argued that in these cases, depending on their behavior (free-floating or sticking to the cupula) and the precise position of the inferior ampulla, either no nystagmus or a slow downbeat nystagmus should ensue when the patient is positioned from sitting to a Dix-Hallpike position. Such scenarios could hypothetically explain commonly seen clinical entities such as "subjective BPPV" and/or cases with a peripheral positional downbeat nystagmus.

Migraine and dizziness

PURPOSE OF REVIEW

Awareness of the importance of migraine in patients with symptoms of vestibular dysfunction is increasing. This article gives an overview of the multiple facets of the link between migraine and vestibular dysfunction.

RECENT FINDINGS

The vestibular and the headache community have published a consensual definition of vestibular migraine, which is an important step to promote research on the topic and the awareness of clinicians. Vestibular migraine is considered the most common cause of spontaneous recurrent vertigo. So far, the evidence for vestibular migraine has been mainly epidemiological, but the recent follow-up of a cohort over 9 years could show the robustness of the diagnosis over time.Additionally, migraine and vestibular dysfunction have multiple potential interactions and links through a range of comorbidities such as Menière's disease, benign paroxysmal positional vertigo, anxiety and motion sickness, which go beyond the diagnostic entity of vestibular migraine.

SUMMARY

The further refinement and wider acceptance of the diagnostic entity of vestibular migraine is an important development as it is one the most common vestibular disorders. But the relationship between migraine and vestibular dysfunction is complex and has many aspects beyond vestibular migraine.