Spontaneous visual exploration during locomotion in patients with phobic postural vertigo.

BACKGROUND: Earlier studies on stance and gait with posturographic and EMG-recordings and automatic gait analysis in patients with phobic postural vertigo (PPV) or visual height intolerance (vHI) revealed similar patterns of body stiffening with muscle co-contraction and a slow, cautious gait. Visual exploration in vHI patients was characterized by a freezing of gaze-in-space when standing and reduced horizontal eye and head movements during locomotion. OBJECTIVE: Based on the findings in vHI patients, the current study was performed with a focus on visual control of locomotion in patients with PPV while walking along a crowded hospital hallway. METHODS: Twelve patients with PPV and eleven controls were recruited. Participants wore a mobile infrared video eye-tracking system that continuously measured eye-in-head movements in the horizontal and vertical planes and head orientation and motion in the yaw, pitch, and roll planes. Visual exploration behavior of participants was recorded at the individually preferred speed for a total walking distance of 200 m. Gaze-in-space directions were determined by combining eye-in-head and head-in-space orientation. Walking speeds were calculated based on the trial duration and the total distance traversed. Participants were asked to rate their feelings of discomfort during the walk on a 4-point numeric rating scale. The examiners rated the crowdedness of the hospital hallway on a 4-point numeric rating scale. RESULTS: The major results of visual exploration behavior in patients with PPV in comparison to healthy controls were: eye and head positions were directed more downward in the vertical plane towards the ground ahead with increased frequency of large amplitude vertical orientation movements towards the destination, the end of the ground straight ahead. The self-adjusted speed of locomotion was significantly lower in PPV. Particularly those patients that reported high levels of discomfort exhibited a specific visual exploration of their horizontal surroundings. The durations of fixating targets in the visual surroundings were significantly shorter as compared to controls. CONCLUSION: Gaze control of locomotion in patients with PPV is characterized by a preferred deviation of gaze more downward and by horizontal explorations for suitable auxiliary means for potential postural support in order to prevent impending falls. These eye movements have shorter durations of fixation as compared to healthy controls and patients with vHI. Finally, the pathological alterations in eye-head coordination during locomotion correlate with a higher level of discomfort and anxiety about falling.

Health-related quality of life and functional impairment in acute vestibular disorders.

BACKGROUND AND PURPOSE: Acute vestibular symptoms have a profound impact on patients' well-being. In this study, health-related quality of life (HRQoL) and functional impairment were investigated prospectively in patients with different peripheral and central vestibular disorders during the acute symptomatic stage to decipher the most relevant underlying factors. METHODS: In all, 175 patients with acute vestibular disorders were categorized as central vestibular (CV, n = 40), peripheral vestibular (PV, n = 68) and episodic vestibular disorders (EV, n = 67). All patients completed scores to quantify generic HRQoL (European Quality of Life Score Five Dimensions Five Levels, EQ-5D-5L) and disease-specific HRQoL (Dizziness Handicap Inventory, DHI). Vestibular-ocular motor signs were assessed by video-oculography, vestibular-spinal control by posturography and verticality perception by measurement of subjective visual vertical. RESULTS: Patients with PV had a poorer HRQoL compared to patients with CV and EV (EQ-5D-5L/DHI: PV, 0.53 ± 0.31/56.1 ± 19.7; CV, 0.66 ± 0.28/43.3 ± 24.0; EV, 0.75 ± 0.24/46.7 ± 21.4). After adjusting for age, gender, cardiovascular risk factors and non-vestibular brainstem/cerebellar dysfunction patients with PV persisted to have poorer generic and disease-specific HRQoL (EQ-5D-5L -0.17, DHI +11.2) than patients with CV. Horizontal spontaneous nystagmus was a highly relevant factor for subgroup differences in EQ-5D-5L and DHI, whilst vertical spontaneous nystagmus, subjective visual vertical and sway path were not. EQ-5D-5L decreased significantly with more intense horizontal subjective visual vertical in CV (rho = -0.57) and PV (rho = -0.5) but not EV (rho = -0.13). CONCLUSIONS: Patients with PV have the highest functional impairment of all patients with acute vestibular disorders. Vestibular-ocular motor disturbance in the yaw plane has more impact than vestibular-spinal or vestibular-perceptive asymmetry in the roll and pitch plane, suggesting that horizontal visual stability is the most critical for HRQoL.

Approach to an experimental model of Mal de Debarquement Syndrome.

INTRODUCTION: Mal de Debarquement Syndrome (MdDS) is the rare condition of enduring rocking sensations and subjective unsteadiness following a lengthy exposure to passive motion. The pathogenesis of MdDS is unknown and the available treatment is limited. Here, we developed an experimental model of MdDS that may facilitate systematic inquiry of MdDS pathophysiology and the development of prevention or treatment strategies for this condition. METHODS: In an initial series of pilot experiments, suitable stimulation devices and conditions were evaluated. The final paradigm consisted of a low-frequency oscillatory motion stimulation, simultaneously deployed as roll and pitch rotation as well as heave on a six-degrees-of-freedom motion platform. Twelve healthy participants were stimulated under this condition for 30 min during free stance. Aftereffects with respect to rocking sensations and posturographic sway were monitored up to 60 min post-stimulation and compared to an initial pre-stimulation assessment as well as to posturographic recordings of spontaneous sway in ten patients with MdDS. RESULTS: Motion stimulation consistently evoked MdDS-like rocking sensations and postural alterations that lasted up to 45 min after cessation of passive motion exposure. Body sway alterations were most pronounced in anterior-posterior dimension during standing with eyes closed and primarily characterized by a distinct peak in the low-frequency sway spectrum close to stimulation frequency. These postural aftereffects further closely resembled spontaneous oscillatory low-frequency sway observed in patients with MdDS. CONCLUSION: Subsequent neurophysiological and imaging examinations are required to investigate whether the model of transient, experimental MdDS actually shares a common substrate with the enduring pathological condition of MdDS.

Subjective body vertical: a promising diagnostic tool in idiopathic normal pressure hydrocephalus?

Postural instability is a frequent symptom of patients with idiopathic normal pressure hydrocephalus (iNPH), and might be due to the misperception of body verticality. The objective of this study was to assess the usefulness of the subjective body vertical (SBV) as a potential tool for diagnosing iNPH. Twenty patients with iNPH underwent tests of SBV in the pitch and roll planes before and after cerebrospinal fluid (CSF) drainage. Ten patients with other central gait disorders served as controls and also underwent tests for SBV. Before CSF drainage, patients with iNPH showed an impaired verticality perception in the pitch plane with a significant backward deviation of the SBV as compared to the control group (iNPH: mean ± SD -3.7 ± 3.6°; control group: -0.8 ± 2.2°; t value = -2.30, p t-test = 0.03). After CSF drainage, the SBV of the iNPH patients normalized for the pitch plane (-0.9 ± 1.9°). There was a correlation between the backward deviation of the SBV and the ventricular enlargement of the frontal horns (Evan's index; r = -0.52; p Pearson = 0.02). An even stronger correlation was found with the enlargement of the third ventricle (Thalamus index; r = -0.64; p Pearson = 0.002). The new and clinically relevant finding of this study is that verticality perception of patients with iNPH is primarily impaired the pitch plane, and it improves after CSF drainage. This disturbance in pitch might be due to a bilateral central vestibular dysfunction of the thalamus. Determination of the SBV in pitch promises to increase diagnostic accuracy in the cases of suspected iNPH.

Real-time computer-based visual feedback improves visual acuity in downbeat nystagmus - a pilot study.

BACKGROUND: Patients with downbeat nystagmus syndrome suffer from oscillopsia, which leads to an unstable visual perception and therefore impaired visual acuity. The aim of this study was to use real-time computer-based visual feedback to compensate for the destabilizing slow phase eye movements. METHODS: The patients were sitting in front of a computer screen with the head fixed on a chin rest. The eye movements were recorded by an eye tracking system (EyeSeeCam®). We tested the visual acuity with a fixed Landolt C (static) and during real-time feedback driven condition (dynamic) in gaze straight ahead and (20°) sideward gaze. In the dynamic condition, the Landolt C moved according to the slow phase eye velocity of the downbeat nystagmus. The Shapiro-Wilk test was used to test for normal distribution and one-way ANOVA for comparison. RESULTS: Ten patients with downbeat nystagmus were included in the study. Median age was 76 years and the median duration of symptoms was 6.3 years (SD +/- 3.1y). The mean slow phase velocity was moderate during gaze straight ahead (1.44°/s, SD +/- 1.18°/s) and increased significantly in sideward gaze (mean left 3.36°/s; right 3.58°/s). In gaze straight ahead, we found no difference between the static and feedback driven condition. In sideward gaze, visual acuity improved in five out of ten subjects during the feedback-driven condition (p = 0.043). CONCLUSIONS: This study provides proof of concept that non-invasive real-time computer-based visual feedback compensates for the SPV in DBN. Therefore, real-time visual feedback may be a promising aid for patients suffering from oscillopsia and impaired text reading on screen. Recent technological advances in the area of virtual reality displays might soon render this approach feasible in fully mobile settings.