VOR gain calculation methods in video head impulse recordings.

BACKGROUND: International consensus on best practices for calculating and reporting vestibular function is lacking. Quantitative vestibulo-ocular reflex (VOR) gain using a video head impulse test (HIT) device can be calculated by various methods. OBJECTIVE: To compare different gain calculation methods and to analyze interactions between artifacts and calculation methods. METHODS: We analyzed 1300 horizontal HIT traces from 26 patients with acute vestibular syndrome and calculated the ratio between eye and head velocity at specific time points (40 ms, 60 ms) after HIT onset ('velocity gain'), ratio of velocity slopes ('regression gain'), and ratio of area under the curves after de-saccading ('position gain'). RESULTS: There was no mean difference between gain at 60 ms and position gain, both showing a significant correlation (r2 = 0.77, p < 0.001) for artifact-free recordings. All artifacts reduced high, normal-range gains modestly (range -0.06 to -0.11). The impact on abnormal, low gains was variable (depending on the artifact type) compared to artifact-free recordings. CONCLUSIONS: There is no clear superiority of a single gain calculation method for video HIT testing. Artifacts cause small but significant reductions of measured VOR gains in HITs with higher, normal-range gains, regardless of calculation method. Artifacts in abnormal HITs with low gain increased measurement noise. A larger number of HITs should be performed to confirm abnormal results, regardless of calculation method.

Impact of artifacts on VOR gain measures by video-oculography in the acute vestibular syndrome.

OBJECTIVE: The video head impulse test (HIT) measures vestibular function (vestibulo-ocular reflex [VOR] gain - ratio of eye to head movement), and, in principle, could be used to make a distinction between central and peripheral causes of vertigo. However, VOG recordings contain artifacts, so using unfiltered device data might bias the final diagnosis, limiting application in frontline healthcare settings such as the emergency department (ED). We sought to assess whether unfiltered data (containing artifacts) from a video-oculography (VOG) device have an impact on VOR gain measures in acute vestibular syndrome (AVS). METHODS: This cross-sectional study compared VOG HIT results 'unfiltered' (standard device output) versus 'filtered' (artifacts manually removed) and relative to a gold standard final diagnosis (neuroimaging plus clinical follow-up) in 23 ED patients with acute dizziness, nystagmus, gait disturbance and head motion intolerance. RESULTS: Mean VOR gain assessment alone (unfiltered device data) discriminated posterior inferior cerebellar artery (PICA) strokes from vestibular neuritis with 91% accuracy in AVS. Optimal stroke discrimination cut points were bilateral VOR gain >0.7099 (unfiltered data) versus >0.7041 (filtered data). For PICA stroke sensitivity and specificity, there was no clinically-relevant difference between unfiltered and filtered data-sensitivity for PICA stroke was 100% for both data sets and specificity was almost identical (87.5% unfiltered versus 91.7% filtered). More impulses increased gain precision. CONCLUSIONS: The bedside HIT remains the single best method for discriminating between vestibular neuritis and PICA stroke in patients presenting AVS. Quantitative VOG HIT testing in the ED is associated with frequent artifacts that reduce precision but not accuracy. At least 10-20 properly-performed HIT trials per tested ear are recommended for a precise VOR gain estimate.

VOR gain by head impulse video-oculography differentiates acute vestibular neuritis from stroke.

OBJECTIVE: Vestibular neuritis is often mimicked by stroke (pseudoneuritis). Vestibular eye movements help discriminate the two conditions. We report vestibulo-ocular reflex (VOR) gain measures in neuritis and stroke presenting acute vestibular syndrome (AVS). METHODS: Prospective cross-sectional study of AVS (acute continuous vertigo/dizziness lasting >24 h) at two academic centers. We measured horizontal head impulse test (HIT) VOR gains in 26 AVS patients using a video HIT device (ICS Impulse). All patients were assessed within 1 week of symptom onset. Diagnoses were confirmed by clinical examinations, brain magnetic resonance imaging with diffusion-weighted images, and follow-up. Brainstem and cerebellar strokes were classified by vascular territory-posterior inferior cerebellar artery (PICA) or anterior inferior cerebellar artery (AICA). RESULTS: Diagnoses were vestibular neuritis (n = 16) and posterior fossa stroke (PICA, n = 7; AICA, n = 3). Mean HIT VOR gains (ipsilesional [standard error of the mean], contralesional [standard error of the mean]) were as follows: vestibular neuritis (0.52 [0.04], 0.87 [0.04]); PICA stroke (0.94 [0.04], 0.93 [0.04]); AICA stroke (0.84 [0.10], 0.74 [0.10]). VOR gains were asymmetric in neuritis (unilateral vestibulopathy) and symmetric in PICA stroke (bilaterally normal VOR), whereas gains in AICA stroke were heterogeneous (asymmetric, bilaterally low, or normal). In vestibular neuritis, borderline gains ranged from 0.62 to 0.73. Twenty patients (12 neuritis, six PICA strokes, two AICA strokes) had at least five interpretable HIT trials (for both ears), allowing an appropriate classification based on mean VOR gains per ear. Classifying AVS patients with bilateral VOR mean gains of 0.70 or more as suspected strokes yielded a total diagnostic accuracy of 90%, with stroke sensitivity of 88% and specificity of 92%. CONCLUSION: Video HIT VOR gains differ between peripheral and central causes of AVS. PICA strokes were readily separated from neuritis using gain measures, but AICA strokes were at risk of being misclassified based on VOR gain alone.

Quantifying the vestibulo-ocular reflex with video-oculography: nature and frequency of artifacts.

Video-oculography devices are now used to quantify the vestibulo-ocular reflex (VOR) at the bedside using the head impulse test (HIT). Little is known about the impact of disruptive phenomena (e.g. corrective saccades, nystagmus, fixation losses, eye-blink artifacts) on quantitative VOR assessment in acute vertigo. This study systematically characterized the frequency, nature, and impact of artifacts on HIT VOR measures. From a prospective study of 26 patients with acute vestibular syndrome (16 vestibular neuritis, 10 stroke), we classified findings using a structured coding manual. Of 1,358 individual HIT traces, 72% had abnormal disruptive saccades, 44% had at least one artifact, and 42% were uninterpretable. Physicians using quantitative recording devices to measure head impulse VOR responses for clinical diagnosis should be aware of the potential impact of disruptive eye movements and measurement artifacts.

Quantitative video-oculography to help diagnose stroke in acute vertigo and dizziness: toward an ECG for the eyes.

BACKGROUND AND PURPOSE: Strokes can be distinguished from benign peripheral causes of acute vestibular syndrome using bedside oculomotor tests (head impulse test, nystagmus, test-of-skew). Using head impulse test, nystagmus, test-of-skew is more sensitive and less costly than early magnetic resonance imaging for stroke diagnosis in acute vestibular syndrome but requires expertise not routinely available in emergency departments. We sought to begin standardizing the head impulse test, nystagmus, test-of-skew diagnostic approach for eventual emergency department use through the novel application of a portable video-oculography device measuring vestibular physiology in real time. This approach is conceptually similar to ECG to diagnose acute cardiac ischemia. METHODS: Proof-of-concept study (August 2011 to June 2012). We recruited adult emergency department patients with acute vestibular syndrome defined as new, persistent vertigo/dizziness, nystagmus, and (1) nausea/vomiting, (2) head motion intolerance, or (3) new gait unsteadiness. We recorded eye movements, including quantitative horizontal head impulse testing of vestibulo-ocular-reflex function. Two masked vestibular experts rated vestibular findings, which were compared with final radiographic gold-standard diagnoses. Masked neuroimaging raters determined stroke or no stroke using magnetic resonance imaging of the brain with diffusion-weighted imaging obtained 48 hours to 7 days after symptom onset. RESULTS: We enrolled 12 consecutive patients who underwent confirmatory magnetic resonance imaging. Mean age was 61 years (range 30-73), and 10 were men. Expert-rated video-oculography-based head impulse test, nystagmus, test-of-skew examination was 100% accurate (6 strokes, 6 peripheral vestibular). CONCLUSIONS: Device-based physiological diagnosis of vertebrobasilar stroke in acute vestibular syndrome should soon be possible. If confirmed in a larger sample, this bedside eye ECG approach could eventually help fulfill a critical need for timely, accurate, efficient diagnosis in emergency department patients with vertigo or dizziness who are at high risk for stroke.