Testing of all Six Semicircular Canals with Video Head Impulse Test Systems
April 18th, 2019
35.7K views
This protocol describes how to correctly perform the video head impulse test with two separate test systems commonly used worldwide. Both the 2D and 3D video head impulse test methods are described.
Overview
This protocol describes the video head impulse test (vHIT) using two systems, EyeSeeCam and ICS Impulse. It aims to optimize testing techniques and highlight potential pitfalls.
Key Study Components
Area of Science
- Neuroscience
- Vestibular Function
- Clinical Testing
Background
- Video head impulse testing assesses vestibular function.
- Two systems are commonly used: 2D and 3D vHIT.
- Proper technique is crucial for accurate results.
- Potential artifacts can affect test outcomes.
Purpose of Study
- To demonstrate techniques for effective vHIT.
- To identify common pitfalls in the testing process.
- To ensure accurate assessment of all six semicircular canals.
Methods Used
- Calibration of vHIT systems before testing.
- Execution of head impulses for horizontal and vertical semicircular canals.
- Use of goggles for eye tracking during tests.
- Evaluation of test results for normal and pathological findings.
Main Results
- Normal findings indicated by matching head and eye velocity curves.
- Pathological saccades identified with low mean gain values.
- Results consistent across both vHIT systems.
- Effective techniques demonstrated for all six semicircular canals.
Conclusions
- Accurate vHIT requires proper technique and calibration.
- Low mean gain values and saccades indicate vestibular dysfunction.
- Both vHIT systems provide reliable assessments when used correctly.
Frequently Asked Questions
What is the purpose of the video head impulse test?
The vHIT assesses the function of the vestibular system by measuring eye movements in response to head impulses.
What are the two systems used in this protocol?
The two systems are the EyeSeeCam (vHIT system A) and the ICS Impulse (vHIT system B).
How are the vHIT systems calibrated?
Calibration involves positioning laser dots and ensuring eye tracking is accurate before testing.
What indicates normal vestibular function during testing?
Normal function is indicated by matching head and eye velocity curves and mean gain values within the normal range.
What are pathological saccades?
Pathological saccades are abnormal eye movements that can indicate vestibular dysfunction.
How many semicircular canals are tested?
All six semicircular canals are tested during the vHIT procedure.
Executive Industry Relevance
Accurate assessment of vestibular function is critical for identifying neurological targets in drug discovery programs targeting balance disorders, vertigo, and neurodegenerative conditions. The video head impulse test (vHIT) provides objective, high-frequency domain evaluation of all six semicircular canals, enabling mechanistic de-risking of vestibular targets. This supports predictive confidence in target validation by linking functional readouts to pharmacological modulation in preclinical models.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of vestibular hypotheses by quantifying semicircular canal function across all six canals.
- Operational Value: Provides rapid (5-10 min), minimally invasive functional readout suitable for iterative target screening.
- Predictive Value: High positive predictive value and near-perfect specificity support reliable target engagement assessment.
Screening & Assay Development
- Assay Readiness: Standardized protocols for EyeSeeCam and ICS Impulse systems ensure reproducible vestibular function measurements.
- Quantitative Output: Generates mean gain values and saccade detection for quantitative comparison across experimental conditions.
- Scalability: Lightweight goggle-based systems facilitate adaptation to high-throughput screening environments.
Translational & Preclinical Research
- Disease Relevance: Directly assesses vestibular organ function, aligning with models of inner ear disease and brainstem pathways.
- Translational Continuity: Enables consistent vestibular phenotyping from discovery through preclinical validation.
- Risk-Adjusted Decisions: Pathological saccades and low gain values provide clear thresholds for go/no-go decisions in target advancement.
Pipeline & Workflow Integration
Positioned at the discovery biology stage, vHIT supports hypothesis testing and pathway clarification for vestibular targets, with quantitative outputs enabling comparison across screening campaigns and preclinical models.
- Discovery Biology: Supports vestibular hypothesis testing by delivering objective, canal-specific functional data.
- Screening: Delivers reproducible, quantitative vestibular function metrics essential for assay standardization.
- Analytics: Mean gain values and saccade analysis provide statistical outputs for cross-condition comparison and target ranking.
- Translational Research: Connects vestibular function assays to preclinical continuity through conserved measurement paradigms.
- Enterprise Reuse: Protocol-driven execution enables cross-lab standardization and reuse across vestibular discovery programs.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity in vestibular target validation through direct functional assessment.
- Operational Value: Standardized procedures minimize variability and ensure reproducibility across sites and systems.
- Strategic Value: Enables earlier identification of off-target vestibular effects, improving capital efficiency in lead optimization.
- Portfolio Impact: Supports risk-adjusted prioritization by identifying vestibular liabilities early in the discovery cascade.
Implementation Considerations
- Requires expertise in vestibular physiology and oculomotor assessment to avoid misinterpretation of artifacts.
- Dependent on video-based eye tracking systems with precise pupil detection and head movement tracking.
- Necessitates cross-team standardization of head impulse delivery and fixation protocols to minimize noise.
- Must account for individual anatomical variations in canal alignment when applying rotational vectors.
- Limited to high-frequency vestibular function; does not assess low-frequency otolith function without complementary testing.
Biopharma FAQs
Why does mean gain value matter for vestibular target validation?
Mean gain value quantifies the ratio of eye velocity to head velocity during high-frequency head impulses, providing a direct measure of semicircular canal function. Values within the normal range indicate intact vestibulo-ocular reflex pathways, while reduced values suggest target engagement or pathway modulation. This metric enables quantitative comparison across genetic or pharmacological perturbations in discovery workflows.
How does isolation of horizontal versus vertical canal testing support discovery pipeline decisions?
Separate testing of horizontal and vertical semicircular canals allows canal-specific functional profiling, enabling researchers to isolate effects on individual vestibular pathways. This granularity supports mechanistic de-risking by identifying whether a compound selectively affects horizontal (lateral) or vertical (anterior/posterior) canal function. Such differentiation is critical for understanding on-target versus off-target activity in vestibular drug discovery.
What quantitative outputs from vHIT enable predictive confidence in preclinical models?
vHIT generates mean gain values and detects pathological saccades (overt or covert) as quantitative outputs that correlate with vestibular function. These metrics provide objective, reproducible endpoints for assessing target modulation in disease models. Consistent gain values and absence of saccades support predictive confidence when translating findings from in vitro or in vivo models to human physiology.
Why do replication requirements matter for cross-functional collaboration in vestibular discovery?
Replication across multiple head impulses (10-20 per side) and both vHIT systems (EyeSeeCam and ICS Impulse) ensures measurement reliability and minimizes artifact-driven variability. Standardized replication protocols allow discovery, preclinical, and translational teams to compare results across sites and studies. This consistency is essential for building confidence in target validation data used in go/no-go decisions.
What statistical analysis capabilities are required before implementing vHIT in a discovery workflow?
Implementation requires the ability to calculate mean gain values from head and eye velocity curves and to detect saccades based on velocity thresholds and timing relative to head movement. Statistical comparison of gain values across experimental groups and assessment of saccade incidence are necessary for data interpretation. These capabilities enable teams to determine whether observed changes exceed biological variability and support target-specific effects.
