Introduction

The rotatory chair test is a cornerstone of vestibular assessment, providing valuable data on the vestibulo-ocular reflex (VOR). However, diagnostic accuracy depends entirely on meticulous technique. Even minor errors can lead to misinterpretation and incorrect clinical decisions. Understanding these pitfalls is essential for clinicians performing or interpreting these tests. Below, we outline the most frequent sources of error, grouped by common keywords.

Key Error Categories (Keywords)

• Calibration Errors: Inaccurate calibration of the eye movement recorder is the most common technical error. If the system does not correctly translate eye position into voltage or digital signal, all subsequent measurements (gain, phase, asymmetry) will be systematically wrong. Always perform a careful calibration before each test session.
• Electrode/Sensor Placement: For electro-oculography (EOG), improper placement of electrodes can create a drift or offset in the signal. For video-oculography (VOG), poor camera alignment or obstructed view of the pupil leads to tracking loss. Ensure proper skin preparation and secure, comfortable fit of goggles.
• Patient Alertness: A drowsy or inattentive patient will have a reduced and variable VOR response. The amplitude of nystagmus can decrease or become irregular. Active mental tasks (e.g., counting backwards, naming objects) are crucial to maintain consistent alertness throughout the rotation.
• Incorrect Stimulus Parameters: Using the wrong velocity, acceleration, or frequency of rotation can alter the results. For example, sinusoidal rotations at very low frequencies (below 0.01 Hz) often produce unreliable data in standard clinical settings. Always follow established protocols (e.g., 0.01 Hz to 0.64 Hz at 50-60°/s peak velocity).
• Improper Head Restraint: If the patient's head is not firmly stabilized, the actual rotational stimulus delivered to the semicircular canals will differ from the chair rotation. Even small head movements can introduce significant artifact. Use a secure headrest and instruct the patient to relax their neck muscles.
• Visual Fixation Contamination: The test must be performed in complete darkness to avoid suppression of the VOR by visual fixation. Any light leak from equipment or a loose blindfold will artificially reduce nystagmus amplitude and corrupt the data. Verify total darkness before starting.
• Data Analysis Oversights: Common errors include misidentifying the onset of nystagmus, using incorrect algorithms for calculating slow-phase velocity, or failing to exclude beats contaminated by blinks or saccades. Manual review of the raw eye trace remains essential even with automated software.
• Environmental Disturbances: Electrical noise from nearby equipment, magnetic fields from MRI scanners, or vibrations in the floor can introduce artifacts into the eye movement signal. Ensure the testing room is shielded and the chair is on a stable base.

Conclusion

The rotatory chair test is a powerful tool, but its reliability hinges on rigorous methodology. By systematically avoiding calibration errors, maintaining patient alertness, ensuring correct set-up, and carefully analyzing the data, clinicians can obtain clean, reproducible results. Regular training and adherence to standardized protocols are the best defenses against these common errors. A high-quality test leads to more confident diagnosis and better patient outcomes.