High-frequency autorotational testing of the vestibulo-ocular reflex

Abstract

Rotational testing is useful for clinical evaluation of vestibular dysfunction affecting the vestibulo-ocular reflex (VOR). Early applications relied on visual observation of nystagmus following turning. In modern use, control theory descriptors (e.g., gain and phase) are applied to patient data for comparisons with normal values. Motorized rotational chairs are used to passively oscillate patients with sinusoidal harmonic acceleration (SHA) stimulus profiles, usually at low frequencies (0.02 to 0.2 Hz). Changes in low-frequency phase and asymmetry, relative to normal values, provide useful indications of pathology. Vestibular autorotation testing (VAT) is a new, portable testing technique that utilizes microcomputers and patients' active head movements at high frequencies (2 to 6 Hz) to test both horizontal and vertical VOR responses. A head strap contains sensors and microelectronics for monitoring both head and eye movements. Higher-frequency VOR testing offers the advantages that the VOR is most active during locomotion at these frequencies and that other ocular motor systems are functionally insensitive above about 1 Hz. Results from VAT evaluation of patients with acute-stage Ménière's disease showed high vertical VOR gains, whereas patients receiving cisplatin chemotherapy showed pronounced low horizontal VOR gains and reduced phase lags. Practical experience in 4 years' clinical testing with the VAT has shown that this test is comfortable, efficient, clinically accurate, portable, and low cost, without requiring the dedicated, installed facility characteristic of other vestibular tests.