Subjective Visual Vertical Test

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The otoliths are vestibular organs that act as gravito-inertial force sensors and contribute to the perception of spatial orientation (earth verticality). The subjective visual vertical (SVV) is a psychophysical measure of the angle between perceptual vertical and true (gravitational) vertical. The otoliths contribute to the estimation of the physical vertical orientation, and individuals with normal vestibular function align the SVV within 2 degrees of true vertical (0 degrees). Impaired SVV has been documented in patients with unilateral vestibular disorders. Most research has focused on measuring the static SVV (head upright and stationary); however, more recently, methods have been developed to measure the SVV during stimulation of the otolith organs using on-axis yaw rotation (bilateral centrifugation), off-axis eccentric rotation (unilateral centrifugation), or head tilt for tests of bilateral or unilateral otolith function. The SVV test may be a useful method to assess utricular function in patients complaining of dizziness and/or imbalance and identify stages of recovery for otolith involvement.