Subjective visual vertical in patients with Usher syndrome.

Abstract

Verticality, or more precisely the ability to perceive spatial orientation with regard to gravity, is based on the integration of visual, vestibular and somesthetic information. The purpose of the present study was to compare the subjective visual vertical (SVV) in patients with Usher (type I and type II) with visual or vestibular impairment, and in healthy participants, in order to explore the importance of the visual and vestibular functions on the vertical’s perception. We evaluated the SVV using a wall housing which projects on the opposite wall a red-light line of about 2 meters, obtained by laser cannon. The evaluation was carried out under two tilt conditions: clockwise and counter-clockwise randomly performed five times in each direction. The response to the SVV task was quantified by the mean of the absolute values of the SVV. Responses to the SVV were significantly less accurate in patients with Usher with respect to healthy participants while it was similar for the two groups of patients with Usher. We hypothesize that visual inputs play a very important role in the perception of verticality and that the symmetrical bilateral vestibular deficit in Usher type I does not have a strong impact in perception of verticality.