Objective: To investigate whether the perception of the visual vertical is intact in patients with idiopathic Cervical Dystonia (CD).

Background: Idiopathic CD is a focal dystonia which leads to a chronic abnormal position of the head. This abnormal position could lead to a distorted perception of the visual vertical (E-effect). And a deviated visual vertical could then reinforce the abnormal position of the head. Due to conflicting results, it is currently unclear whether the perception of the visual vertical is distorted in patients with CD. Moreover, patients with peripheral or central vestibular disorders show a tilt of the visual vertical and the involvement of the vestibular system in CD remains under discussion.

Methods: The Subjective Visual Vertical test (SVV) was conducted in 30 controls (mean age 59,20 year ±17,5) and 24 patients with CD regularly receiving botulinum toxin treatment (mean age 59,29 year ±13,96). Mean disease duration was 13,02 year (±8,72). SVV was measured in a completely darkened room by the Difra Vertitest type DI072010 (Difra, Belgium). The device projects a laser bar of approximately 1 m on an opposing white wall and has an accuracy of 0.1°. Participants were sitting in front of the device on a chair without any armrest or backrest with both feet supported on the floor. The position of the head was not corrected. Participants were asked to set a deviated laser bar to the vertical position with a remote control. After a practice trial, the average of 7 deviations was calculated in °. The fixed order of the 7 starting roll positions of the laser bar was 20° counterclockwise (CCW), 10° clockwise (CW), 5° CCW, 0° (earth vertical), 5° CW, 10° CCW and finally 20° CW.

Results: Patients with idiopathic CD showed a statistical difference (p=0.003) in the perception of the visual vertical compared with controls. An unpaired T-test showed that patients placed the laser bar closer to earth’s gravitational vertical than controls (0,14°±2.22 vs 0,29° ±1.08). This statistical difference is however within normal limits, approaches the measurement error and is therefore not clinically relevant. The data indicate that the E-effect is not present in patients with CD.

Conclusions: The data reinforce previous research that notwithstanding the chronic abnormal position of the head, the perception of the visual vertical in patients with idiopathic Cervical Dystonia remains normal.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/perception-of-the-visual-vertical-is-not-impaired-in-patients-with-idiopathic-cervical-dystonia/