Is perception of visual verticality intact in patients with idiopathic cervical dystonia?

Idiopathic cervical dystonia (CD) is a focal dystonia characterized by an abnormal tilted or twisted head position. This abnormal head position could lead to a distorted perception of the visual vertical and spatial orientation. The aim of this cross-sectional study was to investigate whether the perception of the visual vertical is impaired in patients with CD. The subjective visual vertical test (SVV) was measured in 24 patients with CD and 30 controls. The SVV test is conducted in a completely darkened room. A laser bar is projected on an opposing white wall, which is deviated from the earth's gravitational vertical. Participants were seated with their head unrestrained and were instructed to position this bar vertically. The deviations in degrees (°) are corrected for the side of laterocollis in order to measure the E-effect. We found that patients were able to position the laser bar as equally close to the earth's gravitational vertical as controls (+ 0.67° SD ± 2.12 vs + 0.29° SD ± 1.08, p = 0.43). No E-effect was measured. Notwithstanding the abnormal position of the head, the perception of the visual vertical in patients with idiopathic CD is intact, possibly because of central neural compensatory mechanisms.