Cyclorotation of the eyes and the subjective visual vertical.

Pathological CR of the eyes and deviations of the SVV are among the most sensitive clinical brain stem signs. In acute unilateral brain stem infarctions, deviations of the SVV occur in 94% of cases and CR of one or both eyes is found in 88%. Deviations of CR and the SVV are typically ipsiversive with pontomedullary lesions and contraversive with pontomesencephalic lesions. They may involve a complete OTR, the triad of lateral head tilt, skew deviation and CR. There is a directional linkage between CR and the SVV (i.e. either right or left tilt), but the net tilt angles do not always match quantitatively. Pathological CR and deviations of the SVV obviously represent dysfunction of the VOR in the roll plane, which is subserved by both otolith and vertical canal inputs.