Vestibular Eye Movements Are Heavily Impacted by Visual Motion and Are Sensitive to Changes in Visual Intensities.

Abstract

Eye movement evaluation constitutes the basis of diagnosis in dizzy patients. Through evaluating ocular torsion and vertical skewing during balance provoking stimulation, the aim of this study was to investigate the impact of vision on a typical vestibular eye movement response. Twelve healthy subjects (six young, six old) were exposed to (1) vestibular (VES), (2) visual (VIS), and (3) visual-vestibular (VIS+VES) stimulation. These were carried out as whole-body roll (VES), optokinetic rolling of visual scenes (VIS), and a combination of both (VIS+VES). Visual scenes were presented at two intensity levels. Eye movement velocities were used to evaluate the relative impact of visual and vestibular stimulation. Torsional velocities were lowest for VIS regardless of age. Velocities for the old group did not differ between VES and VIS+VES, whereas those for the young group were higher for VIS+VES. Regardless of age, amplified visual intensity resulted in an increased torsion-skewing ratio, seen as more degrees of torsion per degrees of skewing. The contributions of VIS and VES in proportion to VIS+VES were calculated as 0.18 (0.08) and 0.74 (0.14), respectively. Our findings demonstrate that vertical skewing is physiologically seen in combination with ocular torsion as a response to visual stimulation, with young subjects exhibiting a more dynamic response. The torsion-skewing ratio was sensitive to small changes in visual intensities, which may prove useful when evaluating visual motion sensitivity. The visual contribution to the vestibular eye movement response highlights the clinical importance of visual examinations when evaluating dizzy patients.