Adaptation of the VOR in patients with low VOR gains.

Six subjects with histories of vertigo and with vestibulo-ocular reflex (VOR) gains less than 0.5 were tested in an adaptation protocol. After initial VOR testing in the dark, the subjects had a computer-driven visual display system placed on their heads. The system had the capability for variation of visual image magnification. The magnification was set to be 5% greater than the subject's average VOR gain. Subjects then performed active head movements as they carried out a visual searching task looking for objects in a panoramic scene. After 6 minutes with each image, the magnification was increased by 3 to 5%. The process was repeated for a total of 5 images, for a total increase in magnification of approximately 20% over 30 minutes. The VOR gain was measured again. In 17 of 18 conditions tested, the VOR gain increased. The average increase was 16%. Significant increases in VOR gain occurred at 0.32 and 0.64 Hz. The VOR gain increase in these patients occurred in a visual environment that lowered VOR gain in normal subjects. These results suggest that the VOR has an adaptation mechanism tuned to correct for small changes in required gain. Further research is necessary to determine if this method can result in persistent VOR gain improvements and reduction in symptoms and disability in patients with vestibular disorders.