[Effect of body positions in human optokinetic nystagmus and optokinetic after nystagmus].
We determined whether whole body tilt would shift the axis of optokinetic nystagmus (OKN) and optokinetic-after nystagmus (OKAN) induced by full-field rotation at 35 degrees/sec. Fifteen normal people were positioned upright or tilted 30 degrees, 60 degrees or 90 degrees to both sides. Stripes of 5 degrees were projected on a 10-foot dome around the subject's yaw axis. Each trial lasted 45 sec. The lights were then extinguished, and the subject remained in darkness for 30 sec, while after nystagmus (OKAN) was recorded. Horizontal and vertical eye movements were recorded by video-oculography at 60 Hz. Eye position and velocity data were stored on optic disk cartridge by use of the data acquisition system. A. OKAN: For the subject in the upright position, the OKN velocity vector was aligned with both gravity and the subject's yaw axis with two minor exceptions. When the subject was tilted, a vertical OKN component (VOKN) appeared in a majority of subjects. For all 15 subjects, the mean angle of the OKN velocity vector regravity (Vectorg) was 22.6 +/- 7.2 degrees at 30 degrees tilted position. The Vectorg were 48.5 +/- 10.3 degrees at 60 degrees tilted position, and 76.4 +/- 12.6 degrees at 90 degrees tilted position. This represented shifts of the OKN velocity vector from the body axis of 7.4 degrees, 11.5 degrees and 13.6 degrees, respectively. The horizontal OKN (HOKN) gain remained unchanged in different positions. B. OKAN: The duration of HOKAN and initial slow phase velocity (SPV) of HOKAN decreased as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. The incidence and initial SPV of VOKAN and Re-Body did not change as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. Thus, VOKN was observed during HOKN as subjects were tilted and tended to vector to gravity, but VOKAN was not always observed during horizontal OKAN when subjects were tilted.
Arai
M
M
Department of Otolaryngology, Kitasato University School of Medicine, Kanagawa.
Cohen
B
B
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013997:Time Factors