Accession Number : ADA320735

Title :   Effect of Pitch Tilt on Vertical Optokinetic Nystagmus,

Corporate Author : NAVAL AEROSPACE MEDICAL RESEARCH LAB PENSACOLA FL

Personal Author(s) : Correia, M. J. ; Kolev, O. I. ; Rupert, A. H. ; Guedry, F. E.

PDF Url : ADA320735

Report Date : 23 SEP 1996

Pagination or Media Count : 20

Abstract : Vertical optokinetic nystagmus (VOKN) and VOKN after-responses were measured simultaneously in nine subjects using the cornen-retinal potential (CRP) technique and an infrared video-carnera detection apparatus (ISCAN). The ISCAN method produced a much smaller intersubject variability, a higher linear regression coefficient (0.94) when vertical eye position was regressed against vertical target position (6 subjects; +/- 30 deg, 5 deg increments), and VOKN gains comparable to the scleral search coil method. Detected by ISCAN, VOKN responses were measured at three angles of pitch head (and body) tilt: upright (0 deg), supine (90 deg), and declined 45 deg below horizontal (135 deg). Two stripe velocities (40 deg/s and 60 deg/s) were used. In six of the subjects, upward (slow-phase velocity up) VOKN gain (eye velocity/stripe velocity) was greater than downward (slow-phase down) VOKN gain for both stripe velocities at all tilt angles. The gain for both upward and downward VOKN decreased as stripe velocity increased from 40 to 60 deg/s, which suggests that both upward and downward VOKN systems were starting to saturate. Across subjects, a mean up-down asymmetry index (I) increased monotonically as the tilt angle increased. The slope of the monotonic function was greater for 60 0/% stripe velocity than for 40 0/% stripe velocity. The mean of all subjects' individual asymmetry ratios (ASYM), also increased as tilt increased. Optokinetic after-responses observed in the present study were of two types: (1) resetting of the eye from a beating field (eye position) that occurred during optokinetic stimulation with nystagmus superimposed, and (2) resetting of the eye without nystagmus superimposed. Upward VOKN produced the greatest number of after-responses.

Descriptors :   *ASYMMETRY, *EYE, *EYE MOVEMENTS, *CORNEA, *NYSTAGMUS, VELOCITY, POSITION(LOCATION), STIMULATION(PHYSIOLOGY), TARGETS, VERTICAL ORIENTATION, COEFFICIENTS, RETINA, LINEAR REGRESSION ANALYSIS, TILT, POSITIONING REACTIONS.

Subject Categories : Medicine and Medical Research
      Stress Physiology

Distribution Statement : APPROVED FOR PUBLIC RELEASE