The human vertical optokinetic afternystagmus and the effect of gravity during pitch tilt.
BACKGROUND
Findings concerning human vertical optokinetic afternystagmus (VOKAN) are often not consistent and in some cases even contradictory.


METHODS
VOKAN was studied in nine normal subjects using corneo-retinal potential technique and an infrared video camera detection apparatus (ISCAN). VOKAN responses were measured at three angles of pitch head (and body) tilt: 0 degrees (upright), 90 degrees (supine) and 135 degrees (45 degrees below horizontal). The optokinetic stimulus was stripe movement with a velocity of 60 degrees/s.


RESULTS
Upward slow phase velocity (SP-Up) VOKAN was evoked in 6/9 subjects (67%) at 0 degrees tilt and at 90 degrees tilt, and in 4/9 (44%) at 135 degrees tilt. Downward slow phase velocity (SP-Down) VOKAN was elicited in 3/9 subjects (33%) at 0 degrees tilt; in 2/9 subjects (22%) at 90 degrees tilt and in 0/9 subjects (0%) at 135 degrees tilt.


CONCLUSIONS
The pitch tilt, as a gravity effect, influences significantly on the appearance and the duration of VOKAN.
Kolev
O I
OI
The Naval Aerospace Medical Research Laboratory, Pensacola, FL, USA. stayko.kolev@meteo.bg
Rupert
A H
AH
D000328:Adult; D005133:Eye Movements / Q000502:physiology; D006112:Gravitation; D006801:Humans; D007259:Infrared Rays; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D014743:Videotape Recording