Ganzfeld blankout occurs in bowl perimetry and is eliminated by translucent occlusion.
An intermittent darkening of the visual field (ganzfeld "blankout") is perceived during bowl perimetry. Since this may be a form of rivalry, we hypothesized that occluding the nontested eye with a translucent occluder may eliminate the phenomenon. Ten normal subjects underwent visual field testing with both a translucent and an opaque occluder. Eight of the 10 reported darkening to occur with the opaque patch, while none reported it with the translucent occluder. The darkening occurred with a mean latency of 10.9 seconds, occupied 34.4% of the time, and on average occurred 3.25 times per minute. With the translucent occluder, retest threshold variability was 18.8% less and sensitivity was increased by 0.7 dB. The elimination of this darkening using translucent occluders in bowl perimetry will allow reduced variability and increased sensitivity and comfort.
Fuhr
P S
PS
School of Optometry/The Medical Center, University of Alabama, Birmingham 35294.
Hershner
T A
TA
Daum
K M
KM
D000328:Adult; D003624:Darkness; D004867:Equipment Design; D006801:Humans; D008029:Lighting; D009779:Occlusive Dressings; D012680:Sensitivity and Specificity; D058609:Visual Field Tests / Q000295:instrumentation / Q000379:methods*; D014794:Visual Fields