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.
School of Optometry/The Medical Center, University of Alabama, Birmingham 35294.
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Fuhr
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Hershner
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Daum
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