Oxygenation state and mesopic sensitivity to dynamic contrast stimuli.
OBJECTIVE
Comparative studies suggest that increasing photoreceptor oxygen consumption in dim light, relative to bright light, may make the outer retina susceptible to hypoxia at light levels relevant to aviation at night. Accordingly, this study investigates effects of relevant oxygenation states on sensitivity to a dynamic contrast stimulus at low photopic and mesopic light levels experienced during night flying.


METHODS
Threshold sensitivity to frequency-doubled contrast stimuli was assessed under mild hypoxia (breathing 14.1% oxygen), hyperoxia (100% oxygen), and normoxia (air) using frequency doubling perimetry, viewing at background fields of approximately 10 cd/m2 and approximately 1 cd/m2. Data were analyzed by retinal eccentricity and visual field quadrant.


RESULTS
At low photopic luminance (approximately 10 cd/m2), sensitivity was marginally enhanced when breathing 100% oxygen. At mesopic luminance (approximately 1 cd/m2), sensitivity was consistently poorest with hypoxia and greatest with supplementary oxygen at all eccentricities and in all field quadrants, suggesting oxygen-dependent performance.


CONCLUSIONS
The known effects of oxygenation state on pupil size are likely to influence frequency doubling perimetry thresholds, but oxygen-dependent changes in mesopic sensitivity are greater than expected from altered retinal illumination alone and support outer retinal (photoreceptor) susceptibility to hypoxia under twilight viewing.
Connolly
Desmond M
DM
Human Protection and Performance Enhancement Group, QinetiQ, Farnborough, United Kingdom. dmconnolly@QinetiQ.com
Hosking
Sarah L
SL
D000328:Adult; D001359:Aviation; D015350:Contrast Sensitivity; D005260:Female; D006801:Humans; D018496:Hyperoxia / Q000503:physiopathology; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology; D008027:Light; D008297:Male; D010101:Oxygen Consumption; D010775:Photic Stimulation / Q000379:methods*; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D011680:Pupil; D012684:Sensory Thresholds; D016037:Single-Blind Method; D014787:Vision Tests; D058609:Visual Field Tests; D055815:Young Adult