Document Detail

Spatial contrast sensitivity at twilight: luminance, monocularity, and oxygenation.
MedLine Citation:
PMID:  20464814     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: Visual performance in dim light is compromised by lack of oxygen (hypoxia). The possible influence of altered oxygenation on foveal contrast sensitivity under mesopic (twilight) viewing conditions is relevant to aircrew flying at night, including when using night vision devices, but is poorly documented. METHODS: Foveal contrast sensitivity was measured binocularly and monocularly in 12 subjects at 7 spatial frequencies, ranging from 0.5 to approximately 16 cycles per degree, using sinusoidal Gabor patch gratings. Hypoxic performance breathing 14.1% oxygen, equivalent to altitude exposure at 3048 m (10,000 ft), was compared with breathing air at sea level (normoxia) at low photopic (28 cd x m(-2)), borderline upper mesopic (approximately 2.1 cd x m(-2)) and midmesopic (approximately 0.26 cd x m(-2)) luminance. Mesopic performance was also assessed breathing 100% oxygen (hyperoxia). RESULTS: Typical 'inverted U' log/log plots of the contrast sensitivity function were obtained, with elevated thresholds (reduced sensitivity) at lower luminance. Binocular viewing enhanced sensitivity by a factor approximating square root of 2 for most conditions, supporting neural summation of the contrast signal, but had greater influence at the lowest light level and highest spatial frequencies (8.26 and 16.51 cpd). Respiratory challenges had no effect. CONCLUSIONS: Contrast sensitivity is poorer when viewing monocularly and especially at midmesopic luminance, with relevance to night flying. The foveal contrast sensitivity function is unaffected by respiratory disturbance when twilight conditions favor cone vision, despite known effects on retinal illumination (pupil size). The resilience of the contrast sensitivity function belies the vulnerability of foveal low contrast acuity to mild hypoxia at mesopic luminance.
Desmond M Connolly
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Publication Detail:
Type:  Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  81     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  2010 May 
Date Detail:
Created Date:  2010-05-14     Completed Date:  2010-06-08     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  United States    
Other Details:
Languages:  eng     Pagination:  475-83     Citation Subset:  IM; S    
Human Protection and Performance Enhancement Group, QinetiQ PLC, Cody Technology Park, Bldg. A54, Ively Road, Farnborough, Hampshire GU14 0LX, UK.
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MeSH Terms
Aerospace Medicine
Analysis of Variance
Anoxia / physiopathology*
Contrast Sensitivity*
Mesopic Vision*
Sex Characteristics
Vision, Monocular

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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