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Ayda M. Shahidi, John G. Flanagan, Sunni R. Patel, Monica Jong, Christopher Hudson; The Effect of Hypercapnia on the Sensitivity to Flicker Defined Stimuli. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4839.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of increased end-tidal CO2 on the sensitivity to flicker defined stimuli
The sensitivity of 2 flicker defined tasks was measured in 8 healthy, trained observers (mean age 27, SD = 4.5 years; six males) using the Flicker Defined Form (FDF) stimulus of the Heidelberg Edge Perimeter (HEP; Heidelberg Engineering) and Frequency Doubling Technology (FDT) stimulus of the Matrix perimeter (MP; Carl Zeiss Meditiec) during normoxia and following 15% hypercapnia (end-tidal CO2 increased by 15% relative to baseline). LogMAR visual acuity was 0.0 or better for all participants. A custom-designed computer controlled gas blender (RespirActTM) with a sequential gas delivery rebreathing circuit was adopted to accurately control end-tidal O2 and CO2. The FDF 24-2 ASTA Standard program and the 24-2 FDT Threshold program were performed for the HEP and MP respectively, during each condition. The order of the tests was systematically alternated between individuals but the order was maintained between conditions (i.e. normoxia or hypercapnia) for each individual. FDF and FDT sensitivity was analysed for the full field, the superior and inferior hemi-fields and for all stimuli within 3, 6, 15, 22 degrees eccentricity respectively, using ANOVA. Mean deviation was additionally compared between the two conditions for each instrument.
Flicker defined sensitivity was similar between normoxic and hypercapnic conditions for all geographical locations (p>0.05). Mean deviation was also found to be similar between normoxia and hypercapnia.
Healthy individuals have the capacity to compensate for an increase in CO2 levels such that visual function, at least in terms of flicker defined sensitivity, is not affected.
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