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Tushar Choudhary, Derek Ball, Andy Harvey; The Effect of Mild Hypoxia on Retinal Oxygen Saturation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):43.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effect of mild hypoxia on retinal oxygen saturation using quantitative analysis of hyperspectral retinal images
Ten healthy volunteers (6 male, 4 female, aged (mean±SD) 26±5 years) were recruited. Retinal images were acquired under normoxia & hypoxia using a modified fundus camera (Topcon TRC 50 IA, Japan) fitted with IRIS (image replicating imaging spectrometer) system that acquires images in single snapshot at 8 different wavelengths . Hypoxia was induced by changing the O2 concentration of inhaled air from 21% to 15% using a hypoxia generator (Hypoxico Inc. NY, U.S.). Subjects breathed the hypoxic gas mixture for 10 minutes. Oxygen saturation of the subjects was monitored using fingertip-pulse oximetry. Images were processed using custom algorithms to calculate oxygen saturation. Data are presented as mean±SD and were analysed using paired sample t-tests with significance accepted at P<0.05.
The retinal arterial and venous oxygen saturation was 99.0±2.1% & 72.9±1.4% during normoxia. A reduction in the fraction of inspired oxygen resulted in a decline (P<0.001) in retinal arterial and venous oxygen saturation to 90.6±2.5% and 62.4±2.8%, respectively (Fig.1). The arterio-venous oxygen saturation difference in hypoxia (28.1±1.6%) was found to be 2% greater (P<0.001) than normoxia (26.0±1.3 %) (Fig.2).
The retinal arterial oxygen saturation recorded under normoxia closely approximates the values found using pulse oximetry (Data not shown). Acute inhalation of a hypoxic gas mixture resulted in a decline in both retinal arterial and venous saturation and an apparent widening of the a-vO2 difference. This result is unexpected since most studies report a reduction in the a-vO2 difference on exposure to hypoxia . However, the transient nature of exposure may be too short for the reported increases in cerebral perfusion  and as a consequence we have observed a decrease in retinal venous saturation.  Mordant D. J. et al (2011) Spectral imaging of the retina, Eye (London, England), 25:3, 309-20  Severinghaus, J.W. et al (1966) Cerebral Blood Flow In Man at High Altitude: Role of Cerebrospinal Fluid pH in Normalization of Flow in Chronic Hypocapnia, Circulation Research, 19:274-282
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