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Pang-yu Teng, Justin Wanek, Norman Blair, Mahnaz Shahidi; Response of Inner Retinal Oxygen Extraction Fraction to Light Flicker in Rat. Invest. Ophthalmol. Vis. Sci. 2013;54(15):49.
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Light flicker is known to increase retinal blood flow and oxygen delivery. This increase in oxygen delivery is considered to be a response to an increase in oxygen consumption. Inner retinal oxygen extraction fraction (OEF) is a parameter defined by the ratio of oxygen consumption to delivery. OEF is expected to remain constant with light flicker as long as oxygen delivery compensates fully for the increased oxygen demand. The purpose of this study was to determine the response of inner retinal OEF to light flicker under normal and reduced oxygen delivery conditions in rat.
Retinal vascular oxygen tension (PO2) measurements were obtained in 10 rats using a previously established optical section phosphorescence lifetime imaging system. Imaging was performed before and during light flicker at 10 Hz in animals ventilated with room air (normoxia) and then 10% O2 (hypoxia). PO2 measurements in retinal arteries (PO2A) and veins (PO2V) were converted to oxygen contents to derive inner retinal OEF based on Fick’s principle. Measurements were compared using two-way repeated measures ANOVA.
Before flicker, PO2A was 44 ± 4 and 19 ± 4 mmHg, and PO2V was 28 ± 5 and 11 ± 4 mmHg under normoxia and hypoxia, respectively. During flicker, PO2A remained unchanged, while PO2V decreased under normoxia (27 ± 4 mmHg) and hypoxia (10 ± 5 mmHg). Before flicker, inner retinal OEF was 0.46 ± 0.13 and 0.67 ± 0.16 under normoxia and hypoxia, respectively. Inner retinal OEF increased during flicker under both normoxia (0.50 ± 0.11) and hypoxia (0.74 ± 0.14). There were significant main effects of flicker (p = 0.02) and ventilation (p < 0.001) on OEF, without a significant interaction (p = 0.5).
Inner retinal OEF increased with light flicker, indicating incomplete vascular compensation for the increased oxygen consumption under normal and reduced oxygen delivery.
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