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Lisa Beckmann, Andrey Dmitriev, Xian Zhang, Hao F Zhang, Robert A Linsenmeier; Relating Vis-OCT Measurements of Retinal SO2 to Microelectrode Measurements of PO2. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1681. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine how much of the O2 from the retinal circulation supplies the outer retina rather than the inner retina by comparing measurements of retinal oxygenation via both visible light optical coherence tomography (vis-OCT) and O2-sensitive microelectrodes in rat retina. The inner retinal metabolic rate of oxygen (IR-MRO2) is the amount of oxygen extracted from the retinal circulation. It can be obtained by multiplying retinal blood flow by the difference in O2 saturation (sO2) in retinal arteries and veins. IR-MRO2 is generally larger than the actual O2 utilization of the inner retina (IR-QO2), because some O2 extracted from the retinal circulation supplies the avascular outer retina (R-OR-QO2). Subtracting R-OR-QO2 from IR-MRO2 yields the amount of oxygen used by the inner retina, IR-QO2.
Adult Long-Evans rats, anesthetized with IV ketamine/xylazine were used in this study. We measured IR-MRO2 with vis-OCT. We used a dual-circular scan pattern 1.5 mm in diameter centered around the optic nerve head, acquiring 100 B-scans of 8192 A-lines each. We averaged sO2 and summed retinal blood flow across all arteries and all veins to obtain arterial and venous sO2, and total retinal blood flow. Following vis-OCT imaging, in the same animals, O2 microelectrodes were used to measure gradients of PO2 across the retina. Fitting a previously developed diffusion model to the gradients allowed us to obtain the amount of O2 used by the outer retina (OR-QO2) and the fraction supplied by the retinal circulation (R-OR-QO2). Measurements of blood PO2 ensured that conditions were the same in both types of measurements.
We calculated OR-QO2 and R-OR-QO2 under normoxic conditions. OR-QO2 and R-OR-QO2 were higher under dark-adapted conditions than light adaptation, as expected. In the dark-adapted retina, OR-QO2 is roughly equivalent to the IR-MRO2 value of 3.3 mlO2-min-1-100g-1, with the outer retina receiving approximately 15% of the total oxygen extracted from the retinal circulation. Thus, IR-QO2 is about 2.8 mlO2-min-1-100g-1.
Under normoxic, dark-adapted conditions, approximately 15% of the oxygen extracted from the retinal circulation supplies the outer retina. Therefore, it is important to apply a correction when using IR-MRO2 as a surrogate for IR-QO2.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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