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Mahnaz Shahidi, Anthony Felder, Justin Wanek, Norman P Blair, Michael Robert Tan; A Method for Combined Retinal Vascular and Tissue Oxygen Tension Imaging. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3814.
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© ARVO (1962-2015); The Authors (2016-present)
Since insufficient oxygen delivery by the retinal circulation can result in cell death and vision loss, knowledge of retinal vascular and tissue oxygen content is vital. Several techniques have been developed for assessment of either retinal vascular oxygen tension (PO2) or tissue PO2 (tPO2). However, concomitant and integrated knowledge of intra- and extra-vascular oxygen content is needed for a comprehensive understanding of retinal oxygen dynamics. The purpose of the current study is to report a novel imaging method for combined measurements of vascular PO2 and tPO2 in rats.
Optical section phosphorescence lifetime imaging was performed in 7 Long Evans rats using 2 different oxyphors. One oxyphor was delivered intravenously for vascular PO2 imaging and the second oxyphor was delivered intravitreally for tPO2 imaging. Phosphorescence images of the retinal vasculature and tissue were acquired consecutively at the same location. Phosphorescence lifetime was measured using a frequency-domain approach and converted to PO2 values to obtain depth-resolved vascular PO2 and tPO2 images. From vascular PO2 images, PO2 in retinal arteries (PO2A) and veins (PO2V) was measured and inner retinal oxygen extraction fraction (OEF) was derived. From tPO2 images, tPO2 depth profiles were generated at contiguous regions. Maximum outer retinal tPO2, minimum outer retinal tPO2, and mean inner retinal tPO2 were calculated from the tPO2 depth profiles.
Retinal PO2 and tPO2 images obtained at the same location were overlaid, displaying measurements in retinal arteries, veins and tissue. As expected, vascular PO2 images displayed higher PO2 in arteries than in veins. The tPO2 image showed higher values near the chorioretinal interface compared to more inner retinal locations and near arteries compared to veins. From compiled data in all rats, mean PO2A and PO2V were 43 ± 5 mmHg and 26 ± 4 mmHg, respectively (P < 0.001; N=7). Inner retinal OEF was 0.58 ± 0.12. Maximum outer retinal tPO2, minimum outer retinal tPO2, and mean inner retinal tPO2 were 33 ± 9 mm Hg, 22 ± 6 mm Hg and 23 ± 7 mm Hg, respectively.
A novel imaging method was reported and validated for integrated measurements of retinal vascular and tissue oxygenation, thus enabling a unified and comprehensive assessment of retinal oxygen regulation under physiologic and experimental pathologic conditions.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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