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Anthony Felder, Justin Wanek, Norman P Blair, Mahnaz Shahidi; Quantitative volumetric analysis of retinal tissue oxygen tension. Invest. Ophthalmol. Vis. Sci. 2017;58(8):682.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal function is sustained by oxygen delivered from dual circulatory systems, the contributions of which create complex oxygen gradients through the retinal depth. Localized regions of inadequate oxygenation occur in several retinal diseases, including diabetic retinopathy and vascular occlusions. Previous studies assessed retinal oxygenation in limited spatial dimensions, which precluded the detection of disseminated pathologies. Therefore, techniques that volumetrically assess retinal oxygenation are necessary to understand retinal physiology in health and disease. We report a method for the 3D imaging of retinal tissue oxygen tension (tPO2) and the 2D mapping of outer retinal oxygen consumption (QO2) in rats.
Phosphorescence lifetime imaging was performed in male Long Evans pigmented rats under systemic normoxia (N=6) and hypoxia (N=3), one day after intravitreal injection of an oxyphor. A vertical laser line was horizontally scanned across the retina and a series of depth-resolved phosphorescence optical section images were acquired. An automated customized software algorithm constructed phase-delayed phosphorescence volumes, determined the phosphorescence lifetime at each voxel, and generated a 3D retinal tPO2 volume. The volumetric data was fitted using an oxygen diffusion model to map QO2 in 2D. The effects of systemic condition (normoxia, hypoxia) and retinal depth on mean tPO2 (MtPO2) and the spatial variation of tPO2 (SVtPO2), measured as SD, were determined by mixed linear model. Mean QO2 (MQO2) and spatial variation of QO2 (SVQO2) were compared between normoxia and hypoxia by unpaired t-tests.
3D retinal tPO2 volumes were approximately 500x500x200μm (horizontal x vertical x depth). MtPO2 measured at the chorioretinal interface was significantly correlated with systemic arterial PO2 (P=0.007; N=9). There were significant effects of both systemic condition and retinal depth on MtPO2 and SVtPO2, such that both were lower under hypoxia than normoxia and higher in the outer retina than inner retina (P<0.001). No statistically significant difference was found in MQO2 or SVQO2 between normoxia and hypoxia (P≥0.16).
For the first time, 3D imaging of retinal tPO2 and 2D mapping of outer retinal QO2 were demonstrated, with potential for the assessment of disseminated physiological alterations in animal models of retinal diseases.
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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