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01.03.2012 | Basic Science | Ausgabe 3/2012

Graefe's Archive for Clinical and Experimental Ophthalmology 3/2012

Oxygen tension and gradient measurements in the retinal microvasculature of rats

Zeitschrift:
Graefe's Archive for Clinical and Experimental Ophthalmology > Ausgabe 3/2012
Autoren:
Pang-yu Teng, Norman P. Blair, Justin Wanek, Mahnaz Shahidi
Wichtige Hinweise
This study was supported by the National Eye Institute, Bethesda, MD, USA: EY17918 (MS) and EY01792 (UIC); and Research to Prevent Blindness, New York, NY, USA: senior scientific investigator award (MS) and an unrestricted departmental award.
All authors have full control of all primary data, and agree to allow Graefe’s Archive for Clinical and Experimental Ophthalmology to review this data upon request.

Abstract

Background

Oxygen delivery from the retinal vasculature plays a crucial role in maintaining normal retinal metabolic function. Therefore, measurements of retinal vascular oxygen tension (PO2) and PO2 longitudinal gradients (gPO2) along retinal blood vessels may help gain fundamental knowledge of retinal physiology and pathological processes.

Methods

Three-dimensional retinal vascular PO2 maps were generated in rats by optical section phosphorescence lifetime imaging. A major retinal artery and vein pair, and a smaller blood vessel (microvessel) between them were segmented, and PO2 along each blood vessel was measured. In each blood vessel, an average PO2 (mPO2) was calculated, and gPO2 was determined by linear regression analysis. Reproducibility of measurements was assessed by calculating intraclass correlation coefficient (ICC) of repeated measurements. The correlations of mPO2 and gPO2 measurements with systemic arterial oxygen tension (PaO2) and carbon dioxide tension (PaCO2) was determined.

Results

Measurements of mPO2 and gPO2 in retinal arteries, microvessels and veins were reproducible (ICC > 0.86; p < 0.01; N = 8), except for retinal arterial gPO2. Retinal arterial, microvessel and venous mPO2 were 41 ± 8, 32 ± 8 and 25 ± 7 mmHg, respectively (mean ± SD; N = 27). Retinal arterial mPO2 was correlated with PaO2 and PaCO2 (R > 0.44; p < 0.03), while retinal microvessel and venous mPO2 were only correlated with PaCO2 (R > 0.68; p < 0.01). Retinal microvessel gPO2 (−3.8 ± 1.5 mmHg/100 μm) was significantly steeper (more negative) than venous gPO2 (0.02 ± 0.43 mmHg/100 μm) (p < 0.01; N = 27), and neither were significantly correlated with PaO2 or PaCO2.

Conclusions

Quantitative measurement of mPO2 and gPO2 in the retinal microvasculature was demonstrated. A significant decrease in PO2 was observed along most retinal microvessels, indicative of substantial oxygen extraction by the retinal tissue. This method has the potential to help elucidate retinal microvascular oxygen transport in health and disease.

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