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E. Stefansson, G.M. Zoega, G.H. Halldorsson, R.A. Karlsson, T. Eysteinsson, J.A. Benediktsson; Spectrophotometric retinal oximetry of retinal arterioles and venules. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2588.
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Purpose: Spectrophotometric oxymetry evaluates the relative oxygen saturation of hemoglobin in retinal blood vessels. We measure the optical density ratios (605/586 nm, 605/542 nm) of reflected light in retinal blood vessels. ODR correlates with the level of oxyhemoglobin in blood (Beach et al. J Appl. Physiolo. 1999). We analyse the reproducibility and sensitivity of this method and the response of the retinal hemoglobin saturation to oxygen breathing and glaucoma drug application. Methods: A fundus camera (Canon CR 6–45NM) with an image splitter (Optical Insights) with 542, 558, 586 and 605 nm filters was used. A digital cool camera (SBIG ST–7E) captured four eight bit images (600x500 pixels) and the images were analysed with our computer program. Optical density within and outside of vessels was measured and ODRs calculated. For sensitivity we analysed arterioles and venules from one eye of seven individuals. The effect of breathing 100% oxygen was analysed and the effect of single and repeated applications of dorzolamide eye drops. For reproducibility we analysed the same image five times and five consequtive images. A Mann–Whitney test was used for statistical calculations (GraphPad Prism 4). Results: Sensitivity: The mean ODR605/586 for venules is 0.4553±0.1256 (mean±SD) and 0.2344±0.1571 for arterioles. The mean ODR605/542 for venules is 0.4925±0.1413 (mean±SD) and 0.2614±0.1381 for arterioles. The difference between arterioles and venules is statistically significant (p<0.0001). Reproducibility: Five repeated measurements of the same image gave the SD of the mean as 5% to 11% of the mean values for venules and 12% to 29% for arterioles. When five consequtive images from seven individuals are analysed the average SD of the mean ODR's ranges from 15% to 57%. Conclusions: The difference between ODR's for arterioles and venules demonstrates the technique's sensitivity. This technique detects a difference in the level of oxyhemoglobin in venules and arterioles of the retina. View OriginalDownload SlideView OriginalDownload Slide
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