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PK Jensen, T Eysteinsson, DB Pedersen, K Bang, J Beach, E Stefánsson; Non-Invasive Retinal Oxymetry in Normal Human Subjects . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4367.
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Purpose: Non-invasive retinal oxymetry in normal human subjects. Method: A fundus camera (Canon CR6-45NM) was equipped with a 4 wavelength image splitter (Optical Insights: 542, 558, 586, and 605 nm) connected to a digital cooled camera (SBIG ST-7E). Background corrected images were analysed in a computer using IPLab software. Optical density ratios of retinal vessels within each image were obtained for a set of isosbestic and non-isosbestic wavelengths. The ratios between 605nm and 586nm images were used to calculate the oxygen saturation in the depicted vessels. Reproducibility of results was tested by 4 repeated measurements in the same eye under constant conditions. Normal subjects were imaged in duplicate on 2 successive days. Each subject was given 100% oxygen breathing for 5 min and the saturation measured before, during and after oxygen breathing. In another session the effect of one drop of topical Trusopt given in one eye and the oxygen saturation measured before and 2 hours after application. Results: Four repeated measurements of hemoglobin oxygen saturation in human retinal venules gave 56.0 ± 0.75 % (mean±SD) and the arterio-venous difference was 38.5 ± 1.5 %. The oxygen saturation measurements were consistently elevated by 100% oxygen breathing and fell again after return to room air. In preliminary studies of 3 subjects of the optic disc (capillaries) the oxygen saturation increased 2.3 ± 0.4% (n=3, p<0.01, mean±SD) 2 hours following application of one drop of dorzolamide eye drop (Trusopt, Merck Inc.). Conclusion: The spectrophotometric oxymetry system is easy to use and provides reproducible results. It responds to 100% oxygen breathing as expected. This system may be useful in the study of ischemic diseases in the retina and optic nerve and the evaluation of drug and treatment effect. Preliminary results indicate that dorzolamide eye drops may elevate the oxygen saturation in the optic nerve.
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