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Sveinn Hakon Hardarson, Olof Birna Olafsdottir, Thorunn S Eliasdottir, Robert A Karlsson, Thor Eysteinsson, Einar Stefansson; Oximetry in Retinal Arterioles. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4658. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Several studies have found changes in oxygen saturation in retinal arterioles. An increase in retinal arteriolar saturation may be due to increased blood flow and less loss of oxygen through arteriolar walls from per unit volume of blood. This explanation is, however, unlikely in the case of central retinal vein occlusion, where blood flow is reduced but arteriolar saturation has been found to be normal or high. Possible measurement error due to specular reflex must also be considered.In this study, oxygen saturation in retinal arterioles was measured with a new analysis method to help determine if differences in arteriolar saturation are physiological or methodological in nature.
Measurements were made on 14 patients with central retinal vein occlusion, 14 patients with proliferative diabetic retinopathy and 14 healthy controls. Images were taken with the Oxymap T1 retinal oximeter. Average oxygen saturation was calculated for retinal arterioles in an area around the optic disc with the Oxymap Analyzer 3.0 software (ver. 102310). The software uses all points on the vessel cross-section. Correction for the effect of vessel diameter is implemented. Additionally, a more detailed measurement was made of a small segment in healthy arterioles and venules to compare saturation measurements at the central reflex and to the side of the reflex (figure).
The table shows mean oxygen saturation in the major retinal arterioles.In healthy individuals, saturation in the center of an arteriolar segment was 100.5%±6.6% compared to 95.1%±5.1% to the side of the central reflex (p=0.0002). In venules, this difference was reversed: 50.7%±11.0% in the center of the vessel and 64.7% to the side of the reflex.
Oxygen saturation, measured with a new analysis method, is not decreased in retinal arterioles in central retinal vein occlusion, compared to the fellow eye. Oxygen saturation is higher in retinal arterioles in patients with proliferative diabetic retinopathy than in healthy controls. These results are consistent with results obtained with previous measurement methods.Differences in saturation within a vessel segment are consistent with diffusion of oxygen out of retinal arterioles and into retinal venules. Further studies are needed on possible bias in measurements due to central reflex from vessels.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure. Measurement at the center of a vessel (blue) and to the side of the central reflex (red).
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