Retinal Vessel Oxygen Saturation Measurement Protocols and Their Agreement

Abstract

To assess agreement between different image sizes and analysis protocols for determination of retinal vessel oxygen saturation in the peripapillary retina of healthy individuals. Methods: Retinal oximetry measurements were acquired from 87 healthy volunteers using the IMEDOS Systems oxygen module. The peripapillary retinal vessels were assessed in a concentric annulus around the optic nerve head. Single and average vessel comparisons were made at different image field sizes of 30°and 50°. Comparisons between images obtained at 30°and 50°were made in a subset of 47 of the 87 individuals. Results: All subjects were normotensive and had normal intraocular pressures (9-16 mm Hg). Analyses of agreement between single vessel, averaged vessel, and between different size images were sought by Bland-Altman analyses, of which all yielded a low bias (<1% oxygen saturation). However, agreement between single vessels of consecutive images showed increased limits of agreement compared with saturation values calculated by averaging all or just the four major arcades of one image. Agreement between 30°and 50°images showed a similar bias as when comparing data obtained with the same camera angle setting but exhibited larger confidence intervals (arteries: bias = 0.21% [9.04/-8.62]%; veins: bias = 0.71% [14.82/-13.40]%). Conclusions: Averaging methods yielded the best agreement; there was little difference in average arterial and venous oxygen saturation between protocols, which analyze all vessels versus the four largest vessels. The least agreement was found for single vessel measurements and comparisons between different camera angles. Translational Relevance: Standardization of image capture protocols (same image size and undertaking a vessel averaging approach for oxygenation analysis) will enhance the detection of smaller physiological changes in eye disease.

Retinal Oxygen Delivery and Extraction in Ophthalmologically Healthy Subjects With Different Blood Pressure Status

“…We selected the largest artery and vein of each quadrant (superotemporal [ST], inferotemporal [IT], superonasal [SN], inferonasal [IN]) and ignored smaller vessels, because this approach has been found to minimally affect estimations. 35 To minimize O 2 diffusion losses, measurements were taken close to the border of the optic disc, according to a previously described, semiautomatic protocol. 34 In short, the path of minimal intensity (thus, avoiding the vessel light reflex) between the starting point of the vessel and the first major branching was automatically traced.…”

Oxygen saturation in retinal vessels and their correlation with endothelial microparticles in diabetes mellitus and/or cardiovascular disease

“…Once pupils were fully dilated, three images were obtained per patient with the camera angle set at 30° and the optic nerve head (ONH) centred [19]. Oxygen saturation measurements were performed using the "oxygen tool" and VesselMap software (Version 2, Imedos Systems, Imedos GmbH, Jena, Germany) as described elsewhere [20].…”

“…Oxygen saturations were obtained of all major retinal arteries and veins crossing the measurement annulus. Following this process average arterial and venous vessel saturation for the entire measurement annulus were calculated using the software's "multi-measurement tool" (Visualis software,Imedos Systems, Jena, Germany) [19]. The multi-measurement tool allows for automatic image registration and analysis of several images.…”

“…The multi-measurement tool allows for automatic image registration and analysis of several images. This allowed us to measure the same retinal arteries and veins of three images to calculate averages across images and vessel (separately for arteries and veins) [19]. Finally, we calculated arterial minus venous retinal vessel saturation (A-V SO2) which is thought to be an indirect marker of relative retinal oxygen metabolism and is independent of retinal blood flow velocity [4,21].…”

Retinal oxygen delivery and extraction in ophthalmologically healthy subjects with different blood pressure status

“…We selected the largest artery and ) and ignored smaller vessels, since this approach has been found to minimally affect estimations. 35 To minimize O2 diffusion losses, measurements were taken close to the border of the optic disc, according to a previously described, semi-automatic protocol. 34 In short, the path of minimal intensity (thus, avoiding the vessel light reflex) between the starting point of the vessel and the first major branching was automatically traced.…”