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Jona Valgerdur Kristjansdottir, Sveinn Hakon Hardarson, Einar Stefansson; Retinal Oximetry with a Scanning Laser Ophthalmoscope compared to a Fundus Camera Oximeter. Invest. Ophthalmol. Vis. Sci. 2014;55(13):204.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate scanning laser ophthalmoscope (SLO) oximetry and compare to conventional fundus camera based retinal oximetry.
The two measurement devices were Optomap 200Tx, which is a scanning laser ophthalmoscope (Optos plc.) and Oxymap T1 (Oxymap ehf.), which is a fundus camera based retinal oximeter. Both cameras acquire images of the fundus at two different wavelengths. Oxymap T1 uses filtered white light at 570 and 600 nm; Optomap uses lasers at 532 and 633 nm. Oxymap Analyzer software analyzed the two spectral images and calculated hemoglobin oxygen saturation for retinal vessels. Oxymap Analyzer is designed for Oxymap T1 but was modified in order to work with Optomap. Retinal oximetry images were acquired of 24 subjects (age: 58±19 years, mean±SD) with various ocular conditions using both measurement devices. Oxymap T1 acquires 50° images while the Optomap was set to take 100° images. Retinal oxygen saturation was measured in the main superotemporal vessel pair.
Mean oxygen saturation measured with Oxymap T1 was 93%±7% (mean±SD) in arterioles and 55%±12% in venules. Oxygen saturation in the same eyes measured with Optomap was 98%±14% for arterioles and 68%±18% for venules. The figure shows Bland-Altman analysis for measurement of retinal arterioles and venules separately. Oxygen saturation measurements in venules were correlated between measurement devices (r=0.65, p=0.0006). Arterioles show no statistical correlation (r=0.25, p=0.25).
Optomap scanning laser ophthalmoscope measures on average higher oxygen saturation than Oxymap T1. Optomap has higher standard deviation which indicates greater measurement variability. The oxygen saturation measurements, of the two devices, do not compare perfectly. According to Bland-Altman analysis there is a bias for the measurement of both retinal arterioles and venules. Retinal oximetry with Optomap needs further improvement.
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