Method comparison of two non-invasive dual-wavelength spectrophotometric retinal oximeters in healthy young subjects during normoxia

Abstract

Purpose: Spectrophotometric retinal oximetry is a non-invasive technology for measuring oxygen saturation in arterioles and venules (SaO2, SvO2). We compared two commercially available systems: the Oxymap T1 (Oxymap ehf., Reykjavik, Iceland) and the Dynamic Vessel Analyzer (DVA, Imedos, Jena, Germany). Methods: Twenty healthy adults were included after giving informed consent. Two measurement cycles 30 min apart, including Oxymap T1, DVA, arterialized capillary blood draw of the earlobe (ScO2) and peripheral oxygen saturation using finger pulse oximetry (SpO2) were scheduled. Results: SaO2 (p > 0.0004) but not SvO2 (p < 0.05) was statistically significantly different between the retinal oximeters used. Agreement between devices using repeated SO2 measurements resulted in a standard deviation (SD) of differences of 3.5% in retinal arterioles and 4.8% in venules. Bland–Altman plot using the mean of a participant's two measurements from each device showed an average mean difference of 4.4% (95% confidence limits of agreement: −8.6 to 17.4) and −3.3% (95% confidence limits of agreement: −28.8 to 22.2) for SaO2 and SvO2, respectively. Comparison of mean SaO2 and SvO2 with mean ScO2 and SpO2 indicated that SO2 measurements were generally higher in ScO2 and SpO2. Conclusion: This study shows very good repeatability for both devices, which is consistent with the literature. However, it does not show sufficient concordance between SaO2 measurements from both devices, indicating that patients should be followed by one device only. Differences in absorbance wavelengths used and image post-processing may explain the differences.