Advances in Retinal Oximetry

Abstract

Similar to other organs, the retina relies on tightly regulated perfusion and oxygenation. Previous studies have demonstrated that retinal blood flow is affected in a variety of eye and systemic diseases, including diabetic retinopathy, age-related macular degeneration, and glaucoma. Although measurement of peripheral oxygen saturation has become a standard clinical measurement through the development of pulse oximetry, developing a noninvasive technique to measure retinal oxygen saturation has proven challenging, and retinal oximetry technology currently remains inadequate for reliable clinical use. Here, we review current strategies and approaches, as well as several newer technologies in development, and discuss the future of retinal oximetry.

Figure 1.

Light absorbance coefficients for oxyhemoglobin (red line) and deoxyhemoglobin (blue line) at the isosbestic (570 nm) and non-isosbestic (600 nm) operating wavelengths for the Oxymap T1 system. Reproduced with permission from Eliasdottir. © 2018 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd, based on data from Zijlstra et al.

Figure 2.

Fundus images registered by Oxymap T1. (A) Color-coded oximetry vessel map generated using split captures at the (B) isosbestic (570 nm) and (C) non-isosbestic (600 nm) wavelengths. Arterioles appear in red–orange hues and correspond to O₂ saturation levels of 90% to 100%; venules are colored in blue–green, representing oxygenation in the range of 25% to 50%. Images were provided by Oxymap.

Figure 3.

Primary absorbance wavelengths of different endogenous contrast agents demonstrating that the study of hemoglobin using photoacoustic ophthalmoscopy is possible due to its predominant optical absorption compared to other elements, such as water and lipids, in the visible spectral range (380–740 nm). Reproduced with permission from Yao and Wang. © 2012 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 4.

(A) Coefficients of oxygenated (HbO₂) and deoxygenated (Hb) hemoglobin in logarithmic scale demonstrate the higher extinction coefficients in the visible range responsible for enhanced image quality for the assessment of retinal oximetry. Reproduced from Pi et al. © 2018 The Optical Society under the terms of the OSA Open Access Publishing Agreement (B) Prototype of visual light optical coherence platform. Reproduced from Chong et al. © 2016 The Optical Society.

Figure 5.

Color-coded oximetry maps using hyperspectral imaging technology display different patterns for comparison in a healthy subject (upper row) and a subject with BRAO (lower row). In this subject with BRAO, lower oxygen saturation is observed in the inferotemporal territory of the retina. Reproduced with permission from Mordant et al. © 2011 Macmillan Publishers Limited.