Measuring oxygen saturation in retinal and choroidal circulations in rats using visible light optical coherence tomography angiography

Visible light optical coherence tomography (vis-OCT) has demonstrated its capability of measuring vascular oxygen saturation (sO₂) in vivo. Enhanced by OCT angiography, the signal from microvasculature can be further isolated and directly used for sO₂ extraction. In this work, we extended the theoretical formulation for OCT angiography-based oximetry by incorporating the contribution from motion contrast enhancement. We presented a new method to eliminate the associated confounding variables due to blood flow. First, we performed in vitro experiments to verify our theory, showing a stable spectral derivative within the selected wavelength bands for sO₂ extraction. Then, we tested our method in vivo to measure retinal sO₂ in rats inhaling different gas mixtures: normal air, 5% CO₂, pure O₂, and 10% O₂. Absolute sO₂ values in major arterioles and venules in the retinal circulation can be accurately measured. In addition, we demonstrated the relative changes of sO₂ can be measured non-invasively from choriocapillaris immediately underneath the retinal pigmented epithelium (RPE) in rodents.