Abstract
Accurate, quantitative assessment of retinal blood oxygen saturation (sO2 ) may provide a useful early indicator of pathophysiology in several ocular diseases. Here, with visible-light optical coherence tomography (OCT), we demonstrate an automated spectroscopic retinal oximetry algorithm to measure the sO2 within the retinal arteries (A-sO2 ) and veins (V-sO2 ) in rats by automatically detecting the vascular posterior boundary on cross-sectional structural OCT. The algorithm was validated in vitro with flow phantoms and in vivo in rats by comparing the sO2 results, respectively, to those obtained using a blood gas analyzer and pulse oximetry. We also investigated the response of oxygen extraction (A-V sO2 ), including inter-session reproducibility, at different inhaled oxygen concentrations.
Highlights
Altered oxygen supply is thought to be a critical factor underlying many retinal disorders that may precede loss of visual acuity and observable changes in vascular morphology [1]
The SpO2 in other samples increased linearly between 60% and 100% with the volume proportion of fully oxygenated blood sample. sO2 measured by vis-optical coherence tomography (OCT) demonstrated very good agreement with the measured SpO2
4.3 Oxygen extraction at hyperoxia and normoxia To demonstrate the capability of the proposed method to evaluate oxygen saturation in vivo, we demonstrated the vascular sO2 response in vessels at different inhaled O2 concentrations in one representative eye [Fig. 6]
Summary
Altered oxygen supply is thought to be a critical factor underlying many retinal disorders that may precede loss of visual acuity and observable changes in vascular morphology [1]. Changes in retinal oxygen consumption could affect the blood oxygen saturation (sO2), which is the ratio of oxygenated hemoglobin to the total hemoglobin concentration in arteries and veins. Accurate quantification has been restricted by the two-dimensional nature of these technologies, which can neither distinguish blood vessels at different depths, nor separate hemoglobin absorption from other retinal pigments, such as melanin. Zhang et al developed photoacoustic microscopy (PAM), which uses multi-wavelength measurements to provide depth-resolved sO2 [4, 5]. This method, while more robust, requires an ultrasound detector in contact with the eyelid to collect the retinal thermoelastic expansion after laser excitation
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