Visible light optical coherence tomography angiography (vis-OCTA) facilitates local microvascular oximetry in the human retina

Abstract

We report herein the first visible light optical coherence tomography angiography (vis-OCTA) for human retinal imaging. Compared to the existing vis-OCT systems, we devised a spectrometer with a narrower bandwidth to increase the spectral power density for OCTA imaging, while retaining the major spectral contrast in the blood. We achieved a 100 kHz A-line rate, the fastest acquisition speed reported so far for human retinal vis-OCT. We rigorously optimized the imaging protocol such that a single acquisition took < 6 seconds with a field of view (FOV) of 3×7.8 mm2. The angiography enables accurate localization of microvasculature down to the capillary level and thus enables oximetry at vessels < 100 µm in diameter. We demonstrated microvascular hemoglobin oxygen saturation (sO2) at the feeding and draining vessels at the perifoveal region. The longitudinal repeatability was assessed by < 5% coefficient of variation (CV). The unique capabilities of our vis-OCTA system may allow studies on the role of microvascular oxygen in various retinal pathologies.

Advances in Retinal Oximetry

“…Pi et al 80 utilized vis-OCT angiography to assess oxygen saturation in the retinal capillary beds of rats in response to changes in the inspired concentration of oxygen. Song et al 81 performed microvascular oximetry of the capillary network in the foveal region of human volunteer subjects, finding that oxygen saturation was between the retinal arterioles and venules as expected. As vis-OCT expands into other fields such as OCT angiography, 82 several practical challenges are still being addressed before systems are implemented into clinical practice.…”

Adaptive spectroscopic visible-light optical coherence tomography for human retinal oximetry

“…We selected one vein (V1) and one artery (V2) with diameters of 168 µm and 120 µm, respectively. The four normalization methods are Method 1: no normalization, as reported by Yi et al (17), Chen et al (25), and Pi et al (22); Method 2: normalization by the RNFL, which is typically anterior to the retinal vessels, as reported by Song et al (26) and suggested by Chong et al (19, 20); Method 3: normalization by the anterior vessel wall (AW), which can be highly reflective and is immediately above the blood signal; and Method 4: normalization by the start of signal decay in the blood (z d ). We applied SDBG correction (28) for all four methods.…”

“…Both the sample-dependent and system-dependent SCs have magnified and more unpredictable influences on sO 2 measurement accuracy in human imaging than in small animal imaging because of the reduced light illumination power due to ocular laser safety and patient comfort, stronger eye motion, and larger variation in retinal anatomy (18, 19, 26, 32). In addition, it is more challenging to identify PWs of all human retinal vessels due to enlarged vessel diameters.…”

Balanced-detection visible-light optical coherence tomography

“…Recently, Song et al reported vis-OCT retinal imaging at an A-line rate of 100 kHz [19]; however, they limited the illumination bandwidth to 35 nm to increase power density, which degraded axial resolution to ~ 5 µm and did not solve the RIN problem.…”