Spectral calibration techniques for clinical retinal oximetry with visible-light optical coherence tomography

Abstract

Purpose : Oxygen concentration in retinal blood vessels (sO₂) can be critical biomarkers for diabetic retinopathy and glaucoma, leading causes of blindness worldwide. We previously demonstrated sO₂ measurements in rodent and human retinas with spectroscopic visible-light optical coherence tomography (vis-OCT). However, reliable measurements of sO₂ in a clinical setting remains an open challenge due to constraints on light exposure, imaging time, patient motion, and variation in eye geometry. Spectral calibration to optimize sO₂ measurements under these non-ideal imaging conditions is needed. Here, we investigate, develop, and implement such calibration.

Methods : We developed vis-OCT processing software to optimize sO₂ measurements in humans. First, we identified an optimal spectral range for spectral measurement in which sO₂ was most stable. Next, we developed methods to account for alterations induced by the imaging system and eye optics. Specifically, we accounted for depth-dependent variations in the measured spectrum, such as absorption contrast, spectrally-dependent roll-off, chromatic aberrations, and eye morphology. We then imaged the retinas of 12 healthy subjects aged 22 to 60 at Northwestern Medical Hospital in Chicago, IL, and Langone Medical Center in New York, NY. All imaging was approved by the respective IRBs and strictly adhered to the Declaration of Helsinki. Light exposure in the eye was no higher than 250 μW and imaging time was no longer than 5 s. We extracted sO₂ from vessels larger than 50 μm in diameter using an automated version of our vis-OCT processing software.

Results : We measured the sO₂ in 89 vessels (53 arteries and 36 veins). We found the mean sO₂ in arteries was 97.70 +/- 4.75 % in arteries and mean sO₂ in veins was 53.11 +/- 6.85 %.

Conclusions : We developed analytical methods for depth-dependent alterations to the measured spectrum in vis-OCT retinal oximetry. Our measurements yielded spectra that are highly consistent with those reported in literature, despite variations in imaging conditions. Our results indicate a clear path forward for clinical adoption of vis-OCT.

This is a 2020 ARVO Annual Meeting abstract.

 

(a) B-scan ~ 3mm inferior to optic disk showing vessels (V – vein, A – artery); (b) Measured and fitted spectra from labeled vein; (c) Measured and fitted spectra from labeled artery.