Global blood oxygen metabolism in human retina by dual-channel visible light optical cohenrence tomography

Abstract

Purpose : Measurement of retinal functions and their correlation with structural changes are important in understanding retinal physiopathology. Visible light optical coherence tomography (VIS-OCT) is an emerging technique that offers ultra-high axial resolution as well as microvascular oximetry. However, calculation of global blood oxygen metabolism in human retina also requires blood flow measurements at optic nerve head which is challenging for VIS-OCT. The purpose of this study is to test whether a dual-channel VIS-OCT device can provide both measurements, by combining a conventional near infrared OCT (NIR-OCT) channel simultaneously.

Methods : We developed a novel dual-channel VIS-OCT device that is capable of ultra-high depth resolution at 1.3 μm in water, and full-range imaging capability by reference modulation. The device used a fiber optics design cascading wavelength multiplexer divider (WDM) and optical fiber coupler to enable simultaneous NIR-OCT. We designed a scanning pattern where a series of dense circular B-scans (4096 Aline per B scan) were repeated with an increasing radius around the ONH, covering 0.8-2.5 mm radius around the optic nerve head (ONH). The dense circular scan can 1) enable Doppler OCT in the NIR OCT channel; and 2) allow the reference modulation in the VIS-OCT channel for full-range imaging; 3) enable blood oxygen saturation (sO₂) measurement within vessels. The simultaneous sO₂ and blood flow measurements enables the global oxygen metabolism calculation.

Results : The examples of circular circumpapillary scans in NIR-OCT and VIS-OCT channel are shown in Fig. 1, intersecting all major vessels at ONH. Figure 1a and 1b exemplify NIR-OCT and the corresponding phase contrast for Doppler OCT. We note that the NIR channel is preferable to VIS-OCT for blood flow measurement due to the better penetration through large vessel lumen. Fig. 1c demonstrates that circular full-range VIS-OCT easily covers the curvature of the parapapillary retina within the frame. The averaged sO₂ from arterioles and venules were 95±4% and 76±5% by using spectral analysis methods in VIS-OCT.

Conclusions : The new dual-channel VIS-OCT device with simultaneous NIR-OCT imaging and extended imaging range uniquely allows global oxygen metabolism measurements.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Example image of circumpapillary NIR-OCT, Doppler OCT, and VIS-OCT by the same dual-channel device.