Progress on a full-field swept-source optical coherence tomography (FF-SS-OCT) system for mouse optoretinography (ORG)

Abstract

Purpose : To 1) report the progress on instrumentation and protocol for acquiring optoretinograms (ORGs), i.e. detection of light-evoked functional retinal responses from a mouse retina using a high volume rate full-field swept-source optical coherence tomography (FF-SS-OCT) system; and 2) to compare intensity and phase-based ORGs from mouse retina measured with FF-SS-OCT.

Methods : A FF-SS-OCT system was built by incorporating a swept source with a sweep rate up to 2000 sweeps/s and a high-speed camera having a maximum frame rate of 1 MHz, enabling the acquisition of up to 2000 OCT volumes per second. The system incorporated a visible stimulus channel capable of single and multiple flashes (flicker). The system was designed for optoretinography in the mouse eye. Numerous parameters in the optical, electronic, and software design were studied. Measurements were taken from model and living mouse eyes. In mouse data, both amplitude- and phased-based ORG analysis (stimulus-evoked, time-dependent changes in amplitude and phase of light reflected from the retina) were performed.

Results : Key aspects of the system design were established, i.e., the choice of lenses, optimization for the mouse’s high numerical aperture, balancing tradeoffs between volume rate, SNR, and axial resolution, correction of vibration-induced chirp, and rejection of ghost and back reflections intrinsic to full-field imaging. The phase-based ORG signals allowed detection of the transient responses of the retinal layers to stimuli with much higher precision than amplitude-based ORGs.

Conclusions : FF-SS-OCT is a viable means for acquiring retinal OCT volumetric data at kilohertz rates, making it a good candidate for ORG measurements. While full-field imaging of the mouse eye presents a number of novel challenges, these can be addressed through optical design and signal processing. The phase-based ORG provides higher sensitivity to microscopic movements of tissue, suggesting that it is a better tool for studying mouse models of retinal disease. Future plans include separation of rod and cone ORGs and parallel acquisition of electroretinograms.

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