Progress on measurements and interpretation of the optoretinograms (ORG) in mice: implementation of Full Field Swept Source Optical Coherence Tomography (FF-SS-OCT)

Abstract

Purpose : To give an update on our recent progress in measurements and interpretation of the optoretinograms (ORGs) i.e., detection of light-evoked functional retinal responses using Optical Coherence Tomography. To present the design and implementation of mouse retinal Full Field Swept Source Optical Coherence Tomography (FF-SS-OCT) system for high-speed measurements of mouse retinal ORGs.

Methods : Albino mice were imaged in vivo with a custom mouse retinal FF-SS-OCT employed with a light stimulation channel to allow measurements of high-speed mouse retinal ORGs. For comparison, the same mice were evaluated using our standard ORG probing setup using Scanning Light Ophthalmoscopy / Optical Coherence Tomography (SLO/OCT) retinal imaging system. Before the ORG experiments, mice were dark-adapted. Both intensity-based ORG analysis (time-dependent changes of the depth scattering profiles of retinal layers), and phase-based ORG analysis (time-dependent changes of the phase difference (path length) between retinal layers) have been extracted from the ORG data sets.

Results : The depth scattering ORG profiles extracted using the SLO/OCT system and FF-SS-OCT reveal similar correlations between depth positions and intensity of different retina bands. The phase-based ORG signals extracted from the same data sets, although more sensitive to retina motion and more computationally demanding, provided an order of magnitude higher sensitivity of detecting changes in retina layer positions. The application of FF-SS-OCT system allowed observation of the fast ORG responses in mouse retina with much higher precision if compared to the ORGs extracted using raster scanning SLO/OCT retinal imaging system.

Conclusions : Successful implementation of phase-based ORG signal analysis in mice for data acquired with the SLO/OCT system and FF-SS-OCT allowed direct comparison of the results. Implementation of FF-SS-OCT for extraction of ORG signals opens the possibility of future studies of the fast ORG response in mice, potentially allowing separation of Cone and Rod-based ORGs and direct correlation of the ORGs with the ERGs (electroretinograms). However, slow ORG signals connected with light-evoked water movements between different compartments of the retina can still be more efficiently studied with our standard raster scanning SLO/OCT retinal imaging system.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.