Progress on measurements and interpretation of Optoretinograms (ORG) in mice.

Abstract

Purpose : To present recent advancements in measurements, interpretation, and modeling of the light-evoked functional retinal imaging with Optical Coherence Tomography. To endorse use of the term Optoretinogram (ORG).

Methods : Albino (Balb/c) mice were imaged in vivo with a custom Scanning Light Ophthalmoscopy / Optical Coherence Tomography (SLO/OCT) retinal imaging system. Before the ORG experiments, mice were dark-adapted for over 6 hours. In addition to our standard OCT intensity-based ORG analysis (time-dependent changes of the depth scattering profiles of retinal layers), we have also extracted phase-based ORG signals (time-dependent changes of the phase difference (path length) between retinal layers) from the same data sets. To test the impact of retinal water homeostasis on the light-evoked retinal response, we have induced a mild, diffuse central retinal edema by intraperitoneal (IP) injection of distilled water.

Results : The depth scattering ORG profiles extracted from the OCT data reveal correlations between depth positions and intensity of different outer 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 comparison between ORG responses during mild, diffuse central retinal edema and the normal retina without water injection shows several differences in the kinetics of the retina layers swelling and OCT scattering, suggesting that water movements play an important role in standard light-evoked PRC-NVU functional response. These results also indicate that ORG could be used to assess alterations in retinal water homeostasis

Conclusions : Successful implementation of phase-based ORG signal analysis in mice provided higher sensitivity for detecting changes in retina layer positions, what should potentially allow separation of Cone and Rod based ORGs in mice. Changes in the ORG signals caused by a mild, diffuse central retinal edema further confirmed the water movement between different compartments of the outer retina as the origin of measured ORGs. The use of “ORG” term draws an instructive parallel to the ERG (electroretinogram), which has long been used to assess retinal function in vivo. Specifically, the ORG, like the ERG, comprises multiple components arising from distinct cells and mechanisms.

This is a 2021 ARVO Annual Meeting abstract.