In vivo evaluation of Retinal Ganglion Cells (RGCs) in mice using Temporal Speckle Averaging Optical Coherence Tomography (TSA- OCT).

Abstract

Purpose : To present the results of in vivo visualization and quantification of Retinal Ganglion Cells (RGCs) in mice using Temporal Speckle Averaging Optical Coherence Tomography (TSA- OCT).

Methods : We used a custom-built mouse retinal Scanning Laser Ophthalmoscopy / Optical Coherence Tomography (SLO/OCT) system to acquire non-invasive serial OCT volumes with corresponding SLO intensity and fluorescence data to provide input for Temporal Speckle Averaging (TSA) OCT volume processing. The TSA-OCT processing allows reduction of the speckle contrast and enhancement of the cellular retinal morphology probed by OCT. To showcase the performance of this technique, two mouse lines with fluorescently labeled RGC (based on RGCs transcription factor Brn3b-mCherry and Isl2-GFP) were used.

Results : TSA-OCT greatly enhanced the image quality of the Retinal Nerve Fiber Layer (RNFL) and enabled RGCs visualization (see Figure). While a single OCT volume doesn’t allow visualization of RGC, the application of TSA-OCT opens the possibility of non-invasive probing of RGCs. Use of mice with fluorescently labeled RGCs allowed mapping of RGC position using a fluorescent SLO system, providing direct comparison with RGC somas visualized by TSA-OCT. Additionally fluorescent labeling of the RGC helped with further validation of TSA-OCT imaging by histology providing one-to-one mapping between in vivo and ex vivo images of RGC.

Conclusions : In these studies, we used a novel TSA-OCT to visualize mouse RGCs in vivo. We did not need Adaptive Optics, suggesting that speckle contrast rather than insufficient lateral resolution is a limiting factor in using OCT for non-invasive in vivo [SJK1] evaluation of cellular retinal morphology in mice. Our ability to visualize and follow RGCs in vivo using non-invasive imaging method should allow a reduction in the number of animals needed in future studies. These results open doors for efficient in vivo monitoring of cellular morphology in animal models of glaucoma during disease progression and therapeutic innervation.

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

 

Figure 1. In vivo imaging of mouse retina using OCT. TSA-OCT greatly enhances the image quality of RNFL and enables RGCs visualization.