Spectral Domain Optical Coherence Tomography as a Measure of Axonal Degeneration and Protection in Experimental Autoimmune Encephalomyelitis

Abstract

Purpose: Spectral-domain optical coherence tomography (SD-OCT) is a potential outcome measure for trials of novel neuroprotective therapies to treat diseases such as multiple sclerosis (MS). Using SD-OCT, a number of studies have shown thinning of the retinal nerve fiber layer (RNFL) in MS subjects with and without a history of acute optic neuritis (AON). In-depth studies testing the feasibility of using SD-OCT to measure and quantify RNFL thinning and correlate these findings to axonal damage in animal models are lacking. C57BL/6 mice with experimental autoimmune encephalomyelitis (EAE), a murine model of MS, display AON. We tested the feasibility of measuring RNFL thinning in C57BL/6 mice with AON, and correlated RNFL thickness with axonal loss and inflammation.

Methods: EAE was induced in female C57BL/6 mice as previously described. SD-OCT images were acquired following induction of EAE. Mice (n=8 per time point) were imaged at 15, 20, 30, 60, and 90 days after induction and compared to a sex and age matched naïve group (n=4). Each mouse was imaged using a Bioptigen Envisu R2200-HR SD-OCT device. Annular scans of 1.0 mm were obtained while centered on the optic nerve. Another group of mice was imaged 147 days after induction (n=4) and was compared to a matched naïve group (n=4). The mice were euthanized by perfusion with 4% paraformaldehyde, and the optic nerves were examined for axonal damage and inflammation. For segmentation analysis, RNFL and total retinal (TR) thicknesses were measured as described in a previous publication.

Results: EAE was induced in a cohort of female mice and these mice displayed AON in one or both optic nerves as defined by the presence of inflammatory cells and showed up to a 76% loss of optic nerve axons (range 0-76%; mean 29.4%). No significant change in either TR or RNFL thickness was detected in either the naïve control group or the EAE group. In some instances, one optic nerve displayed greater axonal damage and inflammation than the other.

Conclusions: RNFL thinning was not detected in EAE mice within 5 months post induction of EAE. The lack of thinning may result from an inadequate amount of time to observe the retrograde axonal degeneration of ganglion cells or, alternatively, SD-OCT imaging may not be sensitive enough to detect small changes in thickness during the time frame tested.

Keywords: 551 imaging/image analysis: non-clinical • 610 nerve fiber layer