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Nimesh Bhikhu Patel, Louvenia Carter-Dawson, Ronald S Harwerth; Optical Coherence Tomography RNFL Contrast in Experimental Glaucoma Eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4026. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Circumpapillary retinal nerve fiber layer (RNFL) thickness measures using optical coherence tomography (OCT) provides important information for evaluation of the optic nerve. In glaucoma, with advancing disease the RNFL becomes harder to segment because of a decrease in its reflectance. The purpose of this study was to investigate the relationship between RNFL thickness and layer contrast in an experimental model of glaucoma.
Unilateral argon laser application to the trabecular meshwork was used to elevate the IOP in ten monkeys that were followed longitudinally with OCT. RNFL thickness was derived from elliptical scan paths 550µm from the Bruch’s membrane opening. The RNFL was manually segmented, and major retinal vasculature subtracted from thickness measures. RNFL contrast was quantified using the pixel intensity of the RNFL and the underlying retina up to the RPE. In four post mortem eyes, neural and glial contributions to the RNFL were estimated using immunohistochemistry. Axons were labeled with neurofilament (NF), and glial cells were labeled using glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and antibodies to ionized calcium binding adaptor molecule 1 (IBA-1). The tissue was imaged using confocal microscopy to determine the ratio of neural to non-neural components in the RNFL.
A total of 208 OCT RNFL scans from ten subjects were analyzed. Each b-scan from which elliptical scans were interpolated had a quality of 25dB or greater. There was a linear decrease in RNFL contrast with thickness (RNFL contrast = 0.07 +0.0026xRNFL, R2 = 0.69, p<0.01). In the four post mortem eyes, the glial proportion to the RNFL was negatively related to the RNFL thickness (Glial = 0.89 – 0.005xRNFL, p<0.01).
In experimental glaucoma there is a decrease in RNFL contrast with axonal loss. It is likely that RNFL contrast reflects the tissue makeup, with relative glial contribution increasing with retinal ganglion cell axonal loss. Although an increase in IBA-1 labeling was noted in experimental eyes, this study could not determine a change in the number of glial cells with advancing loss.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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