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Brad Fortune, Juan Reynaud, Christy Hardin, Hongli Yang, Lin Wang, Ian A Sigal, Claude F Burgoyne; Thinning of optic nerve head (ONH) neural rim tissue exceeds peripapillary retinal nerve fiber layer (RNFL) thinning in experimental glaucoma (EG). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3982.
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© ARVO (1962-2015); The Authors (2016-present)
To test the hypothesis that glaucomatous ONH deformation results in greater thinning of the ONH neural rim tissue than the peripapillary RNFL.
Longitudinal imaging of the ONH and peripapillary RNFL was performed every other week by SDOCT (Spectralis) under manometric IOP control (10 mmHg) in 35 non-human primates (NHP, 27F/8M, mean age ± SD: 11 ± 6.8 years) during baseline (5.0 ± 1.4 sessions) and after induction of unilateral EG by trabecular meshwork laser. ONH parameters minimum rim width (MRW) and minimum rim area (MRA) were derived from SDOCT scans consisting of 80 radial B-scans centered on the ONH by determining the minimum distance between each Bruch’s membrane opening (BMO) point and the surface segmentation. RNFL thickness was derived from a peripapillary circular B-scan with 12 deg diameter; and multiplied by scan circumference to obtain RNFL cross-sectional area (RNFLA). All transverse dimensions were based on a visual angle of 248 µm/deg for the rhesus eye. Change from baseline to the final available session was compared for RNFLA versus MRA under the null hypothesis that axon loss alone would affect each parameter identically.
At the final imaging session (10.1 ± 7.7 months after first laser), there was no difference from baseline in control eyes for MRW (p=0.94), MRA (p=0.89) or RNFLA (p=0.95). In EG eyes, MRW decreased from 287 ± 48 µm at baseline to 177 ± 64 at the final session (38 ± 21% loss, p<0.0001), MRA decreased from 0.987 ± 0.17 mm2 to 0.622 ± 0.21 mm2 (37 ± 20% loss, p<0.0001), and RNFLA decreased from 0.943 ± 0.09 mm2 to 0.736 ± 0.19 mm2 (19 ± 19% loss, p<0.0001). MRA reduction was significantly greater than RNFLA reduction (p<0.0001, Figs1,2). BMO area did not change from baseline in control or EG eyes (p=0.73, p=0.82, respectively), but there was a tendency for BMO plane error to increase in EG eyes. MRA angle did not change from baseline in control eyes (p=0.29) but decreased in EG eyes from 45 ± 6.6 deg to 40 ± 7.8 deg (p=0.0001, i.e. toward the BMO plane). In examples of severe deformation, remaining rim tissue consisted of inner retina, not axon bundles, suggesting stretch.
ONH neural rim tissue thinning exceeds peripapillary RNFL thinning in NHP EG. These results support the hypothesis that axon bundles are compressed and/or stretched within the ONH rim by glaucomatous deformation.
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