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B. Fortune, G. Cull, C. F. Burgoyne; Retinal Nerve Fiber Layer (RNFL) Thickness and Retardance at the Onset of Optic Nerve Head (ONH) Surface Topography Change in Experimental Glaucoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4920.
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© ARVO (1962-2015); The Authors (2016-present)
To compare peripapillary RNFL thickness (RNFLT) and retardance at the onset of ONH surface topography change in a non-human primate (NHP) model of experimental glaucoma.
Twelve NHPs had 3 or more weekly baseline measurements of ONH surface topography (HRT, Heidelberg Engineering, GmbH), RNFLT (Spectralis OCT, Heidelberg) and RNFL retardance (GDxVCC, Carl Zeiss Meditech, Inc) in both eyes. Then laser treatments of the trabecular meshwork were begun in one eye each to induce chronic elevation of IOP. Imaging continued on an approximately weekly basis throughout the follow-up period alternating between ONH surface topography and RNFLT during one week and RNFL retardance the next week. Animals were sacrificed shortly after onset of ONH surface topography change, which was defined as the first date when either the mean position of the disc (MPD) fell below the 95% confidence limit of each eye's individual baseline range and/or when the Topographic Change Analysis (TCA) map was subjectively judged as having demonstrated change, whichever came first, but both required confirmation in the two subsequent imaging sessions. Treated and control eye groups were compared by Wilcoxon non-parametric matched pairs t-test.
At the onset of ONH surface topography change there was no significant difference between treated and control eyes for RNFLT (p=0.28). RNFL retardance measured during the imaging session immediately subsequent to HRT-detected ONH surface change (9 ± 7 days after ONH onset) was reduced in treated eyes by an average of 6% (range from +3% to -25%, p=0.005). At its final measurement date, RNFL retardance was reduced in treated eyes by an average of 16% (ranging from -4% to -41%, p=0.0005), while RNFLT measured during the next subsequent OCT session (6 ± 2 days later), revealed no difference between treated and control eyes (p=0.46). At the final OCT imaging session (an additional 15 ± 10 days later), there was still no significant difference between treated and control eyes for RNFLT (p=0.15).
Consistent with our previous reports, this study showed that there is no significant decrease of peripapillary RNFLT at the onset of ONH surface topography change in NHP experimental glaucoma. However, RNFL retardance abnormalities (along with ERG changes) indicate that retinal ganglion cell and/or axonal damage is present at this early stage of experimental glaucoma.
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