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G. Williams, N. G. Strouthidis, B. Fortune, H. Yang, J. Grimm, J. Reynaud, G. Cull, L. Wang, C. F. Burgoyne; Detection of Longitudinal Optic Nerve Head (ONH) and Retinal Nerve Fiber Layer Thickness (RNFLT) Changes In Experimental Glaucoma Using Spectral Domain Optical Coherence Tomography (SD-OCT). Invest. Ophthalmol. Vis. Sci. 2009;50(13):2253.
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To quantify ONH and RNFLT changes in non-human primate (NHP) experimental glaucoma (EG) using longitudinal SD-OCT.
SD-OCT imaging (SpectralisTM, Heidelberg Engineering) was performed on 12 NHPs prior to unilateral trabecular meshwork laser treatment to induce IOP elevation, then every 1-3 weeks post-laser. All images were acquired under isoflurane anesthesia and 30 min after manometrically lowering IOP to 10 mmHg. Images were centered on the ONH and included a 15° radial pattern with 80 B-scans and a circular peripapillary B-scan. Peripapillary RNFLT was quantified using Spectralis RNFL Thickness Profile software. Internal limiting membrane (ILM), Bruch’s Membrane/Retinal Pigment Epithelium Complex (BM/RPE), Neural Canal Opening (NCO, the end of the BM/RPE complex at the ONH), and anterior lamina cribrosa surface (ALCS, where visible) were hand-delineated in vertical and horizontal B-scan sections using custom software. Parameters quantified included prelaminar ILM height, maximum and mean position of ALCS (all relative to the NCO reference plane) depth of NCO relative to peripheral BM/RPE, major and minor NCO dimensions. For each parameter, baseline and latest follow-up values were compared (t-test, p < 0.01) to assess longitudinal change. Associations between ONH parameters, global RNFLT changes, and cumulative IOP insult (mmHg-days) were assessed by linear regression.
After mean post-laser follow-up duration of 6.8 ± 2.7 months, global RNFLT changed by +4% to -70% (mean = -15.3%, p=0.01). RNFL loss was greatest inferiorly (-21%, p=0.008) and least temporally (-7%, p=0.08). The coefficient of variation in control eyes was 1.9%, which was exceeded by loss in 8 of 12 EG eyes, the remaining eyes having only early changes. Within the ONH, maximum (p = 0.0006) and mean (p = 0.001) ALCS position was depressed. Average prelaminar ILM height relative to the NCO reference plane was also depressed (p = 0.0004).There was no significant change for NCO major and minor diameters, nor for the depth of the NCO relative to peripheral BM/RPE (P>0.01). Changes in prelaminar ILM height (p = 0.01) and NCO depth (p = 0.01) were significantly correlated with cumulative IOP insult. Maximum and mean ALCS position were correlated with global RNFL thickness (p = 0.002, p = 0.009 respectively).
Early to severe glaucomatous alterations of the ONH and RNFL are detectable by longitudinal Spectralis SD-OCT imaging in this group of 12 NHP eyes.
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