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Brad Fortune, Juan Reynaud, Christy Hardin, Dawn Jennings, Galen Williams, Claude F Burgoyne; OCT Angiography Evaluation of the Optic Nerve Head Vasculature in Nonhuman Primate Experimental Glaucoma. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3026.
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© ARVO (1962-2015); The Authors (2016-present)
We recently reported evidence of optic nerve head (ONH) neuroretinal rim compression in nonhuman primate (NHP) experimental glaucoma (EG),1 whereby two OCT parameters, the ONH minimum rim area (MRA) and the peripapillary retinal nerve fiber layer area (RNFLA) had predictably similar values in healthy eyes but MRA decreased more than RNFLA in EG. An important question is whether the ONH vasculature also decreases as the rim tissue begins to exhibit compression. Here we apply OCT angiography (OCT-A) to address that question.
Data from N=5 NHP were available for this study. OCT imaging (Spectralis OCT2) included a single 12° circumpapillary B-scan to derive RNFLA, 24-radial 30° B-scans to derive MRA and a 768x768 grid OCT-A and structural scan (15x15°), all obtained weekly in both eyes during baseline and after induction of unilateral EG.1 Raw OCT-A and structural OCT data were exported to custom software for segmentation and 3D measurements. From each structural OCT grid scan we calculated the total ONH rim volume (TRV) bounded laterally by the Bruch’s membrane opening (BMO), posteriorly by the BMO plane and anteriorly by the internal limiting membrane (ILM) segmentations. The ONH total rim vascular volume (TRVV) was calculated from the corresponding OCT-A data of the same grid scan and boundaries. Here we report results from the first time point when MRA was significantly (>12%) reduced from baseline (MRA onset).
One NHP was excluded from analysis because the EG eye was an extreme outlier (Fig1A) whose IOP increased from ~10 to ~60 mmHg within a week and remained near that level for 2 weeks including MRA onset. For the remaining 4 NHP, at MRA onset, EG eyes showed a decrease of 30±13% for MRA (p=0.005, repeated measures 2-way ANOVA), 11±9% for RNFLA (p=0.05) and 21±15% for MRA:RNFLA ratio (p=0.04), confirming rim compression. TRV decreased by 43±17% (p=0.005). In contrast, TRVV had not decreased significantly (p=0.44) and the ratio of TRVV:TRV (the % of the rim consisting of vascular flow) had actually increased from 15±4% to 19±3% (albeit, not significantly, p=0.22).
The ONH vasculature imaged by OCT-A remains unchanged at the onset of rim compression in NHP EG. This suggests that glaucomatous rim compression impacts primarily axons and glia. However, if chronic IOP elevation is very high (~60 mmHg), the vasculature can be compromised.1IOVS 2016;57:4403-11.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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