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Dagny Zhu, Alena Reznik, Chieh-Li Chen, Ruikang K Wang, Carmen A Puliafito; Evaluation of Optic Disc Perfusion in Normal-Tension Glaucoma Patients by Optical Coherence Tomography Angiography. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2745.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate optic disc perfusion in normal-tension glaucoma (NTG) patients using optical coherence tomography (OCT) angiography.
Seven eyes of 4 patients with NTG were scanned with a high-speed 1060-nm wavelength swept-source OCT angiography prototype system. A proprietary phase compensation algorithm was used to construct a three-dimensional model of blood flow in the optic disc. The disc flow index, a dimensionless parameter from 0-1 measuring vessel area, density, and flow velocity, was calculated for each optic disc. Stereo photography was used to quantify the cup-to-disc ratio for each optic disc. Humphrey visual field (HVF) deficits and retinal nerve fiber layer (RNFL) thickness were analyzed and correlated with disc flow index using the spearman correlation coefficient.
The optic discs of NTG patients analyzed spanned a wide range of clinical severity, with cup-to-disc ratios ranging from 0.65 to 0.85 (mean 0.78±0.08) and mean deviation (MD) from -16 to 0.51 (mean -6.7±5.8) and pattern standard deviation (PSD) from 1.6 to 15.5 (mean 7.2±5.2) on HVF. The average disc flow index was 0.26±0.04. Qualitatively, discs with early or moderate glaucomatous optic nerve damage demonstrated a denser microvascular network spanning each level of the retina, choroid, and lamina cribosa compared to more advanced cases. Disc flow index correlated strongly with cup-to-disc ratio (R² = 0.67), suggesting poorer perfusion in discs with larger cups and more severe damage. No such correlation was seen with other measured factors including MD, PSD, and RFNL thickness. Interestingly, the sectoral disc flow index calculated for each quadrant (inferior, superior, nasal, temporal) did not correlate with the structural location of nerve head damage and/or corresponding HVF deficits seen, suggesting a possible compensatory redistribution of blood flow.
OCT angiography provides a non-invasive method for quantifying disc perfusion in patients with glaucoma. Our results provide additional insights into the pathologic role of altered perfusion in NTG for this unique subset of patients with relatively “normal” intraocular pressures. Clinical treatments for improving disc perfusion in glaucoma patients warrant further investigation.
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