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Muhammed Alluwimi, Brett King, William H Swanson; Application of Normative Values to Improve Macular Asymmetry Analysis in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5276.
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© ARVO (1962-2015); The Authors (2016-present)
Asymmetry analysis of macular thickness has been introduced to clinical practice for evaluating damage to the macular region, but without normative values. We previously derived normative values for macular asymmetry, and found high between-subject variability in control subjects which limits capability to detect early macular damage. We have demonstrated that this variation can be reduced by focusing on specific regions closer to the fovea. Here we evaluate the potential of asymmetry analysis in detecting macular damage in patients with glaucoma.
Twenty patients with glaucomatous visual field (24-2) defects (ages 40 to 85 years) and 30 age-similar controls were recruited from a longitudinal glaucoma study. Subjects were imaged with Spectralis OCT (V 5.4, Heidelberg Engineering, GmbH) using the posterior pole protocol. A 64-cell grid is superimposed on a 24°×24° area of the macula, and was manually adjusted to be centered on the fovea; the central line of this grid was oriented in the same direction as the foveal-disc angle. We demarcated 3 zones per hemifield within the central ±8°, where we had found the lowest variability. Asymmetry was calculated as the difference between the average thicknesses of a superior zone and the corresponding inferior zone. In order to validate our findings, high-density scans were used with 10 of the 20 patients to derive en face images of the RNFL bundles at different distances from the inner limiting membrane.
Out of 180 zones in the control subjects, 2 zones were flagged at p < 0.05, and one zone at p < 0.01, but none of 30 controls were flagged with 2 contiguous zones. For patients, asymmetry analysis showed 15 of 20 patients with at least 2 contiguous zones at p < 0.05. RNFL damage seen in en face images confirmed damage in the macular zones flagged by the asymmetry analysis.
By focusing on the central ±8°, we improved the capability of the asymmetry analysis to detect macular thickness reduction in patients with glaucoma. Our results were confirmed with en face images of the RNFL bundles.
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