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P. Gunvant, Y. Zheng, A. Kotecha, D.F. Garway–Heath, E.A. Essock; Predicting Visual Field Loss in Ocular Hypertensive Patients Using Wavelet–Fourier Analysis (WFA) of GDx Scanning Laser Polarimetry . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5504.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our prior efforts have sought to characterize the "double–hump" pattern of retinal nerve fiber layer (RNFL) thickness in terms of shape parameters derived from a Fourier analysis and more recently from an improved method termed Wavelet–Fourier analysis (WFA – Zheng et al., JCIS, 2003). In the present work we use the approach to predict subsequent conversion of ocular hypertension (OHT) to glaucoma. Methods:A total of 96 subjects were followed–up during the period of April 1996 to July 2003 at Moorfields Eye Hospital of which 34 were OHT non–converters (OHTnc), 19 OHT converters (OHTc), 19 glaucoma, and 24 ocular normals, classified on the basis of visual field. RNFL scans using a GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, Inc.), Humphrey visual fields, and ophthalmoscopic exams were obtained in follow–up. Subjects were classified as converters on the basis of reproducible field defects using AGIS criteria. RNFL thickness estimates were obtained for 28 sectors around the disc at 1.75 disc diameters. The WFA classifier was trained and derived using a support vector machine from the normal and glaucoma subjects and then was applied to the 53 OHT patients to predict which would convert based on a single scan obtained prior to the visual field conversion (AGIS) (mean 7.4 months, range 1–24). The WFA method involves application of a two–level Discrete Wavelet Transform (DWT), a Fourier transform (FFT) of the detailed difference information, and application of Principal Component Analysis (PCA) to the DWT and FFT coefficients. A support vector classifier (SVC) was used to classify eyes based on these resultant features. Sensitivity, specificity and ROC area was calculated for the detection of the patients who subsequently converted. Results: Sensitivity/Specificity/ROC area was 0.71/0.77/0.83 when the WFA was applied to classify OHTc and OHTnc subjects and 0.67/0.82/0.75 when the converting and fellow non–converting eyes of the OHTc patients were used. Conclusion:WFA analysis, trained on a separate population of normals and glaucoma patients, can predict impending visual field progression in OHT subjects with moderate ability.
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