Fourier Analysis of Optical Coherence Tomography and Scanning Laser Polarimetry Retinal Nerve Fiber Layer Measurements in the Diagnosis of Glaucoma

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Abstract
Objective To evaluate a new Fourier-based analysis method for diagnosing glaucoma using retinal nerve fiber layer (RNFL) thickness estimates obtained from the optical coherence tomograph (OCT) (OCT 2000) and the scanning laser polarimeter(GDx). Methods We obtained RNFL thickness estimates from 1 eye of 38 healthy individuals and 42 patients with early glaucomatous visual field loss using the OCT and GDx devices. The shape of the RNFL double-hump pattern was assessed using Fourier analysis, and values were entered into a linear discriminant analysis. Receiver operating characteristic (ROC) curves were used to compare the performance of the Fourier-based metrics against other commonly used RNFL analytical procedures. Reliability was assessed on independent samples by the split-half method. Correlations were calculated to determine the extent to which the Fourier discriminant measures and other RNFL measures covaried between the 2 devices and the relationship between these RNFL measures and visual field measures. Results Sensitivity and specificity for the linear discriminant function (LDF) based on the Fourier analysis of the OCT data were 76% and 90%, respectively, and the area under the ROC curve was 0.925 (SEM, 0.028). For the GDx data, the Fourier-based LDF yielded sensitivity and specificity of 82% and 90%, respectively, with an ROC curve area of 0.928 (SEM, 0.029). These values were better than those determined using the GDx number, a previous discriminant function using GDx variables and OCT thickness values. The Fourier-based LDFs and numerous other measures were significantly correlated between the 2 devices. For each device, the visual field measures correlated most highly with the Fourier-based LDF measure. Conclusions For both devices, the LDF based on the output from a Fourier analysis of RNFL data resulted in better diagnostic capability compared with other common RNFL analytical procedures. That this technique improves RNFL analysis is also supported by the better correlations between visual field measures and the Fourier-based LDF measures.