Comparison of retinal nerve fiber layer (RNFL) optical texture analysis (ROTA) versus RNFL thickness analysis for measurement of retinal nerve fiber layer defects in early glaucoma

Abstract

<p><strong>Purpose </strong>: (1) To evaluate the agreement of the angular widths of RNFL defects in early glaucoma measured from ROTA versus RNFL thickness deviation maps with reference to red-free fundus photographs, and (2) to determine the angular widths at which RNFL defects on red-free photographs could be detected on ROTA and RNFL thickness deviation maps.</p><p><strong>Methods </strong>: 63 eyes from 63 early glaucoma patients with detectable RNFL defects on red-free photographs (Eidon, iCare, Finland) were analysed. The smallest RNFL defect with clear margins on the red-free photographs of each eye was measured. The angular widths of RNFL defects on red-free fundus photographs, ROTA images, and RNFL thickness deviation maps (RNFL defects were defined by having 10 contiguous superpixels encoded in red) were measured along the 3.46mm measurement circle centred at the Bruch’s membrane opening. Bland-Altman plots were used to evaluate the measurement agreement. Receiver operating characteristic curve (ROC) analysis was conducted to identify the optimal thresholds of RNFL defect angular width for detection of RNFL defects on ROTA and RNFL thickness deviation maps.</p><p><strong>Results </strong>: The mean age was 59.1±16.0 years; the VF MD was -1.44±2.21dB. All RNFL defects on red free photographs were detected by ROTA (63 eyes, 100%). By contrast, the RNFL thickness deviation maps detected 43 eyes (68.3%) with RNFL defects. The mean difference of angular widths of RNFL defects measured from ROTA versus red-free photographs was -1.3° (p=0.001) and the span of 95% limits of agreement (LoA) was 12.1°. There were proportional biases (p<0.001) between RNFL thickness deviation maps and red-free photograph angular width measurements; the mean difference was -6.7° (p<0.001) and the span of 95% LoA was 58.9°. The optimal angular width for RNFL thickness deviation map to detect RNFL defects on red-free fundus photographs was 21.3° (sensitivity= 74.4%, specificity= 80.0%).</p><p><strong>Conclusions </strong>: Many focal RNFL defects in early glaucoma remained undetected in conventional RNFL thickness analysis even when they reached a significant size in ROTA and red-free photographs. There was substantial disagreement in the measurements of RNFL defect angular widths between RNFL thickness deviation maps and red-free photographs.</p>