Comparative study of retinal nerve fiber layer measurement by StratusOCT and GDx VCC, I: Correlation analysis in glaucoma

PURPOSE. To evaluate the average and regional correlations of retinal nerve fiber layer ( RNFL) thickness measured by StratusOCT ( optical coherence tomography; Carl Zeiss Meditec, Inc., Dublin, CA) and GDx VCC ( Laser Diagnostic Technologies, Inc., San Diego, CA). METHODS. Eighty- nine subjects - 27 normal, 21 with suspected glaucoma, and 41 with glaucoma - were included in this cross-sectional study. The total average and the mean 12- clock- hour RNFL thickness were measured with the StratusOCT and GDx VCC. The discriminating powers of the two techniques for detection of suspected glaucoma and glaucoma were compared by the area under the receiver operating characteristic curves ( AUC). Correspondence between StratusOCT and GDx VCC RNFL measurements in each clock hour was examined with linear regression analysis. RESULTS. The average RNFL thickness in the normal group was measured at 101.38 +/- 7.73 and 55.26 +/- 4.32 mu m by StratusOCT and GDx VCC, respectively. Both nerve fiber analyzers demonstrated a double - hump pattern in the RNFL profiles with maximum RNFL thickness located at the inferotemporal and superotemporal clock hours by the StratusOCT and the superior and inferior clock hours by the GDx VCC. Significant differences were found in the total average and the individual clock- hour RNFL thickness between StratusOCT and GDx VCC RNFL measurements in both the normal and the suspected glaucoma/ glaucoma groups. The GDx VCC superior RNFL measurement demonstrated the largest AUC ( 0.909) for detection of suspected glaucoma and glaucoma, whereas the largest AUC ( 0.901) in StratusOCT was found over the inferotemporal clock hour. The total average RNFL thickness measured with StratusOCT and GDx VCC correlated highly with each other ( r = 0.852). When the respective clock- hour RNFL measurements were compared, the correlation coefficient varied with the position around the optic nerve head, with the highest correlation found over the superior and inferior clock hours ( 11, 12, 1, 6, and 7 o'clock; all with r > 0.700) and the lowest located at the temporal clock hour ( 9 o'clock; r = 0.277). CONCLUSIONS. Despite the substantial differences in the values of RNFL thickness, significant correlations were observed between StratusOCT and GDx VCC RNFL measurements. The variations of the correlation coefficient around the optic nerve head suggested that GDx VCC RNFL measurement does not have a fixed relationship with that of StratusOCT and the use of site- specific RNFL birefringences may improve the estimation of RNFL thickness by the GDx VCC. Nevertheless, the GDx VCC was found to be as effective as the StratusOCT in detecting the loss of RNFL in glaucoma.