Peripapillary retinal nerve fiber layer thickness measurement by 2 different spectral domain optical coherence tomography machines

PURPOSE. To determine agreement between peripapillary retinal nerve fiber layer (RNFL) thickness measurements by 2 spectral domain optical coherence tomography (SD-OCT) instruments. METHODS. This was an observational, cross-sectional study. Both eyes of 89 subjects, 44 healthy subjects (mean age, 47 +/- 15 years) and 45 patients with glaucoma (mean age, 55 +/- 14 years), were imaged using Cirrus OCT (Carl Zeiss Meditec, Inc. Dublin, CA, USA) and Topcon OCT (3D-OCT 1000, Topcon Corporation, Tokyo, Japan). One eye was randomly selected in each subject and peripapillary RNFL thickness measurements were compared. Bland-Altman plots were used to assess the level of agreement. RESULTS. Average peripapillary RNFL thickness measurements were significantly larger with Topcon OCT compared to Cirrus OCT in normal (101 +/- 12 vs 91 +/- 8 mu m, p<0.001) and glaucomatous eyes (89 +/- 18 vs 76 +/- 16 mu m, p<0.001). The limits of agreement for average peripapillary RNFL thickness measurements were poor, (-11 to 32 mu m) in normal and (-4 to 30 mu m) in glaucomatous eyes. CONCLUSIONS. Peripapillary RNFL thickness values obtained by Topcon OCT are significantly higher than those measured by Cirrus OCT in both normal and glaucomatous eyes. Clinicians should be aware of this discrepancy especially when monitoring patients imaged by different OCT instruments; measured values cannot be used interchangeably.