To determine the agreement between peripapillary retinal nerve fiber layer (RNFL) thickness measurements from Stratus time domain optical coherence tomography (OCT) and Cirrus spectral domain OCT (Carl Zeiss Meditec, Dublin, CA) in normal subjects and glaucoma patients.
Evaluation of diagnostic test or technology.
One hundred thirty eyes from 130 normal subjects and glaucoma patients were analyzed. The subjects were divided into Normal (n=29), Glaucoma Suspect (n=12), Mild Glaucoma (n=41), Moderate Glaucoma (n=18), and Severe Glaucoma (n=30) by visual field criteria.
Peripapillary RNFL thickness was measured with Stratus Fast RNFL and Cirrus 200 x 200 Optic Disc Scan on the same day in one eye of each subject to determine agreement. Two operators used the same instruments for all scans.
Main Outcome Measures
Student paired t-testing, Pearson’s correlation coefficient, and Bland-Altman analysis of RNFL thickness measurements.
The average age of the glaucoma group was significantly older at 68.3±12.3 years versus 55.7±12.1 years. The average RNFL thickness (mean ± SD, in μm) for each severity group with Stratus OCT was 99.4 ± 13.2, 94.5 ± 15.0, 79.0 ± 14.5, 62.7 ± 10.2, and 51.0 ± 8.9, corresponding to normal, suspects, mild, moderate, and severe subjects, respectively. For Cirrus OCT, the corresponding measurements were 92.0 ± 10.8, 88.1 ± 13.5, 73.3 ± 11.8, 60.9 ± 8.3, and 55.3 ± 6.6. All Stratus-Cirrus differences were statistically significant by paired t-testing (p < 0.001) except for the moderate group (p = 0.11). For average RNFL, there was a highly significant linear relationship between Stratus minus Cirrus difference and RNFL thickness as well (p < 0.001). Bland-Altman plots showed that the systematic difference of Stratus measurements are smaller than Cirrus at thinner RNFL values but larger at thicker RNFL measurements.
RNFL thickness measurements between Stratus OCT and Cirrus OCT cannot be directly compared. Clinicians should be aware that measurements are generally higher with Stratus than Cirrus except when the RNFL is very thin as in severe glaucoma. This difference must be taken into account if comparing measurements made with a Stratus instrument to those of a Cirrus instrument.