Comparison of Fourier-Domain and Time-Domain Optical Coherence Tomography for Assessment of Corneal Thickness and Intersession Repeatability

PURPOSE: To compare Fourier,domain optical coherence tomography (FD-OCT) with time-domain OCT (TD-OCT) for agreement in corneal pachymetry in the central (2-mm) zone and paracentral (2- to 5-mm) zone, minimum corneal thickness, and instrument intersession reliability in candidates with normal cornea. DESIGN: Prospective comparative trial. METHODS: The study was performed at a tertiary care ophthalmic hospital. One hundred normal candidates with no ocular pathology except mild refractive error were included. FD-OCT and TD-OCT were used for pachymetric analysis within 15 minutes of each other. Repeat testing on both machines was done on the next day. One eye from each patient was randomly selected for analysis of both comparison and reliability. 0 RESULTS: The mean thickness was significantly more for FD-OCT (difference being 5.8, 11.1, and 19.2 mu m for central, paracentral, and minimal thickness). Highest correlation, best linear fit, and smallest range of 95% limits of agreement (LoA) was seen for central corneal thickness, followed by paracentral and minimum corneal thickness (R-2 values for the 3 best fit lines were 0.93, 0.86, and 0.58, respectively). In terms of intersession reliability, FD-OCT was better (coefficients of reliability <1.5% vs 4.5% of TD-OCT) with smaller 95% LoA range, suggesting its better performance. CONCLUSIONS: The corneal thickness measurements between TD-OCT and FD-OCT were highly correlated but not similar. Conversion equations may be used for central and paracentral, but not for minimum, corneal thickness. Even though both the OCT instruments had good reliability, FD-OCT was better. (Am J Ophthalmol 2009;148:282-290. (C) 2009 by Elsevier Inc. All rights reserved.)