Comparison of Topcon Optical Coherence Tomography and Ultrasound Pachymetry

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To establish within-rater repeatability and minimum measurements required for reliable assessment of central corneal thickness (CCT) using Topcon three-dimensional OCT-2000 (Topcon Medical Systems, Oakland, NJ) Fourier-domain optical coherence tomography (FD-OCT) and to test agreement against ultrasound pachymetry (USP).


Twenty participants underwent five scans using FD-OCT followed by five CCT measurements using USP. Each FD-OCT scan produced 12 meridional optical sections, giving 60 sections in total. The FD-OCT CCT was calculated from each section using Topcon FastMap software. Within-rater repeatability was assessed using intraclass correlation coefficient (ICC), within-subject variance (Sw), and within-subject coefficients of repeatability (COR) and variation (COV). Agreement was assessed using analysis of variance, simple linear regression, Bland-Altman analysis, and ICC. The minimum number of FD-OCT scans required to achieve a mean CCT within the 99% confidence intervals of all 60 measurements was calculated.


Mean CCTs were 528 ± 27 μm (FD-OCT) and 544 ± 29 μm (USP). The FD-OCT within-rater repeatability values assessed using ICC, Sw, COR, and COV were 0.99, 5.07 μm, 14.07 μm, and 0.01%, respectively. The USP within-rater repeatability values assessed using ICC, Sw, COR, and COV were 0.96, 5.49 μm, 15.22 μm, and 0.01%, respectively. Both instruments were similarly correlated (p < 0.05), with FD-OCT underestimating CCT by 16.08 μm relative to USP. Four FD-OCT scans were required to achieve a mean within the 99% confidence interval of all measurements for each participant.


Both instruments displayed high repeatability, with strong agreement between devices, although FD-OCT significantly underestimated CCT compared with USP. The FD-OCT agreement with USP remained strong when only four scans were analyzed.

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