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Comparison of Topcon Optical Coherence Tomography and Ultrasound Pachymetry

Northey, Luke Cameron*; Gifford, Paul; Boneham, Gavin C.

doi: 10.1097/OPX.0b013e3182775c8c
Original Articles

Purpose: 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).

Methods: 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.

Results: 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.

Conclusions: 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.




School of Medicine Sydney, The University of Notre Dame Australia, Broadway (LCN); and School of Optometry and Vision Science, The University of New South Wales, Sydney (PG, GCB), New South Wales, Australia.

Luke C. Northey School of Medicine Sydney The University of Notre Dame Australia PO Box 944 Broadway New South Wales 2007 Australia e-mail:

© 2012 American Academy of Optometry