title: Comparison of topcon optical coherence tomography and ultrasound pachymetry.
abstract: OBJECTIVE
  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.
authors.affiliation: School of Medicine Sydney, The University of Notre Dame Australia, Broadway, New South Wales, Australia. lukenorthey@hotmail.com
authors.forename: Luke Cameron
authors.initials: LC
authors.lastname: Northey
authors.forename: Paul
authors.initials: P
authors.lastname: Gifford
authors.forename: Gavin C
authors.initials: GC
authors.lastname: Boneham
mesh_terms: D000293:Adolescent; D000328:Adult; D003315:Cornea / Q000000981:diagnostic imaging* / Q000473:pathology*; D063171:Corneal Pachymetry / Q000379:methods*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012372:ROC Curve; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000379:methods*; D014463:Ultrasonography; D055815:Young Adult