title: Comparison of central corneal thickness measurements with three new optical devices and a standard ultrasonic pachymeter.
abstract: OBJECTIVE
  To compare the RTVue spectral optical coherence tomography (SD-OCT), Sirius Scheimpflug-Placido topographer, Lenstar optical low coherence reflectometry (OLCR) and ultrasound pachymetry (USP) devices in terms of their agreement and repeatability of measuring central corneal thickness (CCT).
  
  
  METHODS
  In this prospective study, 50 eyes of 50 patients were included. Three repeated measures were obtained using SD-OCT, Scheimpflug-Placido topographer and USP and five measurements were determined with the OLCR. Bland-Altman plots were used to assess agreement among the instruments, and 95% limits of agreement (LoA) for each comparison were calculated. Intra-examiner repeatability was assessed using intraclass correlation coefficients (ICCs).
  
  
  RESULTS
  The mean CCT by SD-OCT, Scheimpflug-Placido topographer, OLCR, and USP were 525.90±34.08 µm, 525.92±34.10 µm, 530.30±35.62 µm, and 543.50±37.11 µm respectively. All 4 modalities of CCT measurements correlated closely with each other, with Pearson correlation coefficients ranging from 0.977 to 0.995. The mean differences (and upper/lower LoA) for CCT measurements were -0.05±6.77 µm (13.3/-13.3) between SD-OCT and Scheimpflug-Placido topographer, 4.38±3.79 µm (11.8/-3.1) between OLCR and SD-OCT, 4.38±6.03 µm (16.2/-7.5) between OLCR and Scheimpflug-Placido topographer, 13.20±6.46 µm (25.9/0.5) between USP and OLCR, 17.59±6.76 µm (30.8/4.3) between USP and SD-OCT, and 17.58±8.13 µm (33.5/1.6) between USP and Scheimpflug-Placido topographer. Intra-examiner repeatability was excellent for all devices with ICCs>0.98.
  
  
  CONCLUSIONS
  For most practical purposes, CCT measurements with the RTVue, Sirius and Lenstar can be used interchangeably. Although highly correlated, CCT measurement differences between USP and these 3 optical instruments can be significant depending on the clinical situation.
authors.affiliation: Department of Ophthalmology, Bozok University Faculty of Medicine,Y ozgat 66200, Turkey.
authors.forename: Hasan Ali
authors.initials: HA
authors.lastname: Bayhan
authors.affiliation: Department of Ophthalmology, Bozok University Faculty of Medicine,Y ozgat 66200, Turkey.
authors.forename: Seray
authors.initials: S
authors.lastname: Aslan Bayhan
authors.affiliation: Department of Ophthalmology, Bozok University Faculty of Medicine,Y ozgat 66200, Turkey.
authors.forename: Izzet
authors.initials: I
authors.lastname: Can
keywords: Scheimpflug-Placido topographer; central corneal thickness; optical low coherence reflectometry; spectral optical coherence tomography