Comparison of central corneal thickness measurement by scanning slit topography, infrared, and ultrasound pachymetry in normal and post-LASIK eyes

Objectives To compare central corneal thickness (CCT) measurements by scanning slit topography (SST), infrared pachymetry (IRP), and ultrasound pachymetry (USP), and their agreement in normal and post-laser in situ keratomileusis (LASIK) eyes. Methods Sixty normal and 35 post-LASIK subjects were recruited. Only one eye from each subject was analyzed. Non-contact pachymetry was performed first, and the order for SST (Orbscan IIz) and IRP (Tonoref III) was randomized for each patient, to be followed by contact USP (Echoscan US-4000). Pearson’s correlation, paired t test, and Bland–Altman plots were used to investigate association, difference, and agreement among different instruments respectively. Results The measurements obtained with the instruments were highly correlated. Compared to CCT determined by USP (CCT USP ), CCT determined by SST (after correction with acoustic factor) (CCT SST C ) was thicker by 7 µm in normal eyes ( P