Assessment of central corneal thickness in normal, keratoconus, and post-laser in situ keratomileusis eyes using Scheimpflug imaging, spectral domain optical coherence tomography, and ultrasound pachymetry

Abstract

To compare the central corneal thickness (CCT) in normal eyes, eyes with keratoconus, and eyes after laser in situ keratomileusis (LASIK) using 3 methods. Cornea Clinic, Grewal Eye Institute, Chandigarh, India. In this study, CCT was measured by sequential Scheimpflug imaging, spectral-domain anterior segment optical coherence tomography (AS-OCT), and ultrasound (US) pachymetry. Each of the 3 groups comprised 50 eyes. There were no differences between the 3 groups in age, sex, or intraocular pressure. In normal eyes, CCT was statistically significantly higher by US pachymetry (mean 525.8 microm +/- 41.4) [SD] than by Scheimpflug imaging (mean 519.4 +/- 40.9 microm) and AS-OCT (mean 517.9 +/- 41.5 microm) (both P<.001). In keratoconus eyes, CCT by US pachymetry (mean 446.4 +/- 57.9 microm) was statistically significantly higher than by Scheimpflug imaging (mean 439.6 +/- 62.1 microm) (P = .002) and AS-OCT (mean 441.8 +/- 58.4 microm) (P = .007). In post-LASIK eyes CCT by US pachymetry (mean 462.4 +/- 44.7 microm) was significantly higher than by Scheimpflug imaging (mean 457.9 +/- 33.6 microm) (P = .012) and AS-OCT (mean 455.4 +/- 43.2 microm) (P<.001). In all groups, CCT measured by Scheimpflug imaging and AS-OCT was similar. There was a statistically significant difference between Scheimpflug imaging and US pachymetry and AS-OCT, with US pachymetry measurements being consistently thicker. Thus, CCT should be interpreted in the context of the instrument used.