SCIENTIFIC REPORT Comparison of corneal thickness measurements using Orbscan II, non-contact specular microscopy, and ultrasonic pachymetry in eyes after laser in situ keratomileusis

Aims: To compare central corneal thickness measurements of three pachymetry devices in eyes after laser in situ keratomileusis (LASIK). Methods: Central corneal thickness was measured in 203 eyes after myopic LASIK. Orbscan II scanning slit topography (Bausch & Lomb), SP-2000P non-contact specular microscopy (Topcon), and ultrasonic pachymetry (Tomey) were used in this sequence. Results: Three devices gave significantly different corneal thickness readings (p,0.0001, repeated measure analysis of variance). The measurements of Orbscan II (445.6 (SD 60.0) mm) were significantly smaller than those of noncontact specular microscopy (467.9 (SD 40.2) mm; p,0.0001, Tukey multiple comparison) and ultrasonic pachymetry (478.8 (SD 41.9) mm; p,0.0001). The value obtained with SP-2000P non-contact specular microscopy was significantly smaller than that taken with ultrasonic pachymetry (p,0.001). There were significant linear correlations between scanning slit topography and non-contact specular microscopy (Pearson’s correlation coefficient r = 0.912, p,0.0001), non-contact specular microscopy and ultrasonic pachymetry (r = 0.968, p,0.0001), and ultrasonic pachymetry and scanning slit topography (r = 0.933, p,0.0001). Conclusion: In post-LASIK eyes, Orbscan II scanning slit topography significantly underestimated corneal thickness. Non-contact specular microscopy gave smaller thickness readings than ultrasonic pachymetry, but these two units showed an excellent linear correlation.