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) mu m) 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.