Corneal thickness measurements: Scanning-slit corneal topography and noncontact specular microscopy versus ultrasonic pachymetry

Purpose: To compare central corneal thickness measurements taken with 3 pachymetry systems: Orbscan scanning-slit corneal topography/pachymetry, Topcon SP2000P noncontact specular microscopy, and Tomey ultrasonic pachymetry. Setting: Multicenter study, Tokyo, Japan. Methods: In 216 healthy eyes of 114 subjects, scanning-slit topography, noncontact specular microscopy, and ultrasonic pachymetry were used in that sequence to record central corneal thickness. In another 20 healthy eyes of 13 subjects, 2 sets of measurements were repeated for each pachymetry to assess repeatability. Results: The mean central corneal thickness was compatible between scanning-slit topography (546.9 mum +/- 35.4 [SD]) and ultrasonic pachymetry (548.1 +/- 33.0 mum); however, noncontact specular microscopy gave a significantly smaller mean (525.3 +/- 31.4 mum) than the other 2 tests (P<.001, Tukey multiple comparison). There were significant linear correlations between scanning-slit topography and noncontact specular microscopy (r = 0.846, P<.001), noncontact specular microscopy and ultrasonic pachymetry (r = 0.897, P<.001), and ultrasonic pachymetry and scanning-slit topography (r = 0.852, P<.001). Noncontact specular microscopy tended to show the best repeatability; however, the difference was not statistically significant (P = .663, repeated-measure analysis of variance). Conclusions: Corneal thickness readings were comparable between scanning-slit topography and pachymetry; noncontact specular microscopy gave significantly smaller values. The measurements of the 3 methods showed significant linear correlations with one another. All methods provided acceptable repeatability of measurements. (C) 2003 ASCRS and ESCRS.