Comparison of central corneal thickness measurements by Pentacam, noncontact specular microscope, and ultrasound pachymetry in normal and post-LASIK eyes

To compare central corneal thickness (CCT) measurements taken with Pentacam, noncontact specular microscope (NCSM), and ultrasound pachymetry (US) in normal and post-laser in situ keratomileusis (LASIK) eyes and to assess the agreement between the three devices.Design: Prospective clinical trial. Patients and methods: Central corneal thickness (CCT) was measured in 94 eyes of normal volunteer and in 72 eyes of post-LASIK patients. Measurements were made with the three devices. Results: In normal eyes, the mean (±SD) CCT taken with Pentacam, NCSM, and US was 552.6 ±36.8 lm, 511.9 ±38.6 lm, and 533.3± 37.9 lm, respectively. The average values of CCTtaken with the three instruments were significantly different. In post-LASIK eyes the mean CCT withPentacam, NCSM, and US was 483.02± 6.03 lm, 450.7 ±5.3 lm, and 469.5 ± 5.8 lm, respectively.The average values of CCT taken were significantly different for Pentacam vs. NCSM (P =0.046) and Pentacam vs. US (P= 0.02), but not significant for NCSM vs. US (P = 0.352). The Bland and Altman method for assessing clinical agreement between 3 instruments showed that in normal eyes, the mean values and paired differences of the three CCT devices were found to be statistically independent. In post-LASIK eyes, there was significant association between the difference and the mean of the Pentacam and NCSM, and US and NCSM. Conclusion: The three devices cannot be used interchangeably in normal and post-LASIK eyes. Pentacam tends to give significantly thicker reading than ultrasound pachymetry.