Comparison of Corneal Thickness Measured by Specular, US Pachymetry, and Orbscan in Post-PKP Eyes

ABSTRACT

PURPOSE: To compare the accuracy and reproducibility of central corneal thickness measured by non-contact specular microscopy, ultrasound pachymetry, and Orbscan in the post-penetrating keratoplasty eyes. METHODS: Central corneal thickness was prospectively measured in eyes that had recieved penetrating keratoplasty at least 1 month before. One experienced technician measured all eyes using three methods; non-contact specular microscopy (Topcon SP-2000P; Topcon Corporation, Tokyo, Japan), Orbscan IIz (Orbtek; Bausch & Lomb, Rochester, USA), and ultrasound pachymetry (AL-2000; Tomey, Erlangen, Germany). Three consecutive measurements were performed using each method and the mean values and coefficient of variation were compared. RESULTS: The mean values of central corneal thickness were 550.7+/-63.3 micrometer with specular microscopy, 548.2+/-72.5 micrometer with ultrasound pachymetry, and 472.5+/-151.7 micrometer with Orbscan. There was no significant difference between the measurements obtained by specular microscopy and ultrasound pachymetry (p=0.53), and both methods showed high reproducibility. The corneal thickness measured by Orbscan was remarkably variable and in some patients, Orbscan was unable to measure corneal thickness. CONCLUSIONS: Non-contact specular microscopy appears to be an effective technique, potentially replacing ultrasound pachymetry for measuring central corneal thickness in the post-penetrating keratoplasty eyes.