Comparison of optical low coherence reflectometry and ultrasound pachymetry in the measurement of central corneal thickness before and after photorefractive keratectomy

PURPOSE: To compare an ultrasound pachymeter with an optical low coherence reflectometry (OLCR) pachymeter for measuring pre- and postoperative central corneal thickness of patients undergoing photorefractive keratectomy (PRK). METHODS: In a prospective, noncomparative, interventional study, 48 myopic eyes (mean manifest refractive spherical equivalent: -4.93±2.93 diopters [D]) of 30 healthy patients underwent PRK. Pre- and postoperative central corneal thickness was measured by two examiners (E1, E2) with an ultrasound pachymeter and an OLCR pachymeter. Agreement and inter-rater repeatability were determined using the comparison method described by Bland and Altman. RESULTS: The limits of agreement between the two devices ranged from 17.8 µm (E1) to 20.5 µm (E2) preoperatively and from 22.4 µm (E1) to 16.9 µm (E2) postoperatively. The coefficient of inter-rater repeatability ranged from 9.1 µm (ultrasound pachymeter) to 5.4 µm (OLCR pachymeter) preoperatively and from 7.1 µm (ultrasound pachymeter) to 4.7 µm (OLCR pachymeter) postoperatively. CONCLUSIONS: The OLCR pachymeter seems to show better pre- and postoperative repeatability compared to the ultrasound pachymeter. The agreement between the two devices should be considered acceptable for clinical practice. Photorefractive keratectomy did not affect the postoperative agreement and repeatability of the pachymeters. [J Refract Surg. 2007;23:661-666.]