Central corneal thickness measurement with Pentacam, Orbscan II, and ultrasound devices before and after laser refractive surgery for myopia

PURPOSE: To determine the agreement in central corneal thickness (CCT) measurements between the gold standard method of ultrasound (US) pachymetry (UP-1000, Nidek) and 2 noncontact systems based on Scheimpflug imaging (Pentacam, Oculus) and scanning-slit topography (Orbscan II, Bausch & Lomb) in myopic eyes before and after laser refractive surgery. SETTING: Noor vision Correction Center, Tehran, Iran. METHODS: In this prospective study, 30 consecutive patients having refractive surgery for myopia were enrolled. All 60 eyes were examined with the 3 devices preoperatively and 6 weeks after surgery; the US measurements were performed last. The Pentacam and Orbscan II CCT readings were compared with the US readings. Both the original and corrected Orbscan II readings were used in the analyses. RESULTS: The mean CCT readings with US, Pentacam, and Orbscan II were, respectively, 555 mu m, 548 mu m, and 580 mu m before surgery and 478 mu m, 468 mu m, and 474 mu m after surgery. Preoperatively, the 95% limits of agreement (LoA) with US were -31 mu m and +19 mu m for the Pentacam device and -5 mu m and +57 mu m for the Orbscan II device. Postoperatively, the LoA were -40 mu m and +19 mu m and -51 mu m and +50 mu m, respectively. Corrected Orbscan II measurements gave 95% LoA of -48 mu m and +6 mu m before surgery and -85 mu m and +5 mu m after surgery. CONCLUSIONS: Refractive surgery had a modest effect on the agreement between Pentacam readings and US measurements. With Orbscan II, the 95% LoA width nearly doubled after surgery. Although the Pentacam seems to show better agreement than Orbscan II, especially after refractive surgery, it is not advisable to use the 3 devices interchangeably in every clinical situation.