Central Corneal Thickness in Highly Myopic Eyes: Inter-device Agreement of Ultrasonic Pachymetry, Pentacam and Orbscan II Before and After Photorefractive Keratectomy

To determine inter-device agreement for central corneal thickness (CCT) measurement among ultrasound pachymetry, rotating Scheimpflug imaging (Pentacam, Oculus, Wetzlar, Germany), and scanning slit corneal topography (Orbscan II, Bausch & Lomb, Rochester, NY, USA) in highly myopic eyes before and after photorefractive keratectomy (PRK). This prospective comparative study included 61 eyes of 32 patients with high myopia who underwent PRK. Six month postoperative CCT values were compared to preoperative values in 27 patients (51 eyes) who completed the follow up period. To determine the level of agreement, Pentacam and Orbscan II readings were compared to ultrasonic pachymetry measurements as the gold standard method. Mean CCT measurements with ultrasound, Pentacam, and Orbscan II before PRK were 557 micrometers, 556 micrometers, and 564 micrometers, respectively; and 451 micrometers, 447 micrometers, and 438 micrometers 6 months after surgery in the same order. Preoperatively, the 95% limits of agreement (LoA) with ultrasound measurements were -20 micrometers to 17 micrometers for Pentacam and -21 micrometers to 33 micrometers for Orbscan II. Six months postoperatively, the 95% LoA were -30 micrometers to 23 micrometers for Pentacam and -69 micrometers to 43 micrometers for Orbscan II. Preoperatively, CCT measurements were higher with Orbscan II as compared to ultrasound. Postoperatively, both Pentacam and Orbscan II measurements were lower than those obtained with ultrasound, but Pentacam had better agreement. The use of ultrasound, as the gold standard method, or Pentacam both appear to be preferable over Orbscan II among patients with high myopia.