Corneal power measurements with the Pentacam Scheimpflug camera after myopic excimer laser surgery

Abstract

To evaluate corneal power measurements by a rotating Scheimpflug camera (Pentacam, Oculus) in eyes that have had myopic excimer laser surgery. Private practice, Bologna, Italy. This prospective comparative interventional case series comprised 16 eyes of 16 patients who had myopic excimer laser surgery and for whom all perioperative data were available. Four corneal power measurements obtained with the Pentacam (simulated keratometry, true net power, equivalent K reading, and BESSt formula) were analyzed and compared with values derived using the clinical history method and 2 other formulas for calculating corneal power after refractive surgery (modified keratometric refractive index according to Savini et al. and separate consideration of the anterior and posterior corneal curvatures according to Speicher). Analysis of variance showed a statistically significant difference between all methods (P<.0001). Bonferroni multiple comparison tests showed that the only Pentacam measurements not statistically different from the corneal power values derived using the clinical history method were the equivalent K readings at 1.0 mm, 2.0 mm, and 3.0 mm and those derived with the BESSt formula; however, considerably large 95% limits of agreement (LoA) were calculated between each of these values and those obtained with the clinical history method. The Pentacam device gave corneal power measurements that did not statistically significantly had differ from those predicted by the clinical history method in eyes that had previous myopic excimer laser surgery. Wide LoA are a potential source of error in intraocular lens power calculation in such patients.