Corneal power measurements with the Pentacam Scheimpflug camera after myopic excimer laser surgery Giacomo Savini, MD, Piero Barboni, MD, Vincenzo Profazio, Maurizio Zanini, MD, Kenneth J. Hoffer, MD PURPOSE: To evaluate corneal power measurements by a rotating Scheimpflug camera (Pentacam, Oculus) in eyes that have had myopic excimer laser surgery. SETTING: Private practice, Bologna, Italy. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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. J Cataract Refract Surg 2008; 34:809–813 Q 2008 ASCRS and ESCRS Laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and laser-assisted subepithelial keratectomy (LASEK) can correct myopia by decreas- ing the anterior corneal surface curvature. Because they alter the natural ratio between the anterior and posterior corneal curvatures, these procedures render invalid the conventional keratometric index of refrac- tion (usually 1.3375) used by most topographers and keratometers to convert the measured radius into diopters. 1 These instruments thus cannot correctly calculate the corneal power and usually give a mea- surement that is higher than the actual value. Over- estimating corneal power leads to postoperative hyperopia when intraocular lens (IOL) power must be calculated for eyes that will have cataract surgery. 2 An increasing number of methods have been de- vised to overcome the problem of correctly measuring corneal power after excimer laser surgery. 3 All rely on several assumptions to arrive at an indirect determina- tion of corneal power. Most also require preoperative data such as the attempted correction or the original corneal power, and none can be reliably adopted for Accepted for publication January 21, 2008. From a private practice (Savini, Barboni, Profazio, Zanini), Bologna, Italy, and Jules Stein Eye Institute (Hoffer), University of California, Los Angeles, California, USA. No author has a financial or proprietary interest in any material or method mentioned. Corresponding author: Giacomo Savini, MD, Centro Salus, Via d’Azeglio 5, 40123, Bologna, Italy. E-mail: giacomo.savini@alice.it. Q 2008 ASCRS and ESCRS Published by Elsevier Inc. 0886-3350/08/$dsee front matter 809 doi:10.1016/j.jcrs.2008.01.012 ARTICLE