Accuracy of a dual Scheimpflug analyzer and a corneal topography system for intraocular lens power calculation in unoperated eyes Giacomo Savini, MD, Piero Barboni, MD, Michele Carbonelli, MD, Kenneth J Hoffer, MD PURPOSE: To evaluate the accuracy of the corneal power measurements by a dual Scheimpflug analyzer (Galilei) and a corneal topography system (Keratron) for intraocular lens (IOL) power calculation in unoperated eyes. SETTING: Private practice. DESIGN: Case series. METHODS: The IOL power was calculated for eyes having phacoemulsification and in-the-bag IOL implantation by entering into the Hoffer Q, Holladay 1, and SRK/T formulas 3 corneal power measurements: (1) simulated keratometry (K) by corneal topography, (2) simulated K derived by anterior corneal curvature only using the dual Scheimpflug analyzer, (3) total corneal power derived by anterior and posterior corneal curvatures through ray tracing using the dual Scheimpflug analyzer. The prediction error was calculated as the difference between the predicted and the measured refraction 1 month postoperatively. RESULTS: Forty-three consecutive patients were enrolled. The mean arithmetic error was zero for all combinations of measurements due to constant optimization. Using the Hoffer Q formula, the mean absolute prediction errors were 0.23 diopters (D) G 0.22 (SD) for the corneal topographer simulated K, 0.21 G 0.18 D for the Scheimpflug simulated K, and 0.27 G0.20 D for the Scheimpflug total corneal power (P>.05). No statistically significant different results (compared with the Hoffer Q formula) were obtained with the Holladay 1 and SRK/T formulas. CONCLUSIONS: Both devices provided corneal power measurements that led to accurate IOL power calculation. The total corneal power by the dual Scheimpflug system is the first corneal power measure- ment shown to lead to accurate IOL power calculation without using the standard keratometric index. Financial Disclosure: Drs. Savini, Barboni, and Carbonelli have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes. J Cataract Refract Surg 2011; 37:72–76 Q 2011 ASCRS and ESCRS As new instruments for measuring ocular biometric parameters become commercially available, cataract surgeons face the challenge of selecting the device that is likely to provide the highest accuracy for intra- ocular lens (IOL) power calculation. Today, corneal power can be measured using 5 technologies: manual keratometry (K), automated K, Placido disk corneal topography, scanning-slit corneal topography, and Scheimpflug imaging. 1–3 Although not yet commer- cially available, there is a sixth option for measuring corneal power; that is, optical coherence tomography. 4 We previously observed that the corneal power measurements provided by a single Scheimpflug device (Pentacam, Oculus, Inc.) can be relied on for IOL power calculation, although the accuracy was slightly lower than measurements by Placido disk cor- neal topography or automated K (IOLMaster, Carl Zeiss Meditec AG). 2 Others reported similar results af- ter comparing the Scheimpflug camera with autokera- tometry. 3 The aim of this study was to assess the accuracy of a newer, dual Scheimpflug device that combines 2 Scheimpflug images with Placido disk technology and to compare its performance with that achieved with a validated corneal topography system. PATIENTS AND METHODS This prospective study analyzed eyes of consecutive patients having cataract surgery. Before being included in the study, Q 2011 ASCRS and ESCRS 0886-3350/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.jcrs.2010.08.036 72 ARTICLE