Comparison of keratometric data obtained by automated keratometer, Dicon CT 200, Allegro Topolyzer, and Pentacam

To compare the keratometric values measured by the automated keratometer, two Placido-based computerized topography systems (Dicon CT 200 [Vismed Inc] and Allegro Topolyzer [WaveLight Inc]), and Scheimpflug analysis (Pentacam [Oculus Optikgeräte GmbH]).

The keratometric data of 200 eyes from 200 patients evaluated for refractive surgery were reviewed retrospectively. Mean simulated keratometry (Sim K) and mean corneal astigmatism measured by the four devices were compared using repeated measures analysis of variance with Bonferroni correction. The analysis of agreement between two measurements was assessed using the method of Bland and Altman.

Mean Sim K as measured by the automated keratometer, Dicon CT 200, Allegro Topolyzer, and Pentacam was 43.39±1.50 diopters (D), 43.55±1.50 D, 43.45±1.50 D, and 43.43±1.45 D, respectively. The Dicon CT 200 measured the mean Sim K to be steeper and the automated keratometer measured the mean Sim K to be flatter than the other devices. Significant differences in corneal astigmatism were noted among the four devices except Dicon CT 200 versus Allegro Topolyzer and Allegro Topolyzer versus Pentacam comparisons (P<.013). For mean Sim K, the 95% limits of agreement between the Pentacam and other three devices were significantly wider than the other comparisons. In Bland-Altman plots comparing the Pentacam to the other devices, extreme outliers were present in 11 (5.5%) eyes.

Because of the wide distribution range and presence of extreme outliers, Pentacam data should be used cautiously in IOL power calculation and astigmatic keratotomy procedures.