Accuracy of Scheimpflug corneal power measurements for intraocular lens power calculation.

Purpose: To evaluate the accuracy of corneal power measurements by the Pentacam Scheimpflug system for intraocular lens (IOL) power calculation.
Setting: Studio Oculistico d'Azeglio, Bologna, Italy.
Methods: Consecutive patients having phacoemulsification and in-the-bag IOL implantation were prospectively studied. Intraocular lens power was calculated by entering 3 combinations of data into the Hoffer Q formula: (1) corneal power measurements by corneal topography (simulated keratometry) and axial length (AL) measurements by Ultrascan ultrasound (US) immersion biometry; (2) Scheimpflug corneal power measurements (simulated keratometry) and US AL measurements; (3) corneal power and AL measurements by partial coherence interferometry (PCI) (IOLMaster). The prediction error was calculated as the difference between the predicted and the measured refraction 1 month postoperatively.
Results: Forty-one eyes were evaluated. The mean arithmetic error was zero for all combinations of measurements due to constant optimization. The mean absolute error (MAE) of the Scheimpflug-US combination was good (0.44 diopters [D] +/- 0.30 [SD]) but significantly higher than the topography-US combination and PCI (0.33 +/- 0.29 D and 0.33 +/- 0.23 D, respectively) (P = .043). The percentage of eyes with an MAE of 0.75 D or greater was higher with the Scheimpflug-US combination (7 eyes, 17%) than with the corneal topography-US combination (2 eyes, 4.8%) or PCI (3 eyes, 7.3%).
Conclusion: Corneal power measurements with the Pentacam Scheimpflug system should be used in IOL power calculation formulas with caution because the accuracy is good but is not as high as with standard measurement methods.