Repeatability and comparability of simulated K values between a grid projection-based device and a Placido/dual Scheimpflug device

Abstract

Purpose: To evaluate the repeatability and comparability of simulated K values obtained by the Galilei G4 Corneal Tomographer and the iDesign Wavefront Abberometer. Methods: The right eyes of 100 consecutive pre-laser-assisted in situ keratomileusis (LASIK) patients were included in this study. Patients with a history or signs of previous corneal or ocular trauma and infection were excluded. Paired corneal measurements for flat (K1) and steep (K2) meridians were obtained with both the Galilei and the iDesign. Repeatability was evaluated by calculating the coefficient of variation (CV) of the paired measurements. The comparability between platforms was evaluated by calculation of the mean differences followed by the construction of Bland-Altman plots and calculation of limits of agreement (LOA). Results: While the mean CV for both devices was low (0.17% versus 0.57% for the Galilei and iDesign, respectively), a large proportion of eyes measured by the iDesign (22%) showed an absolute difference of > 0.5 D between paired readings, compared to 1% as measured by the Galilei. The Galilei consistently measured higher than the iDesign. Although the mean difference did not exceed 0.17 D, the LOAs were unacceptablywide at -0.52 D to 0.85 D and -0.69 D to 0.89 D for K1 and K2, respectively. Conclusion: As regards keratometry, the iDesign demonstrated clinically unacceptable repeatability. Both platforms demonstrated sufficiently wide LOA that we could not recommend that they are used interchangeably.