Intraocular lens power calculation in post-myopic-LASIK eyes: comparison of two different corneal refractive power measurements by Pentacam.

OBJECTIVES

To compare the accuracy of two different corneal refractive power measurements in intraocular lens (IOL) power calculation in post-myopic-LASIK eyes.

METHODS

Post-myopic-LASIK patients scheduled for cataract surgery were enrolled. Corneal refractive power centred on corneal apex (Kapex) and pupil centre (Kpupil), decentration of ablation zone, and Kappa angle were measured by Pentacam. Predicted postoperative spherical equivalence (SE) was calculated using Kapex and Kpupil, respectively. Prediction error was calculated as actual SE minus predicted SE. Mean error (ME), mean absolute error (MAE), and median absolute error (MedAE) were compared between Kapex and Kpupil groups, with subgroup analysis in terms of decentred ablation and Kappa angle.

RESULTS

Totally 92 eyes were analysed. ME, MAE and MedAE with Kapex were all lower than those with Kpupil (-0.42 ± 1.06 vs -0.64 ± 1.21 D, 0.89 ± 0.71 vs 1.01 ± 0.92 D, 0.69 vs 0.76 D, respectively; P < 0.05 for ME and MedAE). In both subgroups of larger decentration of ablation zone and larger Kappa angle, ME with Kapex was lower than that with Kpupil to a higher degree (both P < 0.05). Average Kapex was higher than average Kpupil (P < 0.001). Multivariate analysis demonstrated that prediction error with Kpupil was associated with decentration of ablation zone (β = -0.264, P = 0.019), while no such association was found in prediction error with Kapex.

CONCLUSIONS

The Kapex achieved better accuracy in IOL power calculation than Kpupil in post-myopic-LASIK eyes, especially in eyes with large decentration of ablation zone or large Kappa angle.