Comparison of Laser Platform Estimation and Objective Measurement of Maximum Ablation Depth Using Scheimpflug Pachymetry in Myopic Femtosecond Laser In Situ Keratomileusis

Purpose:To compare the preoperative estimation of maximum ablation depth provided by the laser platform with objective measurement using Scheimpflug pachymetry in myopic femtosecond laser-assisted in situ keratomileusis (FS-LASIK).Methods:This is a prospective study carried out at the Rothschild Foundation, Paris, France. In 89 consecutive myopic eyes (45 patients) treated with FS-LASIK, the maximum ablation depth was calculated by measuring the difference between preoperative and 3-month postoperative measurements in central corneal thickness using Scheimpflug pachymetry (Pentacam HR; Oculus Optikgerate, Wetzlar, Germany). These values were compared with the preoperative estimation of the maximum ablation depth provided by the laser platform, without nomogram adjustment.Results:We found a strong linear correlation between laser platform estimation of maximum ablation depth and Scheimpflug pachymetry (P < 0.00001). The mean ablation depth measured using Scheimpflug pachymetry was greater than that predicted by the laser platform, with a mean overall difference of 2.15 <mu>m (P < 0.05). Subgroup analysis revealed a difference in ablation depth measurements of 7.1 <mu>m in the high myopia subgroup, which was the only subgroup where the difference remained statistically significant.Conclusions:In myopic FS-LASIK, laser platform estimation of maximum ablation depth correlates well with measurement of maximum ablation depth using Scheimpflug pachymetry and therefore can be used safely.