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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 Optikgeräte, 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 μm (P < 0.05). Subgroup analysis revealed a difference in ablation depth measurements of 7.1 μm 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.