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Luciana d. Matos, Mariana T. Carvalho, Paulo Schor, Enos Oliveira, Claudia Francesconi, Carlos Arce, Vanderlei S. Bagnato, Luis Alberto V. Carvalho; Complete Characterization of Laser Beam Ablation Profile on PMMA Material as a Function of Practical and Theoretical Parameters and its Consequence to the Improvement of Customized Refractive Surgery Outcomes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4058.
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Many practical and theoretical studies on the ideal refractive laser profile and algorithm in order to obtain optimal corneal ablations and lower residual spherical aberrations have been made. Nevertheless, on the theoretical studies not all practical variables are available and on the practical studies, commercial lasers and non-disclosed algorithms are used. The lack of a better theoretical & practical ablation model has resulted in greater practical spherical aberration outcomes than predicted and the problem still persists on most of the state-of-the-art surgical lasers commercially available (Dorronsoro et al., Opt. Express 14, 6142, 2006). In this study we have conciliated the theoretical and practical advances into one empirical formula which relates the ablation profile with variables such as beam diameter, fluency, material and angle of incidence. This formula may be used by manufactures to improve laser calibration and algorithms in order to improve refractive surgery outcomes.
In this study we have used an Excimer laser (coherent, model Xantos XS) with different beam profiles (top hat and Gaussian), diameters (1.0 to 5.0 mm) and pulse energies (1mJ to 5mJ) to deliver different number of pulses on plane-parallel plates of polymethylmethacrylate (PMMA) material placed at different angles with respect to the beam direction.
The 3D ablation patterns were measured by a non contact high resolution optical profiler and mathematical fitting was performed using a matlab algorithm with different analytic equations. An empirical formula which best approximated experimental data was obtained to describe the profiles as a function of the variables described above.
The empirical formula presented here is a useful tool in conjunction to other theoretical and practical methods in the literature in order to improve laser calibration and manufacture’s ablation algorithms in order to reduce undesired residual aberrations. This study was conducted on PMMA plates and should be repeated on in vitro corneas in order to obtain the material factor, nevertheless we believe that the overall function should remain the same.
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