Purpose. To evaluate to which extent individual Zernike terms can be corrected. Methods. Ablation time and fidelity was analysed using different fluence levels (range 90–2000？mJ/ ) and aspheric ablation profiles. With optimal parameters, the extent to which individual Zernike modes can be corrected was evaluated. Results. The range 188–565？mJ/ resulted as optimum fluence level with an optimum proportion range 50%–90% for high fluence. With optimal parameters, it corresponds to 2.4 s/D at 6？mm OZ, with fidelity variance of 53？ m RMS, and average ablation error of 0.5？ m for each location. Ablation simulation of coma Z[3, 1] showed 98,4% accuracy and 98% fit quality; trefoil Z[3, 3], 99,9% accuracy and 98% fit quality; spherical aberration Z[4,0], 96,6% accuracy and 97% fit quality; secondary astigmatism Z[4, 2], 97,9% accuracy and 98% fit quality. Real ablation on a flat plate of PMMA of coma Z[3, 1] showed 96,7% accuracy and 96% fit quality; trefoil Z[3, 3], 97,1% accuracy and 96% fit quality; spherical aberration Z[4,0], with 93,9% accuracy and 90% fit quality; secondary astigmatism Z[4, 2], with 96,0% accuracy and 96% fit quality. Conclusions. Ablation of aspherical and customised shapes based upon Zernike polynomials up to the the 8th order seems accurate using the dual fluence concept implemented at the AMARIS platform. 1. Introduction With the introduction of the laser technologies for refractive surgery, the change of the corneal curvature to compensate in a controlled manner for refractive errors of the eye [1] is more accurate than ever. The procedure is nowadays a successful technique, due to its submicrometric precision and the high predictability and repeatability of corneal ablation accompanied by minimal side effects. Standard ablation profiles based on the removal of convex-concave tissue lenticules with spherocylindrical surfaces proved to be effective in the compensation of primary refractive errors. However, the quality of vision deteriorated significantly, especially under mesopic and low-contrast conditions [2]. With the introduction of wavefront analysis, it was proved that the conventional refractive LASER techniques were far from ideal, by measuring the aberrations induced by conventional algorithms and the aberrations induced by the LASIK flap cut itself. With the LASIK (Laser in Situ Keratomileusis [3]) treatment, we have an accepted method to correct refractive errors such myopia [4], hyperopia [5], and astigmatism [6]. One of the most significant side effects in myopic LASIK, is the induction of spherical aberration [7], which
References
[1]
C. R. Munnerlyn, S. J. Koons, and J. Marshall, “Photorefractive keratectomy: a technique for laser refractive surgery,” Journal of Cataract and Refractive Surgery, vol. 14, no. 1, pp. 46–52, 1988.
[2]
L. Mastropasqua, L. Toto, E. Zuppardi, M. Nubile, P. Carpineto, M. Di Nicola, and E. Ballone, “Photorefractive keratectomy with aspheric profile of ablation versus conventional photorefractive keratectomy for myopia correction: six-month controlled clinical trial,” Journal of Cataract and Refractive Surgery, vol. 32, no. 1, pp. 109–116, 2006.
[3]
L. Buratto, M. Ferrari, and P. Rama, “Excimer laser intrastromal keratomileusis,” American Journal of Ophthalmology, vol. 113, no. 3, pp. 291–295, 1992.
[4]
I. G. Pallikaris and D. S. Siganos, “Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia,” Journal of Refractive and Corneal Surgery, vol. 10, no. 5, pp. 498–510, 1994.
[5]
K. Ditzen, H. Huschka, and S. Pieger, “Laser in situ keratomileusis for hyperopia,” Journal of Cataract and Refractive Surgery, vol. 24, no. 1, pp. 42–47, 1998.
[6]
M. A. El Danasoury, G. O. Waring III, A. El Maghraby, and K. Mehrez, “Excimer laser in situ keratomileusis to correct compound myopic astigmatism,” Journal of Refractive Surgery, vol. 13, no. 6, pp. 511–520, 1997.
[7]
E. Moreno-Barriuso, J. M. Lloves, S. Marcos, R. Navarro, L. Llorente, and S. Barbero, “Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing,” Investigative Ophthalmology and Visual Science, vol. 42, no. 6, pp. 1396–1403, 2001.
[8]
L. N. Thibos, X. Hong, A. Bradley, and R. A. Applegate, “Accuracy and precision of objective refraction from wavefront aberrations,” Journal of Vision, vol. 4, no. 4, pp. 329–351, 2004.
[9]
T. O. Salmon, Corneal contribution to the Wavefront aberration of the eye, PhD Dissertation, 1999.
[10]
M. Mrochen, M. Jankov, M. Bueeler, and T. Seiler, “Correlation between corneal and total wavefront aberrations in myopic eyes,” Journal of Refractive Surgery, vol. 19, no. 2, pp. 104–112, 2003.
[11]
J. L. Alió, J. I. Belda, A. A. Osman, and A. M. M. Shalaby, “Topography-guided laser in situ keratomileusis (TOPOLINK) to correct irregular astigmatism after previous refractive surgery,” Journal of Refractive Surgery, vol. 19, no. 5, pp. 516–527, 2003.
[12]
M. Mrochen, M. Kaemmerer, and T. Seiler, “Clinical results of wavefront-guided laser in situ keratomileusis 3 months after surgery,” Journal of Cataract and Refractive Surgery, vol. 27, no. 2, pp. 201–207, 2001.
[13]
M. Mrochen, C. Donitzky, C. Wüllner, and J. L？ffler, “Wavefront-optimized ablation profiles: theoretical background,” Journal of Cataract and Refractive Surgery, vol. 30, no. 4, pp. 775–785, 2004.
[14]
T. Koller, H. P. Iseli, F. Hafezi, M. Mrochen, and T. Seiler, “Q-factor customized ablation profile for the correction of myopic astigmatism,” Journal of Cataract and Refractive Surgery, vol. 32, no. 4, pp. 584–589, 2006.
[15]
D. Gatinel, J. Malet, T. Hoang-Xuan, and D. T. Azar, “Analysis of customized corneal ablations: theoretical limitations of increasing negative asphericity,” Investigative Ophthalmology and Visual Science, vol. 43, no. 4, pp. 941–948, 2002.
[16]
D. Huang and M. Arif, “Spot size and quality of scanning laser correction of higher-order wavefront aberrations,” Journal of Cataract and Refractive Surgery, vol. 28, no. 3, pp. 407–416, 2002.
[17]
A. Guirao, D. R. Williams, and S. M. MacRae, “Effect of beam size on the expected benefit of customized laser refractive surgery,” Journal of Refractive Surgery, vol. 19, no. 1, pp. 15–23, 2003.
[18]
M. Bueeler and M. Mrochen, “Simulation of eye-tracker latency, spot size, and ablation pulse depth on the correction of higher order wavefront aberrations with scanning spot laser systems,” Journal of Refractive Surgery, vol. 21, no. 1, pp. 28–36, 2005.
[19]
S. Marcos, D. Cano, and S. Barbero, “Increase in corneal asphericity after standard laser in situ keratomileusis for myopia is not inherent to the Munnerlyn algorithm,” Journal of Refractive Surgery, vol. 19, no. 5, pp. S592–S596, 2003.
[20]
M. Mrochen and T. Seiler, “Influence of corneal curvature on calculation of ablation patterns used in photorefractive laser surgery,” Journal of Refractive Surgery, vol. 17, no. 5, pp. S584–S587, 2001.
[21]
J. R. Jiménez, R. G. Anera, L. Jiménez del Barco, and E. Hita, “Effect on laser-ablation algorithms of reflection losses and nonnormal incidence on the anterior cornea,” Applied Physics Letters, vol. 81, no. 8, pp. 1521–1523, 2002.
[22]
J. R. Jiménez, R. G. Anera, L. J. Del Barco, E. Hita, and F. Pérez-Ocón, “Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams,” Optics Express, vol. 13, no. 1, pp. 336–343, 2005.
[23]
T. Bende, T. Seiler, and J. Wollensak, “Side effects in excimer corneal surgery. Corneal thermal gradients,” Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 226, no. 3, pp. 277–280, 1988.
[24]
G. H. Pettit, “The Alcon/Summit/Autonomous perspective on fixed vs. variable spot ablation,” Journal of Refractive Surgery, vol. 17, no. 5, pp. S592–S593, 2001.
[25]
J. E. A. Pedder, A. S. Holmes, and P. E. Dyer, “Improved model for the angular dependence of excimer laser ablation rates in polymer materials,” Applied Physics Letters, vol. 95, no. 17, Article ID 174105, 2009.
[26]
J. R. Jiménez, J. J. Castro, C. Ortiz, and R. G. Anera, “Testing a model for excimer laser-ablation rates on corneal shape after refractive surgery,” Optics Letters, vol. 35, p. 1789, 2010.
[27]
M. C. Arbelaez and A. S. Mosquera, “The SCHWIND AMARIS total-tech laser as an all-rounder in refractive surgery,” Middle East African Journal of Ophthalmology, vol. 16, no. 1, pp. 46–53, 2009.
[28]
M. C. Arbelaez, I. M. Aslanides, C. Barraquer, et al., “LASIK for myopia and astigmatism using the SCHWIND AMARIS excimer laser: an international multicenter trial,” Journal of Refractive Surgery, vol. 26, no. 2, pp. 88–98, 2010.
[29]
M. C. Arbelaez, T. Ewering, and S. A. Mosquera, “Decision assistant wizard to standardize optimal outcomes in excimer laser refractive corneal surgery,” Journal of Refractive Surgery, vol. 25, pp. 1–11, 2010.
[30]
M. Camellin and S. A. Mosquera, “Aspheric optical zones: the effective optical zone with the SCHWIND AMARIS,” Journal of Refractive Surgery, vol. 19, pp. 1–12, 2010.
