## Impact of ablation efficiency reduction on post-surgery corneal asphericity: simulation of the laser refractive surgery with a flying spot laser beam

Optics Express, Vol. 16, Issue 16, pp. 11808-11821 (2008)

http://dx.doi.org/10.1364/OE.16.011808

Acrobat PDF (404 KB)

### Abstract

We developed a rigorous simulation model to evaluate ablation algorithms and surgery outcomes in laser refractive surgery. The model (CASIM: Corneal Ablation SIMulator) simulates an entire surgical process,which includes calculating an ablation profile from measured wavefront errors, generating a shot pattern for a flying spot laser beam, simulation of the shot-by-shot ablation process based on a measured or modeled beam profile, and healing of the cornea after surgery. Using simulated post-surgery corneal shapes for various ablation parameters and beam fluences,we calculated angular dependence of ablation efficiency and the amount of increase in corneal asphericity. Without considering the effect of corneal healing, our result shows the following; 1) ablation efficiency reduction in the periphery depends on the peak fluence of the laser beam, 2) corneal asphericity increases even in the surgery using an ablation profile based on the exact Munnerlyn formula, contrary to previous reports, and 3) post-surgery corneal asphericity increases by a smaller amount in high fluence small Gaussian beam surgery than in low fluence truncated Gaussian beam.Our model can provide improved ablation profiles that compensate for the change of corneal asphericity and induction of spherical aberration in a flying spot laser system, resulting in better surgery outcomes in laser refractive surgeries.

© 2008 Optical Society of America

## 1. Introduction

1. R. R. Krueger and S. Trokel, “Quantitation of Corneal Ablation by Ultraviolet Laser Light,” Arch.Ophthalmol. **103**, 1741–1742 (1985). [CrossRef] [PubMed]

2. F. Manns, J.-H. Shen, P. Söderberg, T. Matsui, and J.-M. Parel, “Development of an algorithm for corneal reshaping with a scanning laser beam,” Appl. Opt. **34**, 4600–4608 (1995). [CrossRef] [PubMed]

3. M. Mrochen, M. Kaemmerer, and T. Seiler, “Wavefront-guided Laser in situ Keratomileusis: Early Results in Three Eyes,” J. Refract. Surg. **16**, 116–121 (2000). [PubMed]

6. C. B. O'Donnell, J. Kemner, and Francis E. O'Donnell Jr., “Ablation smoothness as a function of excimer
laser delivery system,” J. Cataract. Refract. Surg. **22**, 682–685 (1996). [PubMed]

7. B. Muller, T. Boeck, and C. Hartmann, “Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy,” J. Cataract. Refract. Surg. **30**, 464–470 (2004). [CrossRef] [PubMed]

8. M. Mrochen, M. Kaemmerer, P. Mierdel, and T. Seiler, “Increased higher-order optical aberrations after
laser refractive surgery: A problem of subclinical decentration,” J. Cataract. Refract. Surg. **27**, 362–369 (2001). [CrossRef] [PubMed]

9. M. Mrochen, R. R. Krueger, M. Bueeler, and T. Seiler, “Aberration-sensing and Wavefront-guided Laser in
situ Keratomileusis: Management of Decentered Ablation,” J. Refract. Surg. **18**, 418–429 (2002). [PubMed]

10. N. M. Taylor, R. H. Eikelboom, P. P. v. Sarloos, and P. G. Reid, “Determining the accuracy of an Eye Tracking System for Laser Refractive Surgery,” J. Refract. Surg. **16**, S643–S646 (2000). [PubMed]

12. D. Zadok, C. Carrillo, F. Missiroli, S. Litwak, N. Robledo, and A. S. Chayet, “The Effect of Corneal Flap on Optical Aberrations,” Am. J. Ophthalmol. **138**, 190–193 (2004). [CrossRef] [PubMed]

13. M. Mrochen and T. Seiler, “Influence of Corneal Curvature on Calculation of Ablation Patterns used in Photorefractive Laser Surgery,” J. Refract. Surg. **17**, S584–S587 (2001). [PubMed]

20. C. Roberts, “Biomechanics of the Cornea and Wavefront guided Laser Refractive Surgery,” J. Refract. Surg. **18**, S589–S592 (2002). [PubMed]

24. C. R. Munnerlyn, S. J. Koons, and J. Marshall, “Photorefractive keratectomy: A technique for laser
refractive surgery,” J. Cataract. Refract. Surg. **14**, 46–52 (1988). [PubMed]

27. J. R. Jiménez, R. G. Anera, and L. J. d. Barco, “Equation for Corneal Asphericity After Corneal Refractive Surgery,” J. Refract. Surg. **19**, 65–69 (2003). [PubMed]

28. 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,” J. Refract. Surg. **19**, S592–S596 (2003). [PubMed]

## 2. Method

### 2.1 Interaction of the laser beam at oblique incidence

29. A. Vogel and V. Venugopalan, “Mechanisms of Pulsed Laser Ablation of Biological Tissues,” Chem. Rev. **103**, 577–644 (2003). [CrossRef] [PubMed]

30. T. F. Deutsch and M. W. Geis, “Self-developing UV photoresist using excimer laser exposure,” J. Appl.Phys. 54 (12), December 1983 **54**, 7201–7204 (1983). [CrossRef]

*d*is the ablation depth,

*α*is the absorption coefficient in the material at the laser wavelength,

*F*is the fluence at position

_{r}*r*, and

*F*is the ablation threshold fluence. Establishing precise values for the cornea is challenging, but based on the collected ablation data from many published studies, typical values are

_{TH}*α*=2.9 μm

^{-1}and

*F*=40 ~ 60 mJ/cm

_{TH}^{2}.It may be noted that our choice of absorption coefficient can only be correct in average-sense,as recent dynamic ablation model development has shown that ablation rate can be more accurately represented by a dynamic model with varying absorption coefficient and local water content in the ablated tissue during the time course of ablation pulse [31

31. B. Fisher and D. Hahn, “Development and Numnerical Solution of a Mechanistic Model for Corneal Tissue Ablation with the 193-nm Argon Fluoride Excimer Laser,” J. Opt. Soc. Am. A **24**, 265–277 (2007). [CrossRef]

13. M. Mrochen and T. Seiler, “Influence of Corneal Curvature on Calculation of Ablation Patterns used in Photorefractive Laser Surgery,” J. Refract. Surg. **17**, S584–S587 (2001). [PubMed]

15. J. R. Jimenez, R. G. Anera, L. J. d. Barco, and E. Hita, “Effect on laser-ablation algorithms of reflection
losses and nonnormal incidence on the anterior cornea,” Appl. Phys. Lett. **81**, 1521–1523 (2002). [CrossRef]

*y*from the apex of the cornea with radius of curvature

*R*is (Fig. 1)

_{c}*z*given by

*F*, is approximated by the following equation:

_{r}^{2}Θ while the illuminated area under the laser beam is enlarged by 1/cosΘ, with the resulting fluence varying ‘approximately’ with cosΘ. The relationship holds exactly with a spherical shape, but also holds ‘approximately’ for aspheric shapes when a large beam is employed. In the real simulation, we calculate the local incidence angle for each shot to minimize the error in the estimation of local fluence.

32. S. J. Orfanidis, *Electromagnetic Waves & Antennas* (2004), http://www.ece.rutgers.edu/~orfanidi/ewa/.

*D*and

_{R}*D*are given by:

_{I}*ω*is angular frequency of the laser,

*μ*

_{0}is permeability of vacuum,

*ε*and

_{R}*ε*are the real and imaginary parts of permittivity of corneal tissue at the laser wavelength (

_{I}*ε*=

_{C}*ε*

_{R}-

*jε*),respectively and can be calculated from complex refractive index of cornea,

_{I}*n*=1.52-

_{C}*j*0.04. It is well known that reflectance also varies with incidence angle. So, the final expression of the ablation depth Eq. (1) becomes:

*R*is reflectance at the beam position on the cornea and

_{REFL}*α*is the angle-dependent absorption coefficient. We note that the factor of two in Eq. (1) is required to take into account laser beam intensity instead of field amplitude. With the use of Eq. (7), we can calculate the individual ablated depth profile associated with each shot on the cornea.

_{Z}### 2.2 Ablation profiles and shot pattern generation

*z*(

_{M}*r*), is given by [24

24. C. R. Munnerlyn, S. J. Koons, and J. Marshall, “Photorefractive keratectomy: A technique for laser
refractive surgery,” J. Cataract. Refract. Surg. **14**, 46–52 (1988). [PubMed]

*OZ*is the ablation optical zone diameter and

*r*is the radial distance from the apex of the cornea. The parabolic approximation of the Munnerlyn formula,

*zP*(

*r*), is given by [16

16. R. G. Anera, J. R. Jiménez, L. J. d. Barco, and E. Hita, “Changes in corneal asphericity after laser refractive surgery, including reflection losses and nonnormal incidence upon the anterior cornea,” Opt. Lett. **28**, 417–419 (2003). [CrossRef] [PubMed]

^{*}number of shots) is equivalent to the volume of the ablation profile. The laser beam shots are applied to the corneal tissue in a spatially distributed pattern spread over an area equivalent to the surface area of the OZ diameter. To generate the non-uniform shot pattern of the desired ablation profile, we stretch the uniform shot density pattern as a function of azimuthal angle and radial distance from a reference position on the ablation profile to produce the shot density necessary to achieve the desired ablation depth at every point within the ablation zone. The sequence of these shots is chosen to satisfy the following conditions; 1) no adjacent shots fall in the neighboring area of the previous shot and 2) the sequence is chosen to provide progressive correction over time. Figure 2(a) shows an example of shot patterns generated for the correction of -3D eye with OZ diameter of 6mm.The total number of shots required to correct certain diopters depends on many parameters.For example, with a peak fluence of 540 mJ/cm

^{2}and a Gaussian-shaped beam of 0.4 mm radius (corresponding of

*VPS*=418∙10

^{-6}

*mm*

^{3}), we would need 5,923 shots to correct -12 D myopic eyes with a 6 mm optical zone based on the Munnerlyn formula. For a low fluence laser, peak fluence of 120 mJ/cm

^{2}, truncated Gaussian at 50% fluence level of 1.0 mm radius (Fig. 2), and a corresponding of

*VPS*=383∙10

^{-6}

*mm*

^{3}, we would need 6,457 shots to correct same -12 D myopic eye.

19. C. Dorronsoro, D. Cano, J. Merayo-Lloves, and S. Marcos, “Experiments on PMMA models to predict the
impact of corneal refractive surgery on corneal shape,” Opt. Express **14**, 6142–6156 (2006). [CrossRef] [PubMed]

19. C. Dorronsoro, D. Cano, J. Merayo-Lloves, and S. Marcos, “Experiments on PMMA models to predict the
impact of corneal refractive surgery on corneal shape,” Opt. Express **14**, 6142–6156 (2006). [CrossRef] [PubMed]

28. 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,” J. Refract. Surg. **19**, S592–S596 (2003). [PubMed]

### 3. Results and discussion

#### 3.1 Ablation efficiency reduction at oblique incidence

19. C. Dorronsoro, D. Cano, J. Merayo-Lloves, and S. Marcos, “Experiments on PMMA models to predict the
impact of corneal refractive surgery on corneal shape,” Opt. Express **14**, 6142–6156 (2006). [CrossRef] [PubMed]

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

^{-6}mm

^{3}, (F

_{PK}=540 mJ/cm

^{2}). This pattern has been generated assuming the ablation threshold is 40mJ/cm

^{2}. However, if we use a VPS of 383×10

^{-6}mm

^{3}shot pattern (F

_{PK}=120 mJ/cm

^{2}), based on the ablation threshold of 60mJ/cm

^{2}, the reduction is larger as shown in the graph and this confirms that efficiency reduction largely depends on the ratio of

*F*/

_{PK}*F*[13

_{TH}13. M. Mrochen and T. Seiler, “Influence of Corneal Curvature on Calculation of Ablation Patterns used in Photorefractive Laser Surgery,” J. Refract. Surg. **17**, S584–S587 (2001). [PubMed]

^{2}for the calculation of post-surgery corneal asphericity, the asphericity calculated by using the experimental correction factor came closer to the clinically observed value. Our results support their findings.

#### 3.2 Impact of ablation efficiency reduction on post-surgery corneal asphericity

36. J. R. Jimenez, R. G. Anera, J. A. D?az, and F. Perez-Ocon, “Corneal asphericity after refractive surgery when
the Munnerlyn formula is applied,” J. Opt. Soc. Am. A **21**, 98–103 (2004). [CrossRef]

^{2}respectively, 3> ablation profile (exact Munnerlyn or parabolic approximation) for various magnitudes of attempted correction. When efficiency reduction is ignored, Figs. 4(a) and 4(c) show a very small difference in post-surgery asphericity between the three beam types. However, with efficiency reduction included, Figs. 4(b) and 4(d) clearly show different asphericities among three laser beam types. The largest increase of asphericity is observed with the low fluence truncated Gaussian beam at high threshold fluence and the smallest increase is with the high fluence Gaussian beam for a given correction and a given pre-surgery asphericity. Thus we conclude that the impact of ablation efficiency reduction on the change in asphericity is less significant with a high fluence Gaussian beam than a low fluence truncated Gaussian beam.

36. J. R. Jimenez, R. G. Anera, J. A. D?az, and F. Perez-Ocon, “Corneal asphericity after refractive surgery when
the Munnerlyn formula is applied,” J. Opt. Soc. Am. A **21**, 98–103 (2004). [CrossRef]

#### 3.3 Post-surgery corneal asphericity: comparison of simulation and clinical data

14. P. S. Hersh, K. Fry, and J. W. Blaker, “Spherical aberration after laser in situ keratomileusis and photorefractive keratectomy Clinical results and theoretical models of etiology,” J. Cataract. Refract. Surg. **29**, 2096–2104 (2003). [CrossRef] [PubMed]

23. G. Yoon, S. MacRae, D. R. Williams, and I. G. Cox, “Causes of spherical aberration induced by laser
refractive surgery,” J. Cataract. Refract. Surg. **31**, 127–135 (2005). [CrossRef] [PubMed]

28. 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,” J. Refract. Surg. **19**, S592–S596 (2003). [PubMed]

37. R. G. Anera, J. R. Jimenez, L. J. d. Barco, J. Bermudez, and E. Hita, “Changes in corneal asphericity after laser in situ keratomileusis,” J. Cataract. Refract. Surg. **29**, 762–768 (2003). [CrossRef] [PubMed]

**19**, S592–S596 (2003). [PubMed]

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

^{2}for corneal tissue.

**19**, S592–S596 (2003). [PubMed]

**19**, S592–S596 (2003). [PubMed]

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

^{2}after applying an experimentally derived correction factor. In Fig. 8 in [19

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

^{2}and another one using an efficiency reduction factor proposed by Jimenez et al [15

15. J. R. Jimenez, R. G. Anera, L. J. d. Barco, and E. Hita, “Effect on laser-ablation algorithms of reflection
losses and nonnormal incidence on the anterior cornea,” Appl. Phys. Lett. **81**, 1521–1523 (2002). [CrossRef]

^{2}) did predict smaller change for post-surgery asphericity than one with higher threshold fluence (60 mJ/cm

^{2}). Also, as discussed in [19

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

**19**, S592–S596 (2003). [PubMed]

27. J. R. Jiménez, R. G. Anera, and L. J. d. Barco, “Equation for Corneal Asphericity After Corneal Refractive Surgery,” J. Refract. Surg. **19**, 65–69 (2003). [PubMed]

^{2}=0.96. The result shown here verifies that CASIM predictions of corneal asphericity using a rigorous model can be compared to clinical observations for real patients.

### 4. Conclusions

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

14. P. S. Hersh, K. Fry, and J. W. Blaker, “Spherical aberration after laser in situ keratomileusis and photorefractive keratectomy Clinical results and theoretical models of etiology,” J. Cataract. Refract. Surg. **29**, 2096–2104 (2003). [CrossRef] [PubMed]

**19**, S592–S596 (2003). [PubMed]

**19**, S592–S596 (2003). [PubMed]

**14**, 6142–6156 (2006). [CrossRef] [PubMed]

## Acknowledgments

## References and links

1. | R. R. Krueger and S. Trokel, “Quantitation of Corneal Ablation by Ultraviolet Laser Light,” Arch.Ophthalmol. |

2. | F. Manns, J.-H. Shen, P. Söderberg, T. Matsui, and J.-M. Parel, “Development of an algorithm for corneal reshaping with a scanning laser beam,” Appl. Opt. |

3. | M. Mrochen, M. Kaemmerer, and T. Seiler, “Wavefront-guided Laser in situ Keratomileusis: Early Results in Three Eyes,” J. Refract. Surg. |

4. | 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,” IOVS |

5. | S. Marcos, S. Barbero, L. Llorente, and J. Merayo-Lloves, “Optical response to LASIK Surgery for Myopia from Total and Corneal Aberration Measurements,” IOVS |

6. | C. B. O'Donnell, J. Kemner, and Francis E. O'Donnell Jr., “Ablation smoothness as a function of excimer
laser delivery system,” J. Cataract. Refract. Surg. |

7. | B. Muller, T. Boeck, and C. Hartmann, “Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy,” J. Cataract. Refract. Surg. |

8. | M. Mrochen, M. Kaemmerer, P. Mierdel, and T. Seiler, “Increased higher-order optical aberrations after
laser refractive surgery: A problem of subclinical decentration,” J. Cataract. Refract. Surg. |

9. | M. Mrochen, R. R. Krueger, M. Bueeler, and T. Seiler, “Aberration-sensing and Wavefront-guided Laser in
situ Keratomileusis: Management of Decentered Ablation,” J. Refract. Surg. |

10. | N. M. Taylor, R. H. Eikelboom, P. P. v. Sarloos, and P. G. Reid, “Determining the accuracy of an Eye Tracking System for Laser Refractive Surgery,” J. Refract. Surg. |

11. | M. Bueeler, M. Mrochen, and T. Seiler, “Effect of spot size, ablation depth, and eye-tracker latency on the optical outcome of corneal laser surgery with a scanning spot laser,“ in |

12. | D. Zadok, C. Carrillo, F. Missiroli, S. Litwak, N. Robledo, and A. S. Chayet, “The Effect of Corneal Flap on Optical Aberrations,” Am. J. Ophthalmol. |

13. | M. Mrochen and T. Seiler, “Influence of Corneal Curvature on Calculation of Ablation Patterns used in Photorefractive Laser Surgery,” J. Refract. Surg. |

14. | P. S. Hersh, K. Fry, and J. W. Blaker, “Spherical aberration after laser in situ keratomileusis and photorefractive keratectomy Clinical results and theoretical models of etiology,” J. Cataract. Refract. Surg. |

15. | J. R. Jimenez, R. G. Anera, L. J. d. Barco, and E. Hita, “Effect on laser-ablation algorithms of reflection
losses and nonnormal incidence on the anterior cornea,” Appl. Phys. Lett. |

16. | R. G. Anera, J. R. Jiménez, L. J. d. Barco, and E. Hita, “Changes in corneal asphericity after laser refractive surgery, including reflection losses and nonnormal incidence upon the anterior cornea,” Opt. Lett. |

17. | D. Cano, S. Barbero, and S. Marcos, “Comparison of real and computer-simulated outcomes of LASIK refractive surgery,” J. Opt. Soc. Am. A |

18. | J. R. Jiménez, F. Rodríguez-Marín, R. G. Anera, and L. J. d. Barco, “Deviations of Lambert-Beer's law affect
corneal refractive parameters after refractive surgery,” Opt. Express |

19. | C. Dorronsoro, D. Cano, J. Merayo-Lloves, and S. Marcos, “Experiments on PMMA models to predict the
impact of corneal refractive surgery on corneal shape,” Opt. Express |

20. | C. Roberts, “Biomechanics of the Cornea and Wavefront guided Laser Refractive Surgery,” J. Refract. Surg. |

21. | D. Huang, M. Tang, and R. Shekhar, “Mathematical Model of Corneal Surface Smoothing after Laser Refractive Surgery,” Am. J. Ophthal. |

22. | C. Roberts, “Biomechanical customization: The next generation of laser refractive surgery,” J. Cataract.Refract. Surg. |

23. | G. Yoon, S. MacRae, D. R. Williams, and I. G. Cox, “Causes of spherical aberration induced by laser
refractive surgery,” J. Cataract. Refract. Surg. |

24. | C. R. Munnerlyn, S. J. Koons, and J. Marshall, “Photorefractive keratectomy: A technique for laser
refractive surgery,” J. Cataract. Refract. Surg. |

25. | R. W. Frey, J. H. Burkhalter, and G. P. Gray, “Laser Sculpting System,” (2001), US Patent # |

26. | D. Gatinel, T. Hoang-Xuan, and D. T. Azar, “Determination of Corneal Asphericity after Myopia Surgery with the Excimer Laser: A Mathematical Model,” IOVS |

27. | J. R. Jiménez, R. G. Anera, and L. J. d. Barco, “Equation for Corneal Asphericity After Corneal Refractive Surgery,” J. Refract. Surg. |

28. | 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,” J. Refract. Surg. |

29. | A. Vogel and V. Venugopalan, “Mechanisms of Pulsed Laser Ablation of Biological Tissues,” Chem. Rev. |

30. | T. F. Deutsch and M. W. Geis, “Self-developing UV photoresist using excimer laser exposure,” J. Appl.Phys. 54 (12), December 1983 |

31. | B. Fisher and D. Hahn, “Development and Numnerical Solution of a Mechanistic Model for Corneal Tissue Ablation with the 193-nm Argon Fluoride Excimer Laser,” J. Opt. Soc. Am. A |

32. | S. J. Orfanidis, |

33. | R. W. Frey, J. H. Burkhalter, and G. P. Gray, “Laser Sculpting Method and System,” US Patent 5,849,006 (1998). |

34. | C. Dorronsoro, J. Merayo-Lloves, and S. Marcos, “An Experimental Correction Factor of Radial Laser
Efficiency Losses in Corneal Refractive Surgery,” IOVS |

35. | S. Marcos, “Spherical Aberration: Biomechanics or Physical Laser Effects?,“ presented in |

36. | J. R. Jimenez, R. G. Anera, J. A. D?az, and F. Perez-Ocon, “Corneal asphericity after refractive surgery when
the Munnerlyn formula is applied,” J. Opt. Soc. Am. A |

37. | R. G. Anera, J. R. Jimenez, L. J. d. Barco, J. Bermudez, and E. Hita, “Changes in corneal asphericity after laser in situ keratomileusis,” J. Cataract. Refract. Surg. |

38. | Y. Kwon and S. Bott, “Post-surgery asphericity and spherical aberration due to ablation efficiency reduction and corneal remodeling in refractive surgeries,” in prep. (2008). |

**OCIS Codes**

(170.1020) Medical optics and biotechnology : Ablation of tissue

(170.3890) Medical optics and biotechnology : Medical optics instrumentation

(170.4470) Medical optics and biotechnology : Ophthalmology

(220.1000) Optical design and fabrication : Aberration compensation

(330.4460) Vision, color, and visual optics : Ophthalmic optics and devices

**ToC Category:**

Medical Optics and Biotechnology

**History**

Original Manuscript: April 28, 2008

Revised Manuscript: July 7, 2008

Manuscript Accepted: July 8, 2008

Published: July 23, 2008

**Virtual Issues**

Vol. 3, Iss. 9 *Virtual Journal for Biomedical Optics*

**Citation**

Young Kwon, Myoung Choi, and Steven Bott, "Impact of ablation efficiency reduction on post-surgery corneal asphericity: simulation of the laser refractive surgery with a flying spot laser beam," Opt. Express **16**, 11808-11821 (2008)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-16-11808

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### References

- R. R. Krueger and S. Trokel, "Quantitation of Corneal Ablation by Ultraviolet Laser Light," Arch. Ophthalmol. 103, 1741-1742 (1985). [CrossRef] [PubMed]
- F. Manns, J.-H. Shen, P. Söderberg, T. Matsui, and J.-M. Parel, "Development of an algorithm for corneal reshaping with a scanning laser beam," Appl. Opt. 34, 4600-4608 (1995). [CrossRef] [PubMed]
- M. Mrochen, M. Kaemmerer, and T. Seiler, "Wavefront-guided Laser in situ Keratomileusis: Early Results in Three Eyes," J. Refract. Surg. 16, 116-121 (2000). [PubMed]
- 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," IOVS 42, 1396-1403 (2001).
- S. Marcos, S. Barbero, L. Llorente, and J. Merayo-Lloves, "Optical response to LASIK Surgery for Myopia from Total and Corneal Aberration Measurements," IOVS 42, 3349-3356 (2001).
- C. B. O'Donnell, J. Kemner, and FrancisE. O'Donnell Jr., "Ablation smoothness as a function of excimer laser delivery system," J. Cataract. Refract. Surg. 22, 682-685 (1996). [PubMed]
- B. Muller, T. Boeck, and C. Hartmann, "Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy," J. Cataract. Refract. Surg. 30, 464-470 (2004). [CrossRef] [PubMed]
- M. Mrochen, M. Kaemmerer, P. Mierdel, and T. Seiler, "Increased higher-order optical aberrations after laser refractive surgery: A problem of subclinical decentration," J. Cataract. Refract. Surg. 27, 362-369 (2001). [CrossRef] [PubMed]
- M. Mrochen, R. R. Krueger, M. Bueeler, and T. Seiler, "Aberration-sensing and Wavefront-guided Laser in situ Keratomileusis: Management of Decentered Ablation," J. Refract. Surg. 18, 418-429 (2002). [PubMed]
- N. M. Taylor, R. H. Eikelboom, P. P. v. Sarloos, and P. G. Reid, "Determining the accuracy of an Eye Tracking System for Laser Refractive Surgery," J. Refract. Surg. 16, S643-S646 (2000). [PubMed]
- M. Bueeler, M. Mrochen, and T. Seiler, "Effect of spot size, ablation depth, and eye-tracker latency on the optical outcome of corneal laser surgery with a scanning spot laser," in Ophthalmic Technologies XIII (SPIE, 2003), pp. 150-160.
- D. Zadok, C. Carrillo, F. Missiroli, S. Litwak, N. Robledo, and A. S. Chayet, "The Effect of Corneal Flap on Optical Aberrations," Am. J. Ophthalmol. 138, 190-193 (2004). [CrossRef] [PubMed]
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