Research Article | Open Access
The Effect of Intraocular Pressure on the Outcome of Myopic Photorefractive Keratectomy: A Numerical Approach
Photorefractive Keratectomy (PRK) is a surgical procedure widely performed to correct myopia. In this work, the effect of the intraocular pressure (IOP) on the refractive correction achieved by the PRK surgery was analyzed using a numerical model. Simulations of PRK surgery at 10, 15 and 21 mmHg of IOP were performed and the post-surgical diopters were estimated. For low and medium values of IOP (10 and 15 mmHg), the computed results were close to those used by clinicians based on experience and defined without considering the IOP, while an undercorrection was predicted for the highest value of IOP (21 mmHg). From these results, we suggest that IOP should be considered in the determination of the depth of ablation, in addition to other factors such as the level of myopia or the corneal central thickness.
- J. D. Doughty and M. L. Zaman, “Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach,” Surv. Ophthalmol, vol. 44, no. 5, pp. 367–408, 2000.
- A. Elsheikh, D. Alhasso, and P. Rama, “Assessment of the epithelium's contribution to corneal biomechanics,” Experimental Eye Research, vol. 86, pp. 445–451, 2008.
- C. S. Foster, D. T. Azar, and C. H. Dohlman, The Cornea. Scientific Foundations & Clinical Practice, Lippincott Williams & Wilkins, Philadelphia, USA, 2005.
- R. H. Newton and K. M. Meek, “The Integration of the Corneal and Limbal Fibers in the Human Eye,” Biophys J, vol. 75, pp. 2508–2512, 1998.
- J. I. Barraquer, “Conducta de la córnea frente a los cambios de espesor (contribución a la cirugía refractiva),” Arch Soc Am Oftalmol Optom, vol. 5, pp. 81–87, 1964.
- S. Trokel, R. Srinivasan, and B. Braren, “Excimer Laser Surgery of the Cornea,” American Journal of Ophthalmology, vol. 96, pp. 710–715, 1983.
- P. S. Hersh, K. S. Scher, and R. Irani, “Corneal topography of photorefractive keratectomy versus laser in situ keratomileusis. Summit PRK-LASIK study Group,” Ophtalmology, vol. 105, pp. 612–619, 1998.
- F. J. Potgieter, C. Roberts, I. G. Cox et al., “Prediction of flap response,” J Cataract Refract Surg., vol. 31, no. 1, pp. 106–14, 2005 Jan.
- M. Bryant and P. McDonnell, “Constitutive laws for biomechanical modeling of refractive surgery,” J Biomech Eng, vol. 118, pp. 473–481, 1996.
- D. Cabrera Fernández, A. M. Niazy, R. M. Kurtz, G. P. Djotyan, and T. Juhasz, “Finite element analysis applied to cornea reshaping,” J Biomed Opt., vol. 10, no. 6, 064018, 2005 Nov-Dec.
- A. Gefen, R. Shalom, D. Elad, and Y. Mandel, “Biomechanical analysis of the keratoconic cornea,” J. Mech. Behav. Biomed. Mater., vol. 2, no. 3, pp. 224–236, 2009.
- A. Pandolfi, G. Fotia, and F. Manganiello, “Element Simulations of Laser Refractive Corneal Surgery,” Engineering with Computers, vol. 25, pp. 15–24, 2009.
- P. Pinsky, D. V. D. Heide, and D. Chernyak, “Computational modeling of mechanical anisotropy in the cornea and sclera,” J Cataract Refract Surg, vol. 31, pp. 136–145, 2005.
- V. Alastrué, B. Calvo, E. Peña, and M. Doblaré, “Biomechanical Modelling of Refractive Corneal surgery,” J Biomech Eng ASME, vol. 128, no. 1, pp. 150–160, 2006.
- A. Pandolfi and F. Maganiello, “A model for the human cornea: constitutive formulation and numerical analysis,” Biomech Model Mechanobiol, vol. 5, pp. 237–246, 2006.
- P. Pinsky and V. Datye, “A microstructurally-based finite element model of the incised human cornea,” Journal of Biomedical Engineering, vol. 10, pp. 907–922, 1991.
- E. Lanchares, B. Calvo, J. A. Cristóbal, and M. Doblaré, “Finite Element simulation of arcuates for astigmatism correction,” J Biomech., vol. 41, no. 4, pp. 797–805, 2008.
- K. Anderson, A. El-Sheikh, and T. Newson, “Application of structural analysis to the mechanical behaviour of the cornea,” J R Soc Interface, vol. 1, no. 1, pp. 3–15, 2004; 22.
- T. Colton and F. Ederer, “The distribution of intraocular pressures in the general population,” Survey of Ophthalmology, vol. 25, no. 3, pp. 123–129, 1980.
- D. Cabrera Fernández, A. M. Niazy, R. M. Kurtz, G. P. Djotyan, and T. Juhasz, “A finite element model for ultrafast laser-lamellar keratoplasty,” Ann Biomed Eng, vol. 34, pp. 169–183, 2006.
- Computational Modeling Sciences Department, Sandia National Laboratories. Cubit 10.1 User Documentation. http://cubit.sandia.gov/help-version10.1/cubithelp.htm, 2006.
- Structural Dynamics Research Corporation. I-Deas Tutorials. EDS. 2001.
- D. Hoeltzel, P. Altman, D. Buzard, and K. Choe, “Strip extensometry for comparison of the mechanical response of bovine, rabbit and human corneas,” J Biomech Eng, vol. 114, pp. 202–215, 1992.
- D. Monti, P. Chetoni, S. Burgalassi, M. Najarro, and M. F. Saettone, “Increased corneal hydration induced by potential ocular penetration enhancers: assessment by differential scanning calorimetry (DSC) and by desiccation,” International Journal of Pharmaceutics, vol. 232, no. 1-2, pp. 139–147, 2002.
- H. Aghamohammadzadeh, R. H. Newton, and K. M. Meek, “X-ray scattering used to map the preferred collagen orientation in the human cornea and limbus,” Structure, vol. 12, pp. 249–256, 2004.
- G. A. Holzapfel and T. Gasser, “A viscoelastic model for fibre-reinforced composites at finite strains: Continuum basis, computational aspects and applications,” Comput Methods Appl Mech Engrg, vol. 190, pp. 4379–4403, 2001.
- J. Weiss, B. Maker, and S. Govindjee, “Finite element implementation of incompressible, transversely isotropic hyperelasticity,” Comput Methods Appl Mech Engrg, vol. 135, pp. 107–128, 1996.
- J. C. Simo and R. L. Taylor, “Consistent tangent operators for rate-independent elastoplasticity,” Comput Methods Appl Mech Engrg, vol. 48, pp. 101–118, 1985.
- G. A. Holzapfel, T. C. Gasser, and R. W. Ogden, “A new constitutive framework for arterial wall mechanics and a comparative study of material models,” J Elasticity, vol. 61, pp. 1–48, 2000.
- J. Gardiner and J. Weiss, “Subject-specific finite element analysis of the human medial collateral ligament during valgus knee loading,” J Orthopaed Res, vol. 21, pp. 1098–1106, 2003.
- K. A. Buzard, “Introduction to biomechanics of the cornea,” Refract Corneal Surg, vol. 8, pp. 127–138, 1992.
- C. Munnerlyn, S. J. Koons, and J. Marshall, “Photorefractive keratectomy: a technique for laser refractive surgery,” J Cataract Refract Surg, vol. 14, pp. 46–52, 1988.
- Hobbit, Karlsson and Sorensen, Inc., Abaqus user's guide, v. 5.8., HKS inc., Pawtucket, RI, USA, 1999.
- R. S. Kalski, G. Sutton, Y. Bin, M. A. Lawless, and C. Rogers, “Comparison of 5-mm and 6-mm ablation zones in photorefractive keratectomy for myopia,” Journal of Refractive Surgery, vol. 12, no. 1, pp. 61–67, 1996.
- M. S. Rajan, D. O'Brart, P. Jaycock, and J. Marshall, “Effects of Ablation Diameter on Long-term Refractive Stability and Corneal Transparency after Photorefractive Keratectomy,” Ophthalmology, vol. 113, pp. 1798–1806, 2006.
- Bausch & Lomb, Orbscan II Anterior Segment Analysis System. Operator's Manual, Orbtek Inc., Salt Lake City, UT, USA, 2003.
- H. Studer, X. Larrea, H. Riedwyl, and P. Buechler, Biomechanical model of human cornea based on stromal microstructure. J Biomech 2009. doi:10.1016/j.jbiomech.2009.11.021. In press.
- R. Navarro, L. González, and J. L. Hernández, “Optics of the average normal cornea from general and canonical representations of its surface topography,” J Opt Soc Am A, vol. 23, pp. 219–232, 2006.
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