title: Biomechanical and optical behavior of human corneas before and after photorefractive keratectomy.
abstract: OBJECTIVE
  To evaluate numerically the biomechanical and optical behavior of human corneas and quantitatively estimate the changes in refractive power and stress caused by photorefractive keratectomy (PRK).
  
  
  METHODS
  Athineum Refractive Center, Athens, Greece, and Politecnico di Milano, Milan, Italy.
  
  
  METHODS
  Retrospective comparative interventional cohort study.
  
  
  METHODS
  Corneal topographies of 10 human eyes were taken with a scanning-slit corneal topographer (Orbscan II) before and after PRK. Ten patient-specific finite element models were created to estimate the strain and stress fields in the cornea in preoperative and postoperative configurations. The biomechanical response in postoperative eyes was computed by directly modeling the postoperative geometry from the topographer and by reproducing the corneal ablation planned for the PRK with a numerical reprofiling procedure.
  
  
  RESULTS
  Postoperative corneas were more compliant than preoperative corneas. In the optical zone, corneal thinning decreased the mechanical stiffness, causing local resteepening and making the central refractive power more sensitive to variations in intraocular pressure (IOP). At physiologic IOP, the postoperative corneas had a mean 7% forward increase in apical displacement and a mean 20% increase in the stress components at the center of the anterior surface over the preoperative condition.
  
  
  CONCLUSIONS
  Patient-specific numerical models of the cornea can provide quantitative information on the changes in refractive power and in the stress field caused by refractive surgery.
  
  
  BACKGROUND
  No author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Sánchez
authors.affiliation: From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy.
authors.forename: Kyros
authors.initials: K
authors.lastname: Moutsouris
authors.affiliation: From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy. Electronic address: anna.pandolfi@polimi.it.
authors.forename: Anna
authors.initials: A
authors.lastname: Pandolfi
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D001696:Biomechanical Phenomena; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D004548:Elasticity / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult