title: Biomechanical Modeling of Femtosecond Laser Keyhole endokeratophakia Surgery.
abstract: OBJECTIVE
  To apply a finite element model to endokeratophakia and evaluate anterior and posterior corneal surface changes.
  
  
  METHODS
  Spatial elevation data (Pentacam HR; Oculus, Wetzlar, Germany) were obtained for the front and back corneal surfaces of an eye prior to undergoing an endokeratophakia procedure. These were used to warp a spherical template finite element model of the cornea to create a patient-specific finite element mesh and the initial stress distribution was computed with an iterative approach. The finite element model (Optimeyes; Integrated Scientific Services, Biel, Switzerland) included non-linear elastic characteristics of the stroma. The endokeratophakia procedure was recreated in the model: a donor lenticule (-10.50 diopters [D], 5.75-mm zone, 127-µm thick) was inserted into a lamellar pocket (180-µm deep, 6.25-mm diameter) and two 2-mm small incisions were made at 150° and 330°. Anterior and posterior surfaces, computed by the finite element model, were compared to clinical data to assess accuracy and reliability of finite element modeling.
  
  
  RESULTS
  The postoperative axial curvature produced by the model closely resembled the patient data; average curvature was 48.01 D clinically and 48.23 D in the simulation, and corneal astigmatism was 3.01 D clinically and 2.88 D in the simulation. The posterior best-fit sphere elevation map also matched the patient data, replicating inward bulging of the posterior surface by approximately 40 µm. Stress distribution modeling predicted a stress increase by 159.94% ± 73% in the cap and a stress decrease by 32.41% ± 21% in the stromal bed.
  
  
  CONCLUSIONS
  Finite element modeling of the cornea reproduced the clinically observed anterior and posterior corneal surface changes following an endokeratophakia procedure. This case sets the stage for further study to refine and yield predictive finite element modeling for the evaluation of corneal refractive surgical procedures.
authors.forename: Harald P
authors.initials: HP
authors.lastname: Studer
authors.forename: Kishore R
authors.initials: KR
authors.lastname: Pradhan
authors.forename: Dan Z
authors.initials: DZ
authors.lastname: Reinstein
authors.forename: Elena
authors.initials: E
authors.lastname: Businaro
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Archer
authors.forename: Marine
authors.initials: M
authors.lastname: Gobbe
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Roberts
mesh_terms: D001696:Biomechanical Phenomena; D003315:Cornea / Q000502:physiology*; D003319:Corneal Stroma / Q000637:transplantation; D019781:Corneal Topography; D016039:Corneal Transplantation / Q000379:methods*; D004548:Elasticity / Q000502:physiology*; D054459:Elasticity Imaging Techniques; D020342:Finite Element Analysis; D006801:Humans; D006956:Hyperopia / Q000601:surgery; D008954:Models, Biological; D014019:Tissue Donors