title: Computational Biomechanical Analysis of Asymmetric Ectasia Risk in Unilateral Post-LASIK Ectasia.
abstract: OBJECTIVE
  To develop a computational approach to corneal biomechanical risk analysis in refractive surgery and to investigate its utility in an enigmatic case of unilateral ectasia after bilateral LASIK.
  
  
  METHODS
  Preoperative corneal elevation datasets from both eyes of a patient who developed unilateral post-LASIK ectasia were used to construct geometrically patient-specific, microstructurally motivated finite element models. Models were assessed before and after implementation of case-specific treatment parameters for interocular differences in corneal geometry and strain behavior under physiological loading conditions.
  
  
  RESULTS
  Standard clinical predictors of post-LASIK ectasia risk were similar for the affected and contralateral eyes, and no risk factor asymmetry was identified in tomographic screening that included posterior corneal elevation analysis. However, differences in the magnitude and distribution of strain and stress were observed that are consistent with greater predisposition to biomechanical instability in the affected eye. Load testing with simulated intraocular pressure increases provoked opposite trends in curvature change in the preoperative models representing affected and unaffected eyes, with steepening in the ectatic eye and flattening in the clinically stable eye.
  
  
  CONCLUSIONS
  Patient-specific computational analyses revealed differences in intrinsic biomechanical behaviors that may predispose a cornea to instability after refractive surgery. Strain and stress analyses elucidated differential risk not ascertained with current refractive surgery screening paradigms. This pilot study illustrates a risk analysis approach that implicitly considers the entire corneal three-dimensional geometry and can be performed a priori in a screening setting. [J Refract Surg. 2016;32(12):811-820.].
authors.forename: Ali
authors.initials: A
authors.lastname: Vahdati
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Seven
authors.forename: Naveen
authors.initials: N
authors.lastname: Mysore
authors.forename: J Bradley
authors.initials: JB
authors.lastname: Randleman
authors.forename: William J
authors.initials: WJ
authors.lastname: Dupps
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis; D004548:Elasticity / Q000502:physiology; D020342:Finite Element Analysis; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D009216:Myopia / Q000601:surgery; D011183:Postoperative Complications; D012307:Risk Factors