title: Biomechanical corneal changes induced by different flap thickness created by femtosecond laser.
abstract: OBJECTIVE
  To evaluate the impact of the creation of corneal flaps at different thicknesses on the biomechanical properties of swine corneas.
  
  
  METHODS
  Twelve swine eyes were obtained to form two groups: 100 μm flap thickness and 300 μm flap thickness. Each eye was submitted to the following examinations: raster topography to investigate corneal curvature alterations, ocular response analyzer to investigate corneal hysteresis change, optical coherence tomography to measure central corneal and flap thickness and sonic wave propagation velocity as a measure of stiffness, before and immediately after flap creation. After flap amputation, surface wave velocity measurements were repeated.
  
  
  RESULTS
  Measured flap thicknesses were statistically different for thin and thick flap groups, with an average of 108.5 + 6.9 and 307.8 + 11.5 μm respectively. Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group. With thicker flaps, both parameters decreased significantly from 8.0 +1.0 to 5.1 +1.5 mmHg and from 8.2 + 1.6 to 4.1 +2.5 mmHg respectively. Simulated keratometry values increased in the thick flap group (from 39.5 + 1 D to 45.9+1.2 D) after flap creation but not in the thin flap group (from 40.6 + 0.6 D to 41.4+ 1.0 D). Regarding surface wave velocity analysis, the surgical procedures induced statistically lower results in some positions.
  
  
  CONCLUSIONS
  In the experimental conditions established by this model, thicker flaps presented a greater biomechanical impact on the cornea.
authors.affiliation: Faculdade de Medicina, Universidade de São Paulo, São Paulo, SP, Brazil. fabriciowitzel@hotmail.com
authors.forename: Fabricio W
authors.initials: FW
authors.lastname: Medeiros
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sinha-Roy
authors.forename: Milton R
authors.initials: MR
authors.lastname: Alves
authors.forename: William J
authors.initials: WJ
authors.lastname: Dupps
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D003319:Corneal Stroma / Q000502:physiology / Q000601:surgery*; D019781:Corneal Topography / Q000379:methods; D007429:Intraocular Pressure / Q000502:physiology; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects*; D011184:Postoperative Period; D013524:Surgical Flaps; D013552:Swine; D041623:Tomography, Optical Coherence