title: Corneal biomechanical properties after LASIK, ReLEx flex, and ReLEx smile by Scheimpflug-based dynamic tonometry.
abstract: OBJECTIVE
  To evaluate corneal biomechanical properties after LASIK, ReLEx flex, and the flap-free procedure ReLEx smile by Scheimpflug-based dynamic tonometry (Corvis ST) and non-contact differential tonometry (Ocular Response Analyzer, ORA).
  
  
  METHODS
  Patients treated for high myopia (-10.5 to -5.5 diopters, spherical equivalent refraction) more than one year previously at Aarhus University Hospital were included. Treatments comprised LASIK (35 eyes), ReLEx flex (31 eyes), and ReLEx smile (29 eyes). A control group included 31 healthy eyes. Cornea-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured with ORA. Corneal applanation and deformation were registered with Corvis ST during an air-pulse.
  
  
  RESULTS
  Multiple linear regression analysis showed that CH and CRF were significantly lower after all keratorefractive procedures compared to healthy controls (p < 0.05). No significant differences were observed in CH or CRF between the keratorefractive groups. Corvis ST showed no differences in radius at highest concavity (HC radius), time until first applanation (A1 Time), time until second applanation (A2 Time), and deflection length at highest concavity (HC deflection length) between groups. LASIK treated eyes had significantly shorter time until highest concavity than eyes treated with ReLEx smile (HC Time, p = 0.01). The A1 deflection length was significantly shorter in the keratorefractive groups compared to the healthy controls (p < 0.05).
  
  
  CONCLUSIONS
  Keratorefrative procedures alter the corneal biomechanical properties with regard to corneal hysteresis and corneal resistant factor. The flap-based LASIK and ReLEx flex and the flap-free ReLEx smile result in similar reduction in corneal biomechanics when evaluated by Corvis ST and ORA.
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, Nørrebrogade 44, 8000, Aarhus C, Denmark, iben.b.pedersen@gmail.com.
authors.forename: Iben Bach
authors.initials: IB
authors.lastname: Pedersen
authors.forename: Sashia
authors.initials: S
authors.lastname: Bak-Nielsen
authors.forename: Anders Højslet
authors.initials: AH
authors.lastname: Vestergaard
authors.forename: Anders
authors.initials: A
authors.lastname: Ivarsen
authors.forename: Jesper
authors.initials: J
authors.lastname: Hjortdal
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003315:Cornea / Q000503:physiopathology*; D063171:Corneal Pachymetry; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D013524:Surgical Flaps; D014065:Tonometry, Ocular