title: Cox proportional hazards model of myopic regression for laser in situ keratomileusis flap creation with a femtosecond laser and with a mechanical microkeratome.
abstract: OBJECTIVE
  To compare predictive factors for postoperative myopic regression between laser in situ keratomileusis (LASIK) with a femtosecond laser and LASIK with a mechanical microkeratome.
  
  
  METHODS
  Nobel Eye Clinic, Taipei, Taiwan.
  
  
  METHODS
  Retrospective comparative study.
  
  
  METHODS
  Refractive outcomes were recorded 1 day, 1 week, and 1, 3, 6, 9, and 12 months after LASIK. A Cox proportional hazards model was used to evaluate the impact of the 2 flap-creating methods and other covariates on postoperative myopic regression.
  
  
  RESULTS
  The femtosecond group comprised 409 eyes and the mechanical microkeratome group, 377 eyes. For both methods, significant predictors for myopic regression after LASIK included preoperative manifest spherical equivalent (P=.0001) and central corneal thickness (P=.027). Laser in situ keratomileusis with a mechanical microkeratome had a higher probability of postoperative myopic regression than LASIK with a femtosecond laser (P=.0002). After adjusting for other covariates in the Cox proportional hazards model, the cumulative risk for myopic regression with a mechanical microkeratome was higher than with a femtosecond laser 12 months postoperatively (P=.0002). With the definition of myopic regression as a myopic shift of 0.50 diopter (D) or more and residual myopia of -0.50 D or less, the risk estimate based on the mean covariates in all eyes in the femtosecond group and mechanical microkeratome group at 12 months was 43.6% and 66.9%, respectively.
  
  
  CONCLUSIONS
  Laser in situ keratomileusis with a mechanical microkeratome had a higher risk for myopic regression than LASIK with a femtosecond laser through 12 months postoperatively.
authors.affiliation: Department of Ophthalmology, Taipei Medical University-Shuang Ho Hospital, Taipei County, Taiwan.
authors.forename: Meng-Yin
authors.initials: MY
authors.lastname: Lin
authors.forename: David C K
authors.initials: DC
authors.lastname: Chang
authors.forename: Wen-Ming
authors.initials: WM
authors.lastname: Hsu
authors.forename: I-Jong
authors.initials: IJ
authors.lastname: Wang
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology; 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*; D016016:Proportional Hazards Models; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies; D013524:Surgical Flaps; D014792:Visual Acuity / Q000502:physiology