title: Laser in situ keratomileusis for myopia and the contrast sensitivity function.
abstract: OBJECTIVE
  To characterize the clinical effects of laser in situ keratomileusis (LASIK) on the cornea and visual performance by the contrast sensitivity function (CSF).
  
  
  METHODS
  Clinique d'Ophtalmologie IRIS, Laval, Quebec, Canada.
  
  
  METHODS
  Thirty-four patients aged 18 to 50 years volunteered for this prospective study. All patients had bilateral LASIK to correct myopia between -1.00 and -6.75 diopters (D) and refractive astigmatism less than 2.50 D. The mean spherical equivalent (SE) refractive error in the 68 eyes was -3.93 D +/- 1.67 (SD). A Hansatome microkeratome (Bausch & Lomb) and a Technolas 217C excimer laser (Bausch & Lomb) driven by the PlanoScan program were used. The monocular CSF for spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd) for both day and night vision simulations were made with a CSV-1000E system (Vector Vision) before and 1 month and up to 9 months after LASIK. All patients wore their best spectacle correction for the baseline CSF.
  
  
  RESULTS
  The group (n = 68) averaged preoperative and postoperative CSFs did not differ at 1 month (analysis of variance [ANOVA], P>.05). In a subgroup of 11 eyes that had corneal microstriae, however, there was a significant reduction in the photopic and mesopic CSF at 6, 12, and 18 cpd (ANOVA, P<.05) despite normal Snellen visual acuities. The CSF normalized in 6 to 9 months as the microstriae became less visible.
  
  
  CONCLUSIONS
  Subtle central corneal microstriae after LASIK can reduce the baseline CSF at medium to high spatial frequencies even with 20/20 visual acuity. The CSF normalizes as the microstriae fade over time.
authors.affiliation: Ecole d'optométrie, Université de Montréal, Montreal, Quebec, Canada. nadia.marie.quesnel@umontreal.ca
authors.forename: Nadia-Marie
authors.initials: NM
authors.lastname: Quesnel
authors.forename: John V
authors.initials: JV
authors.lastname: Lovasik
authors.forename: Christian
authors.initials: C
authors.lastname: Ferremi
authors.forename: Martin
authors.initials: M
authors.lastname: Boileau
authors.forename: Catherine
authors.initials: C
authors.lastname: Ieraci
mesh_terms: D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D003315:Cornea / Q000503:physiopathology*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology