title: Femtosecond laser versus mechanical microkeratomes for flap creation in laser in situ keratomileusis and effect of postoperative measurement interval on estimated femtosecond flap thickness.
abstract: OBJECTIVE
  To prospectively compare laser in situ keratomileusis (LASIK) flaps created with a femtosecond laser or a mechanical microkeratome and analyze the effect of the postoperative measurement interval on estimated femtosecond flap thickness using ultrasound (US) pachymetry.
  
  
  METHODS
  Department of Ophthalmology, University Hospital of Coimbra, and Coimbra Surgical Centre, Coimbra, Portugal.
  
  
  METHODS
  Flaps were created with a Hansatome Zero Compression microkeratome (Group 1), Zyoptix XP keratome (Group 2), or IntraLase 60 kHz femtosecond laser (Groups 3 and 4). Flap thickness was determined by intraoperative US pachymetry immediately after flap creation in Groups 1, 2, and 3. In Group 4, pachymetry was performed 20 minutes after the laser treatment. The main outcome measures were flap thickness and deviation from the target value.
  
  
  RESULTS
  Eighty patients had LASIK for myopia or myopic astigmatism. The mean flap thickness was 149.1 microm +/- 24.9 (SD) in Group 1, 124.7 +/- 23.8 microm in Group 2, 143.1 +/- 18.4 microm in Group 3, and 115.5 +/- 12.5 microm in Group 4. The difference in flap thickness between Group 3 and Group 4 was statistically significant (P<.01). The flap thickness deviation from the target value was 22.8 microm in Group 1, 19.0 microm in Group 2, 26.1 microm in Group 3, and 10.4 microm in Group 4.
  
  
  CONCLUSIONS
  Results indicate that the time of measurement after femtosecond affects the estimated flap thickness. Waiting 20 minutes after laser treatment permitted easier separation and may eliminate the effect of variable corneal dehydration on flap measurement by subtraction pachymetry.
authors.affiliation: Hospital da Universidade de Coimbra, Universidade de Coimbra, Portugal.
authors.forename: Andreia Martins
authors.initials: AM
authors.lastname: Rosa
authors.forename: Joaquim
authors.initials: J
authors.lastname: Neto Murta
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Quadrado
authors.forename: Cristina
authors.initials: C
authors.lastname: Tavares
authors.forename: Conceição
authors.initials: C
authors.lastname: Lobo
authors.forename: Robert
authors.initials: R
authors.lastname: Van Velze
authors.forename: António
authors.initials: A
authors.lastname: Castanheira-Dinis
mesh_terms: D000328:Adult; D000886:Anthropometry; D001251:Astigmatism / Q000601:surgery*; D003319:Corneal Stroma / Q000601:surgery*; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000295:instrumentation / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D011184:Postoperative Period; D011446:Prospective Studies; D013524:Surgical Flaps / Q000473:pathology*; D013997:Time Factors