title: Posterior corneal surface changes after refractive surgery.
abstract: OBJECTIVE
  To determine the frequency of changes in posterior corneal surface after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).
  
  
  METHODS
  Nonrandomized, comparative trial.
  
  
  METHODS
  Ninety-five eyes (71 patients) that underwent PRK (n = 45) or LASIK (n = 50).
  
  
  METHODS
  Twenty nonsurgery eyes were used to validate the method of analysis of the posterior corneal curvature (PCC). Seventy nonsurgery eyes were used for comparisons.
  
  
  METHODS
  Float, apex-fixed best fit corneal curvature (ABC), and posterior elevation difference were evaluated in 20 elevation topography maps at 6 zone diameters (3-7 and 10 mm) and at two time points. Corneal elevation maps before and after PRK or LASIK were analyzed by the ABC and float methods and compared with a nonsurgery group.
  
  
  METHODS
  Posterior corneal curvature change (mm) was classified as flattening, steepening, or no change.
  
  
  RESULTS
  Flattening of more than 0.12 mm was found in 22.2% of eyes (n = 10) in the PRK group, a change of +/-0.12 mm was found in 53.3% of eyes (n = 24), and steepening of more than 0.12 mm was found in 24.4% of eyes (n = 11) using the float method and in 28.9% of eyes (n = 13), 35.6% of eyes (n = 16), and 35.6% eyes (n = 16), respectively, using the ABC method. In the LASIK group, the float method registered flattening in 20% of eyes (n = 10), no change in 52% of eyes (n = 26), and steepening in 28% of eyes (n = 14), whereas the ABC method registered flattening in 30% of eyes (n = 15), no change in 40% of eyes (n = 20), and steepening in 30% of eyes (n = 15). The nonsurgery group showed a similar change in PCC at two different time points similar to that of the PRK and the LASIK groups.
  
  
  CONCLUSIONS
  The differences observed in the PCC after PRK or LASIK were not statistically significantly different from those observed over time in the nonsurgery control group.
authors.affiliation: Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: E
authors.initials: E
authors.lastname: Hernández-Quintela
authors.forename: S
authors.initials: S
authors.lastname: Samapunphong
authors.forename: B F
authors.initials: BF
authors.lastname: Khan
authors.forename: B
authors.initials: B
authors.lastname: Gonzalez
authors.forename: P C
authors.initials: PC
authors.lastname: Lu
authors.forename: S G
authors.initials: SG
authors.lastname: Farah
authors.forename: D T
authors.initials: DT
authors.lastname: Azar
mesh_terms: D000328:Adult; D000867:Anterior Chamber / Q000473:pathology*; D003315:Cornea / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer; D008297:Male; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy