title: A comparative analysis of five methods of determining corneal refractive power in eyes that have undergone myopic laser in situ keratomileusis.
abstract: OBJECTIVE
  To evaluate the accuracy of computerized videokeratography, keratometry, and the Gaussian optics formula for measuring corneal refractive power in patients after myopic laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Noncomparative case series.
  
  
  METHODS
  One hundred eyes of 63 patients (mean age, 45.0 +/- 10.9 [standard deviation] years) who underwent LASIK were included in the study.
  
  
  METHODS
  Using the clinical history method as the standard, we evaluated the accuracy of values of corneal refractive power derived from computerized videokeratography (the EffRP value of the EyeSys Corneal Analysis System, which averages corneal refractive power over the central 3 mm), keratometry (K), the Gaussian optics formula (GauRP), and values of EffRP and keratometry as modified according to the amount of LASIK-induced refractive change.
  
  
  METHODS
  Correlation of measured corneal power values to those obtained using clinical history method (HisRP).
  
  
  RESULTS
  Although the values for HisRP were significantly correlated with postoperative EffRP and K values and with GauRP, postoperative EffRP and K values were higher than HisRP (0.87 +/- 0.68 diopters [D] and 1.16 +/- 1.10 D, respectively), and GauRP were lower than HisRP (0.44 +/- 0.66 D) (P < 0.001 for all three comparisons). The differences between HisRP and both postoperative EffRP and K values increased significantly with the amount of myopic correction. The most accurate results were obtained by modifying the postoperative values of EffRP according to the amount of LASIK-induced refractive change; 70% of these values were within +/- 0.5 D and 94% within +/- 1 D of HisRP values.
  
  
  CONCLUSIONS
  Using the clinical history method as the standard, we found that the most accurate method for determining corneal refractive power in post-LASIK eyes was to adjust the postoperative corneal measurement according to the amount of LASIK-induced refractive change.
authors.affiliation: Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, 6565 Fannin, Houston, TX 77030, USA.
authors.forename: Abdelmonem M
authors.initials: AM
authors.lastname: Hamed
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Manjula
authors.initials: M
authors.lastname: Misra
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Koch
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000502:physiology* / Q000601:surgery; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D012189:Retrospective Studies