title: Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis.
abstract: OBJECTIVE
  To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method.
  
  
  METHODS
  Interventional case series.
  
  
  METHODS
  Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre - CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost -0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost -6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results.
  
  
  RESULTS
  Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram (P <.001), and there was no statistically significant difference between the mean keratometric values (P >.5).
  
  
  CONCLUSIONS
  The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.
authors.affiliation: Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA. HShammas@aol.com
authors.forename: H John
authors.initials: HJ
authors.lastname: Shammas
authors.forename: Maya C
authors.initials: MC
authors.lastname: Shammas
authors.forename: Antoine
authors.initials: A
authors.lastname: Garabet
authors.forename: Jenny H
authors.initials: JH
authors.lastname: Kim
authors.forename: Abraham
authors.initials: A
authors.lastname: Shammas
authors.forename: Laurie
authors.initials: L
authors.lastname: LaBree
mesh_terms: D000328:Adult; D002387:Cataract Extraction; D003315:Cornea / Q000502:physiology* / Q000601:surgery; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000517:prevention & control; D020731:Keratomileusis, Laser In Situ; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D055095:Optics and Photonics; D012029:Refraction, Ocular; D012189:Retrospective Studies