title: New algorithm for intraocular lens power calculations after myopic laser in situ keratomileusis based on rotating Scheimpflug camera data.
abstract: OBJECTIVE
  To develop an algorithm to calculate intraocular lens (IOL) power for eyes with previous laser in situ keratomileusis (LASIK) for myopia based on data from a rotating Scheimpflug camera and to compare calculations with those of current formulas.
  
  
  METHODS
  East Valley Ophthalmology, Mesa, Arizona, USA.
  
  
  METHODS
  Observational case series.
  
  
  METHODS
  Relevant IOL calculation and postoperative refractive data were obtained for eyes of patients who had previous myopic LASIK and subsequent cataract surgery. Initial screening and correlation analysis identified Pentacam Scheimpflug keratometry (K) values appropriate for use in calculating a "best K" for IOL power calculations in these eyes. Error analysis identified other eye measures to improve results. Final results were compared with results from 9 other calculation methods available on the American Society of Cataract and Refractive Surgery (ASCRS) web site.
  
  
  RESULTS
  The study obtained data from 101 eyes of 77 patients. More than 200 Scheimpflug K-formula combinations were evaluated for each eye. The true net power in the 4.0 mm zone centered on the corneal apex provided the best adjusted K reading for IOL power calculation in the Shammas no-history formula. The final formula had good outcomes, with 34%, 66%, and 91% of eyes being within ±0.25 diopter (D), ±0.50 D, and ±1.00 D of the refractive target, respectively. These results compare favorably to the best formulas on the ASCRS web site.
  
  
  CONCLUSIONS
  The no-history formula derived using the Scheimpflug device's true net power in the 4.0 mm zone centered on the corneal apex appears to be an accurate method for determining IOL power after LASIK for myopia. Corroboration with additional data sets is suggested.
  
  
  BACKGROUND
  Neither author has a financial or proprietary interest in any material or method mentioned.
authors: From Science in Vision (Povin), Akron, New York, and East Valley Ophthalmology (Hill), Mesa, Arizona, USA. Electronic address: rick@scienceinvision.com.
authors: Richard
authors: R
authors: Potvin
authors: From Science in Vision (Povin), Akron, New York, and East Valley Ophthalmology (Hill), Mesa, Arizona, USA.
authors: Warren
authors: W
authors: Hill
mesh_terms: D000465:Algorithms; D058452:Axial Length, Eye / Q000473:pathology; D002387:Cataract Extraction; D063171:Corneal Pachymetry; D019781:Corneal Topography / Q000379:methods; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D007910:Lenses, Intraocular; D009216:Myopia / Q000601:surgery*; D055095:Optics and Photonics; D011184:Postoperative Period