title: Intraocular lens power calculation in eyes with previous hyperopic laser in situ keratomileusis.
abstract: OBJECTIVE
  To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data.
  
  
  METHODS
  Private practices, Lynwood, California, and Mesa, Arizona, USA.
  
  
  METHODS
  Retrospective comparative observational study.
  
  
  METHODS
  The corrected corneal power (Kc) was calculated in each eye by adding the refractive change at the corneal level to the pre-LASIK keratometric (K) readings. By comparing Kc with the measured post-LASIK K readings (Kpost), the following equation was derived: Kc = 1.0457 Kpost-1.9538. This equation was combined with the Shammas original formula to obtain the Shammas-PHL formula.
  
  
  RESULTS
  The new formula was evaluated in 18 eyes with previous LASIK data and in 24 eyes with no previous LASIK data. Using the Shammas-PHL formula, the mean arithmetic prediction error was -0.03 diopter (D) ± 0.72 (SD) (range -1.57 to +1.54 D) and the median absolute error was 0.38 D in 18 eyes with available pre-LASIK data and 0.05 ± 0.58 D (range -0.56 to +1.40 D) and 0.43 D, respectively, in the 24 eyes with no pre-LASIK data.
  
  
  CONCLUSIONS
  The Shammas-PHL formula can be used in post-hyperopic LASIK cases whether or not the pre-LASIK data are available.
authors.affiliation: Department of Ophthalmology, the Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. jshammas@shammaseye.com
authors.forename: H John
authors.initials: HJ
authors.lastname: Shammas
authors.forename: Maya C
authors.initials: MC
authors.lastname: Shammas
authors.forename: Warren E
authors.initials: WE
authors.lastname: Hill
mesh_terms: D000368:Aged; D000867:Anterior Chamber / Q000033:anatomy & histology; D058452:Axial Length, Eye / Q000033:anatomy & histology; D001699:Biometry; D003315:Cornea / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology / Q000601:surgery*; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D055095:Optics and Photonics; D018918:Phacoemulsification; D011182:Postoperative Care; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology