title: Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis.
abstract: OBJECTIVE
  To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing.
  
  
  METHODS
  AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
  
  
  METHODS
  Retrospective data analysis.
  
  
  METHODS
  The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery.
  
  
  RESULTS
  The study evaluated 25 patients. The mean and range of ERI values determined using post-LASIK data were similar to those determined from pre-LASIK data. Introducing individual or an average ERI in the ray-tracing IOL power calculation procedure resulted in mean IOL power errors that were not significantly different from zero. The ray-tracing procedure that includes an average ERI gave a greater percentage of eyes with an IOL power prediction error within ±0.5 diopter than the Haigis-L (84% versus 52%).
  
  
  CONCLUSIONS
  For IOL power determination in post-LASIK patients, custom ray tracing including a modified ERI was an accurate procedure that exceeded the current standards for normal eyes.
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Electronic address: carmen.canovas@amo.abbott.com.
authors.forename: Carmen
authors.initials: C
authors.lastname: Canovas
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Marrie
authors.initials: M
authors.lastname: van der Mooren
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Rosén
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Piers
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Koch
authors.affiliation: From AMO Groningen B.V. (Canovas, van der Mooren, Rosén, Piers), Van Groningen, the Netherlands; Laboratorio de Optica (Canovas, Artal), Instituto Universitario de Investigacion en Optica y Nanofısica, Universidad de Murcia, Murcia, Spain; the Cullen Eye Institute (Wang, Koch), Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Pablo
authors.initials: P
authors.lastname: Artal
mesh_terms: D000328:Adult; D000368:Aged; D002386:Cataract / Q000150:complications; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D007910:Lenses, Intraocular; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D055095:Optics and Photonics; D011184:Postoperative Period; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology