title: Orbscan II and double-K method for IOL calculation after refractive surgery.
abstract: BACKGROUND
  Precise IOL calculation in post-refractive surgery patients is still a challenge for the cataract surgeon. The purpose of this study is to test whether adding Orbscan II values into the double-K method improves IOL calculation in this group of patients.
  
  
  METHODS
  A prospective study with 43 eyes previously submitted to refractive surgery that underwent cataract extraction. IOL calculation was performed with double-K method. Post-K value was derived from Orbscan total-mean power map. The average corneal curvature of the general population (43.8D) was used as the pre-K value. Refraction results 30 days after surgery were compared with refraction that would be obtained if we used: (1) post-K values from keratometry, (2) post-K values from topography, and (3) pre-K values from Orbscan total-mean power. Anterior chamber depth measures obtained with the IOL Master and Orbscan II were compared.
  
  
  RESULTS
  Mean postoperative spherical equivalent (SE) was -0.25 ± 1.10 D in eyes submitted to radial keratotomy , -1.04 ± 1.42 D in eyes previously submitted to myopic Lasik, and +0.05 ± 1.76 D in those submitted to hyperopic surgeries. Had we inputted post-K values derived from keratometer and from topography, we would have obtained significantly higher postoperative refractive errors in eyes previously submitted to myopic refractive surgery (p < 0.05). Refractions using pre-K derived from the central 8 mm Orbscan instead of 43.8 D were similar in all studied groups (p > 0.05). Anterior chamber depth measured with IOL Master or Orbscan were similar.
  
  
  CONCLUSIONS
  Orbscan measurements used as the post-K values into the double-K method provide a precise IOL calculation, especially in post myopic refractive surgery patients.
authors.affiliation: Department of Ophthalmology, Hospital de Clínicas de Porto Alegre, Federal University of Rio Grande do Sul, Av. Dr. Nilo Peçanha 724/401, São Paulo, Brazil. sergio@oftalmocentro.com.br
authors.forename: Sérgio
authors.initials: S
authors.lastname: Kwitko
authors.forename: Diane R
authors.initials: DR
authors.lastname: Marinho
authors.forename: Samuel
authors.initials: S
authors.lastname: Rymer
authors.forename: Norton
authors.initials: N
authors.lastname: Severo
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Arce
mesh_terms: D000368:Aged; D002387:Cataract Extraction; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D006956:Hyperopia / Q000601:surgery; D020731:Keratomileusis, Laser In Situ; D007646:Keratotomy, Radial; D007910:Lenses, Intraocular; D008875:Middle Aged; D009216:Myopia / Q000601:surgery; D055095:Optics and Photonics; D018903:Photorefractive Keratectomy; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D054140:Refractive Surgical Procedures