title: Calculation of intraocular lens power using Orbscan II quantitative area topography after corneal refractive surgery.
abstract: OBJECTIVE
  To present the prospective application of the Orbscan II central 2-mm total-mean corneal power obtained by quantitative area topography in intraocular lens (IOL) calculation after refractive surgery.
  
  
  METHODS
  Calculated and achieved refraction and the difference between them were studied in 77 eyes of 61 patients with previous radial keratotomy (RK), RK and additional surgeries, myopic LASIK, myopic photorefractive keratectomy (PRK), or hyperopic LASIK who underwent phacoemulsification without complications in 3 eye centers. All IOL calculations used the average from the central 2-mm Orbscan II total-mean power of maps centered on the pupil without the use of previous refractive data. Six IOL styles implanted within the bag were used.
  
  
  RESULTS
  Using the SRK-T formula, the overall calculated refraction was -0.64+/-0.93 diopters (D). The overall achieved spherical equivalent refraction (-0.52+/-0.79 D; range: -3.12 to 1.25 D; 95% confidence interval [CI]: -0.70/-0.34 D) was +/-0.50 D in 53% of eyes, +/-1.00 D in 78% of eyes, and +/-2.00 D in 99% of eyes. The overall difference between the calculated and achieved refraction (0.12+/-0.93 D, P=.27; range: -2.18 to 2.62 D; 95% CI: 0.09/0.33 D) was +/-0.50 D in 39% of eyes, +/-1.00 D in 77% of eyes, and +/-2.00 D in 96% of eyes. This difference was +/-1.00 D in 77% of eyes with RK (P=.70), 82% of eyes with myopic LASIK (P=.34), and 90% of eyes with myopic PRK (P=.96). In eyes with RK followed by LASIK, a trend toward undercorrection was noted (P=.03). In eyes with hyperopic LASIK, a trend toward overcorrection was noted (P=.005).
  
  
  CONCLUSIONS
  In eyes with previous corneal refractive surgery, IOL power calculation can be performed with reasonable accuracy using the Orbscan II central 2-mm total-mean power. This method had better outcomes in eyes with previous RK, myopic LASIK, and myopic PRK than in eyes with hyperopic LASIK or RK with LASIK.
authors.affiliation: Department of Ophthalmology, Paulista School of Medicine, Federal University of Sao Paulo, Brazil. cgarce@terra.com.br
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Arce
authors.forename: Eduardo S
authors.initials: ES
authors.lastname: Soriano
authors.forename: Robert W
authors.initials: RW
authors.lastname: Weisenthal
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Hamilton
authors.forename: Karolinne M
authors.initials: KM
authors.lastname: Rocha
authors.forename: Juan B
authors.initials: JB
authors.lastname: Alzamora
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Maidana
authors.forename: Vijayalakshmi L
authors.initials: VL
authors.lastname: Vadrevu
authors.forename: Kenneth
authors.initials: K
authors.lastname: Himmel
authors.forename: Paulo
authors.initials: P
authors.lastname: Schor
authors.forename: Mauro
authors.initials: M
authors.lastname: Campos
mesh_terms: D048988:Corneal Surgery, Laser; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D006956:Hyperopia / Q000601:surgery; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D009216:Myopia / Q000601:surgery; D055095:Optics and Photonics; D018918:Phacoemulsification; D011446:Prospective Studies