title: Keratometry obtained by corneal mapping versus the IOLMaster in the prediction of postoperative refraction in routine cataract surgery.
abstract: BACKGROUND
  To establish whether simulated keratometry values obtained by corneal mapping (videokeratography) would provide a superior refractive outcome to those obtained by Zeiss IOLMaster (partial coherence interferometry) in routine cataract surgery.
  
  
  METHODS
  Prospective, non-randomized, single-surgeon study set at the The Royal United Hospital, Bath, UK, District General Hospital.
  
  
  METHODS
  Thirty-three patients undergoing routine cataract surgery in the absence of significant ocular comorbidity.
  
  
  METHODS
  Conventional biometry was recorded using the Zeiss IOLMaster. Postoperative refraction was calculated using the SRK/T formula and the most appropriate power of lens implanted. Preoperative keratometry values were also obtained using Humphrey Instruments Atlas Version A6 corneal mapping.
  
  
  METHODS
  Achieved refraction was compared with predicted refraction for the two methods of keratometry after the A-constants were optimized to obtain a mean arithmetic error of zero dioptres for each device.
  
  
  RESULTS
  The mean absolute prediction error was 0.39 dioptres (standard deviation 0.29) for IOLMaster and 0.48 dioptres (standard deviation 0.31) for corneal mapping (P = 0.0015). Keratometry readings between the devices were highly correlated by Spearman correlation (0.97). The Bland-Altman plot demonstrated close agreement between keratometers, with a bias of 0.0079 dioptres and 95% limits of agreement of -0.48-0.49 dioptres.
  
  
  CONCLUSIONS
  The IOLMaster was superior to Humphrey Atlas A6 corneal mapping in the prediction of postoperative refraction. This difference could not have been predicted from the keratometry readings alone. When comparing biometry devices, close agreement between readings should not be considered a substitute for actual postoperative refraction data.
authors.affiliation: The Royal United Hospital, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Dulku
authors.forename: Henry B
authors.initials: HB
authors.lastname: Smith
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Antcliff
mesh_terms: D001699:Biometry; D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D007368:Interferometry / Q000379:methods*; D019654:Lens Implantation, Intraocular; D008027:Light; D018918:Phacoemulsification; D011184:Postoperative Period; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology