title: Biometry accuracy using zero- and negative-powered intraocular lenses.
abstract: OBJECTIVE
  To audit the accuracy of biometry using the SRK/T formula when negative- or zero-powered intraocular lenses (IOLs) are predicted and to compare the results between A-scan, B-scan, and optical methods of biometry.
  
  
  METHODS
  Moorfields Eye Hospital, London, United Kingdom.
  
  
  METHODS
  This retrospective analysis comprised 78 eyes of 54 patients having cataract surgery with zero- or negative-powered IOLs. Axial lengths were measured with A-scan, B-scan, applanation, or optical methods. Differences between SRK/T-predicted and actual postoperative refraction were analyzed for 75 eyes having cataract surgery. Ocular comorbidity, visual acuity, and biometry readings were also compared.
  
  
  RESULTS
  Forty-one percent of 75 patients analyzed were within +/-1.00 diopter (D) of the predicted refraction, although there was a significant tendency toward a hyperopic overcorrection by 1.14 D (95% confidence interval, 0.89-1.39 D). This overcorrection error was consistent across all 3 biometry methods used to estimate axial length and increased with the use of stronger (more negative) IOLs.
  
  
  CONCLUSIONS
  Surgeons should be aware of the tendency for negative-powered lenses to overcorrect and lead to a hyperopic outcome when using the SRK/T biometry formula in highly myopic eyes. A weaker-powered negative IOL is recommended to aim for a more myopic postoperative outcome by about 1.00 to 2.00 D.
authors.affiliation: Moorfields Eye Hospital, London, United Kingdom. maclaren@herald.ox.ac.uk
authors.forename: Robert E
authors.initials: RE
authors.lastname: MacLaren
authors.forename: Mandeep S
authors.initials: MS
authors.lastname: Sagoo
authors.forename: Marie
authors.initials: M
authors.lastname: Restori
authors.forename: Bruce D S
authors.initials: BD
authors.lastname: Allan
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D001699:Biometry / Q000379:methods*; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D009216:Myopia / Q000150:complications / Q000601:surgery; D018918:Phacoemulsification; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D012189:Retrospective Studies