title: Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster.
abstract: OBJECTIVE
  To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error.
  
  
  METHODS
  The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated.
  
  
  RESULTS
  In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0.368 to +1.015) and for A-scan biometry was - 0.24 (interquartile range - 1.335 to +0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3.
  
  
  CONCLUSIONS
  An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.
authors.affiliation: Department of Ophthalmology, Royal United Hospital, Combe Park, Bath, UK.
authors.forename: Simon N
authors.initials: SN
authors.lastname: Madge
authors.forename: C H
authors.initials: CH
authors.lastname: Khong
authors.forename: Meon
authors.initials: M
authors.lastname: Lamont
authors.forename: Atul
authors.initials: A
authors.lastname: Bansal
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Antcliff
mesh_terms: D000293:Adolescent; D000328:Adult; D001699:Biometry / Q000379:methods*; D001837:Body Weights and Measures; D005123:Eye / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D007259:Infrared Rays; D007368:Interferometry / Q000379:methods; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D018918:Phacoemulsification / Q000295:instrumentation; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results; D014463:Ultrasonography