title: Value of dual biometry in the detection and investigation of error in the preoperative prediction of refractive status following cataract surgery.
abstract: OBJECTIVE
  To report the value of dual biometry in the detection of biometry errors.
  
  
  METHODS
  Study 1: retrospective study of 224 consecutive cataract operations. The intraocular lens power calculation was based on immersion biometry. Study 2: immersion biometry was compared with optical coherence biometry (OCB) in terms of axial length, anterior chamber depth, keratometry readings and the recommended lens power to achieve emmetropia. Study 3: prospective study of 61 consecutive cataract operations. Both immersion and OCB were performed, but lens power calculation was based on the latter.
  
  
  RESULTS
  Study 1: 115 (86%), 101 (75.4%), 90 (67.2%) and 50 (37.3%) of postoperative spherical equivalents were within +/-1.5 dioptres (D), +/-1.25 D, +/-1 D and +/-0.5 D of the target, respectively. Study 2: excellent agreement between axial length readings, anterior chamber depth readings and keratometry readings by immersion biometry and OCB was observed (reflected in a mean bias of -0.065 mm, -0.048 mm and +0.1803 D, respectively, in association with OCB). Agreement between the lens power recommended by each technique to achieve emmetropia was poor (mean bias of +1.16 D in association with OCB), but improved following appropriate modification of lens constants in the Accutome A-scan software (mean bias with OCB = -0.4 D). Study 3: 37 (92.5%) and 23 (57.5%) of operated eyes achieved a postoperative refraction within +/-1 D and +/-0.5 D of target, respectively.
  
  
  CONCLUSIONS
  Systematic errors in biometry can exist, in the presence of acceptable postoperative refractive results. Dual biometry allows each biometric parameter to be scrutinized in isolation, and identify sources of error that may otherwise go undetected.
authors.affiliation: Department of Ophthalmology, Waterford Regional Hospital, Waterford, Ireland. sonia.sofia1@gmail.com
authors.forename: Sofia
authors.initials: S
authors.lastname: Charalampidou
authors.forename: Ian
authors.initials: I
authors.lastname: Dooley
authors.forename: Laura
authors.initials: L
authors.lastname: Molloy
authors.forename: Stephen
authors.initials: S
authors.lastname: Beatty
mesh_terms: D001699:Biometry / Q000379:methods; D002387:Cataract Extraction / Q000379:methods*; D006801:Humans; D007432:Intraoperative Period; D019654:Lens Implantation, Intraocular / Q000706:statistics & numerical data*; D016343:Monitoring, Intraoperative; D011184:Postoperative Period; D011237:Predictive Value of Tests; D011300:Preoperative Care; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy*; D012189:Retrospective Studies; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods