title: Effect of visual acuity on biometry prediction error after cataract surgery.
abstract: OBJECTIVE
  To determine the effect of visual acuity on biometry prediction error.
  
  
  METHODS
  Postgraduate teaching hospital.
  
  
  METHODS
  The study was an observational case series of the first operated eye of 2149 consecutive patients who had cataract surgery. Biometry prediction error was defined as the difference between the planned refraction determined by biometry and the spherical equivalent of the final refraction. The principal outcome measure was the percentage of eyes within +/-1.00 diopter (D) of the intended refraction. This outcome was calculated for patients with visual loss caused by cataract alone, defined as eyes with a postoperative acuity of 6/6 or better, and eyes with different levels of postoperative visual acuity.
  
  
  RESULTS
  Complete data were available for 1978 eyes (92%). Of these, 1438 (73%) were within +/-1.00 D of the intended refraction. When the final corrected visual acuity was 6/6 or better, the percentage of eyes within +/-1.00 D of the predicted refraction was at least 78%. When the preoperative acuity was worse than 6/60, 74% in the counting fingers group and 69% in the hand movements group with a final corrected acuity of 6/6 or better were within +/-1.00 D. This trend bordered on statistical significance (P =.05). There was a rapid reduction in the percentage of eyes within +/-1.00 D of the intended refraction as the postoperative acuity decreased because of ocular comorbidity, with a statistically significant difference between eyes with a postoperative acuity of 6/6 or better and each group with an acuity of 6/9 or worse (P<.01).
  
  
  CONCLUSIONS
  In eyes without visually significant ocular comorbidity, cataract must reduce vision to 6/60 or worse before there is an increase in biometry prediction error. In contrast, ocular comorbidity that reduces the postoperative acuity causes an early and marked increase in biometry prediction error.
authors.affiliation: Moorfields Eye Hospital, London, England. csdaniel@doctors.org.uk
authors.forename: Claire
authors.initials: C
authors.lastname: Daniel
authors.forename: Stephen
authors.initials: S
authors.lastname: Tuft
authors.forename: Alex
authors.initials: A
authors.lastname: Ionides
authors.forename: Catey
authors.initials: C
authors.lastname: Bunce
mesh_terms: D001699:Biometry; D002387:Cataract Extraction; D006801:Humans; D011184:Postoperative Period; D011379:Prognosis; D012189:Retrospective Studies; D014792:Visual Acuity