Effect of visual acuity on biometry prediction error after cataract surgery Claire Daniel, BSc(Hons), FRCOphth, Stephen Tuft, MD, FRCOphth, Alex Ionides, MD, FRCOphth, Catey Bunce, MSc Purpose: To determine the effect of visual acuity on biometry prediction error. Setting: 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 bi- ometry 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 re- fraction. This outcome was calculated for patients with visual loss caused by cat- aract 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 pre- dicted 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 bor- dered on statistical significance (P = .05). There was a rapid reduction in the per- centage 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 pre- diction error. In contrast, ocular comorbidity that reduces the postoperative acuity causes an early and marked increase in biometry prediction error. J Cataract Refract Surg 2003; 29:1365–1369 © 2003 ASCRS and ESCRS T he refractive outcome of cataract surgery has been refined by improved biometry formulas, better in- traocular lens (IOL) design, and improved surgical tech- nique. Studies show that ocular comorbidity can affect the visual outcome of cataract surgery. 1–3 The National Cataract Survey 2 and the European Cataract Surgery Outcome Study Group 3 show that 85.0% to 93.5% of eyes without ocular comorbidity had a postoperative vi- sual acuity of 6/12 or better. When ocular comorbidity was present, the percentage dropped to between 65.0% and 72.0%. Murphy and coauthors 4 analyzed a consec- utive series of 1676 eyes that had cataract surgery and found that 72.3% were within 1.00 diopter (D) of the planned refraction. However, the effect on the re- fractive outcome of different degrees of visual acuity loss caused by cataract or ocular comorbidity has not been examined. To determine the effect of preoperative visual acuity and ocular comorbidity on biometry prediction error, we examined the outcome in the first operated eye of a consecutive series of patients having cataract surgery. We compared the biometry prediction error in eyes that had different levels of preoperative acuity loss but a post- operative best corrected visual acuity (BCVA) of 6/6 or better; these patients had no visually significant ocular comorbidity. We also compared the biometry predic- © 2003 ASCRS and ESCRS 0886-3350/03/$–see front matter Published by Elsevier Inc. doi:10.1016/S0886-3350(02)01913-2