title: Computerized repeating and averaging improve the test-retest variability of ETDRS visual acuity measurements: implications for sensitivity and specificity.
abstract: OBJECTIVE
  The goals of this study were to investigate the effectiveness of computerized repeating and averaging of visual acuity measurements in reducing test-retest variability (TRV) and to estimate the increase in sensitivity and specificity that would be achieved in diagnosing visual acuity change.
  
  
  METHODS
  Timed, paired ETDRS chart and computerized acuity mean measurement (CAMM) were performed in 100 subjects. CAMM(n) scores were the running mean of consecutive measurements. Bland-Altman methods were used to calculate 95% ranges for TRV.
  
  
  RESULTS
  The 95% TRV range of ETDRS measurements and the CAMM score after 6 (CAMM6) measurements were, respectively, 8 and 5.7 ETDRS letters (P = 0.02). CAMM6 offered a pragmatically optimum tradeoff between reduced TRV and test time. A measured change of 5 letters or more in the absence of true change was observed in 13% (95% CI, 8%-21%) with the ETDRS chart and 4% (95% CI, 2%-10%) with CAMM6 measurements. To achieve ≥95% test sensitivity (assuming 95% test specificity), change criteria of 15 and 11 letters must be set with an ETDRS chart and CAMM6, respectively. CAMM6 measurement times were longer (mean 234 seconds vs. 74 seconds) for the ETDRS chart.
  
  
  CONCLUSIONS
  Compared with the current gold standard, computerized repeating and averaging of acuity measurements improve specificity and sensitivity when identifying true changes. The 160-second increase in test time should be set against the considerable economic and clinical benefits that may result.
authors: Vitreo Retinal Unit, St. Thomas' Hospital, London, United Kingdom.
authors: Nilpa
authors: N
authors: Shah
authors: D Alistair H
authors: DA
authors: Laidlaw
authors: Shaheen P
authors: SP
authors: Shah
authors: Selvaraj
authors: S
authors: Sivasubramaniam
authors: Catey
authors: C
authors: Bunce
authors: Simon
authors: S
authors: Cousens
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001330:Electronic Data Processing / Q000592:standards*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D014787:Vision Tests / Q000379:methods* / Q000592:standards; D014792:Visual Acuity; D055815:Young Adult