The Freiburg Visual Acuity Test-variability unchanged by post-hoc re-analysis

Graefes Arch Clin Exp Ophthalmol. 2007 Jul;245(7):965-71. doi: 10.1007/s00417-006-0474-4. Epub 2007 Jan 12.


Background: The Freiburg Visual Acuity and Contrast Test (FrACT) has been further developed; it is now available for Macintosh and Windows free of charge at . The present study sought to reduce the test-retest variability of visual acuity on short runs (18 trials) by post-hoc re-analysis.

Methods: The FrACT employs advanced computer graphics to present Landolt Cs over the full range of visual acuity. The sequence of optotypes presented follows an adaptive staircase procedure, the Best-PEST algorithm. The Best-PEST threshold obtained after 18 trials was compared to the result of a post-hoc re-analysis of the acquired data, where both threshold and slope of the psychometric function were estimated via a maximum-likelihood fit.

Results: Testing time was 1.7 min per run on average. Test-retest reproducibility was +/-2 lines (or +/-0.2 logMAR) for a 95% confidence band (using 18 optotype presentations per test run). Post-hoc psychometric fitting reproduced the Best-PEST result within 1%, although the individual slopes varied widely; test-retest reproducibility was not improved.

Conclusions: The FrACT offers advantages over traditional chart testing with respect to objectivity and reliability. The similarity between the results of the Best-PEST vs. post-hoc analysis, fitting both slope and threshold, suggest that there is no disadvantage to the constant slope assumed by Best PEST. Furthermore, since variability was not reduced by post-hoc analysis, for high reliability more trials should be employed than the 18 trials per run used here.

MeSH terms

  • Adult
  • Aged
  • Diagnosis, Computer-Assisted*
  • Humans
  • Middle Aged
  • Psychometrics
  • Reproducibility of Results
  • Sensory Thresholds / physiology
  • Time Factors
  • Vision Tests / methods*
  • Visual Acuity / physiology*