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

  • Clinical Investigation
  • Published:
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Abstract

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 http://www.michaelbach.de/fract.html. 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.

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References

  1. Bach M (1996) The Freiburg Visual Acuity Test-automatic measurement of visual acuity. Optom Vis Sci 73:49–53

    Article  PubMed  CAS  Google Scholar 

  2. Bach M (1997) Anti-aliasing and dithering in the Freiburg Visual Acuity Test. Spat Vis 11:85–89

    PubMed  CAS  Google Scholar 

  3. Bach M (2006) Homepage of the Freiburg Visual Acuity and Contrast Test (‘FrACT’). Retrieved 2006-07-04, from http://www.michaelbach.de/fract.html

  4. Bland JM, Altman DG (1986) Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1:307–310

    PubMed  CAS  Google Scholar 

  5. Bland JM, Altman DG (1995) Comparing methods of measurement: why plotting difference against standard method is misleading. Lancet 346:1085–1087

    Article  PubMed  CAS  Google Scholar 

  6. CEN (Comité Européen de Normalisation) (1996) Ophthalmic optics-visual acuity testing-the standard optotype and its presentation. Beuth-Verlag, Berlin

    Google Scholar 

  7. Dennis RJ, Beer JM, Baldwin JB, Ivan DJ, Lorusso FJ, Thompson WT (2004) Using the Freiburg Acuity and Contrast Test to measure visual performance in USAF personnel after PRK. Optom Vis Sci 81:516–524

    Article  PubMed  Google Scholar 

  8. Foley JD, Van Dam A, Feiner SK, Hughes JF (1990) Computer Graphics, Principles and Practice. Addison-Wesley, Reading

    Google Scholar 

  9. Green DM, Swets JA (1966) Signal detection theory and psychophysics. Wiley, New York

    Google Scholar 

  10. Hess R, Woo G (1978) Vision through cataracts. Invest Ophthalmol Vis Sci 17:428–435

    PubMed  CAS  Google Scholar 

  11. Klein SA (2001) Measuring, estimating, and understanding the psychometric function: a commentary. Percept Psychophys 63:1421–1455

    PubMed  CAS  Google Scholar 

  12. Lieberman HR, Pentland AP (1982) Microcomputer-based estimation of psychophysical thresholds: The best PEST. Behav Res Methods Instrument 14:21–25

    Google Scholar 

  13. Linschoten MR, Harvey LO, Jr., Eller PM, Jafek BW (2001) Fast and accurate measurement of taste and smell thresholds using a maximum-likelihood adaptive staircase procedure. Percept Psychophys 63:1330–1347

    PubMed  CAS  Google Scholar 

  14. Loumann Knudsen L (2003) Visual acuity testing in diabetic subjects: the decimal progression chart versus the Freiburg visual acuity test. Graefes Arch Clin Exp Ophthalmol 241:615–618

    Article  PubMed  Google Scholar 

  15. Macmillan NA (2001) Threshold estimation: the state of the art. Percept Psychophys 63:1277–1278

    PubMed  CAS  Google Scholar 

  16. Peters BT, Bloomberg JJ (2005) Dynamic visual acuity using “far” and “near” targets. Acta Otolaryngol 125:353–357

    Article  PubMed  Google Scholar 

  17. Petersen J (1990) Zur Fehlerbreite der subjektiven Visusmessung. Fortschr Ophthalmol 87:604–608

    PubMed  CAS  Google Scholar 

  18. Ruamviboonsuk P, Tiensuwan M, Kunawut C, Masayaanon P (2003) Repeatability of an automated Landolt C test, compared with the early treatment of diabetic retinopathy study (ETDRS) chart testing. Am J Ophthalmol 136:662–669

    Article  PubMed  Google Scholar 

  19. Schulze-Bonsel K, Feltgen N, Burau H, Hansen LL, Bach M (2006) Visual acuities “Hand Motion” and “Counting Fingers” can be quantified using the Freiburg Visual Acuity Test. Invest Ophthalmol Vis Sci [in print]

  20. Treutwein B (1995) Adaptive psychophysical procedures. Vision Res 35:2503–2522

    Article  PubMed  CAS  Google Scholar 

  21. Treutwein B, Strasburger H (1999) Fitting the psychometric function. Percept Psychophys 61:87–106

    PubMed  CAS  Google Scholar 

  22. Weisstein EW. (2006) “Likelihood.” From MathWorld - A Wolfram Web Resource. Retrieved 2006-06-27, from < http://mathworld.wolfram.com/Likelihood.html >

  23. Wesemann W (2002) [Visual acuity measured via the Freiburg visual acuity test (FVT), Bailey Lovie chart and Landolt Ring chart]. Klin Monatsbl Augenheilkd 219:660–667

    Article  PubMed  Google Scholar 

  24. Wichmann FA, Hill NJ (2001) The psychometric function: I. Fitting, sampling, and goodness of fit. Percept Psychophys 63:1293–1313

    PubMed  CAS  Google Scholar 

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Acknowledgement

Thanks to many users for their inspiring support, providing feedback that helped to root out bugs and suggesting useful expansions. Special thanks to Lew Harvey, Hans Strasburger and Thomas Meigen for tutoring in signal detection theory, psychometric threshold assessment and probability statistics and to Margret Schumacher for assiduous testing. Finally, thanks to two very persistent reviewers who considerably helped to clarify my thoughts.

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Correspondence to Michael Bach.

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Bach, M. The Freiburg Visual Acuity Test-Variability unchanged by post-hoc re-analysis. Graefes Arch Clin Exp Ophthalmol 245, 965–971 (2006). https://doi.org/10.1007/s00417-006-0474-4

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  • DOI: https://doi.org/10.1007/s00417-006-0474-4

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