January 1993
Volume 34, Issue 1
Free
Articles  |   January 1993
On the statistical reliability of letter-chart visual acuity measurements.
Author Affiliations
  • A Arditi
    Vision Research Laboratory, Lighthouse Inc., New York, New York 10017.
  • R Cagenello
    Vision Research Laboratory, Lighthouse Inc., New York, New York 10017.
Investigative Ophthalmology & Visual Science January 1993, Vol.34, 120-129. doi:
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      A Arditi, R Cagenello; On the statistical reliability of letter-chart visual acuity measurements.. Invest. Ophthalmol. Vis. Sci. 1993;34(1):120-129.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

PURPOSE: To determine boundary values of test-retest reliability and sensitivity to acuity change that are unlikely to be exceeded in any clinical situation, for a popular visual acuity chart (Lighthouse/ETDRS) with three scoring methods; to discuss general methodological issues associated with statistical accuracy of optotype chart testing; and to link measures of test reliability to measures of sensitivity to change. METHODS: Five highly practiced subjects were tested using a computer-controlled acuity testing system in a procedure designed to reduce measurement error. Subjects read the computerized chart 156 times, yielding a sample of 78 test-retest comparisons. RESULTS: Under conditions likely to minimize variability, visual acuity may, with 95% confidence, be ascertained only within +/- 0.1 log units, using this chart with the recommended letter-by-letter scoring. Detecting a significant change in visual acuity requires about +/- 0.14 log units for the same degree of confidence. CONCLUSIONS: These measurements may be viewed as approaching the upper limit of reliability of this letter chart. Reliability probably is considerably less in typical usage.

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