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Resolution acuity versus recognition acuity with Landolt-style optotypes

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Abstract

Background

International standards define acuity as the reciprocal of the threshold gap size of a Landolt C optotype. However, the literature is inconsistent as to what type of acuity is measured with Landolt Cs. The present study addresses this question more directly than previous studies by quantifying the effect of an inherent luminance artifact in Landolt-style optotypes.

Methods

Two groups of modified optotypes were used. In the first group, each optotype had a single gap structure with the same average luminance. Between optotypes, the gap structures differed in their degree of fineness. In the second group of optotypes, a standard gap was always present, defining the orientation of the optotype. Additional gap structures of the same average luminance, but different fineness, were inserted at the remaining potential gap locations, thereby balancing luminance across potential gap locations. Visual acuity measures were obtained for each optotype variant, using a computer-based test employing a staircase procedure.

Results

Similar acuity values were obtained for all optotypes of the first group, and for standard Landolt Cs, irrespective of the fineness of the gap structure. With luminance-balanced optotypes of the second group, measured acuity was halved, compared to standard optotypes.

Conclusions

The results support the view that it is recognition acuity, rather than resolution acuity, which is measured with standard Landolt-style optotypes, with the imbalanced luminance distribution serving as a cue. Luminance-balanced optotypes may help to obtain a more veridical estimate of resolution acuity, although recognition acuity may be more relevant in daily living.

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Acknowledgments

We are grateful to Felix Scharff for his help with collecting data, and we thank our subjects for their participation. The study was supported by the Deutsche Forschungsgemeinschaft (BA 877/18).

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Authors and Affiliations

  1. Sektion Funktionelle Sehforschung, Univ.-Augenklinik Freiburg, Killianstr. 5, 79106, Freiburg, Germany

    Sven P. Heinrich & Michael Bach

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  1. Sven P. Heinrich
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  2. Michael Bach
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Correspondence to Sven P. Heinrich.

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The authors have full control of all primary data, and agree to allow Graefe’s Archive for Clinical and Experimental Ophthalmology to review their data upon request.

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Heinrich, S.P., Bach, M. Resolution acuity versus recognition acuity with Landolt-style optotypes. Graefes Arch Clin Exp Ophthalmol 251, 2235–2241 (2013). https://doi.org/10.1007/s00417-013-2404-6

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  • DOI: https://doi.org/10.1007/s00417-013-2404-6

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