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Klaus Rohrschneider, Axel R. Spittler; Measurement Of Visual Acuity - Landolt Rings Versus Numbers Or Symbols. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1894.
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© ARVO (1962-2015); The Authors (2016-present)
Estimation of visual acuity (VA) in clinical practice mostly is performed with numbers or letters, while in children often simple symbols like Lea-Symbols are used. Even for clinical studies and for exact measurement of follow-up the ETDRS charts use numbers. Besides this testing with Landolot rings offers better comparable results without influence of different recognition of shape. However, it remains unclear whether there are differences between measuring with Landolt rings or other optotypes.
Visual acuity of 2366 eyes of 1395 patients of the Low Vision Department aged 5 to 98 years with all kinds of ophthalmologic diseases was measured in identical manner iwith Landolt rings and numbers. In addition subgroups were measured using Lea-test. VA was calculated in logMAR and compared for age groups and different ranges of VA.
Median VA was 0.7 ± 0.52 logMAR (0.2) and 0.6 ± 0.5 logMAR (0.32) for Landolt rings and numbers, respectively. Correlation between both optotypes was 0.967 for all eyes (0.951 for right or left eyes). Mean Landolt ring VA was one line below number acuity (0.1 logMAR), while especially in eyes with low VA there were more cases with better VA for Landolt ring symbols. The differences between both optotypes were not correlated with visual acuity scores, which ranged from -0.08 logMAR (1.25) to 2.6 (0.1/40), although VA decreased significantly with age (p<0.01).
While measurement with numbers especially using the ETDRS charts are the gold standard for scientific assessment of visual acuity, only the use of Landolt rings offers absolute equivalence of different optotypes. The use of Landolt rings is therefore commanded for legal reasons in Europe. For practical reasons numbers or letters are usually used as optotypes. Our results confirm that visual acuity measured with Lamdolt rings is about 1 line worse as compared to numbers which has to be taken into account when comparing different examinations. However it is not possible to exactly recalculate measurements with different optotypes especially in a Low Vision population.
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