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Another look at visual standards and driving

BMJ 2000; 321 doi: (Published 21 October 2000) Cite this as: BMJ 2000;321:972

This article has a correction. Please see:

Better tests are needed to determine driving ability

  1. William Westlake, visiting research fellow
  1. McCusker Glaucoma Unit, The Lions Eye Institute, 2 Verdun Street, Nedlands 6009,Western Australia

    Paper p 990

    The law in the United Kingdom requires that a car driver must be able to read, in good daylight with the aid of corrective lenses if necessary, a vehicle number plate containing letters and figures 79.4 mm high at a distance of 20.5 metres. This is a test of binocular static visual acuity and corresponds to a geometric visual angle of 6/15 Snellen acuity. (In the United States this translates into the equivalent of the 20/20 notation, in which the measurement is expressed at a test distance of 20 feet rather than 6 metres as in the Snellen notation. In other parts of Europe people use both the Snellen notation and a system of expressing the visual angle as a decimal fraction—for example 6/6=1 6/12=0.5 6/60=0.1. The rest of the world uses the Snellen notation.) Because of differences in letter types the driving visual test is clinically similar to a Snellen acuity of approximately 6/10.1

    These tests should be performed with both eyes open because the acuity of the better eye when tested separately is often different from the binocular visual acuity. This is the result of interactions …

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