Graphical representation of visual acuity data.

Accurate graphical depiction of data requires that distances between points map precisely to the quantitative differences they represent. In the case of Snellen visual acuity, consecutive line sizes do not generally correspond to equal increments in visual angle, hence scores plotted against axes marked off in equal intervals provide a false representation of the relation between plotted values. A worked example illustrates the nature of this problem and its solution.