Objective analysis of typographies by image processing based on the optotypes’ guidelines Análisis objetivo de tipografías por procesado de imagen basado en las convenciones de los optotipos

Most near vision reading charts include the visual acuity values. On the one hand, most reading charts are constructed using the Times New Roman typography. On the other hand, visual acuity is commonly measured with optotypes not with typographies. In this paper, an objective analysis by image processing of the stroke width of some typographies (Times New Roman, Arial, Arial Bold, Sloan and Optotipica), suitable to be used in acuity and near vision reading charts, is performed. Taking the tumbling E as the optotype model, two new parameters are defined for each typography compared with that: the degree of similarity to an optotype, DSO, and the spread, Sp. DSO accounts for the similarity of the character to an optotype, whilst Sp accounts for the variability of the stroke width all over the character. The parameters defined show that none of the conventional typographies analyzed is suitable to be considered as an optotype, being Times New Roman the less similar and Arial Bold the most. In this sense, the equivalent visual acuity values of typographies used as optotypes are not univocally determined. Thus, a reflection is needed: do reading charts have to include visual acuity values? And, which is the stroke width needed to compute them?