Reading fields of magnifying loupes.

Abstract

For the purpose of understanding the influence of the use of magnifying loupes on the reading process, the reading field is a relevant concept. Three possible reading fields are distinguished: the monocular reading field, the binocular reading field, and the composite reading field. Theoretical expressions for the widths of reading fields are derived as a function of the physical parameters of the loupe and the geometry of the reading situation. Variation of reading-field width as a function of magnification is illustrated. For verification, experimentally determined reading-field widths were compared with the theoretical ones. There were small systematic deviations, probably caused by achromatic aberrations. In order to learn about the strategies that subjects use when reading with the aid of a loupe, loupe displacement was measured while subjects read text under conditions that provided a variety of reading-field widths. It was found that individual subjects use different strategies (i.e., they use different reading-field widths).