The Legibility of Typefaces for Readers with Low Vision: A Research Review

This article presents a systematic review of the research evidence on the effects of the characteristics of typefaces on the legibility of text for adult readers with low vision. The review revealed that research has not produced consistent findings and thus that there is a need to develop standards and guidelines that are informed by evidence. Reading is critical to full participation in modern society, and as the population ages, the concern for the print accessibility of public documents will rise. For the many individuals with vision loss, reading print presents a major challenge when planning and performing everyday tasks. In Canada, the 2001 Participation and Activity Limitation Survey (PALS) reported that of the approximately 600,000 people with “seeing disabilities,” most have low vision, and that roughly 500,000 people aged 15 and older require accommodations to read newsprint, such as special lighting, large print, or magnification (Statistics Canada, 2001). According to demographic information from the 2000 U.S. census, an estimated 937,000 Americans aged 40 and older were blind (U.S. The research on which this article was based was supported, in part, by a grant from the Canadian National Institute for the Blind (CNIB). The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of CNIB. 402 Journal of Visual Impairment & Blindness, July 2007 definition) and 2.4 million had low vision in 2000. The leading causes of blindness and low vision in the United States in adults aged 40 and older were age-related macular degeneration (AMD), cataract, and glaucoma (Eye Diseases Prevalence Research Group, 2004). The International Council of Ophthalmology’s report, Visual Standards: Aspects and Ranges of Vision Loss (Colenbrander, 2002), recommended that the global vision community use the term low vision for degrees of vision loss less than blindness when individuals can be helped significantly by vision-enhancement aids and devices and that when detailed reporting on the ranges of vision loss are not feasible, the range for low vision should be less than 6/18 (0.3) (20/60) and greater than or equal to 3/60 (.05) (20/ 400). Low vision has also been described as the inability to read a newspaper or recognize faces from a conventional reading distance (40 centimeters, or about 16 inches) while wearing the best refractive correction (Chung, Mansfield, & Legge, ©2007 AFB, All Rights Reserved 1998). Many older people have difficulty reading standard print, including medication labels, even with appropriate magnification and illumination. High levels of magnification can reduce the size of the usable field for many individuals with low vision, and the manipulation of the characteristics of typefaces can reduce or eliminate the need for additional magnification (Arditi, 2004). Previous research on the legibility of typefaces and psychophysical variables related to it has suggested that certain characteristics can affect legibility and reading acuity for both sighted readers and those with low vision (Arditi, 1996; Arditi, Knoblauch, and Grunwald, 1990; Legge, Rubin, and Luebker, 1987; Tinker, 1963). These characteristics include the presence or absence of serifs (Arditi & Cho, 2000, 2005); the width of strokes (Arditi, Cagnello, & Jacobs, 1995b; Berger, 1944a, 1944b); kerning or interletter spacing (Arditi et al., 1995a; Arditi, Liu, & Lynn, 1997; Moriarty & Scheiner, 1984; Whittaker, Rohrkaste, & Higgins, 1989); leading (the space between lines of text) (Tinker, 1963); point size (Legge, Rubin, Pelli, & Schleske, 1985); the height of letters (x-height, defined as the vertical measure of the lowercase “x” in any given font, and t-height, defined as the height of the bottom of the crossbar of the letter “t” in any given font) (Arditi, 2005); contrast (Rubin & Legge, 1989); and color (Legge & Rubin, 1986). The legibility and readability of fonts have been studied by examining the individual characteristics of a font or differences among whole or unmodified fonts (Arditi et al., 1990; Mansfield, Legge, & Bane, 1996; Morris, Berry, Hargreaves, & Liarokapis, 1991). Research on the specific ©2007 AFB, All Rights Reserved Jo characteristics of fonts, such as stroke width or the use of serifs, requires the manipulation of individual parameters while keeping others constant. Alternatively, researching whole fonts may be easily done in practical application, but limits the generalizability to specific characteristics. When the characteristics of fonts are evaluated, the outcome may be contaminated because of the difficulty in knowing whether the reported differences in legibility are related to the size of the type, to different lighting conditions, or to fundamental differences in design. One concept of the legibility of print specifies that the test material should be performed under “threshold seeing conditions,” a psychophysical acuity measurement that defines a threshold value at which a majority of subject responses are accurate. Another concept is related to the performance of various typeface designs when they are presented at sizes that are well above the reader’s threshold. One aspect to be considered may be simply which font design is the most appealing or comfortable to the reader, often described as “readability” (Arditi, 2005; Kitchel, 2002). A significant problem arises when one font design “A” is found to be more legible than another font design “B,” but font “B” is found to be more readable than “A.” The apparent contradiction may be explainable by the inconsistent use of terms. Other criteria that are used to determine the legibility of typefaces are reading speed and critical print size (Chung et al., 1998; Mansfield et al., 1996). The critical print size is the smallest print size at which individuals can read with their maximum reading speed. This is an important measure because it indicates the minimum magnification that is required for effortless reading. urnal of Visual Impairment & Blindness, July 2007 403 With this overview of research and performance measures in mind, the primary objectives of this review were to locate any research related to the effective characteristics of typefaces for readers with low vision, to determine the existence of any standards or guidelines that are related to such legibility, and to address the characteristics of French-language typefaces for readers with low vision. The latter was considered because French uses a number of accent marks that are not used in English, and the typeface that is used may make these marks more distinct or less distinct, and Canada, the country in which this research was conducted, is officially a bilingual country. In addition, research related to the legibility of medication labels was considered. By incorporating methods that are frequently used in systematic reviews, we rated and synthesized the selected literature to formulate conclusions and make recommendations. Although this review is not typical of other evidence-based reviews that have been used in clinical-trials research environments, we incorporated methods that have been used in systematic reviews by integrating specific protocols when searching for studies, developing targeted criteria for inclusion and exclusion, and using systematic methods for rating the quality of studies. The methods used in this review were consistent with previous work related to the Vision Rehabilitation EvidenceBased Review project; see the web site www.piads.ca/112/vrebr.htm for details on the parent project of this article.