Clear Print April 2006
An evidence-based review of the research on typeface legibility for readers with low vision.
June 2006
Lead author: Elizabeth Russell-Minda, M.A., VREBR Project Coordinator
Co-authors: Jeffrey Jutai. Ph.D., C.Psych., VREBR Project Director
Graham Strong, O.D., M.Sc., VREBR Investigator
Collaborators: Kent Campbell, Ph.D., Bloorview KidsRehab
Deborah Gold, Ph.D., CNIB
Julia Morgan, CNIB
Lisa Pretty, CNIB
Lesley Wilmot, CNIB
This report is a collaborative effort of the VREBR Project Team and CNIB Research.
Copyright Statement
This document is considered the property of the VREBR Project Team and CNIB Research. No part of this document shall be copied, quoted or distributed without permission from the authors. Electronic distribution or saving to another file type (such as .rtf or .html, for example) is also prohibited.
Contact Information
Please address correspondence about this document to:
Dr. Jeffrey Jutai, National Director of Research, CNIB
University of Western Ontario,
Dept. of Physical Medicine & Rehabilitation
Parkwood Hospital Site
Hobbins Building, Suite H-403
801 Commissioners Rd. East
London, ON N6C 5J1
(519) 685-4292 x42626
E-mail:
Contents
Objectives of the Report 4
Methodology 4
International Guidelines and Standards 4
Reading and Low Vision 5
Eye Conditions that Affect Reading Ability 5
Age-Related Macular Degeneration 5
Cataract 6
Glaucoma 6
Diabetic Retinopathy 6
Overview of Font Characteristics 6
Spacing 6
Letter Height (x-height and t-height) 6
Serifs 7
Sans-Serifs 7
Stroke Width 8
Variables that Affect Text Legibility and Readability 8
Contrast 8
Type Colour 8
Heaviness 8
Point Size 8
Leading (Spacing between lines of text) 9
Letter Spacing 9
Font Family and Style 9
Other Considerations 10
Medical Labeling 10
Conclusions 11
References 12
Appendix I—Studies and Publications Selected for Review 14
Clear Print: Executive Summary
Readability shouldn’t be an afterthought when producing written materials. It should be the first step in making information accessible to anyone. With this hypothesis in mind, the VREBR Project Team and CNIB Research set out to identify general guidelines for producing accessible print materials. This document summarizes the resulting Clear Print report, published April 2006.
Objectives of the Report
The objectives of the Clear Print report were to:
· review existing research about the legibility and readability of typefaces
· locate any Canadian or international standards or guidelines related to typeface design and legibility
· address any French language typeface characteristics (accent marks, for example) as they affect low vision readers of print copy
Although it was not the primary goal of the study, literature related to the legibility of medication labelling was also considered.
Methodology
The Clear Print study assessed existing research using evidence-based models and methods in order to develop conclusions and make recommendations. Research studies were located using multiple online databases, grey literature sources, and general Web searches.
The search criteria included: controlled or uncontrolled; experimental or non-experimental; randomized or non-randomized; and published or unpublished research. The criteria for “low vision condition” included any eye condition where reading printed copy causes some amount of difficulty. Literature devoted to factors associated with online font or computer accessibility was excluded from the review.
For a list of studies and grey literature sources selected for this review, see Studies and Publications Selected for Review—Appendix I. All of the studies selected for review (17 total) contain research on some form of font legibility in relation to low vision reading. A good majority of the studies included subjects with normal vision and sample sizes were usually small.
International Guidelines and Standards
During the search for international font legibility standards or guidelines for low vision readers, the Clear Print study did not locate any definitive international standards or guidelines on font size and type for reading with low vision. Perhaps the closest example of a “standard” in this regard, is a document published by the International Council of Ophthalmology, entitled Visual Standards: Aspects and Ranges of Vision Loss,[1] which contains information and a chart on the ranges of visual acuity and reading ability.
The study did find that most international library councils, printing houses and foundations for the blind and visually impaired (Canada, US, UK, and Australia), have guidelines and standards for large print materials. (See Appendix II for a detailed listing of these organizations). In general, there was agreement between these organizations on standards for printed material in terms of acceptable font size and other text characteristics that increase legibility and accessibility.
In the search for medication labelling and typeface legibility standards in Canada and the United States, we located several sources outlining rules and regulations concerning standardized formats for health-related information and medication (non-prescription or over-the-counter—OTC) labelling.
Reading and Low Vision
Reading is critical to full participation in modern society. For the many individuals with vision loss, reading presents a major challenge. Low vision can be defined as the inability to read the newspaper or recognize faces, even using corrective lenses, at a normal reading distance of 40 cm.[2] Many older people have difficulty reading standard text, including medical information, hospital forms, and medication labels. Some people who can read standard print may find it tiring and prefer to read large print whenever they can.
Successful rehabilitation primarily involves enhancement of whatever usable vision remains.[3] The most direct method for enhancing vision is magnification, usually consisting of relatively portable and inexpensive hand-held or stand magnifiers, or electronic devices such as CCTVs and other devices. Environmental modifications such as proper illumination and viewing distance are also important variables.
Due to problems associated with high levels of magnification, such as reduction in the size of the usable field, making print more legible or readable can reduce or eliminate the need for magnification.3
Eye Conditions that Affect Reading Ability
In terms of causing difficulties when reading print, the following low vision conditions are among the most prevalent.
Age-Related Macular Degeneration
AMD is the leading cause of visual impairment in the developed world. It is also the most common cause of losing the ability to read print, since it affects central vision, which is used for seeing detail. Since AMD progressively affects the central vision, people with AMD must use peripheral vision to read, which has been shown to be a slow and inefficient process.2-[4], [5], [6],[7]
Cataract
Cataract is another common age-related condition where the lens of the eye becomes cloudy or opaque. If vision is blurred by cataracts, reading performance will be degraded.[8] With severe cataract, people can see light and detect colour contrast, but usually cannot read print. When people with cataracts receive laser treatment, they can usually begin to read large print again. Reading materials with good contrast can help people with cataracts.
Glaucoma
Since glaucoma is considered a “tunnel vision” condition, central vision is usually unaffected, allowing the person to continue to read print. However, peripheral vision is usually affected. As people with glaucoma age, they usually require progressively larger print materials.
Diabetic Retinopathy
Diabetic retinopathy (DR) is a major cause of vision loss for working-age adults. DR can lead to patchy vision resulting in orientation difficulties. Some people with patchy vision have a fairly even sight loss across the visual field and may require print materials with good contrast and large print. Some individuals may lose peripheral sight first, and can continue to read standard sized text for longer periods.
Overview of Font Characteristics
Spacing
The two main types of spacing are fixed-width and proportional. In fixed-width fonts (such as Courier New), each character takes up the same amount of horizontal space. In a proportionally-spaced font (such as Times or Arial), different letters take up different amounts of horizontal space.[9]
Fixed-width font (Courier New)
Proportionally-spaced font (Times New Roman)
Proportionally-spaced fonts can pack more characters into a line of text than fixed width fonts, and are thus preferred by typographers.
Letter Height (x-height and t-height)
The x-height is defined as the height of the letter “x” in any given font, and is the specific height of the lower case letters. The “t-height” is defined as the height to the bottom of the crossbar of the letter “t” in any given font (lower case). Refer to Figure 2 below. Depending on the font, t- and x-height may be different or the same.
Figure 1 Example of t-height and x-height (100 pt. APHont not shown to scale)[2]
Serifs
Serifs are the fine lines that extend horizontally from the main strokes of a letter.[10] Examples of serif fonts include: Times, Palatino, Garamond, Century Schoolbook, and Book Antiqua. Serif fonts are frequently used in newspapers and books where the space for print is tight.
The quick brown fox (Times)
The quick brown fox (Palatino)
The quick brown fox (Book Antiqua)
Sans-Serifs
Sans-serif fonts are those fonts which have letters with straight lines and no curls or appendixes. Examples of sans-serif fonts include: Arial, Helvetica, Tahoma, Avant-Garde, Univers, Century Gothic, Verdana, and all other fonts characterized by clean letterforms.
The quick brown fox (Arial)
The quick brown fox (Tahoma)
The quick brown fox (Century Gothic)
Figure 2 Examples of serifs and sans serifs.[3]
Stroke Width
Stroke width refers to the width of each stroke in a letter. A font may have a uniform stroke width in which the stroke is the same width throughout each letter, for example the font Arial. Or, a font may have a varying stroke width in which some portions of the stroke are thinner than others, as seen in the font Times New Roman. Fonts may also be “heavy” (have a generally wide stroke width), referred to as “bold,” or a thin stroke width, referred to as “light.”
Variables that Affect Text Legibility and Readability
Contrast
Many individuals with low vision have difficulty with objects that are poorly contrasted with their surroundings.[11] People with central vision loss, who use peripheral vision for reading, are especially affected by issues related to contrast. General guidelines recommend that text should be printed with the highest possible amount of contrast. There is also good evidence that for many low vision readers (older or partially-sighted) that light (white or yellow) letters on a dark (black) background are even more readable than dark letters on a light background.
Type Colour
The choice of text colour can affect low vision readers. Partial sight, aging and congenital colour deficits (“colour blindness”) all produce changes in perception that reduce the effectiveness of certain colour combinations. Two colours that contrast sharply to someone with normal vision may be far less distinguishable to someone with a visual disorder.[12] It is difficult to achieve high contrast with colour combinations other than black and white. Colour combinations that provide the maximum contrast, such as black on white, and black on yellow give the best legibility results.[13] It is generally recommended that coloured text be used mainly for larger or highlighted text, such as headlines and titles.[14]
Heaviness
The heaviness of a font can have an effect on legibility. It is generally recommended that medium heaviness be used and light type should be avoided. Bold fonts are preferable for emphasis, rather than italics or all-capitals. [15] Some studies have shown relationships between font heaviness and specific low vision conditions. Bold fonts have been shown to be more useful for people with glaucoma or cataract. Stroke thickness is especially important for low vision readers because thinly stroked letters result in poor contrast.
Point Size
A major problem with point size is that different fonts with the same point size will have different heights and widths.[16], [17] The most accepted guideline for low vision reading materials is that type should be large, preferable at least 16 to 18 points. The relationship between readability and point size differs somewhat among typefaces and this should be taken into consideration when developing print materials. For normally sighted readers, point size should range between 9 and 14.
Leading (Spacing between lines of text)
Leading, or spacing between lines of text, should be at least 25 to 30 per cent of the point size. This is because many people with partial sight have difficulty finding the beginning of the next line while reading.14 Some research points to optimal leading ranges of 1 to 4 points, with heavier typefaces requiring more leading.15 Others have suggested that four point leading should be used when preparing materials for low vision readers.
Figure 3 Examples of leading[4]
Letter Spacing
Closely packed small letters are much harder to read compared to the same letters which are not closely packed.[18] Reduced letter legibility has been termed the “crowding effect.”[19] Individuals with compromised macular functions often have reduced reading performance when letter “crowding” is present.[20] At least one study suggests that where possible, spacing should be wide, and fixed-width fonts, rather than proportionally spaced fonts should be used for individuals with low vision.14
Font Family and Style
While there is little reliable information on the comparative legibility of typefaces, there is some evidence that a Roman typeface, using upper and lower cases, is more readable than italics, oblique, or condensed text. In general, there is disagreement in the research as to which font is the most legible for low vision readers. Standard serif and sans serif fonts (such as Arial or Times Roman) are generally considered to be the best fonts for legibility. There is some evidence that sans serif fonts are more legible when character size is small relative to the reader’s visual ability.14
Other Considerations
Other considerations include margin space, paper finish, and distinctiveness. Extra-wide binding margins are helpful in bound material because it makes it easier to hold the volume flat, and many low vision aids, such as stand and video magnifiers, are easiest to use on a flat surface. Spiral binding can be helpful as well.