Designing for People with Partial Sight
by Aries Arditi, Ph.D
Here are basic guidelines for making effective legibility choices that work for nearly everyone.
How does impaired vision affect reading?
Impaired vision often makes reading difficult by:
Reducing the amount of light that enters the eye
Blurring the retinal image
Damaging the central portion of the retina best suited to reading
Light reduction and blurring reduce the effective contrast of the text, while central retinal damage impairs the ability to see small print and to make eye movements that are crucial to reading.
Text should be printed with the highest possible contrast. There is good evidence that for many readers who are older or partially sighted, light (white or light yellow) letters on a dark (black) background are more readable than dark letters on a light background. However, the traditional dark on light may be aesthetically preferable.
2. Type Color
Very high contrasts are difficult to achieve with color combinations other than black and white. Printed material, generally, is most readable in black and white. Different colors may be important for aesthetic or other reasons, but it is better to use such combinations only for larger or highlighted text, such as headlines and titles.
3. Point Size
Type should be large, preferably at least 16 to 18 points, but keep in mind that the relationship between readability and point size differs somewhat among typefaces.
Leading, or spacing between lines of text, should be at least 25 to 30 percent of the point size. This is because many people with partial sight have difficulty finding the beginning of the next line while reading.
5. Font Family
Avoid complicated, decorative or cursive fonts and, when they must be used, reserve them for emphasis only. Standard serif or sans-serif fonts, with familiar, easily recognizable characters are best. Also, there is some evidence that sans-serif fonts are more legible when character size is small relative to the reader's visual acuity.
6. Font 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.
7. Letter Spacing
Text with close letter spacing often presents difficulties for readers who are partially sighted, especially those with central visual field defects. Where possible, spacing should be wide. Monospaced fonts rather than proportionally spaced fonts seem to be more legible for these readers.
Extra-wide binding margins are especially helpful in bound material because it makes it easier to hold the volume flat. Spiral binding can be helpful as well. Many visual devices, such as stand- and video-magnifiers, are easiest to use on a flat surface.
9. Paper Finish
Paper with a glossy finish can lessen legibility because many people who are older or who have partial sight also have problems with glare.
Visual impairment often makes it difficult to find a book or other document that is buried among similar publications, especially for sets with volumes that differ only in title or number. Use of distinctive colors, sizes and formats on the covers can be especially helpful to older individuals and those who are partially sighted.
Designers can help to compensate for the difficulty experienced by readers who are partially sighted by following the guidelines in this brochure.