As a very visual medium, the web presents unique problems to the millions of people who have low, restricted or no vision. There are four broad categories or vision impairment:
1. Colour Blindness: red-green impairment is the most common, affecting 5% of the male population and 1% of the female. One in twelve people using the web are colour blind.
2. Mild vision impairment: require larger font size, possibly a different background style and/or colour.
3. Moderate vision impairment: require the aid of screen magnification software.
4. Blind/severe vision impairment: require the aid of a screen reader.
The following key guidelines are important considerations for users with mild, moderate and sever vision impairments:
- Do not use colour alone to convey information. (WAI Level 1)
- Ensure that all images have alternative text (Alt text), especially links, logos and images. Use empty Alt text (alt= " ") for decorative images of no informative value. (Level 1)
- If Flash is used, ensure that it works with modern screen readers and provide an accessible alternative for older screen readers. (Level 1)
- If Frames are used, ensure that they all have titles and names that make sense as screen readers navigate in and out of individual frames on a page. (Level 1)
- Ensure that the correct table header tags for column titles are used for tabular data. (Level 1)
- Provide transcripts for any multimedia for example, video and/or audio clips. (Level 1)
- Ensure that text for hyperlinks is appropriate and that it makes sense out of context. Avoid repetition if possible. (Level 2)
- Position labels in forms to the left or above input files and to the right of checkboxes and radio buttons. (Level 2)
- Ensure a consistent and uncluttered page layout. (Level 2)
- Avoid using graphics for text. (Level 2)
- Choose colours that ensure signigicant background and foreground contrast and avoid combinations of red-green and blue-yellow for colour-blind reasons. (Levels 2 & 3)
- Ensure that all font size definitions are relative and re-sizable. (Level 2)
- Offer a high-visual skin and/or link to a page explaining how to change colours and font sizes. (Level 3)
- Offer a 'Skip Navigation' or 'Skip to Content' link to allow the user to skip over navigation links. (Level 3)
- Use a clear non-seriffed font such as Arial, Tahoma or Verdana. (Recommended)
- Avoid using Flash for text as there are re-sizing issues. (Recommended)