TIP 21

Design Websites For Blind / Visually Impaired > Web Accessibility Issues For Blind People

People with visual disabilities are individuals who are blind, have low vision, or have colour blindness. People who are blind need text equivalents for the images used on the Web page, because they and their assistive screen reader technology cannot obtain the information from the image. A person who has a visual disability will not find the mouse useful because it requires hand and eye coordination. Instead, this person must navigate the Web page using only the keyboard. For example, the Tab key is used to move the focus to the item that needs to be selected. A screen reader then announces the item so the user knows where the focus is on the page. The user then presses the Enter key instead of "clicking" the mouse button. Those who have low vision need the assistance of a hardware or software magnifier to enlarge the text beyond simple font enlargement. People who are colour blind or who have low vision benefit from good contrasting colours. When information is presented by colour alone, a person who is colour blind misses that information. Similarly, if information is presented using any attribute by itself (for example, contrast, depth, size, location, or font), a user who has low vision might not detect the difference.

Magnification might reformat the location, change the contrast, or distort the size and fonts of the text and objects on the Web page. It is best to use multiple attributes. For example, if both colour and a fill pattern are used on different bars on a graph, they can be viewed in either colour or black and white. Instead of using size attributes on the font element to denote a heading, the heading element should be used to correctly mark up a heading so that assistive technology can identify headings.

“ With the help of synthesised speech and Braille display technology, even completely blind people can use the Web. ”RNIB

The access needs of blind or visually impaired people can be as variable as the number of blind or visually impaired people visiting your website.

Flexibility therefore is the key to ensuring that your website is accessible to everyone. Those with some vision may need to be able to enlarge text (or make it very small), or change the contrast or colours on the web page. Others will have software installed on their computers to enable them to 'hear' web pages via synthesised speech, or to read the web page by using a Braille display. You must ensure that the design of your web pages does not make it difficult for a blind or visually impaired person to be able to customise the page for his/her own needs.

Designing a website to be accessible to a blind or visually impaired person - or indeed for anyone - can be a complex subject. The following general principles apply to designing for blind or visually impaired users, but are just as relevant to all groups:

1. Provide text equivalents for all non-text objects on the page - speech synthesisers can't read graphics, and graphic text can't be enlarged in the same way as ordinary text.
2. All graphics should have text labels, i.e. alternative attributes in HTML (Hyper Text Mark-up Language).
3. Don't design the page in a way that stops the user from setting their own browser preferences, i.e. don't specify exact sizes for fonts or layouts - design everything in relative sizes.
4. Use descriptive Titles for every page.
5. Use valid HTML - many access programs depend on the use of standard HTML - e.g. some software can give an overview of the page by extracting all the headers and links and presenting them on a single page. If you have no headers on your page and all your links say 'click here' then the accessibility of your website will be very low.
   

There is very useful, more detailed information about designing for blind or visually impaired users at www.rnib.org.uk/digital/hints.htm.

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