Making your site usable for people who have visual impairments or other disabilities is no longer a nicety of modern web design – it is a legal requirement.
If you’d like to understand more about this subject take a look at the following:
1. AA Compliance from W3C: www.w3.org/TR/WAI-WEBCONTENT
2. Checklist of things to consider to make your content more accessible: www.w3.org/TR/WCAG10/full-checklist.html
3. Advice from the Royal National Institute of Blind People: www.rnib.org.uk/professionals/webaccessibility/designbuild/Pages/design_build.aspx