A client of ours wanted a new website but one of the key areas that we need to take care of was the fact that the site may be visited by a lot of visually impaired visitors.
We did some research on this and we have always thought about accessibility with our designs but generally speaking for this particular project the majority of users were older people with failing eye sight due to age or illness.
The main criteria to think about is the readability of the text and for most users this relates to font size – so for this site we added a font sizer that allowed users to increase the general font and it would remain at the chosen size for every subsequent visit.
We had to think about colours and the contrast of colours for menu items, there needs to be a very distinct contrast such as black on white or black. We also had to avoid providing information based on slight colour changes such as when a mouse is over an item and again make any colour changes very distinct, often this is not pleasing to the designer but in this case function was more important.
Another area that can help visually impared users is to generally use less graphics and more plain text making the site easier to read and navigate.
All in all with a project like this you need to identify your target users to see how the website design needs to make it accessible to the maximum number of users.