Available accessibility guidelines do not necessarily guarantee usable Web sites, particularly when specific groups of users with special needs are considered.
We have identified 15 Web design criteria aiming to provide integrated support of accessibility and usability for vision-impaired users. In this article,
we present the results of a study investigating whether the application of such guidelines for vision-impaired users can actually improve their task performance when accessing Web applications. We report on two user tests, both involving vision-impaired users, that aim to provide empirical validation of the design criteria.
During each test, users had to access and navigate two versions of a Web site, one version supporting the selected design criteria and one obtained
with traditional techniques.
Our results indicate that the 15 design criteria improved Web site usability both quantitatively and qualitatively by reducing
the navigation time needed to perform the assigned tasks and by making the Web sites easier to navigate for blind and low-vision users.
However, accessibility alone is not enough. Usability aspects need to be addressed as well. Indeed, accessibility and usability are frequently addressed
as two separate issues, but disabled users need to have both accessible and usable applications. In fact, accessibility and usability are two intertwined
aspects of Web site interaction, and if they are not properly integrated, Web sites can turn out to be either accessible but barely usable or usable but
barely accessible. In both cases Web site navigation by disabled users is likely to be seriously compromised, because they either may not be able to access the desired information (i.e., it is not accessible) or may find difficulty in arriving at what they need (in this case it is not usable).