A Braille display raises the Braille letters with retractable dots. It usually has a length of 20, 40 and even 80 characters.
A blind user can read the screen of his computer with a Braille display or with a speech synthesiser (or both together). He moves on the screen in using moving keys either on a specific keyboard or in using the standard keyboard. A partially sighted user can use the personalisation functions of the exploitation system (fonts, colours, contrast,...) so that he can take best advantage of his visual capabilities, or he can have magnifying software, a kind of electronic magnifying glass.
Note that the speech synthesiser is destined to be more and more used by everybody (Web access from a car computer or from a simple telephone,...).
In order to browse on the Web a visually impaired user can use a standard browser equipped with a screen reader or use a specific browser.
Whatever the chosen solution is, the original document cannot be perceived globally but by fragments. For that reason it is more difficult to apprehend, to manipulate and to understand this document. The user must in a way mentally gather again the fragments to rebuilt the information contained in the document.
The fragmentation concerns in fact the whole interface, especially the command menus and dialog boxes, that cannot be read at the same time as the document itself. As a result the user is affected by a mental load which could be reduced if the ergonomic lack of quality could be compensated with a clear and logical conception of the document.