Keyboards with different sizes and specifications are now available with different key layouts or different key types.
“Writer keyboards can be larger than normal to facilitate the selection of the various keys by people with difficulties in fine movement control or visually impaired people or lower dimensions for users with limited range of motion and, so they are not able to reach all the keys on a standard keyboard. Some keyboards have a more ergonomic key layout to reduce the risk of repetitive strain injuries. ”
“Support technologies for people with disabilities”, http://www.acessibilidade.gov.pt/livros/tapd/html/indice.html