In Japan, some persons with print disabilities find either horizontal or vertical writing particularly difficult. Dyslexic persons often have problems with vertical writing. Meanwhile, persons with autism or optic stenosis often have problems with horizontal writing. An experiment (see Section 3 of this document) conducted by KOUYAMA Tadashi reveals that dyslexic people tend to have more problems with vertical writing. More information (in Japanese) about his experiment is available here.
Use case: A publisher creates an EPUB publication having vertical-writing stylesheets and alternate horizontal-writing CSS stylesheets. By default, vertical writing is used. But some dyslexic users switch to horizontal writing.
Issues are using label:”TF: vertical writing switching”