Based on WCAG 2.0 description of F88: Failure of success criterion 1.4.8 due to using text that is justified (w3.org):
Many people with cognitive disabilities have a great deal of trouble with blocks of text that are justified (aligned to both the left and the right margins). The spaces between words create "rivers of white" running down the page, which can make the text difficult for some people to read. This failure describes situations where this confusing text layout occurs. The best way to avoid this problem is not to create text layout that is fully justified (aligned to both the left and the right margins).
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Article titled Typography on the Web written by Paul Haine—client-side developer—on Opera Developer Community (dev.opera.com) Website in 2008. He said that one of the limitation in Web typography is
no hyphenation, making full justification look ugly when a column of text gets narrow. In the long explanation, visually, fully-justified texts:
…can look more attractive than text with a "ragged" edge, and you’ll see it a lot in magazines and books. On the web, however, it’s problematic due to the lack of automatic hyphenation, which breaks words at appropriate points to better fit them in the line. To fully justify the block of text, all the browser can do is adjust the spacing between the words, which can lead to "rivers of white space" running vertically through the block—this usually happens when the line length within the block is too short and there aren’t enough spaces to adjust subtly…
Even in the narrow column, we often see fully-justified texts on some magazine templates.
Another Web accessibility expert, Mel Pedley, published on accessites.org in 2006, has this post, Designing for dyslexics: Part 3 of 3. The question: justified or not? Pleasing visual effect? Yes, but she has these words:
The problem here is that the brain is a pattern-recognising machine. The uneven word spacing disrupts that pattern recognition. For most people, the effect is minimal when reading printed text. After all, we’re used to justified text in books. But reading from a screen is generally accepted to be more difficult than reading print. Consequently, this effect can become more significant as soon as you move from print to screen.
For a dyslexic reader, it can be catastrophic! The uneven spaces between words, creates visual distractions which are hard to ignore. As a result the reader loses his/her place repeatedly. Unjustified text, although less attractive at first glance, is far easier to read.
In the same Website, Joe Dolson—a Web accessibility consultant—has a post titled Improving accessibility through typography. He said:
Again, your beautiful layout might fall apart badly when you enlarge the text. As fewer words fit onto a line, the spaces between them grow larger and larger. This kind of broken text block becomes increasingly difficult to read.
One of the government Website, nlm.nih.gov, has a checklist which is research-based guidelines. Making your Website senior friendly suggested:
There are three ways to justify type: left, full, or center justified. Left justified text is optimal for older adults.