Glossary · Accessibility term
Dyslexia
Dyslexia is a set of processing difficulties that affect the acquisition of reading and spelling. Reading fluency and spelling are the markers, rather than anything to do with the eyes. That distinction matters, because the popular account of dyslexia is a visual one and the clinical consensus is not. The difficulty underneath it is most often phonological, which is the mapping between sounds and letters. It does not affect intelligence. It sits on a continuum rather than being something you either have or do not. And it rarely travels alone. Attention differences, dyscalculia, language disorder and coordination disorder co-occur with it often enough that the combination is the norm.
In practice
On the web it shows up as effort. Dense text, long lines, cramped spacing and justified alignment all slow reading down, and the effect compounds over a page rather than staying where it started. What reliably helps is duller than the marketing suggests. Adequate text size, generous line spacing, left alignment, shorter lines, real paragraphs instead of walls, and getting out of the way when somebody overrides your styles.
Fonts sold as dyslexia-friendly are popular and the evidence behind them is weaker than the claims made for them. The letterform properties that genuinely help are ordinary ones and none of them requires a special typeface. What matters more than the font is whether your layout survives a reader changing it.
That last point is the WCAG rule, and it is narrower than people think. Text Spacing at Level AA asks that nothing break when a reader adjusts four values. Line height to 1.5 times the font size, paragraph spacing to 2 times, letter spacing to 0.12 times and word spacing to 0.16. It does not require you to build a control for any of that. The requirement is that your page survives the override, not that you provide one. Level AAA is where a mechanism comes in, and it asks for a way to reach a set of outcomes rather than for those outcomes as your defaults. Non-justified text, not specifically left-aligned. Line spacing and line length within stated limits. The browser can supply that mechanism, so at AA all of it is good practice.
Why it matters
Somebody adjusting spacing in their own browser has reached for one of the few controls a reader actually has, and a layout that clips, overlaps or drops text under that adjustment takes it straight back. That is the whole shape of the rule. You are not being asked to design for dyslexia. You are being asked not to break the adjustment somebody already made. How many readers that reaches depends entirely on where the line gets drawn, though. A pooled analysis of 58 studies put dyslexia at 7.1% of primary school children. Published estimates elsewhere run from under 5% to 20%, depending on the diagnostic criterion and the population. So anybody quoting you one confident number is quoting a choice rather than a count.
Test the override, not the font
Open your own page and set all four. Line height to 1.5 times the font size, spacing after paragraphs to 2 times, letter spacing to 0.12 and word spacing to 0.16, expressed in units that follow the font size. Change nothing else. Text that clips, overlaps or disappears is the failure. Buttons that swallow their own labels are the usual casualty. Truncating with an ellipsis in a genuinely constrained region is allowed, and only where the full text is still reachable, on focus or through a link to it.
Where this shows up on the site
Related terms
- Cognitive disabilityCognitive disability is a broad group of conditions affecting how people take information in, hold on to it, and act on it.
- Plain languagePlain language is writing that lets somebody find what they need, understand it the first time, and act on it.
- Low visionLow vision is sight loss that ordinary glasses cannot correct, and it covers far more ground than a single blurred-vision picture suggests.
Knowing the word is the easy part.
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