Font families are a good example of a place where you can make an inclusive design and development choice. Your choice of typeface/fonts can make or break a website, especially from an accessibility point of view. English as a second language (ESL) users, users with low vision, and users with reading, learning, and attention disorders (ex. dyslexia, ADHD), all benefit from accessible typography.
Researchers estimate that 10-17% of the U.S. population has dyslexia. That is a pretty significant percentage, which is even higher than current Internet Explorer, Edge, Firefox and Opera users combined (as of September 2017).
So if we choose a typeface we know that is legible for people with dyslexia (as shown by the top section on the pyramid with severe difficulties), then we also know every group under that section can also read the font. People who are blind or have more serious sight issues other than dyslexia would need additional typography or assistive technology considerations.
For example, people with visual impairments or dyslexia, certain letters or combinations of letters can be confusing, so it’s important that letter shapes are clearly defined and unique. Common offenders are the “I” (ex. India), “l” (ex. lettuce) and “1” (ex. one). Likewise, characters like “b” and “d” and “q” and “p” can sometimes be mirrored (either left-right or up-down) so words could be flipped into a nonsensical words or sometimes into a real word that would entirely change the meaning of the content.
There are some characteristics that can aid legibility. So when you are looking for your next font family, pay particular attention to the following things and you’ll be on your way to choosing an accessible font:
Prominent ascenders (ex. the vertical line in d).
Prominent descenders (ex. the down-pointing line in y).
A d/b or p/q combination which are not an exact mirror image of one another.
Uppercase I, lowercase l, and 1 must all have different characteristics from one another.
Avoid fonts that have tight letter spacing; these will be difficult for some users to read.
Kerning is also important, particularly between r and n. Otherwise, words like “barn” could be read as “bam” or “modern” could change to “modem.”