My wife and son are both dyslexic, so I was interested in this piece in IO9 about a new font designed to help dyslexics read more effectively:
Dyslexie was created by Christian Boer, a dyslexic graphic designer from the Netherlands. The font incorporates a number of typographical features that make it harder for the brains of dyslexics to rotate, swap, mirror, and otherwise confuse letters while they're reading.
Take the letters "p," "b" and "d," for example.... In many fonts, these letters look very much the same, such that by rotating and mirroring them they can be used more or less interchangeably.
In Boer's font, however, the boldness of each letter's base is increased, granting each character a "weight" that hints at its proper orientation. Notice also that the space enclosed by each letter (what is referred to in typography as a character's "bowl" or "loop") is shaped just a little differently than that of the other two. These subtle typographical cues may not seem like much, but they go a long way in helping your brain recognize which letters belong where when they appear in words and sentences.
Scientific American adds:
One of the first things he did was increase the boldness of letters at their bases, to make them appear weighted, causing readers' brains to know not to flip them upside down, as can occur with "p" and "d." Boer also enlarged the openings of various letters, such as "a" and "c," to make them more distinguishable from one another, and increased the length of "the tail" of other letters, like the "g" and y." He also put certain letters at a slant so that they would appear to be in italics, like the "j," a tactic to increase the brain’s ability to distinguish it from the letter "i." Finally, he boldfaced capital letters and punctuation, and provided ample space between letters and words, to allow the brain more time to compute the letters and begin forming them into words and sentences.