I know a guy that communicates via his eyes. He has a chart with the alphabet in rows. Vowels on row 1 and the rest of the alphabet on several rows. The person talking with him iteratively asks 1, 2, 3, etc until he signifies the row. The person talking then iterates the letters in the row, such as a, e, i, etc until the he signifies yes. It sounds slow, but with a little prediction it works pretty well.