For most of Islamic history, learning by hearing and repetition has been the ideal form of education, and often the only one recognized. Real knowledge was in your head. Even when written texts became more available, it was assumed that without someone to check you, you could introduce errors or misunderstandings. The Qur'an itself isn't just a text, but a text meant for recitation, which the blind could do just as well as anyone else. I don't remember where I read this, but I think in the Middle Ages there were even scholars who hoped they might one day become blind as a sign of their religious status.
This continues into the culture today, where the Arab world has produced a number of "blind shaykhs." I once saw a row of blind men sitting in the Umayyad Mosque in Aleppo, Syria. They were people who had memorized the Qur'an, and whom others would therefore come and consult on religious matters. It wouldn't surprise me to learn that a religious career is still encouraged for blind young people in Arab society, as one in which their lack of vision could actually assist rather than impair them.