First off far fewer people had to wear corrective lenses back then then now. A [study] (http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0420.2002.800203.x/full) done with indigenous nomadic people in Africa found almost no trace of myopia in the population pre-entry into civilization, but "normal" rates post-entry after one generation. Modern lifestyle creates myopia, it's very rare beforehand

Literacy rates were low in premodern Europe, 1% in some cases. Few people needed to learn how to read, in fact most Kings were illiterate. 90% or more of any given population were farming, which did not require considerable eyesight. It was a hard life, but not one which required special skills. A myopic person in premodern Europe would have lived like anyone else. If he was an artisan, the situation could be complicated as rates for literacy were higher among goldsmiths and other artisans, and their professions often involved fine work. Most likely, the person's family would have found him an apprenticeship elsewhere, in a different trade.

I wonder if there was an association of myopia with any particular trades/crafts, like jewelers, since a person having such a condition could see detail of smaller items. I'm not asking if such activities cause myopia, but if a craftsman during those pre-technology times utilized this quality of myopia in their favor.