Shouldn’t a vision test and free or subsidized vision correction be an automatic, integrated part of all adult literacy services? I’m not suggesting that adult literacy programs typically have the resources or staff qualified to provide eye tests, but somehow, at the very least, working with a local clinic or partner organization, a vision check should be a part of every incoming student’s initial assessment. I know that many programs ask about this and make references and some may do more, but it seems so fundamental to reading success that it ought to be a standard best practice at all programs.
Even trickier is what to do when the person does turn out to needs glasses: again, in a sane universe, any adult learner who can’t afford glasses should be able to acquire them for free or at a deeply subsidized cost, but this is not how it always works out in the actual universe.
Literacy & Policy 
In my experience, ABE/GED students often need glasses, and are unaware of it, because they haven’t done any reading for years! Subsidized exams and glasses make sense if students are to succeed, instead of failing (once again) because of a physical barrier, although they will blame themselves for being stupid or lazy.