The way I have (totally inexpertly) understood it is that "normal" near/ farsightedness (and various other things optometrists usually look for) relate to
physical issues with your eyes. Vision therapy doesn't address these. Instead, it deals with problems in the
cognitive processing of the signal your brain is getting from the eyes (and especially with effectively merging the signals being received by the two eyes.)
I wouldn't expect vision therapy to have any effect - positive or negative - on near or farsightedness and the need for glasses to address them. I would be cautious around a therapist who claimed a relation.
Similar to comments from other posters, many people I know - and now their kids - experienced rapid deterioration in distance vision in pre-adolescence to adolescence. I've never looked this one one up, but they tell me the new and stronger prescription every year at this age is quite common.
I've found these clinical practice guidelines helpful. Numbers 18 and 20 address vision therapy; you may be able to find info related to your original question in here too, maybe in the first one related to paediatric care?
http://www.aoa.org/optometrists/too...tions/clinical-practice-guidelines?sso=y
