There are countless scientific-based theories as to the cause(s) of refractive errors. There is much disagreement on the matter, and it continues to confound the best and brightest. If Bates was still alive, he would probably be curing them, as he did in his own day! Even that may not convince them -
If you want to really know more about Bates, and how he stood against the establishment, there are plenty of his own documents you should read - he explains it all himself. Start with reading his book, Perfect Sight Without Glasses, and then his monthly publications, and medical articles (all can be had for free on central-fixation.com).