Latest studies i've read link these types of vision impairment to the lack of proper lighting, that reduce the release of dopamine (that is released also when we are exposed to sun) and that lack of dopamine can play a role in lens elongation thus causing vision problems. It is possible that studies, that concluded that computer and phone use (so always reading up close) are the cause, are just seeing correlation betwen this usage and staying indoor more (which closely correlates with computer/phone usage)