I live in Tokyo and this trend has been on the rise for the past few months. It is primarily a fashion thing, which is understandable because glasses can be a great accessory for some outfits.
The problem I have with it recently is that girls wear fake glasses WITHOUT lenses! If you have lenses that are just non-prescription, then that's fine because nobody knows the difference, but having glasses with NO lenses just looks dumb as hell.
In any event, this has become a HUGE trend in Tokyo recently and I can't for the life of me figure out why. Especially when in most cases the girl looks WORSE with glasses than without and it's obvious to everyone that they are fake!