unless your prescription glasses come with a frame from the 80's... I don't think they would protect you much from bugs or debris. My prescription glasses are too small to protect my eyes from a bug...
I got one in my eye while wearing my prescription glasses, I crashed, and the soft tissue around my eye was itchy and swollen for 1 week. Damn bugs, hate them. It's a good thing I was going UP the hill on the granny gear.