[EricH]

FIRST doesn't allow non-side-shielded glasses, even if those glasses are safety-rated prescription glasses.

If they are not safety rated (see discussion above), you can expect to be asked to wear safety glasses under them. And with paintball masks not looking like standard safety glasses, you can expect the safety judges to ask. If you can point them to the rating, you'll be just fine. If you can't, you will be wearing an extra set of eyewear.