Hi,
I also wear glasses for reading, so for shooting I use the same prescription but with lenses made of Polycarbon, with scratch and glare resistant coatings. The Polycarbon lenses are shatterproof.
Is this the best? I dont want to make statements like that, but it is certainly safe than the cheapest pair one can find.
I would never consider skimping on the quality of eye protection, and it is a good idea to wear them whenever you are at a range, even if you are not teh one shooting at that moment.
There are enough incidents when a person was standing close to someone with a double load, or a revolver with bad timing, or stuff coming back from the back-stop (short indoor ranges) etc.
Brgds,
Danny