The advice to get the advice of an optician is probably best. To remove the scratches you must remove part of the lens material, and it's unlikely you'll be able to do that without changing the shape of the lens surface, which will change the way the lens focuses and will make everything out of focus instead of just foggy.

If your optical supplier can remove the scratches, and if it can be done inexpensively, then you know what to do.

If the frames are in good shape, an optical shop should be able to fit new lenses to them, whether they're "out of style" or the latest thing. It's worth considering whether the frames will remain in good shape until you're due to replace the new lenses when you make the decision whether to get only lens replacements.

If it's been more than a few months since you had your prescription checked, an update examination is probably in order before purchasing a new set of glasses.

It's unlikely, although not impossible, that using the weedwhacker actually caused your scratches. It's much more likely that the scratches are from your "cleaning" after "whacking." Of course it's essential that you clean properly after you've whacked, but the emphasis must be on "properly." All of the plastics used for lenses now are "scratchable." The polycarbonate are much more resistant, but not immune, to scratches.

Any abrasive cleanser is dangerous to use on lenses. Many common household cleansers will actually "dissolve" the surface lens material and can cause fogging. Even "wiping off the dust" without moistening the lens may eventually cause enough small scratches to "fog" the lenses.

Note that "safety glasses" or safety lenses in standard style frames usually are made of the same polycarbonate that you can (and in my opinion should) insist on having in your "everyday" glasses, and are no more resistant to scratching or fogging than ordinary lenses. The "safety" part of it is that they'll resist breaking when hit by large flying objects. When doing anything that might scratch your regular lens, you should probably also use a throwaway pair of "safety goggles" to protect even your "safety lenses" when there's a "scratch hazard."

John