We had a brief discussion on this topic before.
Newbie
I will add that there was an NFHS interp a couple of years ago that prohibitted players from wearing sunglasses unless they are also corrective lenses. I'll find it and post it later. I would think that a referee shouldn't wear anything that is not okay for the players.
However, since you are looking for a specific PIAA ruling. I would advise you to check with them directly.
2006-07 Soccer Rules Interpretations
SITUATION 10: (a) Player No. 1 on Team A is wearing sport eyewear and (b) player No. 2 is wearing
non-prescription sun glasses. Are these pieces of equipment legal?
RULING: Legal in (a) and
not legal in (b). (4-1-1)
2005-06 NFHS Soccer Rules Interpretations
SITUATION 8:Are
prescriptive sunglasses legal for play?
RULING: Yes. (4-2-1)