I've got the same thing. Been to the opticians a number of times to get it tightened (can't see enough without my glasses to do it myself...). Been meaning to get their opinion on it but can't see a tiny bit do any harm. Unless it reacts with the acetate?
One hinge keep getting loose after each time I tighten the screw.
I locktite a solution here? I guess it would be, but I might be missing a trick.