my bird has already made 2 small scratches
What species of bird do you have?
Ultimately if you don´t want them damaged, you will have to keep your bird always at a distance from them. If your bird likes to ride your shoulder, then if they reach for the glasses, remove them (your bird) from your shoulder and place on the nearest safe surface - just the same way we would to discourage biting/nipping.
At this point I´ve given up caring for glasses. I just let my birds play on them, they get changed every few years anyway and my birds are only small. But I completely understand this is not an option for bigger bird owners.