I have a pair of glasses that cost a few hundred pounds when I got them they had coating various put upon them. Over time they got very scratched even though the optician said they will not scratch.He later said they could not be repaired and I would need new lenses. I have just got a small bottle of  ( Armour Etch - Glass Etching Cream - 3oz (85g) Bottle) off Ebay and this morning painted the stuff over the lenses, Left for 3 minutes and then washed it off ..Result.. Almost as good as new like having cataracts removed. There is a video from youtube below. She states leave on for 5 mins but I did it for 3 mins just in case and that was fine. Please treat the paste with caution and wear gloves it can burn your skin.

http://www.youtube.com/watch?v=UoUivzsO_S0 ;