I'm the same as littlefish, had mine done about 9 years back, best money I've ever spent!!
Funnily enough, what convinced me to go for it was a 'warm' nights lamping in a speck I thought safe, which wasn't, and having had to pick up my heels for a mile or so, I was trying to make my way slowly to the motor, could I see for steam, could I feck, I was in a position where I could not move until i'd cooled off... Just couldn't see for misting glasses, yet couldn't see without 'em (my next prescription was Labrador)!!
Though it's the best thing i've done, natural deterioration will eventually ki