I seldom get more than a year out of my glasses before the polycarbonate lenses start to degrade long before I am due for a new prescription. Not sure just why. I suspect perhaps it is the hot blast from the oven when I open it, or the wood stove or perhaps some form of UV degradation from welding and/or sunlight. Beyond the usual scratches they seem to get a sort of oxidation that eventually makes everything look hazy. Up close you can see the rough surface of the lens. In bright conditions I can barely see through them.