I have seen many a pair of safety glasses prescription or standard destroyed, as poor cleaning choices rendered their lenses opaque. Now scratches are very difficult to avoid on normal instances, so when you consider what safety glasses are designed for it is understandable that they do get scratched.
Ways of limiting the scratches and increasing the longevity of your safety glasses include. Storing your safety glasses in a case – preferably a hard case so if you drop something on top of them they have a bit of protection. I have seen people store their safety glasses in a sock hung on a peg in the work shed. I thought that this was clever for a couple of reasons; firstly you would know where your safety glasses are when you need them. Also socks are pretty soft and good at cleaning things, they can also be washed when they get dirty/dusty.
Which brings us to the next problem – how do you clean your safety glasses, I know it is unrealistic to think that you will carry a clean microfiber cloth and wait until you have rinsed the dust off the lenses before cleaning them, with either a lens spray or water and microfiber cloth. This would be optimal if you could use a clean dust-free cloth to clean the lenses along with liquid water or lens cleaner). There are premade sachets of lens cleaning solution available that comes with a cloth – we sell a Bolle version.
Alternatively if these things are not available please bear in mind that if you rub dust around on the lens either by not rinsing it off or using a cloth (or your shirt) that is covered in dust you are scratching your safety glasses. So at least try to blow the dust off prior to cleaning and shake out the cleaning cloth. This is at least decreasing the dust and dirt present so there will be fewer scratches seen on the lenses.
The moral of the story is the more thought you put into looking after your safety glasses, the longer they will last and the lenses will be clearer.