The lenses in the paintball goggles are a type of plastic labeled as 'poly-carbonate' (more durabile and lighter than CR 39 which is the more common plastic usede to make lenses for glasses, swimming goggles, and lower impact sports like basketball.) While many of these lenses MIGHT
NOT weaken immediately due to the use of solvent cleaners the higer end goggles will have AR (anti-reflective) coatings that do.
AR coatings help the lens to not reflect light thus allowing more light to pass through the lens. This in turn allows for better vision by having less glare on the lens. Regular solvent cleaners (eg. Windex) will break down this coating and thus reduce the visiblity. It will first seem like streaking that doesn' want to go away which are actually scratches in the coating. As they are cleaned again to remove the streaks the AR coating is cleaned off thus the streaks are gone. However the visibility will be less due to the loss of the coating and the increase in glare.
This is the same principle with tent. Any solvent cleaner with ammonia will slowly harm the tenting on lenses. The non-ammonia version of windex (the clear kind) will not hurt the tent but will destroy the AR coating.
Also, as far as alcohol goes, this is not good for the lenses that have the "anti fog" coating instead of the double lens (eg. BE Xtreme 280). The alcohol can react with the chemicals in the anti fog coating to produce a smoke effect in the coating. Therfore you end up with a permanently fogged mask.
As for lens strength, yes the cleaners do break them down over time. In fact, flouride in tap water can weaken them over time (don't worry, we are talking about a really long time on this one).
So what does one use? I have worked in despensing in an optometist office and in an optical lab for over 10 years and have seen many different failed attempts to "clean" sports lenses (paintball, raquetball, shooting glasses, baseball, etc.). Here is what I would suggest from my experience with these lenses and other lenses of this type. The simple fact is, if you use them often and care for your eyes, replace them occassionally (more often in paintball than the others due to the higher impact and smaller projectile). Get on the internet, search for you type lens and occassionally invest the 10 - 30 bucks for some new eye protection.
Secondly, water is free and easy to come by. I would always suggest it first to clean with water and only WATER on the inside of the lens. Yes anti fog products are ok, but these are not cleaners and should only be applied when the lens is clean.
On the outside, if you really must use a cleaner other than water (and you really don't need to, but if you must) do what ARMAX said, "call your [respective] goggle company" (brackets mine) or your local optician and ask them for suggestions on a cleaner to use. Make sure that it is a tye cleaner that works well with the anti-reflective coating on the lens and is anti-static (keeps dust and other small particles from settleing on your lenses and makes a considerable difference). If you go this way, also get an empty spray bottle and dilute the cleaner in water. A 3:1 (water:cleaner) ratio would be my suggestion.
1) Replace your lenses after a year or two (pending on use) or sooner if shot otfen.
2) Water is the best cleaner. (Plus you can get a great deal on it).
3) Do NOT use solvent cleaners, it simply is not good for your lens in so many different ways.
4) If you have the anti-fog coating use ONLY water on the inside and use anti-fog products only after cleaing the inside.
5) If you must use a cleaner call the goggle company or a local optician/optometrist for a suggested anti-static cleaner.
6) Always use a soft clean cloth to wipe your lenses and do so gently.
Hope this was somewhat helpful.
Grace and Peace
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