One of the most famous sunglass manufacturers for the defence industry today is an American family company named WileyX. They build a unique brand of sunglasses/goggles that are now much copied.
Their SG-1s are probably the most famous model in their line. They have a National Stock Number - which means American soldiers can order them through official channels. This is testemant to how good these sunglasses are.
The frames a flexible, to fit your face and eyes just like any goggles, but smaller and more fashionable.
The lenses are interchangeable within models - WileyX makes a number of sunglasses with interchangeable lenses, they do not interchange between models. There is a great variety of colors, reflectiveness and even light adjusting lenses availible for the SG-1s. Also you can get perscription lenses as well.
SG-1, and most other models, lenses are ballistically rated. This does not mean they are bullet proof, although they can defeat a 12 gauge shotgun pellet from ten feet. They are specifically designed to protect the eyes from small calibre, high impact velocity shrapnel - of great benfit to todays soldiers in an improvised explosive device (IED) saturated threat arena.
Make no mistake, however, these sunglasses/goggles are not just combat items. They look great, and with the itnerchangeable strap/regular arms can change from something you'd where on a motorbike or while jogging to definite fashion spectacles.
SG-1s don't come with any WileyX official documentation, however they should arrive with logos on the elastic strap, regular arms, lanyard and frames. Also you should get a cleaning cloth with a WileyX logo on it.
Overall an excellent choice of eyewear. Currently SG-1s go for about AU$200 from the official Australian store. Ebay is about half price. An excellent bragain.