I had never heard of them before, but I saw some for sale on eBay yesterday. Super geeky, birth control style. Said to work on some sort of built in artificial horizon that fools the brain ofd the wearer.
Maybe like "Peril Sensitive Sunglasses" from Hitchhikers Guide to the Universe; the more danger you're in, the darker they get. What you can't see can't hurt you.
