The lens , besides the pellet protection thing. its also minimal
distortion, meaning the surrounding would not be so distorted even
though the lens is 'curved/Wrap' shape. However, cos of the minimal
distrotion thing, it would make the lens scratched more easily when
drop or careless handling. So, i guess that's why its so ex to make
a prescip one.
But when buying, better to buy from authorised dealer. If not, when
repair. Need to pay additional $$ for that.