I bought a pair of these Prada's on the Champs-Élysées in Paris two years ago and they haven't held up at all.  I have 35 year old RayBan Sunglasses that look like they're brand new because I take great care of my material possessions.  I keep the Prada's in the case, I wipe the lenses and arms to remove oils, etc.  Basically, the design has some flaws.  When the arms are folded and put into the carrying case, any vibration or movement will cause the ends of the arms to rub against the lenses on the peripheral edges.  This rubbing over time has cause a distinct layer of the lens to peel off.  Recently, the nose pad seems to have gotten much looser and it will just be a matter of time before that breaks off.  As I was trying on the display pair in the store, one of the lenses actually popped out of the frame.  The salesperson, being completely embarrassed, quickly replaced the display pair with a new pair from the stock.  They look great and are very stylish, but not well made or well designed.