The material that is used to make bulletproof glass is the same stuff that is used to make shatterproof lenses for your glasses or sunglasses.
It's just a common plastic (called polycarbonate) -- but it's an extremely strong material.
With lenses made from polycarbonate, you don't have to worry about potential damage to your eyes in the event of an accident, or (more commonly), shattering the lenses if the glasses are accidentally dropped.
Prescription lenses can be quite thick and heavy if they are made out of optical glass, which is another reason why plastic is used in the production of lenses.
No matter how strong your prescription is, plastic lenses can be compressed and are very lightweight.
This means that the wearer looks better (no more magnified eyeballs looking out from behind "coke bottle bottoms") and is more comfortable.
Did you know that optical glass weighs more than twice as much as plastic? If any of you have ever worn a heavy pair of glasses, you'll know how uncomfortable the bridge of your nose (with those sore pressure points) can get and how sensitive the back of your ears can feel.
Everyone knows they're not supposed to leave their sunglasses and/or prescription glasses (shaded or not) on the dash in the car.
This is because direct sunlight can heat up glasses so much that (if they are made out of a standard plastic) they can be ruined, softening and melting in the heat.
However, polycarbonate is quite heat resistant.
If you inadvertently leave them cooking on the dashboard, at least the lenses won't be ruined (although you may need a new pair of frames).