Scratch-resistant eyeglass lensesWhoa, Really?
If you drop a pair of eyeglasses on the ground, the lenses probably won't break. That's because in 1972, the Food and Drug Administration began requiring manufacturers to use plastic rather than glass to make lenses. Plastics are cheaper to use, better at absorbing ultraviolet radiation, lighter and not prone to shattering [source: Space Technology Hall of Fame]. Nevertheless, they also had an Achilles heel. Uncoated plastics tend to scratch easily, and scuffed lenses could impair someone's sight. Source: http://curiosity.discovery.com/topic/physics-concepts-and-definitions/ten-nasa-inventions2.htm