Some of you may remember wearing glass prescription lenses years ago. In fact at one time you could only buy glass lenses. Nothing else was available! Several decades ago different forms of plastic lenses became available and with advances in technology such as Cr-39, Polycarbonate, and high index lenses like 1.60, 1.67, 1.70 and 1.74 are now the norm. In fact we have the opposite problem, prescription glass lenses are much harder to find. Some offices do not even use them! These new advances have allowed an amazing amount of excellent solutions for patients. Thinner, flatter, lighter and impact resistance allow for a huge array of solutions for frames and eyewear needs. The issue tho is these lenses in some ways are much better and in others not as good as glass. Glass Lens offer the absolute best optics of any material. Ray-Ban, Persol, and many premium sunglass companies still use glass lenses because it offers the clearest vision possible with amazing scratch resistance. The downside is they are a bit heavier and can break or crack if dropped.