I bought a pair of glass sunglasses last week. The lenses are made by glass. The salesman told me that the color in glass lenses will last forever. And they are also scratch resistance. This kind of lenses can provide clearer vision and better filtration. Glass lenses are also more chemical resistant. But glass lenses are heavier than plastic lenses. Besides, if you have high prescription, the lenses will be thinner or thicker in some areas, which will lead to lighter and darker areas across the lenses.