Our Single Vision High Index Glass 1.70 lenses are for very strong prescriptions and will only work with full frames, where the frame goes all the way around the lens. High index glass lenses have better optical performance than high index plastic lenses and the 1.70 Index glass is the second highest index lens material that we offer. These lenses are a lot more reflective than regular lenses, and that's why we automatically add an anti-reflective coating for you to reduce glare. You're worth it. Please note that we only recommend high index 1.70 glass lenses for frames with small lenses to reduce the weight of your glasses and maximize comfort.