1.56 high index lenses are the only lenses that combine thin, flat surface cosmetics and lightweight comfort with the optical performance of plastic. 1.56 lenses are up to 25% thinner than plastic and comparable to other high index lenses, giving the wearers slimmer glasses and a wider choice of frames. A flattened, aspheric design makes 1.56 hi index lenses up to 50% flatter than regular plastic and 35% flatter than spherical high index lenses, so lenses bulge less from the frame and maintain clear optics.