what is the difference between 1.57 and 1.67 index lenses?
In addition, the 1.59 pure polycarbonate lens tends to scratch more easily than the 1.50, 1.57, and 1.53 lenses, because it's a softer lens material. ... Just like the 1.61 high-index lens, the 1.67 lens reduces the edge thickness for nearsighted (-) prescriptions and the center thickness for farsighted (+) prescriptions.