Question: what is the difference between 1.57 and 1.67 index lenses?
Answer: 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.