Lightweight spectacle lenses made from plastic – special ZEISS "high-index" lenses – are the secret to incredibly thin and lightweight designs, even when high dioptric powers are required. Four different types of material are available (also see our infographic at the end of this article): basic materials, standard materials, high quality materials and high-tech materials. The higher the quality of the source material, the thinner you can make the lenses. In the case of plastic lenses, for example, choosing the high-tech option over the standard material can reduce the weight by up to 50 percent (up to 40 percent in the case of glass lenses). That's quite a weight off your mind! And it applies to progressive lenses, too.