High-index lenses are eyeglass lenses that are designed to be thinner and lighter than regular lenses. They are made from plastics that are specially manufactured to bend light more effectively than regular lenses. The term "high-index" refers to the refractive index of a lens, which is a measure of the lenss ability to bend light. The higher the refractive index, the more efficient the lens is at bending light and correcting vision. High-index lenses are therefore quite powerful and can correct more severe vision problems while taking up the same or less space as other eyeglass lenses. They are generally recommended for people who have significantly high refractive errors and strong prescriptions for nearsightedness, farsightedness, or astigmatism. Eye prescriptions of +/-4.00 and higher can benefit from high-index lenses. We recommend 1.67 high-index lenses for people with prescriptions between +/-4.00 and +/-8.00, and 1.74 high-index lenses for people with prescriptions +/-8.00 and higher. High-index lenses are more expensive than regular lenses because of their manufacturing process and because theyre made with more costly materials.