If you want thinner lighter weight lens than High Index are right for you.

High index lenses are available in either glass or plastic. Different manufacturers make different high index lenses, and what sets each lens apart from the others is its index of refraction (IOR). The higher the IOR, the denser the material. All things being equal, a 1.67 IOR material will result in a thinner and lighter-weight lens than a 1.57 IOR material will.
Generally, the higher the IOR, the higher the cost of the lenses will be. The thinnest, most lightweight lenses are typically the most expensive. With high index lenses, it seems that the less you get, the more you pay.
Regardless of the index of refraction, plastic high index lenses tend to be lighter in weight than glass high index lenses, simply because plastic weighs less than glass to begin with.

If you want high-index lenses, be sure to ask for them, but rely on your eye doctor’s or optician’s advice regarding which index to use. They can explain which index makes the most sense for your exact prescription. Most popular lens designs; single vision, bifocal, trifocal, progressive and photo chromatic come in high-index materials, and your doctor or optician will know which ones are available in your prescription.

High Index lenses are available in clear, polarized and photo chromatic.