The index value of a lens roughly equates to its thinness in use and application. As the thinness goes up, the cost of the lens material goes up too. If you don’t need the thin qualities of a lens for your Rx, save the money and buy a better frame or buy an extra pair of glasses with your lens savings.
Here is a rundown on the lens index value which will help provide some rough judgment on the benefit from a cost standpoint of being a higher index lens.
Material Index Value Common attributes and benefits, Comparable Cost
CR39 1.49 Highest optical quality, lowest cost
Trivex 1.53 High impact resistance, high optical quality, light in weight, highest cost, UV
Polycarbonate 1.58 High impact resistance, high optical quality, light weight, inexpensive, UV
Plastic Mid Index 1.56 22% thinner than CR39, cost effective, UV protection, available as aspheric
Plastic High Index 1.60 30% thinner than CR39, cost effective, UV protection, available as aspheric
Plastic High Index 1.67 39% thinner than CR39, more costly, UV protection, available as aspheric
Plastic High Index 1.74 50% thinner than CR39. Most expensive, UV protection, available as aspheric