Previous to the last few years, the only materials available for use as lenses were glass and a hard resin called CR-39. But recently, high index lenses have become available. High-index materials are named because they have a higher index of light refraction. Basically, they can do the same job that glass or CR-39 does, but high index lenses are much thinner and lighter. With high index lenses, you can avoid having “soda bottle” lenses.
When learning about high index lenses, you may hear many unfamiliar numbers and terms. Here are a few things to remember.
Polycarbonate
The first and still the most popular high index plastic is polycarbonate. Polycarbonate was originally developed for fighter jet cockpits. It is very strong, very light, and resistant to scratches and breaking. Most sports lenses are made of polycarbonate.
Mid-Index
Other high index materials are classified by numbers. The higher the number, the thinner and lighter the lens. The lower numbers are classified as mid-index lenses. Mid-index lenses, such as 1.54, 1.56, and 1.57, are thinner than glass, and nearly as strong as CR-39.
High-Index
High-index lenses are much thinner than regular glass or plastic. Talk with your doctor to decide which high index lens is right for you.