Previous to the last few years, the only materials available to use for 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 speaking about high index lenses, you may hear many unfamiliar numbers and terms. Here are a few things to remember.
The first and still 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 impact. Most sports lenses are made of polycarbonate.
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. These lenses are thinner than glass, and nearly as strong as CR-39.
High index lenses, such as 1.66, 1.74, and 1.9, are much thinner than regular glass or plastic. Talk with your doctor to decide which high index lens is right for you.