After choosing the frame the second most important step is to know what is the best material for your lenses. In the world of optics there are a variety of lens material choices but a few of them are the most commonly used and those are the ones we will focus on. These most commonly used materials are as follows:
Hi-Index 1.60, 1.67, 1.74
Each one of these types of materials have their own pros and cons and depending on your prescription needs and your frame choice one material is abetter choice than the other one.
CR-39 – Most commonly used material for eyeglasses lenses. It is perfect for basic metal and plastic frames. Has great clarity when looking through it, can be treated with an anti scratch coating (to reduce abrasion), U.V. protective coating can be added, as well as it can be tinted easily. If you have a standard type of frame and a week to mild prescription this would be the best lens to pick.
Polycarbonate – Durable impact resistant lens (currently used in the windshield of the space shuttle), is the lightest material available and is naturally 99% U.V. resistant. This material is great for semi-rimless and full rimless (frames where the lenses need to be drilled through) along with sports and safety eye wear because of its durability. The down side is due to its impact resistance it is more susceptible to abrasions as well as the material has a higher rate of chromatic aberration which means the optics are not as clear as the other materials.
Trivex – A newer material in relation to the first two. It was designed to provide the same sort of durability when used in a semi rimless and drill mount frames but with better optical clarity. It is also naturally U.V resistant, can be scratch resistant coated and tins well. Trivex is not as thin as poly but has a higher breaking point. While it is more durable for these features it is not rated for sports or safety eye wear.
Hi-Index 1.60, 1.67, 1.74 – These Hi-Index materials are some of the thinnest materials you can get. As each index goes up in number, the thinner and lighter they can be. While all of them are great for high power lenses only the 1.67 is strong enough to withstand the drilling process for drill mounted frames. All Hi-Index materials are naturally 100% U.V. resistant and all can have a scratch resistant coating applied to them. Even though they technically are a heavier material less of it needs to be used so you net an over all lighter lens.