High Index Lenses
High index eyeglass lenses refer to one of several different kinds of plastic lens material. Eyeglass lenses all have a definite "index", which ranges from 1.56 to 1.74. For strong prescription, the higher the index, the thinner the lens; for weak prescriptions, a low index lens will be no thicker than high index eyeglass lenses. As a result, if you are looking for the "thinnest eyeglass lenses" for your prescription, read more so you do not pay extra money for lenses that are not thinner.
Most people are looking for the thinnest eyeglass lenses, but "thinnest eyeglass lenses" differs from prescription to prescription. If your prescription is under +/-3.00 sphere, a 1.56 index CR-39 lens is the best index for you, because a higher index lens will be more expensive and not thinner. In this article we talk about the thinnest eyeglass lenses for your prescription, but this is a very general discussion. There are a billion different prescription combinations, and there are several factors in each prescription making it unique.
Plastic Lenses - 1.56 Index
Most lenses are plastic (glass is still available, but heavier and more expensive), but the least expensive plastic used for eyeglass lenses is called CR39 hard resin lenses. Hard resin lenses are good for everyday use. These lenses have the least distortion of any non-glass lens. For children or active adults engaged in sporting activities, we strongly recommend polycarbonate (impact resistant) lenses.
If the sphere on your prescription is higher than +/-3.00, you will benefit from the selection of a high index lens type. If the sphere on your prescription is higher than +/-4.00, we recommend a thin lens type. Thinner lenses have three advantages: they do not look thick, they do not magnify or minify your eyes when seen by others, and they are lighter.
Polycarbonate Lenses - 1.59 High Index
Polycarbonate lens material is the best choice for children, active adults, and sporting activities. Polycarbonate lenses are virtually shatterproof, provide the best eye protection of any lens, and includes 100% UV protection inherently. If the sphere on your prescription is +/-3.00 or higher, you should choose polycarbonate lenses. Polycarbonate lenses are very difficult lenses to tint and are not recommended for people who want custom dark sunglass lenses (we suggest Trivex lenses in this case). The suggested prescription range for polycarbonate lenses is plano (0, no Rx) to +/-6.00 sphere.
Trivex High Index Lenses
Trivex is a relatively new plastic lens material that is being used as a substitute for polycarbonate lenses. Trivex is optically superior to polycarbonate and it is lighter. Like polycarbonate it provides 100% UV protection and it is extremely durable. Most importantly, Trivex is a great substitute for polycarbonate lenses that need to be tinted, because Trivex can be easily tinted but polycarbonate cannot. Trivex is much better suited for tinting and is an excellent choice for rimless drill mounted frames. The suggested prescription range is Plano (0, no Rx) to +/-8.00 sphere. Trivex may be slightly thicker than polycarbonate lenses, but due to its specific gravity the weight will be similar.
High Index Lenses - 1.60 High Index
High index lenses with 1.60 high index are good for people with prescriptions over +/-4.00 sphere, because they are thinner and lighter. Thinner lenses have three advantages: they do not look thick, they do not magnify or minify your eyes when seen by others, and they are lighter. The suggested prescription range is +/-4.00 to +/-8.00 sphere. Thinner, lighter and more expensive than mid-high index or hard resin lenses, high index lenses are a good choice for every day use.
High Index Lenses - 1.67 High Index
High index lenses with 1.67 high index are good for people with prescriptions over +/-6.00 sphere, because they are thinner and lighter. Thinner lenses have three advantages: they do not look thick, they do not magnify or minify your eyes when seen by others, and they are lighter. The suggested prescription range is +/-6.00 to +/-8.00 sphere. Thinner, lighter and more expensive than mid-high index or hard resin lenses, high index lenses are a good choice for every day use.
High Index Lenses - 1.70 and 1.74 Ultra High Index
High index lenses with 1.70 high index and 1.74 are the thinnest lenses on the market, and are made only for people with the highest prescriptions. If your prescription is lower than +/-6.00 sphere, there is no need for you to spend the extra money for an ultra high index lens. If you do have a strong prescription, however, the 1.70 and 1.74 high index lenses will be a good deal thinner than the 1.67 and 1.60 high index lenses; the higher your prescription, the thinner the lenses will be.