Posted on September 02 2015
For many centuries, eyewear was usually made from glass, which was called crown glass. However, advances in the 20th century led to a great number of new lens materials that has made wearing glasses more convenient. These materials are stronger, lighter and more powerful. Some of the most popular lens materials today are plastic, polycarbonate, Trivex and high index plastic.
Although glass is a less common lens material today, it is still an option. Glass provides great optical performance and is quite scratch resistant. However, it is one of the heavier materials. Plastic lenses (called CR-39) were one of the first replacements of glass for lens materials. One reason why plastic lenses became popular was their weight – they weigh about half as much as glass lenses. Plastic lenses are also cost efficient, so they will often be the least expensive option in lens material. Perhaps consequently, plastic is the most commonly-used lens material today. It does have some disadvantages, though. Untreated, plastic lenses can scratch easily, are not as impact-resistant and do not have UV protection. Some of these problems can be addressed through coatings.
Polycarbonate lenses have become a popular choice for lens materials, evidenced by the fact that they are the second-most-used material today. The advantages of polycarbonate lenses are that they are much more impact-resistant that plastic or glass (up to ten times more resistant). So they are an excellent choice for children and those with active lifestyles. Polycarbonates are also lighter in weight than plastic or glass, so it can be more comfortable. Although polycarbonate is scratch-prone, most manufacturers coat the lenses to prevent scratches. One disadvantage is that some people with very strong prescriptions find lower clarity with polycarbonates, especially along the edges of the lens.
The development of lens materials continues, and one of the newest materials is called Trivex (first offered in 2001). Like polycarbonate, Trivex also provides strong impact resistance and has UV protection. Furthermore, it is lighter in weight than polycarbonate and tends to have less visual distortions or aberrations than that material. However, Trivex lenses are slightly thicker than polycarbonate ones, and they may cost more than polycarbonates depending on the style of lens.
Some lens materials refract light more than others. The measurement of how much the material bends light is called the index of refraction. Materials with a higher index of refraction bend light better and are called “high index.” There are high index lenses made of both plastic and glass. These materials are advantageous for those with strong prescriptions, saving them from incredibly thick glasses. High index lenses can be both very powerful and thin. This material can also be an option for people who want very thin lenses, even if they do not need powerful ones. A drawback of high index lenses is that they can be more expensive and may not be available for all frames. Additionally, high index glass is heavy, weighing more than even glass lenses.