Plastic CR-39 lenses have been the standard lens materials for eyeglasses for many years. Plastic lenses are half the weight of glass lenses, have better ultraviolet (UV) light protection, are less prone to shattering, and can be tinted more easily. With an added scratch-resistant coating, they are nearly as resistant to scratches as glass lenses. Plastic CR-39 lenses are about the same thickness as glass lenses.
Polycarbonate Lenses are one of the first "thinner, lighter" lens materials. They are both thinner and lighter than traditional Plastic CR-39 lenses and are 10 times more impact-resistant than glass or regular plastic lenses, making them the preferred choice for safety glasses, athletes, and eyewear for children and adults who desire lightweight, protective lenses. This is also a good option for those with prescriptions a slightly thick prescription. Polycarbonate lenses offer 100% protection from UV light, as do Trivex lenses.
High Index is a term used to describe a variety of plastic lens materials that are thinner and lighter than regular Plastic CR-39 lenses. For a given prescription power and lens design, the factor that determines lens thickness is the index of refraction (a.k.a. refractive index) of the lens material. Materials with a higher refractive index bend light more efficiently than materials with a lower index of refraction. Plastic CR-39 lenses have a refractive index of 1.498 and Polycarbonate lenses have an index of refraction of 1.58. Any lens material that has a refractive index higher than glass (1.523) is considered a high index material.
Today's high index plastic lenses sold in the United States range in refractive index from 1.54 (Trivex lens material) to 1.74. One of the most popular high index lens materials has a refractive index of 1.67. Lenses of this material are about 50% thinner than lenses made of standard Plastic CR-39 lens material.
Replacement Lens Express will be happy to help you determine which high index lens material is best for your prescription, frame selection and budget.
Trivex lenses are the new rival for polycarbonate lense; they are thin, lightweight and much more impact-resistant than regular Plastic CR-39 or Polycarbonate lenses. Trivex lenses have crisper optics, and may have sharper central vision than Polycarbonate lenses. They may also have less chromatic aberration then Polycarbonate lenses as well as sharper peripheral vision. The index of refraction is 1.53, making them about 10% thicker than Polycarbonate lenses. Trivex lenses offer 100% protection from UV light, as do Polycarbonate lenses, however, they do need a scratch-resistant coating to prevent scratches. Todays modern coatings can make the surface of these lenses nearly as hard as glass. We would be happy to discuss the pros and cons of Trivex lenses so that you can decide which material is the right choice for your needs and budget.