Glass is the hardest lens material and offers the best protection against scratches. But glass lenses can shatter more easily than plastic lenses, are twice as heavy as plastic lenses, and don’t provide as much protection from the sun’s harmful ultraviolet (UV) rays. Unless your main concern is scratch protection (and you don’t mind wearing heavy glasses that might slide down your nose frequently) heavy, your better choice in a lens material for your eyeglasses is anything but glass.
For many years, CR-39 plastic has been the standard lens material for eyeglasses. (The “CR-39” is the name given to the resin formulation by the original manufacturer.) CR-39 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. And with an added scratch-resistant coating, they are nearly as resistant to scratches as glass lenses. CR-39 plastic lenses are about the same thickness as glass lenses.
Polycarbonate lenses are made of a type of plastic that is more impact-resistant than standard plastic lenses. Polycarbonate lenses are also much thinner and lighter in weight. Polycarbonate lenses also have built-in ultraviolet protection. Because of these properties, it has been the lens material of choice for children’s lenses, sport lenses and safety lenses. However, some people complain that polycarbonate lenses fail to give them the crispest, clearest vision.
Trivex is a new material that is similar to polycarbonate lenses but with higher quality optics, and thus provides clearer vision. Trivex is lighter in weight than standard plastic and is about the same thickness as polycarbonate. Trivex is a more rigid material, making it a better selection for rimless or drill mount frames. Trivex is just as impact resistant as polycarbonate and may also be prescribed for children’s lenses, sport lenses and safety lenses. Trivex is also more tintable compared to a Polycarbonate lens. Trivex has 100% UV protection.
Refer to www.hoyavision.com for more information about HOYA’s Trivex lens called the Phoenix.
Hi-index lenses are made of a special plastic material that refracts light in a different way than regular plastic lenses. With hi-index lenses, vision can be corrected with less material, making the lens much thinner. Plastics are graded in numbers, such as 1.50 or 1.67. The higher the number, the thinner the lens. Because they are thinner, hi-index lenses are also lighter, making them more comfortable to wear. This is important to patients with high prescriptions, as their glasses can be made more cosmetically attractive and appealing.