Lenses | Materials
Plastic or CR-39:
CR-39 lenses, known as plastic lenses in layman’s terms, are the most popular lenses used today. CR-39 monomer is used for casting plastic lenses for prescription eyewear, sunglasses and other plastic products requiring high abrasion resistance and high quality optical properties. Plastic lenses from CR-39 monomer give less chromatic aberration compared to polycarbonate lenses, as measured by the Abbe number.
The lens is light weight compared to glass, and may be made in just about any prescription, though many people with higher prescriptions prefer to use Hi-Index Lenses. Plastic lenses are great for prescription sunglasses due to their tent ability factor and you can virtually tint a plastic lens to any color.
Plastic Lenses are available in clear, polarized, and photo chromatic and Hi-Index.
Crown glass and flint glass are the two types of glass used today to create glass lenses. The main obstacle to manufacturing flint glass in the 18th century was the difficulty of removing bubbles and unevenness in the glass mixture.
This material is heavier than plastic or Hi Index but had a greater resistance to scratches and a higher Abbe number which means that they have clearer optics.
Glass lenses are available in clear white, polarized, photo chromatic, and Hi-Index.
These lenses are thinner and lighter than plastic and glass lenses and generally have an index of refraction between 1.53 and 1.59. The most common lenses that fit into this category are Polycarbonate, Phoenix, Trivex and Trilogy.
This group of lens materials is considered to be extremely strong and lightweight. More durable than regular plastic, polycarbonate, phoenix, trivex, and trilogy lenses are shatter-resistant. They have the best impact resistance of any lens material, making them the lens of choice for sports eyewear, children, safety or active lifestyles. These lenses are not only thinner and lighter in weight than traditional plastic eyeglass lenses, they also offer ultraviolet protection.
Mid Index lenses are available in clear, polarized and photo chromatic.
The Higher the Number, the Thinner the Lens.
High index lenses are available in either glass or plastic. Different manufacturers make different high index lenses, and what sets each lens apart from the others is its index of refraction (IOR). The higher the IOR, the denser the material. All things being equal, a 1.66 IOR material will result in a thinner and lighter-weight lens than a 1.57 IOR material will.
Generally, the higher the IOR, the higher the cost of the lenses will be. The thinnest, most lightweight lenses are typically the most expensive. With high index lenses, it seems that the less you get, the more you pay.
Regardless of the index of refraction, plastic high index lenses tend to be lighter in weight than glass high index lenses, simply because plastic weighs less than glass to begin with.
If you want high-index lenses, be sure to ask for them, but rely on your eye doctor’s or optician’s advice regarding which index to use. They can explain which index makes the most sense for your exact prescription.
Most popular lens designs; single vision, bifocal, trifocal, progressive and photo chromatic come in high-index materials, and your doctor or optician will know which ones are available in your prescription.
High Index lenses are available in clear, polarized and photo chromatic.