Contact Lenses - Urban
Legends
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Glass
Glass was the first material to be used for spectacle lenses, and for many years was the only option available. They provide good vision correction and are scratch resistant, but compared to plastic material they are heavier and not as impact resilient. Although glass lenses can be chemically treated to increase durability, they can shatter if accidentally dropped or hit by blunt force.
CR-39 Plastic
The most common type of plastic spectacle lens material, CR-39 is made from a hard resin that is lighter and more impact-resistant than glass. Compared to glass, this material has a softer surface so a scratch coating (preferably applied at the time of manufacturing) makes the lenses more resistant to scratches appealing. The higher refractive index* allows the material to bend light to a greater degree, meaning that less curvature is needed to achieve a specific prescription power. Since less material is being used, the lenses are consequentially lighter. In order to maximize the benefits of high-index lenses, they should always come with a scratch coating for protection and an anti-refection coating for better clarity. A simple rule of thumb: the higher the index number, the thinner the lens.
Aspheric Plastic
Aspheric lenses provide visual and cosmetic benefits for stronger prescriptions. Unlike spherical lenses, aspheric lenses flatten progressively from the center to the edge. This results in enhanced overall vision, reduced thickness, and decreased peripheral visual distortion. When used for high farsighted prescriptions, they make eyes look more natural instead of magnifying them into “bug eyes.” Those with strong nearsighted prescriptions benefit from thinner lightweight lenses. Aspheric lenses can be ordered in high index materials for the ultimate in attractive thin lenses.
Polycarbonate
These lenses are one of the most impact-resistant materials available, and they naturally filter out UV light. When vision has been significantly impaired in one eye, polycarbonate is used to better protect the good eye from impact damage. These lenses are the optimal choice for children, industrial safety, and sports glasses. Polycarbonate lenses are considered a high index material as they are thinner than CR-39. Polycarbonate lenses should always have scratch-resistant coating on both the front and back surfaces to protect its surface and prolong the life of the lens.
High Index Plastic
A variety of new plastic materials bend light more than conventional CR-39 lenses. High index lenses provide significant advantages over traditional plastic or glass. They are made of a denser resin material that makes high nearsighted prescriptions thinner, flatter, and lighter. It eliminates the thick “coke bottle” effect of high nearsighted prescriptions and the “bug eye” effect of high farsighted prescriptions. The process improves peripheral vision, filters out UV light (both UVA and UVB), and makes the lenses more cosmetically
Trivex™
Trivex™ is a new performance lens material that combines superior optics, impact resistance, and lightness. Because of their strength, Trivex™ lenses can be ground thinner, resulting in cosmetic benefits and greater comfort. These are great for rimless frames because they don’t distort or break at drillholes, and they give an excellent jewel-like appearance to edges that are polished. They are a good choice for high-performance safety eyewear for both children and adults who are highly active. The excellent impact resistance makes Trivex an a possible alternative to polycarbonate. In its uncoated form, it is easier to tint and lighter in weight than polycarbonate.
