|Trivex material has passed the ANSI Z87.1 standard for safety.|
|NXT sun lens material features the same characteristics of weight and clarity as Trivex.|
|Crizal Kids UV lenses use Essilor’s Airwear polycarbonate lens material so the lenses are easy-to-clean, thin, light, and shatterproof.|
|When released, PPG’s Tribrid will be an excellent choice for children and their parents who wish to have a thinner lens.|
Impact-resistant lens materials are a ‘must’ when dispensing to children.
The variety of features in today’s lens materials make them excellent choices for children. One of the most important characteristics is impact resistance. Just as lens material options have grown over the years, so have the levels of impact resistance.
There are three levels of impact resistance: standard, safety, and ballistic. Each has a test that helps establish how impact resistant the lens is and which classification it falls under. The test for standard impact resistance involves free-fall dropping a 5/8-in. stainless steel ball for 50 in. onto the lens’ convex surface. If the lens cracks or breaks it fails. This test is commonly referred to as the “drop ball” test and is found in the ANSI Z80.1 standard. All prescription eyeglasses, other than safety eyeglasses, must meet this standard. Most lens materials fall into this category like CR-39‘ (and similar materials), 1.56, 1.67, 1.74, etc.
Safety lenses that are recommended for industrial and other potential eye hazard situations fall into two categories: basic and high. For standard safety impact resistance, the test consists of a 1-in. ball dropped 50 in. in a free fall. A safety lens classified as high impact must be capable of not breaking when it is hit by a 0.25-in. ball traveling at 150 ft. per second. The lens is then observed for cracks or fracturing. Both these tests are referred to in the ANSI Z87.1 standard.
There are other tests that show how other materials may supersede the Z87.1 standard. For a lens to pass a military or ballistic impact-resistance test, it must withstand a 0.15-in. diameter irregularly shaped projectile traveling at 640 ft. to 660 ft. per second. This test is found in the MIL-PRF-31013 ballistics standard to denote a military level impact resistance.
|MAKING THE STANDARD What is ASTM International and how does it fit into the impact-resistance discussion? Similar to what ANSI does, ASTM creates standards, but it does so for non-prescription sports eyewear, particularly those used in sports such as racket sports, field hockey, basketball, baseball, and soccer. Letting potential buyers know that a product complies with ASTM standards can give the buyer confidence that the product will withstand the rigors of these sports and protect their eyes from equipment and errant fingers or elbows.|
When working with kids, what you really want is a material that is as tough as you can get it. Since children play hard, they need a lens material that can protect their eyes from harm. While standard impact lenses that meet the Z.80.1 drop-ball test are fine for adults, kids need more. That’s why most ECPs supply safety-level lenses, usually at the “high impact” level.
Polycarbonate and Trivex‘ material are the main lens materials considered great choices for children’s eyewear. ECPs know these materials have passed the ANSI Z87.1 standards for safety and will hold up well in rambunctious situations where kids may find themselves.
ECPs also know that it’s important to consider how well the child will see through a lens. Polycarbonate lenses have a 30 Abbe value while Trivex material has an Abbe value of 45. This is especially important when a younster’s prescription starts to creep higher on the refractive scale. Another consideration is that kids’ bridges are not quite as developed as their adult counterparts so it’s important for them to have lightweight lenses. Polycarbonate weighs 1.20 g/cmÂ³ while Trivex material weighs in at 1.11 g/cmÂ³. Both of these values indicate very light lenses will result from using these materials.
While you may not have a clear lens option for a child that falls under the military or ballistic standard, there are sun lens options available in this category that can be used to create prescription sunwear for children. Since kids spend a lot of time outdoors playing, having ballistic-level sunwear is a good idea. This is particularly important for the child who participates in activities that involve shooting, playing with a ball, or an object that moves at a high rate of speed. An excellent lens choice for this type of prescription is NXT‘. These lenses are made with Trivex material and feature the same characteristics of weight and clarity previously mentioned. They are available in polarized, fixed tints, and photochromatic options, meaning you will be able to find an appropriate lens solution for any activity the child participates in.
|ACTIVE LIFESTYLES ECPs understand the importance of asking questions about lifestyle to their adult patients, but it’s equally important to ask these questions of their young counterparts and their parents as well. What sports and hobbies are they involved in? Even the most sedentary of children need impact-resistant lenses, but those children who participate in sports will need more than one pair of glasses to ensure they have all the protection they need.|
Tribrid™ is a lens material introduced by PPG Industries, Inc. in the U.S. last year that has properties that make it a viable option for kids’ eyeglasses (at press time, Tribrid hadn’t been released yet in the U.S.). Its Trivex material is well suited for children with prescriptions from +/-3.00D but some kids have prescriptions that are stronger than this and would benefit from a higher-index material that would make their lenses more cosmetically appealing. Tribrid is thinner and lighter than lower-index materials and it offers clear vision too. In addition, it also provides better impact resistance than traditional 1.60 lenses. Tribrid is slightly lighter at 1.23 g/cmÂ³ compared to a 1.60 lens (1.30 g/cmÂ³) and it also has an Abbe value of 41 compared to a 40 for a 1.60 lens. But how strong is Tribrid?
COLTS Laboratory, an independent testing facility for our industry, carried out the Gardner Impact Test. This test measures the amount of weight a lens can tolerate to see how resilient or brittle it is. PPG compared the results of this test between Tribrid and a traditional 1.60 lens material. Tribrid lenses sustained 294 lbs. per inch compared to a 1.60 lens which sustained 53 lbs. per inch. This is a significant difference and indicates how durable and resilient the Tribrid material is. When Tribrid is launched, it will be an excellent choice for children and their parents who wish to have a thinner lens.
With so many lens materials available today, it’s important that ECPs keep up on the technical aspects of the lenses so they know which ones to recommend for various patients. Arguably, nothing could be more important than which lens materials to recommend for kids’ eyeglasses. Be sure to make the choices that work best for your youngest patients.
Joy L. Gibb is the lead optician at Daynes Eye and Lasik in Bountiful, UT.
WHERE TO FIND IT:
American National Standards Institute
202-293-8020 • ansi.org
Essilor of America, Inc.
800-542-5668 • essilorusa.com
877-MY-SUN-LENS • nxt-vision.com
PPG Industries, Inc.
800-323-2487 • ppgtrivex.com
724-325-5100 • ppgtribrid.com