WHAT MAKES LENSES IMPACT RESISTANT?

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While dispensing eyewear to help patients see well is our first priority, it is also our responsibility to offer lenses that protect the wearer.

While the primary benefit of the eyewear we dispense is to enable our patients to see well, when lenses are made of impact-resistant materials, they can also protect the wearer. As eyecare providers we have a duty to offer proper options to individuals who require protection and at the bare minimum provide information about and offer access to impact-resistant lenses to all eyeglass wearers we treat. Possessing more knowledge about the lens materials we recommend not only goes a long way toward contributing to proper eye health, but it also sets us apart from other providers.


WHO NEEDS THEM?
All children as well as active individuals whose lifestyles expose their eyes to harm require the appropriate protection that will keep them safe from potential impact. As dispensers, it’s our duty to protect children under the age of 18, with their naturally active lifestyles. Let’s face it, kids like to have fun. They run, they play, they throw things, and sometimes that fun gets out of hand. With impact-resistant eyewear, at least we’ve made it our responsibility to protect their eyes when things do become dangerous.

The same is true for adults who lead active lifestyles, participate in sports or whose jobs require them to have protective eyewear. The best and fastest way to determine who among your adult patients require protection is simply to ask them some basic questions. Using a lifestyle questionnaire when gathering information about your patients can help you both reach this goal faster. (See Questioning Patients About Impact Resistance,” p. 50).


HOW ARE THEY PRODUCED?
The two most common impact-resistant prescription lens materials found on the market today are Trivex and polycarbonate. Both have beneficial qualities to protect wearers. While the two materials possess similar attributes, they are produced in two completely different processing methods.

Even though polycarbonate has been around for decades, it gained prominence in the market during the 1980s because it was lighter in weight and allowed thinner lenses to be produced. It boasts impact resistance that is 10 times that of standard CR-39 materials. It is also 20% lighter and thinner than plastic.

Polycarbonate is created from a thermoplastic, and when it’s produced, it starts off in a pellet form that is injected into a lens mold. In these molds, the pellets are heated and compressed until they bond and melt, becoming one solid material. This injection-molded process is what makes the lens super soft yet still extremely durable upon impact. The process takes mere minutes, and once cooled, you are left with a finished lens blank.

Trivex, on the other hand, was developed in 2001 by PPG Industries. It too boasts incredible impact resistance similar to polycarbonate yet has one distinctive advantage when processed. Instead of beginning as a formed thermoplastic pellet, Trivex is a urethane-based monomer that is poured slowly into molds, which allows for sharper optics when compared to polycarbonate. The reasoning for this is due to what is known as chromatic dispersion within the lens. In simplest terms, the Trivex process is gentler on the lens produced, greatly reducing the stress and compression required to create the finished lens.


WHAT MAKES THEM IMPACT RESISTANT?
Compared to other materials such as glass, CR-39 and other plastics, polycarbonate and Trivex are made softer. When an object hits glass, or CR-39, there is a higher risk that the lens will shatter and harm the wearer. These materials are just more brittle when they experience an impact, which makes polycarbonate or Trivex the champions of choice for kids, sports and safety eyewear, and also for grooved and drill-mounted lenses that require impact resistance when they are being finished.

Keep in mind that another benefit of all impact-resistant lenses is that they feature inherent, built-in UV-400 protection. Some additional items to consider when dispensing impact-resistant polycarbonate and Trivex lenses are photochromic and polarized options for use outdoors.

Also, regardless of the lens material, reflections are always present with optical lenses, and a proper anti-reflective coating will always provide a greater benefit to achieving clearer optics.

On the horizon, keep an eye out for news about high-index lens materials and their development into impact-resistant properties. Collectively speaking, high-index lenses are made thinner, and once they are approved as impact resistant too, can be added to your lens availability lists.


Frank Gimbel, ABOC-AC, is an advanced certified optician and owner of Gimbel Eye Associates in Wayne, PA.

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