Are you aware of the science behind AR coatings?
Even though anti-reflective (AR) lens treatments have existed for several decades, new strides in technology continue to improve their functionality. With so much evolution within this product category, there are a few things you may not know about contemporary AR treatments.
1. HOW AR IS APPLIED
The most common device for applying AR is a chamber with vacuum levels similar to those in outer space. A physical vapor deposition process is used, and the machinery is in HEPA-filtered clean rooms to remove even the tiniest of particles. Each layer is deposited by heating its respective compound until it atomizes. These particles randomly fall on the lens, which is spinning in the vacuum chamber to ensure an even coating.
This process is used for Essilor of America, Inc.’s Crizal Prevencia lenses, HOYA Vision Care, North America’s Super HiVision EX3 lenses and Shamir Insight, Inc.’s Glacier Plus UV AR coating.
Seiko Optical Products of America, Inc.’s Super Surpass ECP AR lenses are processed differently, using a rising vapor to coat the spinning lens. Lenses treated with Carl Zeiss Vision, Inc.’s DuraVision BlueProtect coating use ion bombardment to “pack” the coating more rigidly for improved durability.
2. THE MATERIALS USED
The outermost layer of the AR stack is often a hydrophobic gel or coating that resists water. These stacks contain many mineral base recipes created from chromium, hafnium, silicone dioxide and other minerals. Each manufacturer’s formula is different, which affects how the lens resists scratching, physically appears in color reflection and how easy it is to keep clean.
3. HOW AR WORKS
First-generation AR treatments had just a single layer, which only addressed a single wavelength of light in the color spectrum. The coating material was not the proper index, and the resulting coating on glass lenses was a deep purple. Modern AR lenses use multi-layered treatments to address a wide range of wavelengths in the visible spectrum. The stack layers are deposited microns thick and are measured in angstrom units. The thickness of AR treatments falls between the 0.2—0.3 micron range. The layers that address light reflectance are deposited in alternating high and low indexes. This index difference is what mitigates reflected light. To remain durable and flexible, the treatment is engineered with a balanced recipe that resists scratching, thermal expansion, torque and abrasion.
4. HOW AR STAYS CLEAN
The most common complaint about older AR lenses was that they didn’t stay clean due to dust, lint, smudges, oils and other debris collecting on them. To eliminate this issue, AR manufacturers use fluorocarbon chemistry to develop hydrophobic (water-resistant) and oleophobic (oil-resistant) top layers so grease, dust and water roll off the lens surfaces, which keeps them cleaner longer.
Premium AR treatments also have high water-contact angles, making them ideal to be worn in the rain, where droplets easily roll off the wearer’s lenses. Most premium AR treatments also contain anti-static properties to ward off dust and lint from the lens surfaces too.
5. HOW AR BATTLES HARMFUL LIGHT
Concerns over eye health also created a need to protect lens wearers from harmful UV and blue light radiation. UV light is present outside and may also be emitted by some sources indoors. Blue light is transmitted via LED devices, such as handheld electronics, TVs and computer screens, as well as high-efficiency light bulbs. To reduce both UV and blue light radiation, AR formulators have crafted recipes that remove them both. Some do it by adding a chemical into their lens materials, while others adjust the AR stack of an AR treatment. This altered stack provides both UV and blue light protection.
Knowing the technical side of AR treatments will help you better recommend them to your patients.
Frank Gimbel, ABOC-AC, is an advanced certified optician and owner of Gimbel Eye Associates in Wayne, PA.