Easy as 1, 2, 3
Technical advances make poly and Trivex easier to work with than ever
By Susan P. Tarrant

Poly and Trivex are solid options for everyday eyewear. Shown: Etro Vision style VEE 9802 by Viva International

Some old-school ECPs may be reluctant to stray from the tried-and-true CR 39 because it's what they know. They know it's a good lens material that offers optical clarity and a base material that is easy to work with.

They think that polycarbonate, for all its benefits of shatter-resistance, scratches easily. What's more, they think the lenses are prone to crazing during edging and that swarf presents a problem. And they don't even consider tinting. As far as Trivex goes, it is just too new, and its edging process is too unknown. They also think that equipment hasn't caught up to these new materials yet. They should think again.

Significant advances have been made in the production of these materials, and the processes we use to grind and edge them. So much so that working with these materials has become as easy as one, two, three.

1. MANUFACTURING STRIDES

Polycarbonate is an injection-molded lens, and in its earlier days the material was less than desirable. It provided safety benefits through its shatter resistance, but it had problems with material stability and optical quality, and it was prone to scratches. But that's been rectified.

Consistency. There is a lot-to-lot level of consistency now, thanks to recent manufacturing advances. Labs, and ultimately ECPs, know each lens is going to be as good as the one before it and after it.

Trivex lenses can stand up to abuse and still provide optical quality. Image courtesy of PPG

Injection molding. It's where it all starts for the poly lens. As the processes have improved, so have the resulting materials. The greater understanding of injection molding has gone hand-in-hand with understanding how to process the lenses produced in that manner more consistently and how to avoid problems such as levels of unwanted cylinder in the lens.

Hardcoating. Polycarbonate is the softest lens material. It's more flexible, more pliable, and more giving on impact. This provides safety benefits, but it also gives poly its reputation as a scratchable material.

The surface hardcoats for polycarbonate have been improved, so poly lenses have become more workable, as well as wearable.

Tintability. Because of the material's density, poly was previously untintable. But now, tintable coatings can be put on the backside of a polycarbonate lens.

The lens needs to be ordered with the tintable backside coating because it's less hard than usual. These tints represent a significant advance in poly technology.

2. EQUIPMENT ADVANCES

With a better manufactured lens came improved processing methods, including the edging process. Huge strides have been made in lab equipment, especially for retail labs where the need for simplicity and efficiency is paramount.

ECPs no longer have to worry that poly lenses necessitate special care and edging methods, as all-material edging equipment really lives up to its name.

Fining and polishing. The improved leap pads and equipment consumables have made fining and polishing stages of lens processing faster and more accurate.

	Tinting is now possible for poly. Image of Izod styles 733 and 735 courtesy of ClearVision Optical

Dry cutting...sort of. Unlike other lens materials, polycarbonate needs to be edged without water. So equipment was created that could edge with or without water.

However, edging polycarbonate creates debris called swarf that can be problematic and hard to remove from the lens. Today, some equipment introduces water late in the edging process to deal with swarf.

Variable speeds. Because of its softness, edging polycarbonate is akin to peeling the skin off an onion. It needs to be done dry, but it also needs to be edged at a slower speed than other material.

With the advent of variable speed settings came the ability to slow it down a bit for poly to avoid overheating and crazing.

Lens edge polish. On edging machines that offer lens edge polish, polycarbonate lenses will polish to a higher luster than CR 39 unless it is subsequently hand-polished.

While it's not an "improvement" per se, it does speak to another benefit of using poly.

Drilling. Polycarbonate (and Trivex, see sidebar) is a logical choice for rimless frame styles. But three-point mounts require drilling into the lens, a tricky process for poly.

Equipment vendors have risen to this challenge and introduced automated drilling capabilities for even the most difficult lenses.

Computerization. It's all about ease-of-use, especially if you're operating an independent in-office lab or a small-chain lab.

The computerization of edging functions for complete automation has reduced the need for skilled operators and increased the ease with which small labs can edge any lens material.

3. ECP AWARENESS

There is a third partner who has played a huge role in the advancement and acceptability of polycarbonate—the ECP.

Practitioners have become more open to learning about and trying all lens materials because of increased trust in technology and the desire to offer patients the best material for their needs.

Duty to warn. ECPs are responsible for informing young patients and their parents about impact-resistant lens materials like poly and Trivex.

By making polycarbonate so much easier to edge in-house, any ECP can feel more confident in recommending poly or Trivex for those situations that call for it, knowing they can continue patient service through lens finishing.

Educational partnership. Part vendor, part ECP, this approach has seen manufacturers setting up hot lines for poly processing questions, and has made ECPs more willing than ever to accept poly.

Better service. The desire to offer fast lens turnaround and quality assurance by edging in-house, merged with offering patients the best lens material, adds up to a better practice and better patient service.