Processing polycarbonate historically has been challenging. The trials involved in working with this material are compounded by the specific demands of athletic eyewear. It is important for the laboratory to take care that lenses cut for sports activities meet minimum specifications.

In addition, special attention is required to ensure that the proper measurements are taken and that the polycarbonate lenses are fit into the frames correctly. Particular equipment needs to be used in order to cut poly, and the machines must be treated appropriately. To ensure that lab techs have all the pertinent information about processing poly at their fingertips, we invited several experts to tackle the toughest questions about this rugged lens material.

PROBLEM: It's difficult to size polycarbonate lenses for sports eyewear

SOLUTION: There is a fine line between too small and too large when it comes to athletic frames. It takes a bit of experience to mount the lens to ensure snugness without placing stress on the lens, and sports goggles need a good fit. Don't rush the job­remember that people are wearing it for protection. To determine whether you've done the job properly, ask yourself, 'Would you let your mother or your child wear it?' If you would feel comfortable letting someone close to you wear the sports goggle, you've done a good job.

--Tracey Morrison, director of sales and marketing, Optical
Works Corp.

PROBLEM: Athletic goggles are ruined when they're heated in order to insert

SOLUTION: Some sports goggles, particularly those made of all-plastic materials, require that the lenses be cold-mounted. You need to make sure the lens size is accurate so that it's not too loose in the frame. You can do this by "eyeballing" the size, or by following a demo lens.

--Stuart Watson, director of training, National Optronics

PROBLEM: Polycarbonate lenses come out too large

SOLUTION: Lens materials all react differently to edger wheels. Polycarb- onate is usually over-sized because most edgers cut it dry, then finish the last half-revolution of the cycle wet to give it a veneer, or smooth finish. To eliminate this problem, make sure the edger is sized for each specific material, and have the wheels recalibrated on a regular basis.

--John Stellano, senior technical
engineer, WECO International

PROBLEM: Polycarbonate waste material scratches the lenses in the edger

SOLUTION: Use a water filtering system when cutting polycarbonate in order to prevent the "swarf" from being recirculated and scratching the lenses in the edger. If you use a direct water system, the poly waste can clog the pipes. A nylon bag that ties to the bottom of the drain will collect the waste, and you can empty it out when necessary. However, this problem is becoming a non-issue with the increased use of patternless edgers.

--Clark Smith, regional manager,
Santinelli International

PROBLEM: Polycarbonate lenses get scratched while they're being processed

SOLUTION: To prevent the softer polycarbonate material from scratching during processing, use slip-stop guards to protect the lenses. These clear round disks should be placed between the lens and the leap pad and on the backside of the lens where the chuck makes contact.

--Matt Vulich,
vice president, sales, A.I.T. Industries

PROBLEM: The optical centers of the lenses in sports eyewear come out in the wrong place

SOLUTION: To get the O.C.s in line with the pupils, measure the vertical heights just as you would with a progressive fitting cross. The best optics in the lens are in the center, and the farther from center the eyes go, the more chromatic aberration they're likely to encounter. Athletes should not experience any difficulties with the adjusted O.C. placement because they tend to move their heads, rather than just their eyes, in order to follow the ball.

--Greg Dean, technical training manager, Briot, a division of ABB Optical

PROBLEM: Some patients have difficulty seeing well through swimming goggles and diving masks that are custom-made with polycarbonate lenses

SOLUTION: There is less room for error with these types of specialty eyewear because they fit the face differently. Pay attention to the index of refraction and the vertex distance of the lenses. Swim goggles and scuba masks typically sit further away from the face than regular glasses, so you need to calculate the focal length. Be sure to decenter the lenses so that the major reference points (MRP) are where they're supposed to be. And take O.C. heights.

--Michael Urban, product manager, Gerber Coburn

PROBLEM: It is difficult to edge polycarbonate lenses for sport goggles that wrap around the face

SOLUTION: Many styles of athletic goggles have a severe wrap to them. When you're using a traditional pattern edger, you need to use lenses that are ground on an 8 base curve or higher, and you most likely still will need to place the bevel on the lens by hand. The curve of the eyewire also will have to be modified to accommodate the lenses. However, sport goggles can be processed more easily on a 3-D patternless edger because these machines can curve the bevel so that it's a perfect fit without straightening the goggle. With a good 3-D system, you don't have to special-order lenses with a higher base curve.

--Bill Galindo, president, ODI/Topcon

PROBLEM: Polycarbonate jobs gunk up the edger

SOLUTION: Poly is edged dry, but water is usually used at the end of the cycle. When the lens material becomes wet, the water tends to make it remelt and stick to the lens, rather than flushing it away. The poly material gets glazed over on the bond that holds the diamonds on the diamond wheel, lens sizing becomes erratic, and edge quality is diminished. So it's important to keep the wheels clean and to keep the build-up in the edger from recontaminating the lenses. The wheels are best kept clean by using a truing stick. However, it must be used delicately because overuse also will diminish bevel quality.

--Joe Meaney, technical manager,
LOH Optical Machinery
 EB

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