Lenses like HOYA’s InStyle claim increased contrast, clarity, and edge-to-edge performance.
Free-form technology can be a pretty confusing category, starting with the fact that there are a few terms to describe the same lens category: digitally surfaced, direct-to-surface, cut-to-polish, and free-form. Here are some frequently asked questions about free-form technology that may help clarify the situation.
What is free-form technology?
In the ophthalmic lens business, free-form technology is a process that includes three elements: design, equipment, and processing. In other words, free-form technology begins with a design concept.
While free-form technology provides great design freedom for designers, it’s no guarantee the lens will provide good vision. That’s why a good design is essential. You also need highly capable free-form equipment. Inferior and inaccurate equipment, or good equipment that is not properly used will yield poor results. Even with a good design and good equipment, if you don’t process free-form lenses properly, you’re not going to get a good outcome. All three elements of free-form technology must be properly executed to obtain a top quality free-form lens.
How does a free-form generator differ from a traditional one?
A traditional generator uses a diamond-impregnated wheel that grinds away lens blank material as it shapes a lens surface. Since it rough cuts the lens as it grinds, it leaves the lens fairly hazy. A free-form generator uses industrial diamond cutters to rough cut the lens and a single diamond point to complete the generating process. The lens is not ground in a free-form generator, it is milled, similar to the way a lathe would be used on wood so the machine essentially peels away the lens material.
The free-form generator and its cutting tip are controlled by machine language known as CNC (computer numeric control). Labs like Expert Optics Inc., Luzerne Optical Laboratories, Ltd., Rite-Style Optical Co., and US Optical have free-form generators that use CNC technology.
Rite-Style has free-form generators that use computer numeric control technology.
How does a free-form generator know what progressive addition lens (PAL) design to produce?
Traditional PALs had their designs molded on the front side of the lens so all a generator had to do was cut the patient’s Rx into the backside of the lens. Most free-form lenses have their designs on the back of the lens, which means the free-form generator will create the progressive surface during processing.
Every lens manufacturer develops computer software called “point files” for their designs. These files guide the free-form generator so they know where and how much to exactly remove the lens material in order to create the desired surface. This combination of software control and pin-point computer-controlled surfacing accuracy means the free-form generator can cut away material precisely producing virtually any complex multi-curve surface. Coburn Technologies’ DTL Generator Series is a good example of a generator that does this.
What advantage does free-form surfacing have for labs?
One advantage is the reduction of lens blanks a lab needs to stock. For traditionally surfaced PALs, a large inventory of base curves and add powers have to be carried in stock for each design, material, and treatment a lens uses. This could equal a minimum of 50 blanks or more to cover all base curves and add power combinations within a single clear material like polycarbonate. If you want a lens polarized in polycarbonate, you’ll need another 50 blanks and if you want it with Transitions® treatment in polycarbonate, you’ll need another 50.
Another advantage is the elimination of hard laps and the fining steps. Free-form lenses come out of the generator ready to head directly to the polisher. The fining steps are eliminated because the generated lens surface has only about one micron deviation in the peaks and valleys on the new lens surface. A soft lap is used for polishing along with a soft pad system to preserve the newly generated curves. A conventional hard lap with grinding grit would remove the complex optics the free-form generator incorporated into these lenses.
Why do I need to take all these additional fitting measurements?
Premium free-form progressive lenses are designed to optimize the vision a wearer receives with them. One way of doing that is to provide lenses to 0.01D accuracy instead of the traditional 0.25D accuracy. Another way is to compensate for all controllable fitting parameters that can affect the lens power a wearer receives in the “as worn” position they’ll have with these lenses in the frame they’ll wear.
Lens manufacturers like Shamir are asking for additional measurements like pantoscopic tilt, face-form tilt, and vertex distance.
Traditionally, opticians provided monocular PDs and fitting height measurements. Aspects of frame fitting that affect lens power include pantoscopic tilt, face-form tilt (wrap), and vertex distance (known as “position-of-wear” measurements). Any difference among any of these from their configuration during the refraction to the finished eyewear will affect the final power of the lenses. That’s why manufacturers are asking for these additional measurements. Lenses like Shamir Insight, Inc.’s Autograph II, HOYA VISION CARE, North America’s HOYAlux iD MyStyle, and Seiko Optical Products of America, Inc.’s Supercede lenses use these measurements.
Are single vision free-form lenses worth dispensing?
Just as with progressive free-form lenses, single vision free-form lenses are designed to reduce aberrations and distortion in a lens. These lenses are optimized just like their progressive lens counterparts, but only for distance viewing since that is the sole power on the lens. This can significantly improve the lens’ effective viewing area. The demographic group of those aged 40 and under embraces new technology and is very comfortable paying for it, especially when it is explained that these lenses will provide them with enhanced performance.
Why do free-form lenses cost so much?
As with any new technology, there are costs involved with the development of the equipment and its related software. As far as free-form equipment is concerned, costs can range from a couple of hundred thousand dollars to well over a million. It all depends on how deeply you wish to get into the production of free-form lenses. Software development for free-form lenses is an ongoing venture that must be factored into the cost to eyecare professionals (ECPs) for these products. Also, manufacturers get a “click” fee every time a lab runs one of their design programs. That cost is included in the price the ECP pays for the lens.
Coburn’s DTL Generator Series is a good example of a free-form generator that can cut away material precisely producing virtually any complex multi-curve surface.
Which free-form lens is the best?
You first need to decide which features are the most important to you. Here are a few to consider: a wide and clear distance zone, a roomy corridor, a wide reading zone, no distortion, no swim, variable inset, and vertical placement of the near zone (adjusted for the Rx and add power), multiple fitting heights (instead of just one), having the Rx compensated for position-of-wear measurements, available in selected lens materials (like CR-39®, Trivex®, polycarbonate, 1.60, and 1.67), photochromic, and polarized forms, etc.
Once you have the list, consider putting the features in priority order so that the absolutely “must- have” features are at the top of the list. Check out the Free-Form Progressive Lens Availability Chart developed by First Vision Media Group, Inc. (available online at TotallyOptical.com). This document lists all the free-form progressive lenses on the market and includes their availability information.
Once you’ve chosen one or more designs, it’s time to do a wearer trial. Do a trial with about 10 wearers for each design you favor and let your patient’s experiences indicate which one to use.
How do I explain the difference between free-form and traditional lenses?
Many ECPs explain the analogy of the performance differences between a regular and high-definition television. You can also give some examples of the features the lenses deliver. For example, some lenses like Augen Optics’ High Definition Lens, HOYA’s InStyle, Seiko’s Surmount, and Shamir’s Spectrum claim increased contrast, clarity, and edge-to-edge performance.Be sure you’re wearing a pair of free-form lenses too so you can share your experience with patients. Sharing your experiences with wearers tells them that you have confidence in the product you’re recommending.
Free-form technology is here to stay and will continue to grow. Your patients are researching these lenses online so you need to be ready to answer their questions.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI. Ed De Gennaro is Director, Professional Content of First Vision Media Group.