Article

WHAT’S THE BIG DEAL ABOUT DIGITAL SURFACING?

This Back to Basics article explains the concepts and processes behind these advanced lenses

BACK TO BASICS

WHAT’S THE BIG DEAL ABOUT DIGITAL SURFACING?

This Back to Basics article explains the concepts and processes behind these advanced lenses

BY JENEAN CARLTON, ABOC, NCLC

We live in an age where digital technology has affected almost every aspect of our lives. Digital technology has made a big impact on the optical industry as well, particularly when it comes to fabricating lenses. Digitally fabricated lenses are referred to by other terms including: direct surface, direct-to-polish, backside progressives, free-form, or Free Form lenses. All of these terms refer to lenses that are fabricated with digital surfacing technology.

Lens manufacturers and labs have been talking about the benefits of digital lens surfacing for years but industry novices and veterans alike often have a hard time understanding how digital surfacing differs from traditional lens surfacing. More importantly, they don’t recognize how digitally fabricated lenses benefit patients.

The fine-tuning step in the digital lens generation process
Photo courtsey of Satisloh

TRADITIONAL SURFACING

Prior to digital surfacing, lenses were fabricated with a multi-step, labor-intensive process that required much more time and multiple pieces of equipment. With traditional surfacing, all progressive semi-finished lenses had the corridor on the front surface of the lens. The distance prescription was ground into the back surface of the lenses. Before processing, lab employees determined the lens’ base curve based on the Rx power, then pulled the correct semi-finished blanks.

Then the real work began. Technicians prepared the lens power to be ground into the back surface of the lenses. Traditionally surfaced lenses were almost always ground on the back surface of the lenses. The front surfaces of the lenses were treated with a thermally cured scratch resistant hard coat and the corridor for progressive lenses was molded on the front surface. The lenses went through layout, marking, and blocking procedures and then were ready to be generated. Generators made use of a diamond-encrusted cutting wheel that removed the determined amount of lens material to provide the accurate power.

Lenses next needed to be fined and polished with identically shaped tool surface for each lens. These tools are called lap tools. The fining process smoothed out the rough surface created by the generator and the polishing process made the lenses smooth and transparent.

Finally, the lenses underwent the finishing process.

As you can see, the traditional method of surfacing lenses was very labor intensive and time consuming. The process to digitally fabricate lenses is a vast improvement over traditional methods.

Inside the cutting chamber
Photo courtesy of Coburn Technologies

HELLO, DIGITAL SURFACING

State-of-the-art equipment is used to process digitally surfaced lenses. This equipment consists of a diamond-point lathe cutter. Think of this as a sculpting tool, directed by a computer file, to sculpt the prescription into the back surface of a semi-finished lens blank. With free-form lenses the cutter can also sculpt the lens design as well.

Digital surfacing equipment employs a soft lap polishing tool to smooth out the lens surface. A laser is used to etch progressive markings onto the lenses if needed.

Many manufacturers offer digital surfacing equipment, including Schneider Optical Machines, Satisloh, Coburn Technologies, Augen Optics, DAC International, and more. Digital surfacing equipment is costly and is one of the reasons digital lenses come at a premium price. The second reason these lenses can be pricey involves the software and lens designs.

CREDIT THE DESIGN

Lens design and lens fabrication are separate entities altogether. Consider that a lens design is a pattern and with digitally surfaced lenses this pattern is stored as a ‘points file’. The points file tells the surfacing equipment exactly how to sculpt the power into the lens. If the lens design offers great vision and smooth transitions from the fitting cross all the way down to the near vision reference point, and also provides clear vision in the peripheral zones of the lenses, it is because of the lens design—not because the lens was fabricated with digital surfacing. Digital surfacing is a means of fabricating lenses, not designing lenses.

SOFTWARE-BASED

Most lens manufacturers offer lens design software by licensing it to laboratories. Lens designs are proprietary and made available to labs via manufacturer databases or by being directly loaded onto a laboratory’s computer.

The laboratory’s software creates a “points file” by calculating all of the measurements needed to fabricate the lenses. This data includes the patient’s prescription and computations for the lens design. The points file is received by the surfacing equipment and directs the lathe cutter to sculpt the prescription and the design into a semi-finished lens blank.

We all know that some lens designs perform better than others. Because of this, digital design software varies in price and can ultimately drive up the wholesale cost of finished PAL designs.

DESIGNS MAKES THE DIFFERENCE

Optical engineers create lens designs using software programs that utilize high-order mathematics to optimize each point on a lens. If a progressive lens design has an ultra-smooth transition from one zone to the next, it is due to the high skill level of its designers.

Conversely, a poorly executed design will not provide smooth transitions of power from the beginning of the corridor to the near vision zone, or it will exhibit distorted vision in the peripheral areas of the lenses.

PROGRESSIVE DESIGNS

Before digital surfacing became available, ceramic pucks were milled to create a progressive design. Glass molds were heated and slumped over the pucks until the softened glass reproduced the design. These glass molds were then used to create fixed, front-surface designed progressive lenses.

This meant that the quality of glass mold was directly related to the quality of the lens design. Digitally produced progressives skip the ceramic mold step by creating the glass molds directly with digital equipment.

What’s the benefit? Lens designs have a much higher degree of accuracy that results in a dependable design each and every time.

FREE-FORM

Free-form surfacing technology goes one step further by eliminating the need for glass molds all together, by cutting the progressive design and the prescription on the back surface of the lenses simultaneously.

With free-form lenses it’s best to include the patient’s Position-of-Wear (POW) measurements for every order so the lenses can be optimized for each patient. Power accuracy is within 1/100th (0.01) of a diopter, compared to 1/8th (0.12) of a diopter with traditional surfacing. Patients experience improved clarity as thousands of points across the lens surface are optimized for each prescription.

COMPENSATED RX’S

Digitally fabricated lenses that incorporate the patient’s POW measurements are fabricated with a compensated prescription. This is because in the as-worn position, the orientation of the lenses is different than the position of the lenses mounted in the phoropter during the exam.

A lens being cut in a digital generator
Photo courtesy of Schneider Optical Machines

Lenses in a phoropter are typically set at a 12mm vertex distance and the have no pantoscopic tilt. We must take into consideration the fitting of the finished eyewear for the patient to appreciate the same level of visual acuity as achieved during the exam.

Each Position-of-Wear measurement has the potential to change the effective power of the lens. This is particularly true when considering lenses of higher power and the peripheral areas of the lenses.

Compensated prescriptions have been calculated so that the patient will achieve the same visual acuity achieved during the exam through the optical center as well as peripheral areas of the lens.

SELECTING A PAL

There are basically three categories for digitally surfaced progressives: optimized, customized, and individualized. Some professionals refer to these lens choices as being good, better, and best PAL designs.

    OPTIMIZED PALs use proprietary software with computer numerical control (CNC). CNC means that the movements and functions of the digital surfacing equipment are controlled using a program that contains coded alphanumeric data.

    CUSTOMIZED PALs also use CNC technology but incorporate Position-of-Wear measurements, including monocular PDs, segments heights for each eye (often these measurements can differ from eye to eye), pantoscopic angle, wrap angle, and the vertex distance.

    The third and best option for digital progressives is INDIVIDUALIZED PAL. These lenses are perfectly tailored to each individual as long as the patient’s unique measurements are included with the order. If they are not included, the laboratory must use average measurements. Individualized PALs can incorporate biometric data. These factors include aberrometry, analyzed prescriptions, noting which eye is dominant, how the eyes naturally move, head posture, and eye center of rotation measurement.

Regardless of which PAL design is chosen, the best way to ensure patients experience superior vision with digitally surfaced lenses is to match the recommended base curve with the lens design. This way, off-axis aberrations are minimized, patients experience wider fields of vision with less “swim,” and are able to truly appreciate the difference in vision that digital lens fabrication has to offer.

BENEFITS

With state-of-the-art equipment, great lens designs, and by following the manufacturer’s guidelines for matching the appropriate base curve to the design, digital surfacing technology is able to deliver optical products with a level of customization and optical optimization that wasn’t possible in the past.

Digital technology allows both the front and back surfaces of the lenses to work in tandem to result in optically clear, distortion-free (or at least drastically reduced) lenses that are customized for wearers.

Digitally surfaced lenses are the future of the optical industry, and becoming more familiar with the technology benefits your patients as well as your business.

Digital Surfacing

The process of fabricating digitally surfaced lenses is complex. Advanced equipment, software, and design files are needed to accurately manufacture these lenses. Try to find all of the answers to each statement relating to digital surfacing.

ACROSS

2. Patients experience improved clarity as _____ of points across the lens surface are optimized for each prescription.

4. Lens designs are proprietary and made available to labs via manufacturer _____ or by being directly loaded onto a laboratory’s computer.

5. Free-form surfacing technology goes one step further by _____ the need for glass molds all together.

7. With traditional surfacing all progressive semi-finished lenses had the _____on the front surface of the lens.

8. Individualized PALs can incorporate _____ _____. (2 words)

12. Digital surfacing equipment employs a soft lap _____ tool to smooth out the lens surface.

15. There are basically three categories for digitally surfaced progressives: optimized, customized, and _____.

17. Before digital surfacing became available, _____ pucks were milled to create a progressive design.

18. The points file is received by the surfacing equipment and directs the ______ _______ to sculpt the prescription and the design into semi-finished lens blank. (2 words)

19. Digitally fabricated lenses are referred to by other terms including: direct surface, direct-to-polish, back-side progressives, free-form or _____ lenses

20. Generators made use of a _____ encrusted cutting wheel that removed the determined amount of lens material to provide the accurate power.

21. A laser is used to etch _____ _____ onto the lenses if needed. (2 words)

23. CNC means that the movements and functions of the digital surfacing equipment are controlled using a program that contains coded _____ data.

25. With free-form lenses it’s best to include _____ _____ _____ measurements for every order so the lenses can be optimized for each patient. (3 words)

26. Digital design _____ varies in price and can ultimately drive up the wholesale cost of finished PAL designs.

27. Digital surfacing equipment is costly and is one of the reasons digital lenses come at a _____ _____. (2 words)

28. Before processing, lab employees determined the lens’ base curve based on the Rx power, then pulled the correct _____-_____blanks.

DOWN

1. Regardless of which PAL design is chosen, the best way to ensure patients experience superior vision with digitally surfaced lenses is to match the recommended _____ _____ with the lens design. (2 words)

3. Prior to digital surfacing, lenses were fabricated with a multi-step, _____ _____ process that required much more time and multiple pieces of equipment. (2 words)

6. We live in an age where _____ _____ has affected almost every aspect of our lives. (2 words)

9. If a progressive lens design has an ultra-smooth transition from one zone to the next, it is due to the high _____ _____ of its designers. (2 words)

10. The front surfaces of the lenses were treated with a _____ _____ scratch resistant hard coat and the corridor for progressive lenses was molded on the front surface (2 words)

11. The _____ process smoothed out the rough surface created by the generator and the polishing process made the lenses smooth and transparent.

12. The laboratory’s software creates a _____ _____ by calculating all of the measurements needed to fabricate the lenses. (2 words)

13. Optical engineers create lens designs using software programs that utilize _____ _____ _____ to optimize each point on a lens. (3 words)

14. Digitally produced progressives skip the ceramic mold step by creating the _____ _____ directly with digital equipment. (2 words)

16. The process to digitally fabricate lenses is a vast improvement over _____ methods.

22. Think of this as a _____ tool, directed by a computer file, to sculpt the prescription into the back surface of a semi-finished lens blank.

24. Digital technology allows both the front and back _____ of the lenses to work in tandem to result in optically clear, distortion free (or at least drastically reduced) lenses that are customized for wearers.

For the solution, see Page 36