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The countless “buzz” words introduced by lens manufacturers to market the latest generation of ophthalmic lenses can be intentionally, and unnecessarily overwhelming. Let’s take a look at digital and free-form lenses in more detail and define some of the associated terminology, in addition to comparing a random selection of designs from a few of the many digital lens manufacturers. Finally, we’ll review how best to present this exciting new technology to patients.

DIGITAL VS. FREE-FORM

Contrary to popular belief, “digital” and “free-form” are not interchangeable terms. The main distinction is that a free-form lens is always digital, but a digital lens is not always free-form. Any lens produced using digital equipment can be referred to as digital.

What exactly is digital manufacturing and surfacing, and how does it differ from traditional? Traditionally, for progressive lenses, ceramic pucks were milled to create a progressive design as a convex surface. Then, glass molds were slumped over the pucks at high temperature until the soft glass reproduced the design as a concave surface. The glass molds were then used to manufacture fixed, front surface design, lens blanks.

In traditional surfacing, the most appropriate base curve for the prescription is selected from a limited number of options. A cup generator diamond, or diamond tip tool, cuts the toric back surface of the lens. Hard fixed power tools (laps) are then used to smooth and polish the required curves on the back surface of the lens. However, the tool selected is often a compromise due to the power steps of the tools and rounding errors, which can result in a degree of inaccuracy in the power of the finished product.

Digital mold manufacturing skips the ceramic mold step, creating the glass mold directly. By eliminating this step, accuracy in reproduction can be improved. It is important to point out that digital production cannot improve an old design; it simply improves the consistency of reproduction. The optimum digital designs incorporate free-form technology.

Digital lens manufacturing to its final prescription eliminates the mold making step, since it’s possible to cut the progressive design as well as the prescription at the same time, on the concave side of a single vision lens blank. Using free-form technology, a lab calculation engine can produce these lenses in an almost unlimited variety of designs and precision, depending on the wants of the patient and ECP.

Free-form technology is broken down to three elements: lens design, lab processing, and state of the art equipment. First, the patient’s prescription is optimized using proprietary software. Then, this mathematical data is transmitted to Computer Numeric Controlled (CNC) lathes as a point file, which then generates the surface curves using a polycrystalline diamond stylus driven by multi-axis technology, instead of the diamond-impregnated grinding wheel used in traditional surfacing. A single diamond tool then skims the lens surface to refine the surface to high precision. This surface is then buffed using a CNC polisher. During the free-form manufacturing process, both the prescription and lens design are created on the back surface of the lens blank with the utmost precision. Free-form technology can produce a lens much more precisely, to power increments of 1/100th (0.01) of a diopter, compared to 1/8th (0.12) of a diopter in traditional surfacing. Increased precision delivers an improved field of vision due to thousands of points across the lens surface being customized for the prescription; together with reduced lens aberrations, all contribute to providing unsurpassed clarity. However, process control is vital to the success of free-form surfacing. Even the slightest lack of calibration between the surfacing file and the surfacing equipment can result in significant inaccuracies of the design.

ASPHERIC AND ATORIC

A spherical lens employs a single base curve in all directions across each surface. If aspheric, the surface flattens (plus Rx), or steepens (minus Rx), from center to edge. However, this amount of asphericity is the same at all axes, hence the term rotational asphere. Asphericity is a way of enhancing the peripheral field of vision, especially in a high plus lens, and improves the lens cosmetics. However, this works best when the prescription involves a spherical correction only.

When astigmatic correction is needed, one surface of the lens is ground with two different curvatures at 90 degrees to each other; this is called a sphero-cylindrical, or toric lens. The same way aspheric is defined as non-spherical, atoric literally means non-toric. CNC generators enable atoric surfaces to be produced in digital lens designs by varying the asphericity in each of its two meridians. This optimizes the lens design for both the sphere and cylinder powers of the lens resulting in a flatter design (plus lenses) with improved visual performance in the lens periphery. Many digitally manufactured lenses incorporate atoric designs. This is a good complement to flat top bifocals, for example, when the prescription has cylinder greater than 1.00 diopter.

Digital and Free-form PALs
​ There are three main sub-categories of digital and free-form PALs: optimized, customized, and personalized, often referred to as good, better, and best.

(Good) Optimized PALs
An optimized digital lens employs proprietary software, combined with CNC lathes to customize thousands of points across the lens surface using default fitting data. Required fitting measurements: monocular PDs and segment heights.

(Better) Customized PALs
Incorporates all the benefits delivered by the optimized design, with additional enhancements using actual measured Position of Wear (POW) data. Required fitting measurements: monocular PDs, segment heights, lens tilt, wrap angle, and vertex fitting distance

(Best) Personalized PALs
A personalized, digital PAL incorporates all the above, but individualizes the lens using designs that are more task specific, and/or incorporates biometric data like aberrometry analyzed prescriptions, or values from proprietary fitting instrumentation such as Eye Center of Rotation distance, head or eye turning ratios, or the effects of the dominant eye.

POW MEASUREMENTS

POW measurements make a difference because each factor has a positional power effect. When the position, or orientation of the lenses in front of the eyes changes, the effective power changes from the patient’s perspective, more relevant in higher powers. While these values are small at the lens center, they can be significant in the periphery, even in low prescriptions. In order to compensate for these changes, POW measurements are used to calculate a “compensated Rx” which is then ground so that when the patient looks through the lens in the “as worn” position, the patient will be receiving the prescribed Rx centrally as well as peripherally.

Here are examples of digital, free-form lenses available from four manufacturers

ESSILOR

Essilor's line of digital progressives includes Varilux S 4D lenses, their uniquely personalized PAL. Varilux S Series lenses use patented Nanoptix Technology to change the fundamental structure of a PAL. Essilor reports that the lens surface is made up of thousands of optical elements which are re-engineered to allow light to pass through without the unwanted deviation typically attributed to an ophthalmic lens. In essence, each point in the lens has its own unique optical center.

Essilor also reports that more than 30,000 calculations were used to create Synchroneyes Technology, which helps the eyes work better together as a visual system by calculating both right and left lenses as a pair. Patented 4D Technology takes into account the leading dominant eye, how the eyes naturally move, and the patient’s natural head posture, all of which plays a role in improving visual response time. Essilor's Visioffice System is required to provide this data. The Varilux S Series also includes:

• Varilux S Fit lenses—Personalized using POW measurements; does not require the Visioffice System.

• Varilux S Design lenses—Optimized/customized PAL incorporating both Nanoptix and Synchroneyes Technology; does not require POW measurements.

Another design in Essilor's extensive PAL portfolio is Varilux Physio lenses. Varilux Physio and Varilux S Series lenses incorporate Essilor's W.A.V.E. Technology: Wavefront Advanced Vision Enhancement and W.A.V.E. Technology 2, respectively. These are intended to identify and reduce high order aberrations in the lens to provide clearer and sharper vision at any distance, greater color contrast, and wider fields of vision. W.A.V.E. Technology 2 provides improved performance in low light conditions. All Varilux, digitally surfaced lenses use a proprietary Digital Surface Process Control (DSPC), Essilor's patented digital surfacing process which ensures precision and accuracy. According to Essilor, it is not offered in any other manufacturer's digital surfacing processes.

Varilux Physio DRx lenses are an optimized back surface design in which the progressive design is precisely ground onto the back surface of a single-vision blank using proprietary software and CNC generators. Varilux Physio Enhanced lenses are customized and Varilux Physio Enhanced Fit lenses offer a personalized option. As with Varilux S Series lenses, both Varilux Physio Enhanced and Varilux Physio Enhanced Fit lenses feature dual surface, digital designs.

HOYA

Hoya’s portfolio includes a variety of free-form progressives that use Hoya Free-Form Design and Manufacturing Techniques. Their most personalized free-form lens is the Hoyalux iD MyStyle which is individualized using four elements: lifestyle, habitual (current) eyewear data, the prescription, and frame fitting details. This lens requires POW measurements from specialized instrumentation such as Optikam. An online questionnaire called iDentifier gathers data about the patient’s lifestyle and visual needs, summarized in a Personal Vision Profile. This allows for unique customization based on the patient’s visual requirements, previous lens experience and lifestyle needs.

Hoya’s proprietary Integrated Double Surface Design Technology uses image recalculation to optimize the design on both the front and back surfaces to effectively neutralize a significant amount of the marginal astigmatism in the periphery of the lens. Unlike other front surface, or back surface progressive lens designs, Hoya’s Integrated Double Surface lens designs place the vertical components of the prescription on the front surface of the lens and the horizontal components on the back surface; the result being two aspheric surfaces that combine to provide progressive optics.

The iD Lifestyle 2 designs, which include the Clarity for the emerging presbyope, and the Harmony for the seasoned PAL wearer, fall into the optimized category. Their atoric options are the Summit ECP IQ and Summit CD IQ.

SEIKO

Seiko Superior is an “ultra-personalized lens” that features three options for the basic design (Balanced, Near-priority and Farpriority), 11 options for the corridor length, 51 options for the near zone inset and 21 options for the frame pantoscopic tilt. It is available in a wide variety of materials and coatings with add powers from +0.50 to +4.00 (8 & 9mm corridors to +3.00). With the available ultra-short 8mm corridor (minimum fitting height 12mm) the lens can be neatly accommodated in even the shallowest frames, an achievement difficult to obtain with previous progressive lenses.

In the past it was not possible to fully compensate for differences in the position and height of the nose and ears, even with custom surfaced lenses. Seiko has solved this issue of “pantoscopic tilt” in our Superior lenses. The lenses are surfaced to the pantoscopic tilt of the patient’s frame in the as-worn position which makes it possible to perform optimal aspheric correction from 0 to 20 degrees in 1 degree increments.

The Superior design also processes complex convex curves onto the concave back surface of the lens, permitting the use of flatter base curves on plus power prescriptions. The result is lenses that are up to 25 percent flatter in profile, even when compared to our other internal free-form designs.

SHAMIR

Based on a new concept in lens design, Shamir Autograph III is a balanced progressive lens, holistically adapted to the patient’s prescription, ensuring a clear and comfortable visual experience for all wearers with the following features:

• As-Worn Quadro: Four times greater design stability to frame tilt variations, in any chosen frame.

• IntelliCorridor: Unique power profile for clearer vision in the transitional zone.

• Natural Posture: Ergonomic design for comfortable natural posture.

• EyePoint Technology III: Simulation of real world images for hyperopic and myopic presbyopes.

CARL ZEISS VISION

Zeiss has a variety of digital PALs, the Individual 2 being their latest personalized introduction. It not only factors in POW measurements, but also proprietary Center of Rotation Evaluation (CORE) technology to calculate the patient’s eye center of rotation measurement. According to their research, this provides superior off-axis vision and improved binocular alignment. Zeiss were pioneers in developing the back surface digital PAL using a single vision blank to grind the digital progressive design into the back surface using precision free-form processing. According to the late Darryl Meister, a Zeiss optics expert, “Placing the progressive optics on the back surface minimizes ‘image swim’ eliminating the contribution of unwanted magnification effects due to front surface ‘shape’.”

The Progressive Choice Plus is one of Zeiss’s customized digital options. Based on the GT2 design, it offers seg heights of 13, 15, 17, 19, and 21mm. Incorporates CORE technology, but no POW measurements.

In the optimized category, the Progressive Choice is offered in 13, 15, 17, and 19mm seg heights. Does not incorporate CORE technology; defaults at 13mm.

iScription designs require data collection using the iProfiler Plus which evaluates high order aberrations present in the eyes. According to Zeiss, this data is used to design a lens that compensates for such aberrations.

INFORM AND EDUCATE THE PATIENT

One of the optician’s roles is to inform and educate the patient as to the value of both their purchase, and the skilled services of an optician.

One suggested approach is to develop a portfolio of PAL designs from which to choose that fit a wide variety of lifestyles and visual demands. Also, obtain centration charts for each showing the location of the reference points to verify if the selected frame will work with the chosen lens. Laying the frame over the centration chart after appropriately marking up the demo lenses, will let you know if the lens will cut out correctly, avoiding inadequate near power due to “finishing” cutting off some, if not all of the near zone. Develop a script and practice with co-workers, family, and friends until it comes across as un-scripted. This is very important; most people can recognize a sales pitch.

Opticians are an integral part of the eye care professional team, not just sales people; present yourself and the product in such a manner. The patient needs to trust and have confidence in the optician, and this will only happen if the optician appears knowledgeable and confident in themselves. Ask lifestyle questions to determine a patient’s visual demands. From your portfolio of lenses, select the most appropriate and educate the patient as to its benefits.

We have both a duty and responsibility to always offer what is best for the patient. A patient doesn’t always need the newest lens on the market. If already a PAL wearer and their current style is working well, why fix what isn’t broken? However, if working with a complex Rx, or the patient is either having difficulty with their current lens style, or they are a new PAL wearer, possessing a detailed knowledge of the options available is invaluable.

When talking with the patient, try not to get too technical. Use layman’s terms, but also take the time to educate them. For example, having an aspheric and a non-aspheric lens in high plus powers made up in a frame, can show both the cosmetic and vision benefits of one design over another. A demonstration speaks a thousand words. Some details to share include how their lenses will be digitally designed using proprietary software, their prescription first being optimized for their chosen frame and the way it sits on their face. Discuss how this data is then transmitted to state of the art, computer controlled equipment to precisely engineer the lenses. When taking POW measurements, discuss them and how this supplemental data will improve the performance of their new lenses. This is also a great time to discuss how online shopping for eyewear does not permit such precision and personalization.

We live in a very informed society, and many patients like to know details. This “sharing” of information and additional steps taken to obtain the required data, all increase the patient’s perceived value of the product and our service.

Many analogies can be used when discussing the differences between traditional and digital lenses. Perhaps the most common, and most effective, is comparing the picture quality of regular versus HD televisions. Most patients today can relate to this.

It goes without saying that premium digital lenses should always be combined with premium anti-reflective (AR) treatments. Dispensing a digital lens without such is essentially doing the patient a disservice. If investing in a high quality pair of digital lenses, the patient is not getting the full benefit, if distracting light scatter and glare are reducing the patient’s acuity and defeating the purpose of the digital design.

These new innovations make it a very exciting period in our profession. Eye care professionals have an amazing array of products to offer patients, providing we know what is out there, and how to use it. This ultimately leads to a satisfied patient who will not only return, but share their experience with others.