The first 50 years of the progressive lens could be appropriately described as an evolution. As in biological evolution, each generation built on the past while reaching forward to a new future. Many different lenses competed for the same small share of the market, and only a few would survive long enough to pass along their successful traits to the next generation of presbyopic lenses. The growth of the lens and its abilities was slow, but steady.
At first, manufacturers aimed to create a lens that could just deliver progression from distance to near. (Comfortable natural fields of view would be a project for later designs.) As this was accomplished, progressive lenses became a viable alternative to traditional multifocal lenses. Not by any stretch of the imagination were all progressives equal; but, they were reaching a point where several prominent designs were imitated, often to the detriment of progressive evolution on the whole.
Today, the progressive journey could better be described as a revolution. Now, the implementation of new designs is more accurately measured in months rather than years.
The industry has gone from developing basic progressive designs that merely work, to creating specialized progressive designs that work best for unique viewing situations and personalizing the ideal progressive design for each particular patient.
As eye-care professionals, we should set our practices for warp speed and prepare our patients for the ride of their lives. Truly, if they follow your lead, the prospects for clear, natural vision never seemed better.
Most practices choose a few primary progressive designs that serve as the base for their presbyopic prescribing needs, and each practice bases this decision on the ability of each lens to satisfy the needs of the greatest number of presbyopic patients.
Usually the benchmark of success is dictated by quick and trouble-free patient adaptation, as well as the infrequency of re-dos. If your patients are happy, youre happy. And, the front-running designs available today offer you and your patients a wide variety of lens materials and enhancements, such as photochromic and polarization options.
Make a Good Fit Designs change constantly, but the basics of good fitting remain the same. Ask any laboratory in the countryone of the biggest problems with a failed progressive lens, regardless of brand, usually results from improper measurements. This is one area where all manufacturers and labs agree, and so, virtually every progressive design utilizes the same simple fitting instructions.
Specialization
The first problem is getting the measurements, and the second problem is getting them with a high degree of accuracy. Progressive designs have consistently improved, but so too has the need for accurate measurement. Dont be lulled into thinking that the new design is more forgiving, or that it will offset any errors in measurement. The fact is that as the designs have become more intricate, the need for precision has increased.
To assure the greatest degree of ease and accuracy, take monocular measurements with a device such as a corneal reflex pupillometer. This instrument enables the dispenser to measure both the binocular and monocular pupillary distances at the same time. Attaining both measurements assures accuracyone can be used to verify the other. The monocular distances, when added together, must equal the binocular distance. If, for some reason, there is a discrepancy between the two readings, take new measurements.
A simple and accurate technique for obtaining fitting heights involves use of a demonstration lens or transparent tape, a felt-tipped marker and a penlight. If the frame does not have a demo lens, the transparent tape should be affixed in a vertical direction to the properly sized and fitted frame. Make sure that you are positioned on an equal level with and directly across from the patient. Direct the penlight from your left eye to the patients right eye and vice versa to create a reflex of light on the patients mid-pupil. Mark the point where the reflex shines through the tape. A measurement from the marked reflex dot to the lowest portion of the frame will give you the correct fitting height.
Lastly, verifying cutout is essential. In the past, this step was needed to ensure that the blank from which the job will be cut is large enough to assure accuracy. Today, with the popularity of smaller frames, cutout charts indicate whether there will be enough usable reading area left after edging. Verification at the fitting table will help prevent non adaptation-related delays and orders that cannot be processed. Using cutout charts with the patient when ordering lenses indicates the level of precision built into the lens and reassures the wearer about the lenses efficacy.
Remember the old saying about computer programming (because it certainly applies here, too): Good information in, good results out. Even the best lens designs can easily be compromised by inaccurate measurements.
The progressive lens market has entered decisively into the age of specialization because standard progressive designs fell short in a number of key areas.
Specialized progressive designs have now become mainstream, and such lenses are the closest we can currently get to the ultimate goal of mainstream individualized custom fits for all wearers.
In order to properly prescribe to meet patients needs, doctors need to keep at least one of these special categories for use as a companion to primary designs. Lets review some key areas of progressive specialization.
Short-corridor progressive lenses. In the area of newer, more stylish, narrow B-box frames, the standard fitting heights of 18mm to 21mm do not work. If fitted at recommended heights, then distance vision suffers, and if lowered to accommodate the frame, then near vision suffers.
Short corridor progressive lenses were needed in order to engineer smoother transitions from distance to near in a shorter fitting height. Some examples of short-corridor progressive lenses include:
Accolade Freedom (Essilor), which can be customized for fitting heights as low as 15mm through the patented Frame Optimization technology. The design of the lens is based on the patient prescription, the dimensions of the frame and the fitting measurements (A and B heights, pupillary distance and seg height). This results in faster patient adaptation; nine out of 10 patients adapt to their new lenses immediately.1
Sola Compact Ultra (Carl Zeiss Meditec), which can be used with fitting heights as low as 13mm, the lowest recommended minimum fitting height of any leading short-corridor progressive lens. Compact Ultra wearers will see more of a printed page clearly, without uncomfortable head movements.2
Definity Short (Essilor), which may be used with fitting heights as small as 15mm. This lens is available as a CR-39 lens, polycarbonate lens, high-index 1.60 lens or Thin&Lite 1.67 lens. Its features include polarization, smaller areas of distortion throughout the lens, reduced peripheral distortion and a wide intermediate zone.1
Varilux Ellipse (Essilor), which is a progressive lens specially designed for small frames with a fitting height as low as 14mm.1
Gradal Brevity (Carl Zeiss Meditec), which fits lenses with heights as small as 16mm. It offers thin, flat lenses with reduced distortion that are specifically designed for todays small frames.2
Hoyalux iD LifeStyle cd (Hoya), which features the companys freeform design technology. The vertical progressive components on the front surface of the Hoyalux iD LifeStyle cd are standardized to provide the shortest, most effective progression in the vertical direction. This results in reduced vertical eye movement and fast interaction between far and near vision. On the back surface of the lens, horizontal progressive components are customized to each prescription.3
Piccolo (Shamir), a precision-engineered, short corridor progressive lens that is made for frames with a fitting height of at least 16mm. This lens design allows for improved peripheral vision.4
Computer progressive lenses. The average American spends at least four hours each day in front of a computer. And when it comes to lenses, use of a computer screen turns normal progressive usage upside down.
Instead of using the lens for all distances, the priority is now shifted to intermediate and near vision. The computer progressive lens designs were needed to raise and widen these zones for increased comfort viewing at each.
Browser (Prio) lenses are primarily intended for computer use, but they work very well for any patient who requires clear intermediate and near vision, such as musicians, seamstresses or mechanics.5
Business (Zeiss) computer lenses were developed for typical workplace configurations and offer the patient comfortable vision through the entire near and intermediate range. When frequent head movements arent required, this lens makes everything from 14 inches to four feet away appear clear.2
InterView (Essilor) will take your computer-using patients away from standard reading spectacles, expanding their intermediate range of clear vision. A choice of two power levels allows you to more closely meet the needs of your presbyopic patients, according to their age and visual requirements.1
Office (Shamir) acts as more than a computer lens. It is an ideal occupational lens for anyone who needs edge-to-edge, visible distortion-free near and intermediate vision.4
Tact (Hoya) can be fit for near vision, with a generous intermediate zone for patients requiring vision for reading and close work. Or, the fit may be modified when the emphasis is on intermediate vision requirements, such as computer work.3
Wraparound progressive sun wear lenses. Like the short-corridor progressive lenses, wraparound sun lenses are another example of frame style dictating the need for a different lens design. Standard dresswear demands flatter lens profiles, while wraparound sunwear demands a steeper, 8-base profile.
To allow the wearer to enjoy similar viewing zones when transitioning between different styles of frames, the steeper sun lenses need to be aspherized to control surface geometry.
Attitude (Shamir) was developed for use with a wide variety of wraparound frames. It protects the eyes while effectively expanding vision zones and enhancing peripheral vision. Shamir Attitude is based on the companys Genesis PAL. The Attitude features a single base curve and is suitable for an extensive range of prescription strengths.4
AO bActive (Carl Zeiss Meditec) lenses are used in processing 8-base wraparound progressive lenses. This design enhances peripheral vision for wraparound lifestyle frames by incorporating a unique back-surface grinding technique that takes into account the wrap angle of the frame and the as worn position of the frame on the patients face.2
Wrap Solution (KBco) polarized lenses are a solution to the dilemma faced by laboratories and eye care professionals alike: how to provide clear optics for patients who want to wear prescription wraparound frames. This series of polarized lenses is specifically designed for oversized fashion and performance wraparound frame prescriptions.6
Image (Younger Optics) is a decentered design for use with steeply wrapped frames. This lens is designed with sunwear in mindwith an emphasis on maintaining clear, unobstructed distance vision.7
Individualization
Beyond designs intended for use in general applications and specialized designs that work well in more specific applications, the ultimate prize that eluded the industry until now was a design that could be individualized for each wearers unique needs. The main barrier to this final goal was not the ability to design, but rather, the inability to produce the design due to the limitations of standard processing equipment. Designers could always model very complex solutions to human visual problems, but those solutions tended to exceed the ability of the bitoric generator and rigid tooling used to process standard lenses. The industry was at a standstill until the recent introduction of new, more precise processing technology.
The digital, or freeform, process is the revolution that the industry needed. Though in its infancy, this new approach to lens surfacing will revolutionize lens processing. Freeform lenses can achieve a higher level of performance. The new technology makes it possible to actually produce working lenses, which, in the past, could only be imagined.
The future now seems limitless, and the revolution will continuebut for now, here are a few of the major advancements that freeform lenses can make possible.
Keep in mind that the lenses ability to achieve these benefits depends on the manufacturers design; lenses that use freeform processing are not equal and will not deliver benefits universally.
It is no longer necessary to start each job from a predetermined front-side mold. In practice, though, molding will continue to be used because it enables manufacturers production levels to remain high. The major step forward is that freeform technology can now produce those molds by directly surfacing them, eliminating the need for slumped molds, which could only reproduce simple designs that dont correct for higher-order aberrations (e.g., coma). By grinding a digitally direct mold, the scope of the ground surface is able to address a wider range of correction with greater accuracy and more consistent reproducibility.
Freeform technology also allows for coma control to be introduced into the surface of a lens. When coma is controlled, the wearers contrast sensitivity improves. Because contrast sensitivity is a critical part of human vision, this innovation paves the way to higher spectacle lens performance.
With freeform, the manufacturer can calculate and grind each surface directly, so that lenses are personalized to each wearers specific needs. Because we no longer have to begin with a cookie cutter selection from a limited number of blanks, each lens can be tailored to maximize the performance for each unique prescription.
New calculation engines evaluate (in both type and intensity) the aberrations that will result from combining a unique prescription with a particular lens design. After viewing the resulting trouble spots, the freeform process can correct for them and restore the lens to the original, intended parameters.
Also, progressive lenses have always struggled to limit unwanted cylinder. This unwanted cylinderusually on either side of the viewing corridorcauses a swimming effect.
Now, freeform technology can correct this problem by aligning the opposing axes so that they are equalized and vertical. This eliminates swim and creates the perception of wider useable intermediate and reading areas.
As manufacturers develop the freeform process, the resulting lenses will continue to deliver improved performance. This approach to lens production is in its infancy, but as the process evolves, expect to see a growing shift of wearers from traditional progressive designs to the more natural vision of lenses produced through the freeform process.
Looking at the world through freeform lenses can be as clear as watching your favorite team in high definition.
So, what is the role of the eye-care practitioner and optical dispensers in this revolution? You are the only one with the ability to recommend lenses to your patients. Unless you form the final bridge to your patients through a written prescription and sound professional recommendations, the revolution will lose forward momentum and patients will struggle with outdated technology. The lenses of the future are here now, so why not use them?
Mr. DiSanto is an independent industry trainer. A graduate of
1. Manufacturers Web site. Essilor
2. Manufacturers Web site. Carl Zeiss Meditec. Available at: www.vision.zeiss.com/us. (Accessed October 2008).
3. Manufacturers Web site. Hoya. Available at: http://65.161. 187.167/index.php?SID=4888218fdfe4f203444486&page_id=7875. (Accessed Octobet 2008).
4. Manufacturers Web site. Shamir. Available at: www. shamirlens.com/ecp/ecp.aspx. (Accessed October 2008).
5. Manufacturers Web site. Prio. Available at: www.prio.com/ products/lenses1.cfm. (Accessed October 2008).
6. Manufacturers Web site. KBco. Available at: www.kbco.net/WrapSolutions/. (Accessed October 2008).
7. Manufacturers Web site. Younger Optics. Available at: www.youngeroptics.com/. (Accessed October 2008).
