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The Keys to Fine Tuning Progressives

Introducing the Autograph III, A Results-Based Progressive

By Mark Mattison-Shupnick, ABOM

Release Date: February 15, 2014

Expiration Date: March 15, 2015

Learning Objectives:
Upon completion of this program, the participant should be able to:

  1. Understand the way that the prescription affects progressive lens design.
  2. Learn how new evaluation techniques and design tools can alter the resulting sizes and effectiveness of the functional areas of progressive lenses.
  3. Learn how new Autograph III provides new visual benefits for all the progressives' functional areas, for every customer, regardless of prescription.

Credit Statement:
This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO). Course STWJH511-2


img1You know what to expect when a new progressive lens is introduced; you request a pair for trial, there are a variety of claims by the manufacturer, you wear it either yourself or it's worn by someone you trust and you listen to the buzz amongst your peers. You order it and depending on your own or your customer's reactions, your purchases continue (or not). No wonder there's a healthy level of skepticism amongst ECPs during new product introductions.

Free-form lenses, however, hold a variety of keys that can make the trial and error of progressive lens adoption a thing of the past. After all, most already agree that patients, in general, prefer their new freeform lenses to previous lenses. What's left to fix? Actually, there's still a lot of work to do.

Some presbyopic customers see no real improvement with their new freeform lenses, others, especially hyperopes; still have more issues than myopes. Emmetropes or near emmetropes just don't like to have to wear their glasses at all. The root of one of these problems is that the prescription has, for the most part, defined the location and effective size of the functional viewing areas (distance, mid-range and near) as well as how well the lens periphery is managed.

In minus prescriptions, the world that the patient sees is minified so the lens acts more like a wide-angle lens. As the eyes move to the reading point (converge), minus distance powers create base in prism for the wearer. Because the image is displaced towards the apex of the prism, their eyes converge less than if they would have if the lens had been Plano.

Plus lenses are the opposite. First, plus lenses magnify so less of the real world fits into the window of the size of the lens. In the small viewing areas of some progressives, only a very small portion of the magnified image fits in the viewing zone. Then, when reading, the plus distance power creates base out prism as the eye converges. This results in a requirement for extra convergence i.e., more than the difference between a measured far and near PD. That means that for all your patients in all the varieties of prescriptions, the functional areas of clear vision are not the same. In fact, the same progressive brand, when used for a variety of your customers, with the full range of prescriptions, creates different visual experiences for each. That's one of the reasons for complaints from some, just acceptance and a wow experience from others. Prescriptions affect lens success for the people who wear them.

Introducing new Autograph III, prescription progressives created using a series of newly refined design tools that fixes the size and location of the functional area of clear vision in progressive lenses.

EYE-POINT TECHNOLOGY III

Shamir Optical's original design software called Eye-Point Technology created a lens surface considering base curve, the prescription, patient measurements and frame details producing wider corridors and less peripheral distortion/blur. In this 3rd generation of the program, Eye-Point Technology III uses improved new tools that allow the fine control of field height and width i.e., manage the change of power through the intermediate at an infinite number of points so that resulting object sizes, seen by the wearer, can be made the same regardless of prescription. This new software uses dual surface analysis of the prescription, frame dimensions, monocular PD and height, lens tilt, faceform and vertex to produce a lens to equalize real object size.

In this iterative analysis design system, the concave surface is adjusted to deliver a variety of predictable vision benefits. First, it assembles the entire prescription and Add. Then, it moderates the functional areas to equalize the size of the portion of the page seen clearly through the mid-range portion of the lens i.e., the size of the horizontal and vertical viewing zone created for a specific Rx in the frame chosen.

Let's use our piano keys image as a way to illustrate this. Through the same mid-range zone of standard progressives, made into a plus and minus prescription, piano keys appear to be different sizes as seen by the wearer. There is less usefulness in the plus prescription at mid-range. For example…

ShamirTechII

Another way to look at it is through the width of the intermediate zone. The result is half the availability of the number of keys, or less is clear.

MinusPlus

Eye-Point Technology III creates different lens designs for each patient for each Rx, for each eye. The size of the functional area is adjusted so there is the same number of keys made visible i.e., the plus prescription wearer is not disadvantaged because of magnification. It looks like this.

ShamirTechIII

Then, the software adjusts for binocular image size for the right and left eye prescriptions to agree as best as possible. This design technology adjusts the horizontal effects of the total lens along the eye path, from the fitting cross through the mid-range to the reading portion, for the lens and frame ordered.

NATURAL POSTURE FOR READING

These days we can usually tell when a progressive lens wearer is reading, they do the "chin up head tilt". That's because the corridor length and the rate of power change have been somewhat uniform, especially in fixed front design progressives. What happens to the reading zone's location in minus and plus prescriptions? Let's consider two effects. First the most important, the place where reading posture is most comfortable. Then what happens to reading position when affected by the power of the lenses as the eye travels down the eye path.

img2First, patients rotate their eyes down vertically to read in progressives due to the location of the near reading zone. There is a preferred position and that position is about 30 degrees downward. Here's what I mean. Sit up straight, hold a book in both hands, close your eyes and take a deep breadth. Then, let your breadth out. Your head will tip slightly forward, your eyes will rotate slightly down and your arms have found a comfortable position i.e., when the muscles are working equally so holding that position seems effortless. That's called "resting position". It's the best head/eye position for reading and book holding position for comfort. It turns out to be about a 30-degree visual angle, looking down. Therefore, with the tools available to selectively manage the power change positions of Autograph III of the corridor and near, the reading position is designed to end up at 30-degrees.

However, the lens prescription causes the image to also move vertically (prism effects) as the eye moves; the more powerful the prescription, the more the effect. Since lenses are prisms, the image moves towards the apex. In minus lenses the base down effect results in a reading image higher than if there were no power. In plus lenses, it's the opposite. The result is that the eye or posture has to change to read.

In Autograph III, the vertical position of the reading area is dynamically located taking minus and plus vertical power into consideration so that reading occurs at that 30 degree resting position. For minus lenses, image position is calculated to end up at 30- degrees. Intuitively, that would suggest that prism be added to move the reading down, plus lenses, up. However, that doesn't consider that it's the targeted reading resting position of 30-degrees. As a result, the digitally enhanced design moves minus positioning up, plus down so that the final reading, at resting position is attained.

NaturlaPosture

IntelliCorridor

Chart1Then if a 30-degree head position is fixed for reading, the corridor and the rate of power change must be managed. Because the power profile of the corridor can be managed somewhat independently, the power can be designed to produce the right power along the corridor for the way that a patient needs it. For example, reading text on a smartphone has the same or smaller font sizes of a newspaper and is held closer. Therefore, more reading power is needed sooner as the eye follows the corridor down the lens. IntelliCorridor dynamically controls the power of the corridor at hundreds of points, from fitting cross to reading point so the right power can be delivered.

In the power profile graph, standard progressives gain power slowly, and then faster through the mid-range portion achieving full add. IntelliCorridor manages the rate of change allowing a faster change of power initially so that tablets and smartphones are in easy focus, then slowing that rate of change to become full add.

Here's another way of looking at it. In the stepped illustration, compare the position of the piano keys, tablet and book positions. A standard progressive changes rapidly from computer range to the position for tablet/smartphone, then longer to reading. Autograph III provides more of each by better spacing the rate of change as said before, by controlling the vertical and horizontal power designs.

Great, almost done. The last part of lens design is frame considerations i.e., the way that a frame changes the way lenses sit in front of the eyes. You know those, they are lens tilt, both vertically (pantoscopic angle) and horizontally (faceform angle) and vertex. However, there are two vertex measures to take into consideration.

IntelliCorridor

As-Worn Quadro

Finalizing the overall lens powers using as-worn measurements for the frame chosen delivers the prescribed powers as the effective power, the way that the glasses ‘see'. Using the tilt and faceform angle as well as the distance the lens sits from the wearer's eyes (vertex) improves the prescription of the overall design, especially the periphery.

I often get the question in classes, "Are these measurements really needed? As soon as the patient leaves my office, they lean against their glasses, get sweaty and the glasses slide 2mm down the nose, or they decide to wear them in a place different than we agreed they would wear them…" it goes on and on. The answer is simple; yes it makes a difference.

Most lenses are ordered without as-worn measurements so lenses are fabricated using the ‘average' fitting values. So, while the redesign of the lens improves the periphery with the average values, any of the sliding, tilting, rotating, sitting on that happens to glasses makes it worse. To minimize any of the ways that fit changes the way that glasses ‘see', start with the most precise fitting measurements possible, simple. That also means that you take extra time to pre-adjust the frame before the measurements are taken.

Good optics in glasses also considers the vertex for which the patient was refracted, the distance that the refractor/phoropter lenses were from the eyes. Here's an example: a patient with an -8.00sph, +2.00 add Rx was examined at 14mm vertex but chooses a frame that places the lens at 10mm. If an -8 lens is moved 4mm closer its effective power becomes -8.25 ((D2/1000)*4). A small change for the distance power which may be acceptable but at near, the lens is too much minus so will seem like the Add is weak.

As-Worn Quadro adds a 4th dimension to the precision of Autograph III by requesting the refracted (phoropter or refractor) as well as the fitted vertex of the lenses. Refracted vertex is not a new item in optics, after all its used everyday by contact lens fitters to compensate for the ordered contact lens power. As worn measurements are the right way to make the best lenses, they remove more of the compromises made when creating a prescription lens and who better than professional opticians to become experts at as worn technologies. New tablet devices can make the measuring of position of wear easy. In fact, tablet based measuring devices add to the technological identity when taking these measurements and you know you're making a difference when the patient says, "no one has ever done this before".

Ordering Autograph III

To order lenses, start with the patient's prescription (from a trial frame with tilt at zero or from the refractor), vertex noted. List the frame data of A, B, ED and DBL (or tracer file). Then add monocular PD and height, face-form angle, pantoscopic tilt and fitted vertex.

Conclusion

New Autograph III tackles the individual visual issues of hyperopic and myopic presbyopes redesigning the size or the functional areas of the lens. For reading, it minimizes postural discomfort and head movements experienced with older fixed design progressives by using a unique power profile that can be more useful for tablet and smartphone use. When adding vertex (refracted and fitted) to the other measurements of tilt and faceform, it provides greater design definition to frame tilt variations in any chosen frame.

Autograph III provides the keys to fine tune the location and effective size of the functional viewing areas of progressives.