Progressive Design in the Digital Age
By Pete Hanlin, ABOM
Release Date: October 2010
Expiration Date: October 30, 2011
- Learn the importance of the progressive lens design as it is accomplished with the newest of lens fabrication techniques and technologies
- Understand the potential of the Digital Surfacing process to create individual and personalized designs
- Learn the various design format capabilities of DRx™ and DualOptix™.
Pete Hanlin, ABOM
This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO). Course STWJMI340-1
This course is supported by an educational grant from of America.
Is it the design of a building that makes it safe
and livable or is it the way it is constructed?
There was nothing wrong with the process
used to build the Tower of Pisa. However, the
design did not take into account the foundation necessary to keep the structure stable.
What’s the lesson? Even the best process cannot deliver performance in the absence of a
On the other hand, a good design can benefit
from new technologies. For example, in the
movie Avatar, part of the film’s magic was created by the extreme high definition provided
by audio/visual technology. However, those
same technological advances will not
“improve” the quality of a lesser-rated film.
The same holds true with progressive lenses. A
technologically advanced design will fail if not
fabricated correctly, and the most advanced
lens making processes will not improve a lesser
design. The optician must consider both the
importance of the design and the process used
to create the lens.
Starting with the design, there are several fundamentals a PAL must provide. The foundation
of a great PAL design is built on four things:
- Natural Reading Posture - the wearer must
be able to hold his head in a natural posture
while reading through the lens.
- Proper Near-Zone Placement - while reading, the near zone is properly located in front
of the eyes (and this position is different for
- Binocularity - the eyes work together to form
one image. This requires binocular peripheral
balance. When binocularity is challenged,
depth perception is lost.
- Sharp Central Focus- the central zones of the
lens must provide sharp vision. This is the
number one expectation of progressive lens
Natural Reading Posture
The “natural reading posture” of a person—
who does not wear correction—uses a downward gaze achieved almost solely through head
movement. The subject looks down at an
angle of about 40 degrees, and uses eye movement primarily for scanning the length of the document. Once the head makes its initial
movement, it rarely varies from that position
by more than 5-10 degrees.
Most progressives require the wearer to reduce
the amount of downward head gaze—relying
instead on eye movements. This creates an
unnatural posture in which the eyes are looking
downward 30 degrees or more. Additionally, the
head must be moved when moving from the top
to the bottom of a printed page. Although most
wearers will eventually “get used to” this position, it will never feel completely natural.
As a result, modern progressives are designed
with this in mind. They allow the wearer to move
the head downward by 35 degrees or more. The
result is to require less than 25 degrees of downward eye gaze for a more natural reading posture. Further, lenses that achieve 85 percent of
the add power in about 12mm or less allow wearers to see the top of a normal page. This means
that the wearer can read a page without exerting
any effort. This is what is meant by “natural reading posture.”
Proper Near-Zone Placement
Even the “widest” progressive designs have a
spherical reading zone that is much narrower
than a FT28 bifocal. To ensure the wearer
receives a suitable width of clear near vision,
the reading area must be centered in front of
the eye when the wearer is viewing at a near
distance. The primary factors used to determine the correct inset are:
- The focal length of the add (which determines the optimal reading distance and therefore the amount of convergence).
- The amount of prism generated by the distance Rx (since prism influences convergence
Most modern progressives accomplish this
by employing a variable inset. In Varilux progressives, for example, the designs feature an
inset that ranges from under 2mm per eye to
over 4mm. As a result, the near position varies
so only the distance PD has been specified
when ordering progressives.
For good binocularity to occur, the optics of
a PAL must be similar for both eyes in every
viewing position. When the eyes are presented
with disparate images, one eye is “suppressed.” The result is the loss of stereopsis, or
Even low levels of astigmatism will disrupt
vision if it is imbalanced. Premium lens
designs support binocular vision by providing
“balance.” This is important because when
both eyes turn right and left, they are looking
through opposite sides of the design. If the
optics of each lens is not similar, binocularity is
challenged. The visual system can handle
peripheral aberration as long as it is the binocularly “equivalent”. This allows the eyes to
work together to maintain stereopsis (depth
perception). This design feature is available in
a number of lenses.
The central zones of the lens must provide
sharp focus. While peripheral astigmatism is
given a lot of attention, there are also aberrations
in the central area of a progressive lens that affect
vision. Called higher order aberrations (the most
notable being coma), they decrease sharpness
(expressed as contrast sensitivity) although they
do not typically disturb acuity.
These aberrations are perhaps most noticeable
to emmetropic and near emmetropic presbyopes.
These patients sometimes refuse to wear progressives for distance vision because the higher order
aberrations reduce sharpness. These patients
often “see better” at distance without their eyewear due to the blurring effects.
Analyzing the wavefront, for varying pupil sizes
for viewing distance, bright to dim lighting, age
and the variety of prescriptions (ametropia) presented by the patients that enter your office, the
effect of changing pupil size can be included in
the calculations completed to design the new
Varilux Physio Enhanced lens.
Delivering the Design –
All of these foundational design aspects can be
delivered using any processing format including
traditional surfacing. However, there are three
primary limitations associated with traditional
surfacing. First, traditional surfacing is limited by
the use of physical tools, which limits the number
of surfaces that can be created by the designer.
Second, these tools also limit the accuracy of the
distance portion of the lens due to “rounding”.
And finally, traditional surfacing cannot place a
design on the rear surface of the lens, so only one
surface can be used for the design.
Digital surfacing does not have these limitations. With digital surfacing, labs can produce
unlimited shapes and exceptional accuracy on
one or two surfaces of the lens to achieve the
intended design. It’s still important to remember
that the foundation of a great PAL is found in the
design, not in the way the lens is processed.
There’s nothing “magical” about digital surfacing. It is just a different way to make a lens.
Unlike traditional lens surfacing, digital surfacing is not limited by physical tools. Traditional
surfacing uses physical molds and laps/tools. It is
impractical to create millions of different tools to
create different surfaces, so the lens designer is
usually limited to the number of bases and adds
(usually 144 molds) and a 1,000 or so laps
(sphere and cylinder power).
In digital surfacing, surface designs are stored
as computer files and can be modified as needed based on patient data when the actual lens is created. It’s relatively easy to store millions of design
files compared to physical tools. Then the computer translates the design exactly to either lens
surface and controls the lathe that creates that
design. Because of this innovation, lenses can be
created in infinite numbers of designs using a
digital surfacing process. As a result, the optician
can deliver to the patient a better solution for
their needs, based on any variety of factors. It
also means that specialized lenses can be created
for any of the many solutions a patient might
want in eyewear.
Don’t be fooled however by the claim that a
lens created specifically for an individual, at the
time of generating in the lab, is always better. The
freedom of digital surfacing is only meaningful if
you are using it to customize various qualities of
the final lens design being delivered, and that
takes technical ability to create customization.
For example, the ability to customize the progression length by 0.1mm increments is not helpful if the progression length is over 12mm.
Remember, just like the Avatar example,
advanced processing technology will not
“improve” the quality of a lesser design.
In traditional surfacing, the molded surface
of the lens ensures that design will be almost
perfectly accurate every time. However, the
physical tools used to create the Rx are inventoried in 0.1D increments, and the resulting
“rounding” will result in up to 0.06D deviations in distance power. Since digital surfacing
is accurate to within 0.01D, the control of
power is tighter. But even with the tightest
digital surfacing process, there is slightly
greater potential for design variation.
When the surfacing process is not tightly
controlled, the variations increase. This is
especially problematic for digital surfacing,
where even a slight lack of calibration between
the surfacing file and the surfacing equipment
can result in significant variation in the accuracy of the design.
A digitally surfaced PAL is only as good as
its combination of design and process. If the
process is bad, the design will not be accurate.
Digital software process control is a lab
requirement. It ensures that the surfacing
equipment is calibrated every day and the processes used to create the lenses are capable of
the highest levels of control and consistency.
Without this control, there are no guarantees
that you will receive the lens that design calculated because the process changed the final
result. Ensure that the lab used has invested
significantly in process control and lens design
verification after surfacing.
Traditionally surfaced PALs are
limited to one design (D), placed on
the lens’ front surface. Traditional
surfacing is not capable of producing
a progressive surface on the back of
the lens. This limits the designer in
the same way having only a single speaker limits how you can listen to music. With one
speaker, all you can do is adjust the volume.
A full back surface is also a “single
surface” format (called DRx in Varilux lenses). Using digital surfacing,
the designer combines the prescription (d) with the design (D)
to create a greater number of
resulting designs. This method is not limited
by an inventory of physical tools. So, the
designer can make changes to elements of
the design, even though there is still only
one speaker. In our music analogy, it would
be like adding an equalizer; now in addition
to playing the music, we can “tweak” the
sound by increasing the base, the treble, or
Having the ability to add
design on two surfaces
increases the flexibility of
design (D) and therefore the
number of solutions that are
possible for wearers. With
two surfaces (DualOptix), a designer can create an unlimited number of effects. Beyond just
“tweaking” the levels of sound, effects like “stereo” can be included to enhance the experience. What does that mean?
Specifically, the main benefit of allowing the
designer to use both surfaces is the ability to
simultaneously control focus and distortion.
In single surface PALs, the designer must
(and does) find a compromise between focus
control and the reduction of distortion.
When using a single surface progressive, the
more distortion is controlled the less focus
can be controlled (and vice versa). With two
surfaces, it is possible to control both focus
and distortion simultaneously.
In a traditional progressive (+2.50 add), the
front surface is used to create the add power.
Distortion is present because the front curvature
cannot be optimized for both the distance and
the near power. That is because changing power
by 2.5 diopters does not require a 2.5-diopter
change in base curve. Moving the add to the
back surface does not improve the situation
because the same base curve is definitely not
optimal for two powers 2.5 diopters apart. However, by disassociating the power change from
the curvature change, distortion can be reduced
below the levels found in single surface progressives. In addition, the use of asphericity cannot
“do away with the base curve effect.” Asphericity
can reduce marginal astigmatism and power
error; it cannot eliminate distortion.
In review, digital surfacing provides three
- It removes tooling limitations but any customization must be made meaningful.
- There is a potential for greater precision but
the process must be controlled.
- It allows the designer to use both sides of
the lens, which can allow simultaneous control
of focus and distortion
New Varilux Progressive
Lens Formats – Customization, Personalization and
Digital surfacing allows for three progressive
lens formats. Traditional progressives and full
back surface progressives use a single surface
to strike a balance between providing good
focus, reduction of distortion and increased
DualOptix creates a two design surface progressive. This allows a variety of customization, personalization and individualization
segmentation opportunities for ECP and
wearer. From the design point of view, it can
provide more precise control of both focus
and distortion. The results are clearer central
vision, exceptionally well-controlled peripheral vision and overall design, based on the preferences the patient chose to include.
Customization of design is achieved using the
DualOptix format because the effect of
changing pupil size, for a variety of real life conditions, can be compensated for along with the
If the patient’s lens positioning information (vertex, tilt and wrap angle) is added, a personalization of the lens’ central power and overall design
is created for the wearer.
If one then adds a patient’s biometric data, eye
rotation center distance and, reading behavioral
data, individualization of the design can be
Remember, the DualOptix format by itself does
not improve the design and digital surfacing is
just the tool to create that design. DualOptix is a
format to further improve a fully individualized
lens design for the patient. In fact, new digital
surfacing technique and design science capabilities can be used to add many features to a product portfolio. Table 1 lists the designing features
that deliver vision benefits for ECPs and their
|Design and RX on same
|Material and polarized lens availability
||Full back surface, DRx
||Varilx Comfort DRx
Varilux Physio DRx
|Adjust the reading area size to the
frame chosen and seg height measured
|Full back surface, DRx
|Adjusts the design for the range of
pupil sizes for age, lighting, distance
||Varilux Physio Enhanced (W.A.V. E. 2)
Varilux Comfort Enhanced (W.A.V.E)
||Design adjusted for all fitting
parameters; PD, Ht, vertex, tilt
and wrap angle
||Varilux Physio Enhanced Fit
|Personalization + Eye and
face anatomy, ergonomics
|Considers the ethnicity factors that
||Varilux Physio Enhanced Azio
Varilux Physio Enhanced India
||Design adjusted for fitting parameters
plus eye rotation distance and
||Varilux Physio Enhanced eyecode
Essilor eyecode Single Vision
|Design adjusted for fitting parameters,
ERC , behavioral data plus head or eye
||Varilux Ipseo IV eyecode
Design is everything. The degree to which
one improves the design can add to a
patient’s satisfaction. The final progressive
delivered to the patient, at this point of digital time, can be improved by adding a variety
of new science. Digital surfacing makes it
Recommend the best level of design with
customization, personalization or individualization that your patient can afford. They are
interested in it and will spend for it. Finally,
when they receive their glasses, they’ll thank
you for it and come back for more.