Progressive Design in the Digital Age
-Pete Hanlin, ABOM
This presentation has been submitted to the American Board of Opticianry for one hour of continuing education credit. These notes and slides are being provided to educators and speakers for use in Essilor sponsored presentations. Use of these descriptions, images, and slides in other presentations is permitted (and encouraged), but any alterations to the content of this presentation should be approved by Essilor of America. Please contact Pete Hanlin at
[email protected] if there are any questions regarding the information or use of this presentation.
Overview Importance of the Design Potential of the DS Process Design Formats & Capabilities Introducing Introducing
Importance of the Design Design is everything! ...poor design leads to poor performance... (Somehow, designer forgot to leave his name on the base...)
Importance of the Design New processing technologies do enhance great designs...
...but they cannot make an average design exceptional!
Importance of the Design There are several fundamentals a PAL design must provide- to name a few: –Natural Reading Posture (rate of progression) –Properly Placed Near Zone (correct inset) –Binocularity (balanced peripheral vision) –Central Focus (sharp vision in all zones)
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. The lesson being even the best processes do not deliver performance in the absence of a good design!
That said, a good design (content) CAN benefit from new technologies. Avatar is the most profitable film of all time, and part of its magic is created by the extremely high definition provided by modern advances in audio/visual technology. However, those same advances will not "improve" the quality of a mediocre film (such as Waterworld). Other than improving the sharpness of Kevin Costner's gills, viewing Waterworld is still going to be a 3 hour beating! The foundation of a great PAL design is built of the following blocks: 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- when the wearer is reading, the near zone must be properly placed in front of the eyes (and this position is different for each wearer) Binocularity- the eyes must be able to work together, which requires binocular balance in the periphery- when binocularity is challenged, depth perception is lost Sharp Central Focus- the central zones of the lens must provide sharp vision- this is the #1 expectation of progressive wearers.
Natural Reading Posture Natural reading posture characteristics: Head tilts down 40° Eyes vertically scan 15°
PALs should require at most 25°downward gaze Non-Optimal PAL
No Eyewear
Optimal PAL
Natural Reading Posture The ideal progression length is around 12mm to 85% of the ADD power >12mm requires eye to look downward >25° <12mm increases peripheral astigmatism
Patent FR 2 699 294 "...a very low sphere gradient for a so short power progression and a maximum gradient value located in the intermediate vision zone"
Properly Placed Near Zone The near zone must be optimally placed Convergence inset is determined by: Prismatic effects of the Rx Convergence required at focal length of ADD Patent FR 2 683 643 "...a near zone which gets higher and more nasally decentered with the increase of the addition"
BASE ONE BASE TWO BASE THREE BASE FOUR BASE FIVE
0.75 1.81 1.94 2.09 2.69 2.92
1.00 1.92 2.03 2.09 2.71 2.94
1.25 1.98 2.09 2.09 2.72 2.97
1.50 2.09 2.09 2.09 2.74 2.99
1.75 2.29 2.29 2.29 2.80 3.00
2.00 2.29 2.29 2.29 2.95 3.04
2.25 2.29 2.29 2.29 3.11 3.29
2.50 2.29 2.29 2.29 3.21 3.39
2.75 3.05 3.05 3.05 3.51 3.70
3.00 3.05 3.05 3.05 3.72 3.90
3.25 3.05 3.05 3.05 3.90 4.17
3.50 3.05 3.05 3.05 4.10 4.30
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 45 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. All Varilux progressives allow the wearer to move the head downward by 35 degrees or more. The result is less than 25 degrees of downward eye gaze. This is important for reasons described in the next slide. The graph on the left shows the amount of effort which must be exerted to hold the eye in position. As you can see, when the eye is in a position within a range from straight ahead to a downward gaze of just under 30 degrees, there is no effort required. Since 2 degrees of eye movement causes the visual axis to travel approximately 1mm across the lens, this means the eye can look about 14mm down the lens without effort. This is important, because it is unnatural to hold the eyes in any position requiring effort (try looking down at the floor without moving your head- if you keep looking down you will feel your head being "pulled" to the floor). All Varilux lenses provide 85% of the ADD power in about 12mm or less. In most reading positions, 85% of the ADD power is required to see the top of a normal page. This means the Varilux wearer can read a page without exerting any effort. This is what is meant by "natural reading posture." During the development of Varilux Comfort, Essilor R&D discovered an algorithm which provided the lowest level of peripheral astigmatism for any given progression length. This algorithm was patented and has been used in all subsequent Varilux designs. 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 near. Essilor progressives accomplish this by employing a variable inset. 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 and ADD power is also taken into account (since prism influences convergence as well). Subsequently, all Varilux designs feature an inset that ranges from under 2mm per eye to over 4mm. The concept of a varied inset was patented during the development of Varilux Panamic.
Binocularity The optics of a PAL must be similar in every viewing position The eyes must work together to maintain stereopsis (depth perception)
Binocularity Even low levels of astigmatism will disrupt vision if it is imbalanced The visual system can handle peripheral aberration- as long as it binocularly equivalent
Dissimilar
Similar
Patent EP 0 994 375 "...a very low difference in sphere for two corresponding points of the right and left lenses, and this for all points of the space"
Central Focus The central zones of the lens must provide sharp focus Astigmatism is usually located in the periphery Higher order aberrations (HOAs) reduce sharpness in the central zones of a PAL
Central Focus Control of the wavefront results in the sharpest possible central vision W.A.V.E. Technology™ provides clinically proven improvements in vision Varilux Physio
Comp A
Comp B
Patent FR 05 07378 "In a wide angular zone (150 to 160) with a vertex 4 below the fitting cross, the high order aberrations, including coma, are reduced, allowing a clear far vision zone. At the same time, the near vision zone is easily accessible at 25 of gaze excentricity downward"
Importance of the Design ALL of the fundamentals of design can be delivered by ANY processing format: Traditional Surfacing Digital Surfacing
A progressive must also not interfere with binocular vision. When the eyes are presented with disparate images, one eye is "suppressed." The result is the loss of stereopsis, or depth perception.
Varilux designs support binocular vision by providing "balance." This is important because when the eyes view through the peripheries of the lenses they are looking through opposite sides of the design. If the optics of each lens are not similar, binocularity is challenged. The images show the level of difference between each point in the lens. Each image represents the level of similarity throughout the lens. A pair of plano SV lenses would be primarily white across the entire graph. The lenses on the left represent an unbalanced design, the lenses on the right represent Varilux Panamic (this design concept was patented during development of Varilux Panamic). A lot of attention is given to the control of peripheral astigmatism, but there are also aberrations in the central area of a progressive lens which must be controlled. These are higher order aberrations (the most notable being coma), and although they do not disturb acuity, they do decrease sharpness (expressed as contrast sensitivity). These aberrations are perhaps most noticeable to emmetropic presbyopes and low ametropes. These patients sometimes refuse to wear progressives during distance vision- because the higher order aberrations reduce sharpness. They literally "see better" at distance without their eyewear! Varilux Physio and Varilux Physio Enhanced control higher order aberrations in the central zone of the lens. The images depict the wavefront produced over a 6mm area (the center dot is at the FRP and the other dots are 2mm in each direction). This technology is called W.A.V.E. Technology (the customized form being called W.A.V.E. Technology 2), and has been clinically proven to provide measurably sharper vision compared to nonwavefront controlled PAL designs. The results of these clinicals have been reviewed and approved for presentation by several professional associations including the AAO. The application of wavefront correction to progressive design was patented during development of Varilux Physio. All of these foundational design aspects can be delivered using any processing format- including traditional surfacing. In a age when digital surfacing is being promoted, it is important to remember that the foundations of a great PAL are found in these design concepts- not in the way the lens is processed.
Potential of Digital Surfacing Solutions of Digital Surfacing
Limitations of Traditional Surfacing •Tooling required for each shape (designer is limited by # of tools)
•Tool can create unlimited shapes (designer is not limited by tools)
•Tooling limits accuracy of lens
•Tool is exceptionally accurate*
•Only one surface can be used for the progressive design
•Both surfaces can be used for the progressive design
How Digital Surfacing Works A DS generator is similar to a lathe
Lens starts as a block of material...
...a single point cutter removes material from the spinning blank to create a 3D surface...
...finished surface can be virtually any shapewith the potential for great precision.
So if the foundation of a PAL's performance is the design, what does DS contribute to performance? There are three primary limitations associated with traditional surfacing which will be detailed in the following slides. First, traditional surfacing is limited by the use of physical tools- which limit the number of surfaces which can be created by the designer. These tools also limit the accuracy of the distance portion of the lens due to "rounding." Finally, traditional surfacing cannot place a design on the rear surface of the lens, so only one surface can be used for design. NOTE: Remember to go in a "Z" pattern on this slide- cover the limitation and then the solution, then the limitation followed by a solution. The asterisks beside "accurate" on the digital side is just to get them thinking (we'll be talking about the necessity for process control later). There’s nothing "magical" about digital surfacing. It is just a way to make a product, just like a woodworker uses a lathe to shape a bowl from a piece of wood. The control in the case of the lathe is limited by the woodworkers skill. In digital surfacing, the lathe is controlled by equipment which relies on a computerized path. The important point being the digital surfacing process does notin and of itself- add anything to the design of the lens.
In digital surfacing, the cutter is precisely controlled by motors which follow a path contained in the form of a computerized (digital) file.
Increased Tool Capability Traditional Surfacing is limited by physical tools Molds for complex front surfaces Laps/Tools for simple back surfaces
Digital Surfacing uses "digitized" tools (digital files) A virtually unlimited number of shapes can be produced Designer is free to create an ∞ number of surfaces
Distance Power and/or Progressive Design Progressive Design
Distance Power
Increased Tool Capability The impact of DS capability is limited by: the quality of the initial design the ability to create meaningful customization
Otherwise, digital surfacing is just another way to make a lens
=
Increased Precision The DS process is capable of greater precision than traditional surfacing
+/-0.06D
- DESIGN +
Traditional tooling creates "rounding errors" which cause up to 0.06D of distance power error
+ DISTANCE POWER -
TRADITIONAL SURFACING +/-0.12D
Digital Surfacing
- DESIGN +
Digital tooling can be accurate to within 0.01D of target powers
Traditional surfacing uses physical tools (molds and laps/tools). Therefore, the number of designs is physically limited (it is impractical to create millions of different tools to create different surfaces, so the designer is limited to 144 molds and a 1,000 or so laps). In DS, there is only one physical tool- surface designs are stored in computer files (and its relatively easy to store millions of design files). So, the designer is free to create more designs in a DS format. There is a perception in the market that a lens that is created specifically for an individual is always better. But the freedom that comes with digital surfacing, is not, by itself, a good thing. That freedom is only meaningful if you are using it to customize a quality lens design in the first place, and whether you have the technical ability to create customization that is meaningful – not just customization for its own sake. For example, the ability to customize the progression length by 0.1mm increments is not helpful if the progression length is over 12mm! In traditional surfacing, the molded nature of the lens ensures that design will be almost perfectly accurate every time. However, since traditional surfacing uses physical tools that are inventoried in 0.10 increments, "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.
Increased Precision DS processes must be tightly controlled UNCONTROLLED DIGITAL SURFACING
+ DISTANCE POWER -
UNCONTROLLED TRADITIONAL SURFACING
- DESIGN +
Process variations usually affect only the distance power of traditionally surfaced lenses.
- DESIGN +
When DS is used to create a PAL design, process variations will affect the design
Increased Precision Essilor has > 20 years invested in DS R&D Essilor Digital Surfacing Process Control (DSPC) is a complete quality assurance system every laboratory required to test/calibrate processes daily
A "DS PAL" = design + process If the process is bad, the design will not be accurate All major manufacturers have a defined process
No other manufacturer has invested more in R&D of digital surfacing processes. DSPC ensures that the surfacing equipment at every DS lab producing Varilux lenses is calibrated every day and the processes used to create the lens are capable of the highest levels of control and consistency.
DSPC
Digital Surfacing Process Control DEPARTMENT DEPARTMENT MANAGER M ANAGER E. COMTE COMTE Ass istant M.HA GER
CA LCULAT ION T. BAUDART
SURFACING MANAGER
INDUSTRIALIZ ATIO N W ORKSHO P L.GRELICHE
TECHNO INDUSTR IALIZATION G.MART IN
PRODUC TS INDUSTRIALIZ ATIO N B.GODEAU
TECH NIC AL LE ADER BLOC KING M.LE GALL
B . ROMA IN
D.B OULET
TEC HN IC AL LEAD ER MAC HINI NG/POLISHI NG X. BULTEZ
P.WA SANCHAI (T A)
B.BEE SON
C.PETCHARAT (P oy)
M.MODH D. DRUGEON
K.SANRAYU (JO Y)
J.SHERIDAN J. CO NCIALDI
PH.CORNE
SURF ACING MA NA GER W .MAYUREE (T OY)
B.TAY LOR J-L. ARBESS IER
Y.FELTEN
M. ME TTEL
SURFACING MANAGER B.GELB
C.ING ON (ING)
M.KALUZA
JF. BELLY T.NIDA (KE RNG)
N. BE LHACHMI Apprenti
P .RENAUD S .P ICHOUX
G .B OLT EAU
M.DURA NT
B.CALLIER
P.DE MION
M.LIBB RE CHT
N. FARIA
J. DE B ARROS
S .S POHR
F.LAFON
F. G AUCHI- MA RT INO Intérimaire
Y.DUPIN
K.SCHROW ANGEN
K.PHANUW AT (JO)
J.MONAGHAN V. MA RTIN Conges 18 mois
K.CHETTHAPHON ( EARTH) M.JA COB I. K ATE SANEE ( KATE )
T. T OVEY
S. WE ERAPON ( MAN)
B . LYONS H. NG UY EN
CRETEIL OUDRY
A . S AUZE Apprentice
DALLAS
BANGKOK
D = Design d = distance power
Increased Design Flexibility
Traditional surfacing is limited to one design Design (D) placed on the front surface Distance power (d) surfaced on the back Playing music through a single speaker system limits the ability to design sound effects...
D
d
Traditional PAL
D = Design d = distance power
FBS PALs are also limited to one design Design (D) placed on the back surface Distance power (d) surfaced on the back The location of the speaker is changed...
d
FBS (DRx™)
Traditional surfacing is limited to one design (placed on the front surface), because the process is not capable of producing a progressive surface on the back surface of the lens. This limits the designer in the same way having only a single speaker limits how music can be played. You can play beautiful music through a single speaker- but there is not much freedom to change the sound (basically all you can do is adjust the volume).
Using only one surface for progressive design also limits the effects the designer can create...
Increased Design Flexibility
D
Its easy to say Essilor invests millions of dollars in digital R&D... Here is one proof. Essilor hires over 50 researchers who are focused solely on process research and the development of process controls. Each of these people from around the world are dedicated to ensuring that lenses produced in Essilor labs (and our partners) are "on target." (Note: Essilor has more researchers dedicated solely to process control than most ophthalmic manufacturers have in their entire R&D department.)
...and the flexibility of DS does allow the designer to customize to a limited degree
The FBS is also a "single surface" format. However, as already mentioned, the DS process does allow the designer to create a greater number of designs, because it 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 we can not only play the music, but we can "tweak" the sound by increasing the base, the treble, or the midrange.
D = Design d = distance power
Increased Design Flexibility
Digital surfacing can support two designs Designs (D) are placed on both surfaces Distance power (d) is digitally surfaced on back Two speakers makes it possible to create stereo and other sound effects...
d
From a designer's standpoint, the really exciting aspect of DS is the ability to place a design on two surfaces! With two surfaces, the designer can create an unlimited number of effects. Beyond just "tweaking" the levels of sound, the designer can create effects not possible with a single speaker. Likewise, with two speakers you can create effects like stereo.
D D Using two surfaces makes it possible for the designer to create new optical effects...
DualOptix™
Increased Design Flexibility Two designs allow the designer to address both defocus and distortion simultaneously
Management of Distortion
Controlled Correction
Patient's Blurred Vision A single surface can control focus or distortion (usually a compromise of the two)
Two surfaces can be used to control focus & distortion simultaneously... Management of Focus
Increased Design Flexibility An example of two-surface design: Rx -1.00 sph / +3.00 ADD 6B
-1.00
6B
6B
-1.00
d
D D
9B
+2.00
TRADITIONAL
-1.00
d
d D
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 provision of focus and reduction of distortion. When using a single surface, 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!
6B
D
+2.00
FBS (DRx™)
7B
+2.00
DualOptix™
Single surface progressions cannot provide the optimal curvature for both the distance and the near powers (and asphericity alone cannot overcome all "base curve effects"). Disassociating the power change from the curvature change reduces distortion to levels not otherwise possible.
Here's ONE example of how two surfaces improve progressive optics. In a traditional PAL, the front surface is used to create the ADD power. This creates distortion- because you cannot optimize the front curvature for both the distance and the near powers (because changing power by 3 diopters does not require a 3 diopter change in base curve). Moving to the back surface does not improve the situation (because the same base curve is definitely not optimal for two powers 3 diopters apart). Only by disassociating the power change from the curvature change can distortion be reduced below the levels found in single surface PALs. By the way, asphericity CANNOT "do away with the base curve effect." Asphericity can reduce marginal astigmatism and power error- it cannot eliminate distortion. Hoya is the only other manufacturer using both surfaces of the lens (Hoyalux iD), and the benefit is similar (control of skew distortion).
Review Digital surfacing provides three advantages Removes tooling limitations but customization must be meaningful
Potential for greater precision but the process must be controlled
Allows designer to use both sides of the lens allows simultaneous control of focus and distortion
New PAL Formats D d
d D
D
d D
D = Design d = distance power
Traditional PAL • A single surface PAL • Design on front • Distance power on back • Compromise between control of focus / distortion DRx™ (FBS) PAL • A single surface PAL • Design on back • Distance power on back • Greater accuracy • Compromise between control of focus / distortion DualOptix™ PAL • A two-surface PAL • Designs on front & back • Distance power on back • Greater accuracy • Control of both focus / distortion
There are three PAL formats currently available on the market. Traditional PALs & FBS PALs use a single surface which strikes a balance between providing good focus and reduction of distortion. DualOptics PALs are two-surface designs which can control both focus and distortion (the result being clear central vision and exceptionally well-controlled peripheral vision).
Both FBS (DRx) and DualOptics gives us greater precision. DualOptics also gives us unlimited ability to customize.
Advantages of DS Formats Benefits of both FBS and DualOptix™ More precise compared to Traditional PALs
Additional Benefit of DualOptix™ Control of both focus and distortion
d
d D
D FBS
Essilor uses the DualOptix format for customization- since it offers the greatest ability to control focus and distortion.
D DualOptix™
Types of DualOptix™ Customization Personalization to Head/Eye Ratio (Varilux Ipseo IV) W.A.V.E. Technology 2 (Varilux Physio Enhanced) Maximized Zone Width (Varilux Comfort Enhanced/All Varilux) DUAL ADD TECHNOLOGY (DEFINITY) FrameOptimization Technology (Accolade Freedom) Additional benefits common to ALL DualOptix PALs Atoricity (to reduce peripheral aberration) Customized Near Zone Inset (to promote reading) Customized to Fitting Height
d D
Length of Progression Distribution of Zones (wider distance angle)
D
DS Design Capabilities DEFINITY- reduces astigmatism/distortion Widest Intermediate Least Swim
Varilux Physio Enhanced- customized wavefront Sharpest Vision Possible
New Varilux Comfort Enhanced- peripheral width Wide/Smooth Vision
Accolade Freedom- instant adaptation 95% adaption in first 5 minutes
Benefits of DualOptix PALs Varilux Ipseo IV is the only PAL featuring a DualOptix design which adapts to the wearer's individual visual strategy the design is individualized to 7 parameters wavefront correction pupil map sphere slope management position of wear visual zone width distance Rx atoricity progression length zone distribution
Benefits of DualOptix PALs Varilux Physio Enhanced is the only PAL providing customized wavefront correction W.A.V.E. Technology 2 personalizes the design to 4 parameters wavefront correction pupil map distance Rx atoricity progression length zone distribution
wavefront correction
customized wavefront correction
pupil size
Remember, the DualOptics format by itself does not improve the design- digital surfacing is just a tool! However, Essilor designers have used the DualOptics format to accomplish many types of customization and design improvement.
Benefits of DualOptix PALs DEFINITY is the only PAL to split addition to achieve levels of astigmatism not possible in a single surface PAL DUAL ADD TECHNOLOGY customizes the design to 2 parameters distance Rx atoricity progression length
Conclusions The foundations of PAL design can be delivered in ANY format Two new DS formats are available: DRx™ greater precision than traditional PALs
DualOptix™ greater precision than traditional PALs unlimited ability to customize
