progressive lens optics - part 2

Progressive lenses Part 2The new generation

35 | June 17 | 2005 OT

Continuing Education and Training

had also paid a great deal of attention tothe quality of vision in the lateral regionsof the progression zone. Conic sections ofchanging eccentricities, from one section ofthe lens to another, replaced the circularsections employed in the Varilux 1 design.The effect of which was to reduce the powerin the peripheries of the progression zone,the result being termed ‘horizontal opticalmoduation’. Binocular vision wasoptimised as a result of an asymmetricdesign.

During the decade following theintroduction of Varilux 2, othermanufacturers introduced progressive lensdesigns, focusing on specific opticalcharacteristics. Some emphasised largedistance and near vision zones,concentrating the inevitable astigmatism inthe lens periphery (American OpticalUltravue, Rodenstock Progressiv R, BBGRZoom, Sola Graduate, etc). Othermanufacturers took a different approach,reducing the amount of unwantedastigmatism in the periphery by spreadingit more widely in the lens (AmericanOptical Truvision Omni). Others placedspecial emphasis on the concept of lensasymmetry and comfortable binocularvision (Zeiss Gradal HS).

A further step in the enhancement ofprogressive lens performance was madewith the third generation, multi-design

Mo Jalie SMSA, FBDO (Hons), Hon FCGI, HonFCOptom, MCMI

Module 2 Part 6Lens Dispensing Today

The Aves lens employed an inverted conicalsection on one side and an eccentricsection of an oblate ellipsoid on the other,combined so that each surface contributedan equal cylindrical effect with axes at rightangles to one another. The result, which isdepicted in Figure 1, is a sphere of ever-increasing power from top to bottom.Although described and a few samplesmade, Owen Aves’ design appears not tohave been put into production, not leastbecause the problem of adding aprescription cylinder for the correction ofastigmatism could not be solved.

Progressive lens developmentsThe first commercially successful lens wasintroduced by Essel (one of the foundingmembers of Essilor International) underthe name of Varilux (1959). The designconsisted of large spherical distance andnear zones, linked by a series of circles ofever-decreasing radii between the distancevision sphere and the near vision sphere.Today, such a design would be described asvery hard, more attention having been paidto ensuring large distance and near zonesthan to the quality of peripheral vision oneither side of the progression corridor.

The second generation of progressivelenses, Varilux 2, was introduced in 1973. Ittoo provided large distance, intermediateand near fields of vision, but the designers

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The first patent for a progressive power lens, and a method ofproducing it, appears to have been granted to a Britishoptometrist, Owen Aves, in 1907 (British Patent No. 15 735,

Improvements in and relating to multifocal lenses and the like,and the method of grinding same).

About the authorMo Jalie is Visiting Professor at

the University of Ulster.

Sponsored by Rodenstock

Progress through partnership

www.rodenstock.co.uk

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No changein powerProgressive change

in power

Conicalcomponent

Ellipticalcomponent

FFiigguurree 11Owen Aves’ progressive power lens


36 | June 17 | 2005 OT


Sponsored by Rodenstock - Progress through partnership

concept with the Varilux Multi-Design lens(1988). This lens used distinct designs tomatch the wearer’s changing needs withadvancing presbyopia. The multi-designconcept aimed at optimising visual comfortfor each stage of presbyopia, makingadaptation to changes in near additioneasier for the wearer.

Essentially, the multi-design conceptrelates to the change of power progressionprofile with near addition, generallyresulting in a longer progression lengthand a soft design for low additions – thecorridor length becoming shorter and thedesign harder as the addition increases.Similar design philosophies wereintroduced by American Optical AO M3,BBGR Selective/Natural, HOYA Hoyalux, etc.Some manufacturers offered designs whichcombined flatter aspheric base curves witha progressive surface – the first being theRodenstock Progressiv S design.

The fourth generation of progressivelenses (introduced by Essilor under thename of Varilux Comfort in 1993), offeredwearers more natural vision than anyprevious progressive lens design. The nearvision area for Varilux Comfort is locatedhigh in the lens so that the wearer canreach it easily and naturally when loweringtheir gaze. To explore the near andintermediate vision fields, fewer head andeye movements are required and the wearerenjoys more comfortable posture. Theseadvantages arise from the specific powerprofile in the progression zone adopted forVarilux Comfort. For example, in the case ofa +2.00D addition, 85% of the fulladdition is reached just 12mm below thefitting point compared to a minimum of14mm or 15mm for previous progressivedesigns.

Larger fields of clear vision were offeredby Varilux Comfort, as well as additionalcomfort in peripheral and dynamic vision.Due to the softness of the lens periphery,the necessary horizontal head movementrequired to explore the full width of thefield was greatly reduced. Furthermore, thiswas accompanied by a dramatic reductionin swimming effects, thus improvingwearer comfort in dynamic vision. Thanksto its asymmetry, Varilux Comfort alsooffered balanced binocular vision, whilst atthe same time, integrating the multi-designconcept of previous Varilux generations.Several competitive designs from othermanufacturers appeared during the 1990s.

In 2000, the fifth generation progressivedesign, Varilux Panamic, was introduced.This new design was based on the successachieved by Varilux Comfort in providing alarge field of vision, which resulted fromthe softness and regularity of the lensperiphery. The Varilux Comfort designshowed that vision was a global processand wearers would perceive their field aslarge if they had the ability to see

Table 1Availability of lens designs described

MMaatteerriiaall PPhhoottoocchhrroommiicc PPoollaarriissiinnggAAmmeerriiccaann OOppttiiccaall AO b’Active CR39 Green & Brown Grey 15% AO PRO Easy CR39 Brown NG & Grey NG

Polycarbonate1.60 mid index

BBBBGGRR Evolis CR39 Brown NG & Grey NGPolycarbonate Brown & Grey1.67 high index

EEssssiilloorr Varilux Panamic Glass 1.60 Photobrown ExtraGlass 1.80CR39 Brown & GreyPolycarbonate Brown V & Grey V Brown & Grey 15%1.60 mid index1.67 high index Brown V1.74 very high index

Varilux Ipseo 1.67 high indexVarilux Ellipse CR39 Brown & Grey

Polycarbonate Brown V & Grey VHigh index 1.67 Brown V

HHooyyaa Hoyalux iD 1.60 mid index Eyas 1.60 Suntech1.67 Eynoa1.70 Eyry

NNiikkoonn Presio-Ci CR39 Brown & GreyPresio-Ei 1.60 mid indexPresio-Fi 1.67 high index Presio-Gi 1.74 very high indexPresio W 1.60 mid index

1.67 high index

PPeennttaaxx AF 1.60 1.60 mid indexMini AF 1.60 1.60 mid indexAF 1.67 1.67 high indexMini AF 1.67 1.67 high indexPF 1.74 1.74 very high indexSuper Atoric ‘F’ 1.60 1.60 mid indexSuper Atoric ‘F’ 1.67 1.67 high index

RRooddeennssttoocckk ImpressionILT CR39 Colormatic™& Impression XSILT 1.60 mid index

1.67 high index1.74 very high index

Impression HyperopILT & 1.67 high indexImpression Hyperop XSILT

Nexyma 40 & Nexyma 80 CR39

RRuupppp ++ HHuubbrraacchh Ysis 1.60 mid index

SSeeiikkoo P-1W 1.56 mid indexP-1W 1.67 high index Brown V & Grey VP-1SY 1.67 high indexP-1SY 1.74 very high index

SShhaammiirr Genesis CR39 NG Brown & Grey 15%Trivex1.60 mid index Brown V & Grey V1.67 high indexGlass 1.60 index Photobrown ExtraGlass 1.70 indexGlass 1.80 index

Autograph CR391.60 mid index Brown V & Grey V

SSiiggnneett AArrmmoorrlliittee Navigator CR39 Brown & Grey1.56 SunSensors Brown & Grey1.59 polycarbonate1.60 mid index CCNNTTDD.. OOVVEERR


37 | June 17 | 2005 OT


comfortably through the lens periphery.In the Varilux Panamic design, the

balance between the central zone and theperiphery was shifted towards theperipheral zones of the lens, so thatperipheral effects were less dramatic than inprevious progressive designs. This change inemphasis also brought the advantages ofreducing the swimming effects obtained byrotation of the head and eyes around thefield, and improving binocular fusion inthe lens periphery. Clinical trials were toprove that wearers felt that the keyimprovement found with Varilux Panamicwas an enlargement of the near vision field,providing a wider field of vision in allzones of the lens. The wearer tests showedthat distortion was reduced by 20% inperipheral vision, enabling objects to bedetected quicker. There was also asignificant reduction of swimming effectsin binocular vision, ensuring a widerbinocular field – and the intermediate andnear fields appeared wider.

Over the last five years, rapid strideshave taken place in ophthalmic lensproduction technology. In particular,computer numerically controlled (CNC)grinding technology has been developed tothe stage that a lens can be transferreddirectly from a CNC generator to CNCpolishing without fear that the form of thesurface may be altered by the polishingprocess. This freedom from the restrictions,which go hand in hand with the olderlapping process and its need for smoothingand polishing tools of equal curvature tothe surface being processed, has led to theterm ‘free-form surfaces’, which can be ofvirtually any form as dictated by thecomputer controlling the cutting process.

Through a combination of bettersoftware, faster computer processing andfree-form surfacing, it has become possibleto modify some aspects of a progressivedesign to take into account the individualcharacteristics of the frame in which thelenses are to be mounted. For example,variations in fitting details for an individualwearer, such as the vertex distance andpantoscopic tilt, can be allowed for in thedesign when this information is given tothe manufacturer, along with the requiredprescription of the lens (RodenstockImpressionILT, Rupp + Hubrach Ysis,Shamir Autograph, Zeiss Individual).

New generation designs from othermanufacturers include the BBGR Evolis, theNikon Presio W, the Pentax Super Atoric ‘F’,the Seiko P-1SY, the first of the new designsto have the progression on the concavesurface, and the SOLA MAX One. The stillawaited (in the UK) Johnson & JohnsonDefinity lens shares the progression between

MMaatteerriiaall PPhhoottoocchhrroommiicc PPoollaarriissiinngg

Kodak Concise & Precise CR39 Brown & Grey1.56 SunSensors Brown & GreyPolycarbonate1.60 mid index InstaShades Grey & Brown1.67 high indexGlass 1.60 index Photobrown Extra

SSOOLLAA Percepta CR39 Brown NG & Grey NG GreySpectralite Brown NG & Grey NGPolycarbonateGlass 1.60 index Photobrown

SOLAOne CR39 Brown NG & Grey NGSpectralite Brown NG & Grey NG1.60 mid index

SOLAOne Ego 1.67 high index

YYoouunnggeerr Image CR 39 Brown & Grey Brown & GreyTrivex Grey VPolycarbonate Brown V & Grey V Brown & Grey

ZZeeiissss Gradal Individual Glass 1.60 mid index Umbramatic Brown & GreyClarlet 1.60Clarlet 1.67

Unless otherwise stated, the plastics photochromic versions refer to Transitions availability.

NG = Next generation V = Transitions V

Table 1Availability of lens designs described (continued)

the front and back surfaces, as does Hoya’sHoyalux iD design, which is a double-sidedprogressive.

Also available from most of the majormanufacturers are vocational progressivelenses designed for intermediate and nearvision use. Because the addition for theselenses is less than the full near additionrequired by the wearer, and the progressivecorridors are extended into the upperportion of the lens, the aberrations in thelens periphery remain small and widerfields of clear, useful vision are achieved.Such designs are usually advocated for useat the desk, particularly at a computerworkstation (AO Technica, BBGR Extenso,Essilor New Interview, Hoya Tact, etc).Typically, these lenses are made to the nearvision prescription but incorporate a powerdegression from near to intermediate ofsome -1.00D to -1.50D.

A fuller description of themanufacturer’s latest designs follows,with each lens’s availability summarisedin Table 1.

Manufacturers’ latest designs

American OpticalAO PRO Easy is a general-purposeprogressive lens that incorporates newerdesign techniques and technologies used inother American Optical progressives, suchas AO Compact and AO b’Active. Thesetechniques and technologies have providedAO PRO Easy with an optimised corridorlength of 15mm and improved peripheralperformance, whilst maintaining provenreliability and ease of wear.

This new design from Dr JohnWinthrop, the originator of the AOTruvision OMNI lens, is of bipolarconstruction with the power increasingsmoothly between the distance and nearreference points (Figure 2). AO PRO Easyoffers excellent performance in thedistance, near and intermediate viewingzones, whilst providing good quality ofvision in the peripheral viewing area.Figure 2a shows the variation in meansurface power for a lens of power planoadd +2.00, and Figure 2b the surfaceastigmatism for the same power. The

a) Mean surface power b) Surface astigmatism

+0.12

+1.87

FFiigguurree 22AO PRO Easy progressive power lens


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minimum recommended fitting height toprovide an adequate near vision area is18mm.

The AO b’Active lens, designed forwearers who require wide horizontal fieldsof aberration-free distance vision (activeviewing zone), provides an area of very lowastigmatism on the temporal side of theprogressive zone. This is illustrated inFigure 3, which compares the surfaceastigmatism of the design with that of aconventional progressive lens. Theminimum recommended fitting height toprovide an adequate near vision area is20mm.

BBGRBBGR is the third largest supplier ofprogressive lenses in Europe. Its Evolisprogressive lens won the Silmo d’Or Awardfor Innovation in 2002 as a new concept inprogressive lens design. Within the Evolisdesign, BBGR developed three designs –one dedicated to each type of ametropia.Each design is charachterised by a specificmeridian, so has a specific power profileand progession length. Evolis is a soft,multi-design in terms of both the degree ofametropia and the near addition, with acorridor length of 17mm. However, 85% ofthe addition is obtained, in the case ofminus lenses, 10.4mm below the distancereference point, in the case of lowametropes, 11.5mm below the distancereference point and, in the case ofhypermetropes, 12.2mm below the distancereference point. The recommendedminimum fitting height is 16mm for a

myope and 18mm for a hypermetrope and,subject to these minima, is suitable forfitting in compact frames.

EssilorEssilor’s Varilux Comfort design has to dateoutsold every other progressive lens on themarket. The company’s policy of striving toperfect the Varilux lens led, in 2000, to thenew design, Varilux Panamic, which retainedall the benefits of the Comfort lens andachieved an even smoother surfacetopography in the periphery of the lens.This enabled the design to address thecomfort of the overall field of vision andprovide a significant improvement in theoverall effect of the lens in wear. VariluxPanamic was positioned as the premierVarilux product alongside Varilux Comfortand Varilux Liberty, which continue to beoffered.

The latest design from Essilor takes intoaccount the actual degree of head and eyerotation, which the wearer employs whenviewing through the intermediate and nearzones of the lens. Research1 has shown thateach individual has specific head and eyebehaviour, which can be measured and theprogressive surface then designed toincorporate the wearer behaviour. Thisprinciple has been incorporated into apersonalised progressive design from Essilor– the Varilux Ipseo.

Figure 4 illustrates the visual pointpositions on the lens for two successfulprogressive lens wearers (A and B). Thepositions of the visual points weremeasured when the wearers were asked to

AO b’Active lens Conventional progressive lens

FFiigguurree 33Active viewing zones for AO b’Active progressive power lens

Wearer A ‘eye turner’ Wearer B ‘head turner’

FFiigguurree 44Visual point positions for a patient who A) mainly turns their eyes, and B) mainly turns their head


40 | June 17 | 2005 OT



Eye turner Part eye/parthead turner

FFiigguurree 55Eye turners and head turners

Head turner

Requires a widefield for

foveal vision

Compromise basedupon merit function

FFiigguurree 66Progressive designs for eye turners and head turners

Requires minimumdistortion from a

soft periphery

Eye turner Part eye/parthead turner

Head turner

a) VisionPrint systemA – Indicators for head/eye proportionsB – Head/eye ratioC – Stability coefficient

A

B C

b) The information displayed on the screen

identify targets, which appeared at random inthe intermediate field of view. Wearer A isquite clearly an ‘eye turner’, who perceivesobjects quite clearly over a wide zone of thelens. Such a wearer would claim that the widthof their intermediate field was as wide as thelens itself. Wearer B, on the other hand, tendsto ‘point the nose’ at objects in theintermediate field and, for whatever reason,prefers not to view through peripheral parts ofthe lens.

The experimental set-up is shown inFigure 5; the relative movement of the head isdetected by sensors attached to the head whenthe patient is asked to view an object in thetemporal portion of the field. Knowledge ofthis characteristic can help the practitioner tochoose the best progressive design for anindividual wearer (Figure 6).

A new instrument, the VisionPrint System(Figure 7), has been produced to determineeye/head movement for a specific individual,the results of which can be incorporated intothe progressive surface. Essentially, theVisionPrint System consists of three lamps; thecentral lamp is viewed at 40cm from thecentre of the patient’s forehead, with twoseparate lamps, 40cm on either side of thecentral lamp. The patient is directed to look atthe lamp, which is illuminated, and their headmovement recorded by an ultrasonic signalwhich is emitted by the system and reflectedby a transponder attached to the special trialframe the patient is wearing. As far as thepatient is concerned, the lamps areilluminated at random and following a short15-second cycle to familiarise the patient, thetest sequence continues over a 90-second cyclewhich enables the system to calculate anddisplay the eye/head ratio, along with aconsistency factor referred to as the ‘stabilitycoefficient’.

In order to quantify the relative eye/headmovement, a variable is used called the Gain,and is equal to the ratio of the angularmovement of the head to the total angle of thetarget:

Gain = head angletarget angle

Thus, if the target angle is 45˚ and the headrotates 15˚ to view the target, the Gain is 0.33.Clearly a Gain of zero would indicate that thepatient was an eye turner, whereas a Gain of1.0 would indicate that the patient was a headturner.

People who tend to turn mainly their headswhen viewing lateral objects will benefit froma design which provides optimum centralacuity, i.e. a softer design, whereas people whotend to turn mainly their eyes, will benefitfrom a design which provides good acuity overa wider field, i.e. a harder design. TheVisionPrint system enables the practitioner todetermine the wearer profile of the individualquickly and accurately and provides a methodfor communicating the information to the

FFiigguurree 77The VisionPrint System from Essilor


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laboratory for incorporation in the designof the surface. Thus, each Varilux Ipseo lensis designed for the individual wearer,manufactured by free-form technology and,in recognition of its individual nature,micro-engraved with the patient’s initials.

Essilor normally recommends aminimum fitting height of 18mm for theVarilux designs but a recent addition to therange, the Varilux Ellipse, is specificallydesigned for the fashionable shallow frame.With this lens, 85% of the near addition isreached only 9.2mm below the distancereference point, allowing it to be mountedwith a minimum recommended fittingheight of just 14mm.

Hoya Lens UKDescribed as an integrated double surfacedesign, the Hoyalux iD lens was the first ofa new generation to be released in the UK,which incorporated some of the progressivepower on the convex surface and some onthe concave surface. In the design of thelens, Hoya incorporated the progressivecomponent that gives rise to a verticalchange in power on the convex surface ofthe lens, and the progressive componentthat gives rise to the horizontal change inpower on the concave surface of the lens. Asimple simulation of how this results in aspherical increase in power in the nearportion is obtained by considering themagnification effects of two plano cylindersthat have been combined at right angles toone another.

Figure 8 illustrates a target in the formof graph paper, which is viewed through aplano convex cylinder with its axis vertical.Since the cylinder has power only at rightangles to its axis, the squares are magnifiedin the horizontal meridian only, and whenviewed through the cylinder, appear ashorizontal rectangles.

In Figure 9a, the target is shown with aplano convex cylinder placed with its axishorizontal over the progression area torepresent the vertical progressioncomponents. In Figure 9b, the planoconvex cylinder has been placed with itsaxis vertical over the progression area torepresent the horizontal progressioncomponents. The result is shown inFigure 9c; the magnifications combine toproduce images which are the same shapeas the object over most of the central field.

If the magnification produced by thelens in the peripheral field is irregular, dueto rapid changes in the shape of thesurface, peripheral objects will appear tochange direction. This is often referred to asthe ‘swimming’ effect by the new wearer, asimages viewed through peripheral portionsof the right and left lenses apparently moveat different speeds.

The swimming effect is a combinationof distortion produced by the increasingpower between the distance and nearportions, and changes which take place insurface topography as the result of trying toachieve the correct blend between the

various zones of the lens. The effect isparticularly troublesome to the newprogressive lens wearer, especially whenlooking at the floor, or walking down stairs,when the visual system is attempting toprocess information which is arriving fromoblique sight directions.

Hoya has considered this problem insome detail and derived a method wherebyit can control the deformation using theconcept of a point deformation index. Itrepresents each point in object space as asmall circle and calculates, by ray tracing

through the lens, the spectaclemagnification throughout the progressionzone and near portion of the lens. If thespectacle magnification is the same in everydirection, then the object circles will beimaged as circles and, apart from themagnification itself, there will be nodeformation by the lens of that point.

Spectacle magnification (the ratio of theretinal image size in the corrected eye tothat in the uncorrected eye) can beexpressed in terms of the two angles, ω’and ω (Figure 10). The object point, Q, is

FFiigguurree 88Meridional magnification by a plano-cylinder

FFiigguurree 99The vertical and horizontal progressive components of the Hoyalux iD progressive lens

a) Vertical progressivecomponent on convex side

b) Horizontal progressivecomponent on concave side

c) Combined progressivecomponents

FFiigguurree 1100Spectacle magnification

Q

Q’Q’

a

b

q

θ’

θ

Q

ω

ω’

SM = ω’ω


42 | June 17 | 2005 OT



represented by the circle of radius q and theimage formed by the lens is seen to bedrawn out into an ellipse of semi majoraxis, a, and semi-minor axis, b. Thespectacle magnification for each of themeridians a and b is expressed as:

SMa = a/q and SMb = b/q

Figure 10 illustrates a severe case ofdeformation where it can be seen that notonly are the two spectacle magnificationsdifferent, but the aximuth of a differs fromthe azimuth of q (θ’ is greater than θ).

The point deformation index, P, isdefined as:

P = a – bb

and depends only upon the shape of thespectacle magnification ellipse. It does notdescribe its orientation. It is immediatelyapparent from Figure 11 that when thespectacle magnification ellipse has its majoraxis vertical or horizontal, it does nottrouble the wearer as much as when themajor axis lies obliquely. The ellipsesdrawn alongside each view show theorientation of the major axis of the ellipse.

The normal point deformation index,PN, is at a maximum when θb = 0˚ or when

θb = 90˚, and represents the deformationcomponent along the horizontal and thevertical meridians respectively.

The skew point deformation index, PS,is at a maximum when θb = 45˚ or whenθb = 135˚, and represents the deformationcomponent along the 45 and 135meridians respectively. It is the skewdeformation index, PS, which gives rise tothe most objectionable feeling ofdeformation and the swimming effect.

The total point deformation index, P,and the skew point deformation index, PS,are evaluated for a large number of pointsin object space, and plotted as shown inFigure 12, to provide the designer with anindication of the areas of the lens wherethe wearer is not likely to experience spatialdistortion. As a result, the apparentcurvature of objects is reduced to levelswhere it is barely perceptible (Figure 13).

The double aspheric Hoyalux iD lens iscurrently available in Eyas 1.60 indexplastics material with two differentprogressive lengths, 14mm and 11mm, theshorter length being designed for shallow-eye frames. Hoya recommends that the14mm design should be fitted in a frame,which provides a minimum height of18mm from the bottom rim of the frame tothe pupil centre, and a minimum distanceof 10mm from the pupil centre to theupper edge of the lens, or to the bottomedge of the upper frame rim. The compact11mm design should be fitted in a framewhich provides a minimum height of14mm from the bottom rim of the frame tothe pupil centre, and a minimum distanceof 10mm from the pupil centre to theupper edge of the lens, or to the bottomedge of the upper frame rim. The fittingpoint is designed to be mounted in front ofthe centre of the pupil.

Hoyalux iD lenses are supplied withHiVision ViewProtect coating, whichcombines a 99% transmission multi-layerAR coating with a scratch resistant hardcoating and a hydrophobic top coat.

NikonThe Presio X series of progressive lenses hasbeen available in the UK for several years.The codes FX, DX and CX, relate to 1.67,1.56 and 1.498 index materials respectively.They are available with either 14mm or16mm length progression lengths.

The more recent Presio-i progressivedesign from Nikon is available in fourdifferent materials, ranging from 1.50 to1.74. It is available in all materials witheither 13mm or 15mm progression lengths,with the Presio i-13 having the widest nearvision area in the range. Nikon terms thePresio-i design an ‘interfaced’ shallow-baseaspheric, resulting in significantly reducedaberration and easy adaptation for bothnew and existing progressive lens wearers.The recommended minimum fittingheights are 18mm for the Presio i-13 and21mm for the Presio i-15. In each case, thereshould be a minimum distance of 9mm

FFiigguurree 1111Effect of different orientations of the spectacle magnification ellipse

FFiigguurree 1122Distribution of deformation indices, P and PS

Total deformation index plot Skew deformation index plot

FFiigguurree 1133Hoyalux iD balanced view control


43 | June 17 | 2005 OT


from the distance reference point to theupper rim of the frame.

The latest design from Nikon, the PresioW, is a double surface design available ineither 1.60 or 1.67 index materials. Theconcave surface is calculated not only tocomplete the prescription of the lens, butalso to minimise the aberrations producedby the progressive surface – and if the lensincorporates a cylindrical correction, it is aatoroidal in nature.

Presio-i and Presio W are supplied withthe Nikon HCC hard, multipurposecoating.

PentaxLike Nikon, Pentax (Seiko Optical UK)offers its aspheric progressive design in arange of materials and corridor lengths. TheAF is termed a ‘retina forward’ design whichsignifies that in order to optimise the lensperformance the designers have traced raysfrom the retina forward through the eyeand the lens to the stipulated objectposition. The corridor length is 16mm andPentax recommends a minimum fittingheight of 23mm for this design.

A shorter corridor version, the Mini AF isalso available with a corridor length of14mm and a recommended minimumfitting height of just 18mm. The AF designis available in 1.60, 1.67 and 1.74 index(PF) materials, the latter with a choice ofeither 12mm or 14mm length corridors.The newest Pentax progressive lens is theSuper Atoric ‘F’ progressive lens, the designof which commences when the companyreceives the prescription order. Theprescriber is offered the facility to select apreferred base curve and the most appositeasphericity is then built into the designaccording to the choice of bending. Thus, apair of lenses of quite different powers canbe made free from aberrationalastigmatism, even if they have the samebase curve or incorporate prismaticcorrections. The working distance can alsobe specified to ensure that the optimuminset is provided. Four different corridorlengths can be specified – 10mm, 12mm,14mm or 16mm – with minimum fittingheights of 15mm, 16mm, 18mm or 23mmrespectively.

RodenstockRodenstock introduced its originalMultigressiv design in 1995. WithMultigressiv 2 came online optimisation ofthe concave surface with an asphericalsurface being applied to sphericalprescriptions and an atoroidal surface beingused when the prescription calls for acylindrical correction.

In 2000, a new design, MultigressivILT, waslaunched which applied Individual LensTechnology (ILT) to the design, enablingthe optimum progressive power surface tobe computed from a knowledge of theprescription data and base curve of the lens.With this new design, the progressivesurface was switched from the front to the

back surface of the lens and, in the case ofastigmatic prescriptions, the surface alsoincorporated the cylindrical correction. Thefront surface of the lens is a simplespherical surface, with the near additionand necessary aspheric correction for theform, being built into the concavesurface.

With astigmatic prescriptions, theconcave surface is an atoroidal progressivesurface. One advantage of this method ofconstruction is that the geometrical inset isno longer dependent on the convex surfacegeometry when the inset is fixed by theprogressive surface geometry, but can nowbe calculated individually for the lensprescription. Correct positioning of themeridian line results in larger clear visionzones for distance and near, and a widerprogressive zone with smoother transitionto the lens periphery.

The ImpressionILT lens is Rodenstock’sflagship progressive power lens design. Justlike the MultigressivILT, it has a concaveprogressive power surface, which iscombined with the cylinder in the case ofastigmatic lenses, but it can alsoincorporate the precise positioning of thelens in its design. In addition to theindividual CDs and progression heights,practitioners can submit the vertex distance,pantoscopic angle and the dihedral (faceform) angle of the front. The dihedral angletakes into account the bow of the front ofthe frame and may be defined as the anglebetween a vertical tangent plane to thefront surface of the frame, and the verticalplane tangential to the front surface of thelens. The computer software allows input ofall the different fitting parameters asvariables in deciding the optimum form ofthe concave surface, so the resulting lens is

custom designed for the individual fittingof the frame to the face.

Rodenstock’s newest lens is specificallydesigned for medium and highhypermetropes. The Impression Hyperop isproduced in 1.67 high index material anddesigned for powers in the range from+6.00D to +13.00D, with cylinders up to+6.00D. The design is available in fourdifferent forms. ImpressionS Hyperop andImpressionS XS Hyperop are the normal andshort corridor versions designed forstandard fitting parameters, whereasImpressionILT Hyperop and ImpressionILT XSHyperop enable the practitioner to supplylenses with the surfaces individuallycalculated for the patient’s measured vertexdistance, pantoscopic and dihedral angles.Each lens is individually calculated to be ofminimum thickness using Rodenstock’sShape-to-ShapeTM surfacing technology.

Rodenstock has introduced another newtype of near vision lens providingintermediate and near vision. Nexyma 80and Nexyma 40. The figures 80 and 40relate to the main viewing distance,expressed in centimetres, for which the lensis prescribed (Figure 14). Nexyma 80provides a wide clear zone for a mainviewing distance of 80cm, and would befound particularly helpful for use at acomputer workstation. Nexyma 40 providesa wide viewing area at 40cm and,compared with a single vision lens for near,would provide an extended range of visionfrom the near point out to beyond armslength.

Rupp + HubrachRupp + Hubrach (R+H) offers threedifferent progressive designs, Sentoris,Selectal and the new Ysis tailor-made design

Extendedvision area

Main visionarea

Extendedvision area

Main visionarea

Clear visual zones in Nexyma 40

Clear visual zones in Nexyma 80 A and B

80cm

40cm

80cm

40cm

Nexyma 40

Nexyma 80

FFiigguurree 1144Rodenstock Nexyma reading lenses


44 | June 17 | 2005 OT



which takes into account such factors as thepatient’s posture, frame position, amountof head tilt used for near vision tasks andwhich area of the lens is likely to be usedmost frequently.

The amount of head tilt which thepatient uses for near vision tasks ismeasured with the help of a special headtilt measuring gauge. This involves a sensorattached to the frame and a receiver, whichdisplays the vertical angle between thevisual axes when the head is held in theprimary position and the visual axes in thepatient’s normal reading posture. Thedevice is simple to use. The patient is firstasked to stand in a relaxed position lookingstraight ahead viewing a distant object.They are then seated and asked to look at abook whilst in their normal, comfortableposture for near. The difference between thetwo readings on the scale is the head tilt.This value is then incorporated as part ofthe data used to determine the optimumprogression length and other parameters ofthe progression surface. The speciallydesigned order form enables this and otherfeatures of the frame fit to be taken intoconsideration in the design of the free-formconcave surface.

R+H has developed an integratedconsumer marketing package to reinforcethe message that Ysis is a special luxury lensdesign personalised for individual clients.The spectacles are supplied in an ‘Ysis safe’,which also contains a crystal and a ‘visionmap’ profiling the wearer priorities, whichwere taken into account in the design of thelenses. R+H products are now available inthe UK from BBGR Ltd.

SeikoThe Seiko range of lenses is now distributedin the UK by Seiko Optical UK. It currentlyoffers both front and back surfaceprogressive designs, the front surface designis called the P-1W, available in both whiteand Transitions V®, Brown or Grey. Thewhite version is available with a choice ofeither 14mm or 16mm corridor lengths,with minimum recommended fittingheights of 18mm and 21mm respectively.

The Seiko P-1SY, the first design to takeadvantage of free-form technology andcombine the cylinder with the progressionon the concave surface of the lens, isavailable in 1.60, 1.67 and 1.74 indexmaterials with a choice of three corridor

lengths – 10mm, 12mm or 14mm. Theminimum recommended fitting heights forthese are 15mm, 16mm and 18mmrespectively.

Since the progression is located on theback surface of the lens, when suppliedwith a 10mm progressive corridor (with aminimum fitting height of 15mm) theP-1SY can be fitted into shallow eye frameswithout compromising the near field. Seikoalso recommends that in the case ofdistance powers greater than 3.00D, if apatient is changing from a convex surfaceprogressive design to one with a concaveprogressive surface, then the additionshould be increased by 0.25D. All Seikolenses are automatically supplied withmultipurpose hard, MAR coatings. The1.67 index version is available in bothwhite and Transitions V material (brownor grey).

Seiko’s latest offer is the Super P-1,which was awarded the Good DesignAward 2003/04 by the Japan IndustrialDesign Promotion Organisation.

Shamir OpticalShamir Optical Industries has set up a UKsubsidiary in Cambridge, under the nameof Altra Optics UK, to ensure rapiddistribution of its range of lenses. Wellknown as the supplier of progressivemoulds to several lens manufacturers,Shamir has been producing its own rangeof progressive lenses for several years. Thebest known in the UK are the Genesis andthe short-corridor Piccolo designs.

Shamir has developed a uniquecomputer design facility known as Eye-Point TechnologyTM, at the heart of which isa dedicated ray tracing program written byShamir scientists. The program enables thedesigners to trace rays from the eye throughthe lens to the object and quantify the lensperformance point-by-point over the lens.The progressive surface can then beoptimised for any given set ofcircumstances, including personalising thelens according to variations in vertexdistance and pantoscopic angle.

Genesis is an aspheric progressive design,which is available in both glass and plasticsmaterials. The minimum recommendedfitting height for Genesis is 19mm.

The new flagship design is the ShamirAutograph design with a concave, free-formprogressive surface. It can be tailored

individually according to the prescriptionand fitting data which is entered for eachlens. The minimum recommended fittingheight for Autograph is 19mm.

Signet ArmorliteSignet Armorlite offers the Navigatorprogressive lens in several differentmaterials, together with the Kodak rangewhich includes Kodak Progressive, KodakPrecise and the short corridor Kodak Concise.

The company’s ranges include theCorning plastics 1.56 index photochromicSunsensors material in both Brown andGrey, and Kodak InstaShadesTM Grey andBrown in 1.60 index material. InstaShadeswas developed by Signet Armorlite toprovide a very fast acting 1.60 indexphotochromic material, where thephotochromic molecules are sandwichedbetween the RLX coating and the monomerin the mould during the casting operation.Upon polymerisation, the photochromicmatrix lies just beneath the front surface ofthe lens.

Signet publishes minimumrecommended fitting heights for all itsprogressive designs and includes aminimum depth of lens below the top rimof the frame to ensure that the patientobtains an adequate distance portion onthe lens (Figure 15).

SOLA OpticalThe SOLA range of progressive lensesincludes the Graduate, the XL, the Perceptaand the SOLAOne – all available indifferent materials. The newest design isSOLAOne Ego, which is a personalisedprogressive design individually customisedto take into account the wearer’s lifestyle.Profiling the patient’s lifestyle and visionneeds is undertaken at the dispensing tablewith the aid of iPilot, a computer baseddispensing system designed to run on aPDA (such as a Palm Pilot). iPilot promptsthe dispensing optician through a series ofquestions in order to assess visual activitiesmost frequently undertaken by the wearer.Sophisticated algorithms derived fromSOLA’s extensive database are used toanalyse a number of lifestyle factors. Fromthis data, a customisation code iscomputed, which is then used to order acustomised SOLAOne Ego lens.

SOLA refers to its free-form lensprocessing as High Definition (HD)Technology, stating that it can deliverthe ideal lens design surface for eachwearer’s prescription and fittingparameters.

Younger OpticsThe Image progressive lens from YoungerOptics (California) is available in the UKfrom the Norville Group in several differentmaterials, including the two strongestplastics media, Trivex® and polycarbonate.Younger recently updated its polarisingNuPolar technology and most of its designsare available in NuPolar form.

CC DDSA Navigator 22 15Kodak Precise 20 12Kodak Progressive 22 15Kodak Concise 17 12

D

C

FFiigguurree 1155Minimum recommended fitting parameters for Signet Armorlite progressive lenses

MMeeaassuurreemmeenntt


45 | June 17 | 2005 OT


1. What power would be found 12mmbelow the distance reference point ofa Varilux Comfort design of power+1.00 Add +2.50?

a. +2.12b. +2.62c. +3.12d. +3.62

2. What is the minimum recommendedvertical dimension of a mountedlens, measured through the pupilcentre for a Hoyalux iD design with a14mm corridor?

a. 35mmb. 28mmc. 18mmd. 14mm

3. The results from the VisionPrintsystem at the time of dispensing are:Gain 0.8, Stability Coefficient 0.1.Which one of the following mostaptly describes the subject?

a. Eye turner – low confidence in resultb. Eye turner – high confidence in resultc. Head turner – low confidence in resultd. Head turner – high confidence in

result

4. Which one of the following lenses isthe odd one out?

a. Hoya Hoyalux iDb. R + H Ysisc. Shamir Autographd. Zeiss Gradal Individual

MCQs

Progressive lenses Part 2 – The new generationPlease note there is only ONE correct answer

Module 2 Part 6 of Lens Dispensing Today

5. Near vision with a progressive lens isusually possible when 85% of the fullnear addition has been obtainedalong the progressive corridor. Howdoes the distance of this point, inrelation to the distance referencepoint, vary with modern multi-designprogressive lenses?

a. It gets longer as the add increasesb. It remains the same for all reading

additionsc. It gets longer as the lens power

becomes more negatived. It gets longer as the lens power

becomes more positive


a. Rupp + Hubrach Ysis b. Rodenstock ImpressionILT

c. Essilor Varilux Panamicd. Seiko P-1SY

7. The first progressive lens to bemarketed with the progression on theconcave surface was the Variplasdesign from Essel during the 1960s.Which was the second?

a. Essilor Varilux Comfortb. Seiko P-1SYc. Pentax AF 1.50d. BBGR Evolis

8. Which one of the following is NOT ashort-corridor, progressive design?

a. Shamir Piccolob. Essilor Varilux Ellipsec. Rodenstock Nexyma 40d. Zeiss Brevis

9. Which one of the followingdevelopments has NOT contributed tothe recent ability to custom designprogressive lenses, which can takeinto account fitting parameters suchas vertex distance and pantoscopicangle?

a. Sophisticated softwareb. Arrival of free-form surfacingc. More powerful computing facilities d. Arrival of CNC generators

10. Which one of the following lenses isNOT designed solely for intermediateand near vision use?

a. Essilor New Interviewb. Rodenstock Nexyma 40c. SOLA SOLAOned. Zeiss Clarlet Business

11. What is the recommended minimumvertical depth of a spectacle framemeasured through the pupil centre,for the Kodak Precise progressivelens?

a. 37mm b. 32mm c. 30mm d. 29mm


a. Hoya Hoyalux iDb. Nikon Presio-Gic. Pentax PFd. Seiko P-1SY

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ZeissThe current flagship progressive lenses fromCarl Zeiss are based upon the company’ssuccessful Gradal design, for which a convexprogressive surface is employed and thelens completed by incorporating anaspherical or atoroidal concave surface asthe prescription demands. The GradalIndividual design enables the precisepositioning of the lens to be incorporatedin the design. In addition to the monocularCDs and progression heights, practitionerscan submit the vertex distance, and

pantoscopic angle relating to the framefitting, which are taken into account in thedesign of the progressive power surface.

Effectively, the design process firstdetermines the parameters of the concavesurface, assuming a given progressivesurface design, and then re-computes theprogressive surface to take into account theindividual fitting values supplied by thepractitioner. New algorithms have beendeveloped which allow the progressivesurface to be designed in about 20 secondsinstead of the former two to three hours of

interactive work with the computer.For small frames, Zeiss offers Gradal

Brevis and the individually tailored GradalShort I and, as vocational lenses forintermediate and near vision use, theClarlet Business and the Gradal RD.

Reference

1. Simonet P et al (2003) Eye-headcoordination in presbyopes. Points de vueNo 49 17-21.

progressive lens optics - part 2

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