www.journalofoptometry.org
ORIGINAL
ARTICLE
The
effects
of
two
longpass
filters
on
visual
performance
Federica
Cozza
a,b,
Matteo
Monzio
Compagnoni
c,
Chiara
Airoldi
d,
Chiara
Braga
b,
Gabriele
Nigrotti
b,
Natalia
Vlasak
e,
Silvano
Larcher
f,
Fabrizio
Zeri
a,b,g,∗,
Silvia
Tavazzi
a,baDepartmentofMaterialsScience,UniversityofMilanoBicocca,Milan,Italy
bResearchCentreinOpticsandOptometry(COMiB),UniversityofMilanoBicocca,Milan,Italy cDepartmentofStatisticsandQuantitativeMethods,UniversityofMilanoBicocca,Milan,Italy dDepartmentofTranslationalMedicine,UniversityofEasternPiedmont,Novara,Italy eHoyaVisionCare,Uithoorn,TheNetherlands
fHoyaLensItaly,Milan,Italy
gOphthalmicResearchGroup.SchoolofLifeandHealthSciences,AstonUniversity,Birmingham,UK
Received19March2019;accepted13July2019
KEYWORDS Contrastsensitivity; Glare; Longpass; Macularpigment; Visualacuity Abstract
Purpose:Thisstudycomparedvisualperformanceandopticalpropertiesofthreefilters. Method:Twogroupsoftwenty adultswererecruited:wearersofprogressiveadditionlenses (PAL,46---73 years)andwearers ofsingle visionlenses (SVL, 26---55years). Three spectacle filters(Hoya, Japan) were compared:clear control,Standard Drive(STD), andProfessional Drive(PRO)lenses.OpticaltransmittancewasmeasuredbyaJascoV-650spectrophotometer. Bestcorrectedvisual acuity(BCVA)wasmeasuredin photopic (BCVAphotopic)and mesopic (BCVAmesopic)conditionsandunderglare(BCVAglare).Photopiccontrastsensitivity(CS)was alsomeasured.
Results:Thethreelongpassfiltersshowcutoffat426±2nm(STD/PRO)and405±2nm(clear lens).BCVAglareimprovedwithDrivefilterscomparedtotheclearone(p<0.05)from0.03to -0.02(STD)andto-0.01(PRO)forPALandfrom-0.08to-0.12(STDandPRO)forSVL.ForPAL, BCVAmesopicimprovedfrom0.15to0.12(STD,p<0.05)and0.13(PRO),whilenosubstantial differencewasobservedforSVL.CSshowed someimprovements withDrivelensesat some angularfrequenciesbetween6and18cycles/deg,mainlyforthePALgroup.NoBCVAphotopic differenceswerefound.Aftertestingallfilters,eachfortwoweeks,79%(PAL)and60%(SVL) ofparticipantspreferredDrivelenses.
∗Correspondingauthorat:DepartmentofMaterialsScience,UniversityofMilanoBicocca,V.RobertoCozzi55,I-20125Milan,Italy. E-mailaddress:fabrizio.zeri@unimib.it(F.Zeri).
https://doi.org/10.1016/j.optom.2019.07.001
Conclusions:Drivelensesarefoundtomaintainorimprovesomevisual functionscompared tothe clearlens.Theimprovementofmesopic visualacuity,visualacuityunderglare,and contrastsensitivityismainlyattributedtothe reductionofintraocularlightscatteringas a consequenceofthetotallightattenuationinthespectralrangebelowthecutoff.
©2019SpanishGeneralCouncilofOptometry.PublishedbyElsevierEspa˜na,S.L.U.Thisisan openaccessarticleundertheCCBY-NC-NDlicense( http://creativecommons.org/licenses/by-nc-nd/4.0/). PALABRASCLAVE Sensibilidadde contraste; Deslumbramiento; Longpass; Pigmentomacular; Agudezavisual
Efectossobreeldesempe˜novisualdedosfiltrosLongpass
Resumen
Objetivo:Esteestudiocomparóeldesempe˜novisualylaspropiedadesópticasdetresfiltros. Método:Sereclutarondosgruposdeveinteadultos:losqueutilizabanlentesdeadición pro-gresiva(PAL,de46a73a˜nos),ylosqueutilizabanlentesmonofocales(SVL,de26a55a˜nos). Secompararontresfiltrosdegafas(Hoya,Japón):controlclaro,StandardDrive(STD),y Pro-fessionalDrive(PRO).LatransmitanciaópticasemidióconunespectrofotómetroJascoV-650. Semidiólaagudezavisualmejorcorregida(BCVA)encondicionesfotópicas(BCVAphotopic)y mesópicas(BCVAmesopic)ycondeslumbramiento(BCVAglare).Tambiénsemidiólasensibilidad alcontrastefotópico(CS).
Resultados:Los tres filtros deamplio espectroreflejaron un puntode corte de426±2nm (STD/PRO)y405±2nm(lentesclaras).BCVAglaremejoróconlosfiltrosDriveencomparación conlosfiltrosclaros(p<0,05)de0,03a-0,02(STD)y-0,01(PRO)paraPAL,yde-0,08a-0,12 (STDyPRO)paraSVL.ParaPAL,BCVAmesopicmejoróde0,15a0,12(STD,p<0,05)y0,13(PRO), noencontrándosediferenciasustancialparaSVL.CSreflejóalgunasmejorasconlaslentesDrive aciertasfrecuenciasangularesentre6y18ciclos/deg,principalmenteparaelgrupoPAL.No seencontrarondiferenciasparaBCVAphotopic.Trasprobartodoslosfiltros,cadaunodeellos durantedos semanas,el79% (PAL)yel 60%(SVL) delos participantesprefirieronlaslentes Drive.
Conclusiones:SehaencontradoquelaslentesDrivemantienenomejoranciertasfunciones visualesencomparaciónconotraslentesclaras.Lamejoradelaagudezavisualmesópica,la agudezavisualconsensibilidaddedeslumbramientoycontrasteseatribuyeprincipalmentea lareduccióndeladispersióndelaluzintraocular,comoconsecuenciadelaatenuacióntotal delaluzenelrangoespectralinferioralpuntodecorte.
©2019SpanishGeneralCouncilofOptometry.PublicadoporElsevierEspa˜na,S.L.U.Esteesun art´ıculoOpenAccessbajolalicenciaCCBY-NC-ND( http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Blue-lightfilteringspectaclelenseshavereceivedincreased attention in recent years because of their potential to reduce the effects of light scatter and chromatic aber-rations, and the possible protection they offer against photo-oxidative effects induced by photons of relatively highenergy.1---4Indeed,theaccumulationoftheretinoid flu-orophore N-retinylidene-N-retinylethanolamine within the retinalpigmentepitheliumisexpectedtoincreasethe vul-nerability of the retina to high-energy blue radiation.3---6 Spectacles,contactlenses,andintraocularlenseshaveall been proposed for filtering blue light. However, finding the balance between effectively reducing blue-light haz-ardsandmaintainingorimprovingvisualfunctionsremains a challenge, and one debate in the literature.6---18 Some authors,6---8,10,18 found visual acuity improvement and/or contrast sensitivity improvementwhen using filters which filter blue light both in normal subjects and in subjects
thedashboard,streetlights,andoncomingtrafficwhen driv-ingatnight.Atthesametime,theselensesareexpectedto showanimprovementofcontrastandbrightnessperception, eveninpoorlightandbadweather.
Togainfurtherinformationonthisissue,weperformed acomparison betweentwo Drivelenses and aclear lens, whose optical properties were also preliminary characte-rized.Weusedpshychophysicalmeasurementstoevaluate whetherspectaclelensesincorporatingthesefiltersoffered anyrealbenefit.
Methods
ParticipantsGlare is expected to be related to intraocular light scatter.19---21Therefore,twoseparategroupsofparticipants were recruited:older adults wearing progressiveaddition lenses(PALgroup),whotypicallyexhibitahigherlevel of intraocularlightscatter,aswellasyoungeradultswearing singlevisionlenses(SVLgroup),whotypicallyhavereduced intraocular light scatter.19---21 In orderto ensure against a two-sidedtype1errorof0.05,andtodetectaunitary min-imumdifferencebetweenthedifferenttypesoflenseswith a power of0.80, 20 participantswere recruited for each group.Theinclusioncriteriaweretheabsenceofanyocular pathology,havingabinocularbest correctedvisual acuity (BCVA)ofatleastlogMAR=0.1(logarithmsoftheminimum angleofresolution),havinggoodbinocularvision(no anoma-liesinocular motility, heterophoriasatdistance andnear and fusional reserves at distance within the limit of the expectedvalues,22nosuppression,andastereoscopicacuity ofatleast60arcsec),andbeingregularwearersofeither progressiveadditionlenses(tobeincludedinthePALgroup) orregularwearersofsinglevisionlenses(tobeincludedin theSVLgroup).Thelattercriteriaenabledeachparticipant to wearthe testlensesas normal,andthereforebe fully exposedto the conditionsofthe experiment. One partic-ipant in the PAL group dropped out the study during the secondphase(Fig.1).ThestudywasapprovedbytheEthics Committeeof the UniversityofMilanoBicocca (prot.Int. 0059770/17,classif.II.18,C.IPAunimibC.AOO:AMMU06,C. reg.prot.:RP01).Beforebeingenrolled inthe studyeach subject expressedhis/her informed consent and gavethe researchers permission to collect and treat personal and optometricdata.Thesubjectstookpartintheproject spon-taneouslyandforfree.
Visualassessment
A preliminary eye and visual examination was performed todeterminewhethereachsubjectwaseligibleinrespect to the inclusion criteria and to find the best ophthalmic correction (preliminary visual assessment in Fig.1). Oph-thalmoscopyandslit-lampexaminationwerecarriedoutto detect any ocular anomaly. The presence of an anomaly in ocular motility was investigatedby the H pattern test thatisconsideredreasonableforthepurposeandeasierto performinaclinicalsettingthanothertechniques.23---25 Non-cycloplegicsubjectiverefractionatdistancewascarriedout byaphoropter procedure.Themean sphericalequivalent
wascalculatedforeacheyeasthealgebraicsumofthevalue ofthesphereandhalfofthecylindricalvalueandreported separatelyforthetwogroups.TheadditionfornearinPAL groupwasfirstlydeterminedaccordingtotheexpectedage andthenadjustedsubjectively.25Bestcorrectedvisual acu-ity(BCVA)wasmeasuredwiththeopticalcorrectionatfar distancearrangedinatrialframeatadistanceof4musing high-contrast(97%)ETDRSchartdisplayedonanLCD opto-typesystem(VisionChartCSO,Florence,Italy).Thevisual acuitythresholdwasdetermined inlogarithmof the min-imumangleofresolution(logMAR)usingaletter-by-letter criterion.26Dissociatedheterophoriaseitheratdistanceand near,weremeasuredthroughanalternatingcovertestand prismbar.Fusionalreservesatdistanceweremeasuredwith prismbar.ApossiblesuppressionwasevaluatedbytheWorth 4-Dottest at distance,and stereoscopic acuity was mea-suredthecirclessubtest(Wirtrings)oftheStereoFlyTest (StereoOpticalCo.)atadistanceof40cmwiththeoptical correctionatneardistancearrangedforbotheyesinatrial frame.
After theenrolment inthe study,eachparticipantwas asked to choose a frame among a limited setof frames. Threepairsofglasseswiththesamechosenframeandthe optical prescription determined in the preliminary visual examinationweredispensedforeachsubjectwiththethree differentlensesstudied,whose propertiesarereportedin theMaterialsparagraphbelow.Severalpsychophysical mea-surementswerecollectedbothonthefirstday(whenglasses weredispensed)andafterfifteendaysofwearforeachtype oflens(threephasesinFig.1).Allthemeasurementswere takenwiththedispensedglasses.Particularattentionwas placedonmaintainingappropriateprimarypositionofgaze throughPALspectacleswhenassessingvisualperformances inPALgroup.Duringtheseexperimentalphases,both pho-topic BCVA (BCVAphotopic) and mesopic BCVA (BCVAmesopic) weremeasuredbinocularlythroughapaperETDRSchartat 4m.Inthephotopiccondition,theilluminationintheroom was450±50lx,whileBCVAmesopicwasmeasuredindimming roomlighting(8±2lx), afteranadaptation period offive minutesindarkroomconditions.DifferentversionsofETDRS chartswereusedforthe measurementsofBCVAphotopic and BCVAmesopicinordertoavoidapotentiallearningoftheletter array.BCVAunderglare(BCVAglare)wasmeasuredbinocularly at3mthrough anhigh-contrastETDRS optotypesetonan LCDmonitorwhilethesubjectsweredazzledbytwowhite LEDlamps(C.O.I.,Italy,mod.50.041.00)locatedlaterally onthesidesoftheLCD.TheemissionspectrumoftheseLED sourcesisreportedintheinsetofFig.2,asmeasuredbya spectrophotometerHamamatsuC10082CAH.Finally, binoc-ularphotopiccontrastsensitivity(CS)wasdetectedthrough FunctionalAcuity ContrastTest(backgroundluminance of 60.0±3.3cd/m2)at3-meterobservationdistanceand the thresholdmeasuredaslogarithmofthecontrastsensitivity (logCS).Theinvestigatedangularfrequencieswere1.5,3.0, 6.0,12.0,18.0cycles/deg.
Materials
Figure1 Flowdiagramofthestudydesign.
(Eyas®,Hoya,Japan)withthe samerefractiveindexnD at thewavelengthoftheFraunhoferDspectralline(589.3nm). In addition to nD, some otherproperties of the three fil-tersarereportedinTable2,whereVistheAbbenumber. Theopticaltransmittancespectraofthethreelenseswere measuredusingaJascoV-650spectrophotometer.Thesingle vision controllenseswerefrontasphericalstandardsingle vision lenses(Nulux®, Hoya,Japan),the singlevision STD andthePROwerebothpowerbypowerasphericaloptimized on back side atoric lensesoptimized for a standard posi-tionofwear.Theprogressiveadditionalcontrollenseswere madewithafrontdesignapproach,14mmcorridorlength andpower-basedvariableinset.TheSTDandthePROwere bothFreeFormintegrateddoublesurfacedesignwith15mm corridorlength,individualinsetbasedonpower,individual monocularpupildistance,andworkingdistancethatis cal-culatedatstandardof40cmforSTDversionand at60cm (dashboard)forPROversion.Aprecalibrationwasincluded tobetterfittheframechosenbythesingleparticipant. Studydesign
AdiagramshowingthestudyprocedureisreportedinFig.1. A singleblind crossoverstudy wasperformed. Althougha
Figure2 Transmittancespectrum ofthe threetypesof fil-ters (planolenses) and spectrum of humanmacular pigment takenfromtheopticaldensity(OD)reportedinWerneretal.29
(transmittance=10− OD).Inset:Measuredemissionspectrumof
thewhiteLEDlampsusedasglaresourcetomeasureBCVAglare. clearlensesattheendofthestudy(afterthethirdphase). Finally,oncethe subjectshad wornallthreelenses,they wereaskedtomakeasubjectivechoiceaboutwhichlenses theywantedtokeepattheendofthestudy.
Statisticalanalysis
Descriptive statistics wasproducedforthe measurements collectedduringpatients’visits.Numerosity(N)andrelative percentage values (%) have beenreported for each level ofthe categoricalvariables, whileforthenumerical ones mean,standarddeviation(SD),minimumandmaximumhave beencalculated.Analyseswereperformedforallsubjects andseparatelyforSVLandPALgroups,differencesbetween thesegroupswereevaluatedusingchi-squareandt-testsfor independentsamples(p-value<.05).
Foreachtypeoflens(clear,STD,andPRO)acomparison was carriedout by t-testto identify similarities between the data collected at baseline and the data collected in the post-treatment phase after fifteen days. A raw com-parisonbetweenSTDdriveandPROdriveversusClearlens wascarriedoutbypairedt-test,separatelyforSVLandPAL group.
Concerningthedatacollectedattheendofthesecond weekofwear,alinearmixedmodel(recommendedfor2×2 crossovertrialswithbaselinemeasurements27,28)was imple-mentedtocomparethe2lenses(STDDRIVEandPRODRIVE). In this model, post-treatment measurements of all three investigatedtypesoflenses(Standard,STDDRIVEandPRO DRIVE)havebeenevaluated.Sincemeasurementswiththe threefilterswereperformedonthesamesubject, correla-tionwithinthesubjectwastakenintoconsiderationandthe singlesubjectwasconsideredintherandomeffectsofthe model.Inthemixedmodel,themeasurementcollectedwith
clearlenses;thesequenceofdeliveryofspectaclesandthe periodwereincludedasfixedcovariates.ThetypeofDrive lens(STDorPRO)wasalsoincludedwiththeaimto evalu-atethe differencesintheperformancebetweenmeasures ofPROandSTDlenses,conditionedtothevalueobserved withtheclearlens.28
AllanalyseswereperformedusingtheStatisticalAnalysis SystemSoftware(version9.4;SASInstitute,Cary,NC,USA). Statisticalsignificance was setat 0.05 level. All p-values weretwo-sided.
Results
InSVL group, 11males and 9 females (age range: 24---55 years;mean±stddev:47.8±14.7years)wereenrolled.In PALgroup,10malesand10females(agerange:46---73years; mean±std dev: 59.5±7.2 years) were enrolled. Demo-graphiccharacteristics ofthe whole sample,and the two groupsseparately,arereportedinTable1.
Theopticaltransmittancespectraofthreeplanolenses (clear,STD,andPRO)arereportedinFig.2.Acutoff wave-lengthcanbedefinedasthewavelength correspondingto 50%transmittance.Fortheclearlensthecutoffisfoundat (405±2)nm,whilethecutoffofSTDandPROisshiftedto longerwavelengthanditisfoundat(426±2)nm.Boththe STDlensandthe PROlenshaveatransmittancethatdoes notsubstantiallydependonthethicknessofthe lensand, therefore,ontheopticalpower.Indeed,thelongpass char-acteroftheselenseswithcutoff at(426±2)nmisdueto abulkinternallayer offixedthickness thatthe manufac-turerhascalled‘‘high-definitiontreatment’’.InFig.2,the spectrumofhumanmacularpigmentisalsoshownastaken fromtheopticaldensityreportedinWerneretal.28Itwill becommentedinthediscussionsection.
Table1 DemographiccharacteristicsandMeanSphericalEquivalentvaluesofthe20participantstothestudy,consideredas awholeandseparatelyforSVLorPALlensgroup.
Wholesample(n=40) SVLagroup(n=20) PALbgroup(n=20) p-value
Gender Men 21(52.5%) 11(55%) 10(50%) 0.75* Women 19(47.5%) 9(45%) 10(50%) Age(years) Min;Max 24;73 24;55 46;73 <0.0001** Mean(SD) 47.8(14.7) 35.9(9.8) 59.5(7.2) MSEc(D)righteye
Min;Max − 6.88;5.38 − 6.88;2.38 − 5.13;5.38 <0.001** Mean(SD) − 1.20(2.91) − 2.49(2.50) 0.09(2.67)
MSEc(D)lefteye
Min;Max − 7.00;5.88 − 7.00;2.75 − 5.00;5.88 <0.001** Mean(SD) − 1.08(3.07) − 2.44(2.67) 0.29(2.88)
BinocularBCVA(logMAR)
Min;Max − 0.26;0.08 − 0.24;0.08 − 0.26;0.06 0.27** Mean(SD) − 0.11(0.09) − 0.13(0.09) − 0.09(0.09)
aSinglevisionlenses. b Progressiveadditionlenses. c Meansphericalequivalent. * pvalueaccordingto!2.
** pvalueaccordingtot-testforindependentsamples.
Table2 Propertiesofthelensesusedinthestudy.
Clearlens STD PRO
Anti-reflectioncoating SuperHi-vision® ARDrive® ARDrive®
nD 1.592 1.592 1.592
V 41 40 40
Figure 3 Mean values of measured binocular BCVAphotopic,
BCVAmesopic,andBCVAglare forthethreetypesoflensesinPAL group (a) and in SVL group (b). Asterisks indicate that the observeddifferencecomparedtoclearlensisstatistically sig-nificant (p<0.05, grey asterisks for STD compared to clear lenses,blackasterisksforPROcomparedtoclearlenses). and b(SVL group)asa functionofthe angular frequency. CS showed statisticallysignificant improvements withthe PRO lens respect to the clear lens only at 6 cycles/deg forthePALgroupand at1.5 cycles/degfortheSVLgroup
(p<0.05).Conversely,thedifferencebetweenSTDandclear lensesbecomeevidentandstatisticallysignificantat6,12, and18cycles/deginthePALgroup(p<0.05)butonlyat12 cycles/degintheSVLgroup.
Table3shows the correspondingdata foreachtypeof lens,includingalsostandarddeviationsandp-values. Con-cerning the comparison between the two types of Drive lenses (STD and PRO), both for PAL wearers and for SVL wearers,the95%confidenceintervalofthedifferenceswas evaluatedforeachmeasuredvariable(conditionedto the valueobservedwiththeclear lens).Theestimated differ-enceswerefoundtoshowa95%confidenceintervalwhich containsthenullvalue.Theresultsoftheparticpants’ sub-jectivechoicearereportedinTable4.Mostparticipantsin thePALgroupchoseDrivelenses(15subjectsoutof19,79%) withonlyfoursubjectselectingtokeeptheclearPALlenses. Drivelenseswerealsothefirstchoiceofparticipantsinthe SVLgroup(12subjectsoutof20,60%).Thedifferenceinthe frequencydistributionbetweenPALgroupandSVLgroupwas notsignificant(!2=2.31;n.s.).
Discussion
Table3 Mean,andstandarddeviation(SD)ofthemeasuredvaluesforeachvariableandeachtypeoflens. Lenstype
Clearlens STDDRIVE PRODRIVE p-value* p-value**
PhotopicBest CorrectedVisual Acuity PALagroup − 0.08±0.08 − 0.07±0.08 − 0.08±0.09 .891 .37 SVLbgroup − 0.13±0.09 − 0.13±0.07 − 0.14±0.07 .601 .290 MesopicBest CorrectedVisual Acuity PALagroup 0.15±0.11 0.12±0.09 0.13±0.11 .033 .197 SVLbgroup 0.07±0.07 0.06±0.07 0.07±0.08 .597 .804
BestCorrectedVisual Acuityunderglare
PALagroup 0.03±0.14 − 0.02±0.17 − 0.01±0.13 .007 .017
SVLbgroup − 0.08±0.07 − 0.12±0.09 − 0.12±0.09 .002 .008
logCSc1.5cycles/deg PALagroup 1.65±0.14 1.67±0.14 1.70±0.12 .320 .138
SVLbgroup 1.76±0.15 1.81±0.19 1.83±0.17 .163 .032
logCSc3.0cycles/deg PALagroup 1.81±0.13 1.84±0.11 1.86±0.10 .376 .177
SVLbgroup 1.98±0.14 2.00±0.17 2.00±0.12 .450 .579
logCSc6.0cycles/deg PALagroup 1.84±0.15 1.92±0.15 1.91±0.10 .011 .008
SVLbgroup 2.06±0.14 2.06±0.16 2.06±0.16 .987 1.000 logCSc12.0 cycles/deg PALagroup 1.50±0.15 1.59±0.20 1.54±0.21 .013 .081 SVLbgroup 1.77±0.15 1.87±0.16 1.82±0.21 .019 .222 logCSc18.0 cycles/deg PALagroup 1.10±0.23 1.21±0.31 1.16±0.27 .030 .109 SVLbgroup 1.45±0.25 1.49±0.22 1.44±0.20 .336 .815 a Progressiveadditionlenses.
b Singlevisionlenses. c Contrastsensitivity.
* Valueaccordingtot-testforpaireddataonmeanvaluesofSTDDRIVEvsclearlens. ** Valueaccordingtot-testforpaireddataonmeanvaluesofPRODRIVEvsclearlens.
Figure4 Meanvaluesofbinocularcontrastsensitivityforthe three typesin PAL group (a)and in SVL group (b). Asterisks indicatethattheobserveddifference comparedtoclearlens isstatisticallysignificant(p<0.05,greyasterisksforSTD com-paredtoclearlenses,blackasterisksforPROcomparedtoclear lenses).
Table4 Numberofsubjects,andrelativepercentage,who
wantedtokeepeachtypeoflensaftertestingallthethree typesforawearingperiodoftwoweeks.
PALgroup SVLgroup
Clearlens 4(21.1%) 8(40.0%)
STD 9(47.4%) 9(45.0%)
PRO 6(31.5%) 3(15.0%)
and !750nm 400nm S(!) TPRO(!) d! !750nm 400nm S(!) Tclear(!) d! (1.b)
represent the percentage ofthe total numberof photons in the visible range transmitted bythe Drive filters com-paredtotheclearlens,whereTclear("),TSTD("),andTPRO(") arethe transmittancespectraofthethreetypesoffilters (Fig.2).Forexample,forthetypicalemissionspectrumS(") of awhite LED, theseratios werecalculated to be 96.0% (STD)and93.6%(PRO).Byassumingadifferentlightsource, namelysolarradiation,theywerecalculatedequalto92.9% (STD)and91.3%(PRO).Thecalculatedvaluesindicatethat theattenuationofthetotalnumberofphotonsinthe visi-blerangecomparedtotheclearlensisverysimilarforthe twoDrivelensesanditisintherangeofsomepercentage points.Ifradiantenergyisconvertedintoluminousenergy bytakingintoconsiderationthespectralluminousefficiency functionV(")ofthehumaneyeinphotopiccondition,30the ratios !750nm 400nm S(!) E (!) V (!) TSTD(!) d! !750nm 400nm S(!) E (!) V (!) Tclear(!) d! (2.a) and !750nm 400nm S(!) E (!) V (!) TPRO(!) d! !750nm 400nm S(!) E (!) V (!) Tclear(!) d! (2.b) representthepercentageoftheluminousenergy transmit-tedbytheDrive filterscomparedtotheclear lens,where E(")isthe energy ofonephotonofwavelength"(in vac-uum).ForthetypicalemissionspectrumS(")ofawhiteLED, theseratioswerecalculatedtobe95.20%(STD)and94.4% (PRO). Byassuming adifferent light source, namely solar radiation,they were calculatedequal to 95.1%(STD) and 94.4%(PRO).
Conceringchromaticaberration,the shiftofthecutoff from(405±2)nmto(426±2)nmisexpectedtoreducethe chromaticaberrationofthehumaneye.Longitudinal chro-maticaberrationoftheeyeisreportedbymanyauthorsto be ofthe orderofabout 2diopters whenconsideringthe whole visible range.31---35 Basedon these data reported in theliterature,longitudinalchromaticaberrationisreduced of about 0.3 diopters when reducing the spectral range form405---750nm(rangeoftransmissionoftheclearlens)to 426---750nm(rangeoftransmissionoftheDrivelenses). Con-cerningthe aberrationofthelensitself,thelongitudianal chromaticaberrationoftheclearlensandthatoftheDrive lensescanbeevaluatedtakingintoconsiderationtheirAbbe numberVandtheirrefractiveindexataspecificwavelength (Table1).ThedifferencebetweenclearandDrivelenseswas foundtobemorethanoneorderofmagnitudelowerthan thereduction(∼0.3diopters)ofthelongitudinalchromatic aberrationoftheeye.
Intraocular light scattering can be generated by dif-ferent components of the eye and it can show different characteristics.19---21,36,37 Forexample,backwardlight scat-tering in the crystalline lens was found to vary with wavelength"intothenucleusasthereciprocalofthefourth power ("− 4) as predicted by the Rayleigh model.37 Con-versely,inthesuperiorlayersandforforwarddirectionsin
thenucleus,lightscatteringwasfoundtobelessdependent on wavelength.37 Intraocular scatteringwasalso found to dependstronglyonpigmentationoftheeyeandage, scat-teringshowingnearlyperfect"− 4dependenceonlyinyoung andwell-pigmentedeyes.21Eveniftheoveralldependence onwavelengthcandeviatefromtheperfect"− 4law, intraoc-ularlight scatteringis knownto typically increaseat the shortestwavelengthsinthevisiblerange.Theeffectsbegin tomanifestatthelowestwavelengthsintheageperiod cor-respondingapproximatelytotheSVLgroupofthisworkand thenextendtolongerwavelengthwithage.Thereforethe Drivelenses,whichattenuatelightbelow(426±2)nm,are expectedtoplayaroleinreducing intraocularscattering, mainlyinthePALgroup,buteventuallyalsointheSVLgroup. ThePROlensesshowaweakadditionalopticalbandcentred at450nm(Fig.2),whichdoesnotappearintheSTD spec-trum.Thisbandisduetoasurfacetreatmentthatdiffers fromthe STDlens. Interestingly,thisbandisverycloseto themaximumofabsorptionofthemacularpigmentofthe humaneye(alsoreportedinFig.2forcomparison),which peaksatabout460nm.28,37,38Althoughthefunctionof mac-ular pigmentremains uncertain, it is suspected ofacting asanaturalopticalfilter,absorbingpartofthebluelight, thus partially reducing chromatic aberration and intraoc-ularscattering.39---43 Inthe spectralrangeofabsorptionof themacularpigment,betweenabout430nmand500nm,it appearsthattheeyenaturallyprotectsitselffrom scatter-ingandaberration,atleastforyoungandhealthysubjects. However,itcouldbeinterestingtoinvestigatewhetherthe PROfilter,withitsadditionalbandatabout450nm,has posi-tiveeffectsincaseofapossibedecreaseofmacularpigment densityinelderlyorpathologicalsubjects.
accompa-nied byasignificantimprovementinBCVAphotopic.Alsothe additionalbandat450nmofthePROlensdoesnotseemto producedetectableeffectsinBCVAphotopic.
The other optometric analysis carried out in photopic conditionisthe CSassessment. Thefirstpoint concerning CSisthecomparisonbetweenclearlens(blackdiamondsin Fig.4)andSTD(graycirclesandgrayasterisksinFig.4).In general,ascanalsobeobservedinTable3,allmeandata ofCStakenwithSTDtypeareequalorbettercomparedto thecorrespondingvaluefortheclearlens.No statistically significantimprovementatthe lowestangularfrequencies isfoundinbothgroups(PALandSVL).InthePALgroupthe differencesbecomeevident andstatisticallysignificantat 6,12,and18cycles/deg(p<0.05;Fig.4aandTable3).In theSVLgroupthedifferencebetweenSTDandclearlensis significantonlyat12cycles/deg(Fig.4b).Datafortheother Drivelens(PRO)showthatallmeandataofCStakenwith PROtypeareequalorbettercomparedtothecorresponding valuefortheclearlens(Table3,Fig.4).CSisstatistically betterthanCSwithclearlensesat6cycles/deginthePAL group(blackasterisk inFig.4a),and at1.5 cycles/deg in SVLgroup(blackasteriskinFig.4b).Intheliterature,mixed resultsarereported.Forexample,Zigmanfoundthata yel-lowfilterimprovedsignificantlyCSofsubjectswithhealthy eyesinthe3---12cycles/degrangeofspatialfrequency.8On thecontrary,blue-lightfilteringspectaclelensesdidnot sig-nificantly affect the contrast sensitivityin arecent study ofLeungetal.16 Inthe presentwork, acertaindegree of improvementofphotopicCSbyDrivelensescanbeinferred comparedto theclear lens.Compared toBCVAphotopic,the measurementofCSisamorecompleteassessmentofvisual performance,44,45thusmakingtheeffectsduetotheshiftof thecutoffdetectable,atleastatsomeangular frequency. Thisimprovementcanbemainlyattributedtoareductionof intraocularscattering,whichisknowntoplayamajorrole inCSreduction.46,47Ontheotherhand,thereduction(about 0.3diopters)oftheeyechromaticaberrationwiththeDrive lenses is not expected to play a role in improvimng CS. Indeed,thespectralluminousefficiencyofthehumaneye inphotopicconditionisrelativelylowattheshortest wave-lengths inthe visible range.30 Experimental evidence was providedbyKrugeretal.,33whofoundnodifferenceswhen measuringCSwithorwithoutaneutralizinglensinplace. Theneutralizinglenswasdesignedtofocusallwavelengths approximatelyinthesameplaneintheeyesothattherewas nolongitudinalchromaticaberration.AstheeffectonCSis absentbyneutralizingtheaberration,itisexpectedtobe absentevenchromaticaberrationispartiallyreduced(∼0.3 diopters),asinthecaseofDriveslenses.Ascanbeobserved forthePAL groupinFig.4a,ithappenedatseveral angu-larfrequenciesthattheSTDlenswasbetterthantheclear lens(threegreyasterisksinFig.4a)comparedtohowmany timesithappenedwiththePROlens(oneblackasteriskin Fig.4a).However,thedirectcomparisonbetweenthetwo lensesdid not support any significantdifference between STDandPRO.Indeed,whencomparingthetwoDrivelenses, based on 95% confidence interval for CS data, there was nostatisticalevidenceofdifferencebetweenthem. There-fore,thepossiblepositiveeffectsoftheadditionalbandat 450nmisnotsufficientlymarkedtogenerate,onaverage,a detectablevariationinSCtests,evenintheoldersubjects ofthePALgroup.
In additionto BCVAphotopic,BCVAmesopic has beenstudied inthis work and, although clinically small, a statistically significant improvement compared to the clear lens was observed.BCVAmesopic changedinPALgroupfrom0.15 log-MARto0.12logMARinthecaseofSTD(p<0.05)andto0.13 logMARinthecaseofPRO.Nosubstantialdifferenceswere observedbetweenthethreelensesforBCVAmesopicinthecase ofSVLgroup.Itiswellknownthatthecurveofthespectral efficiencyofthe humaneye depends onthe environmen-talconditions.Inmesopiccondition, themaximumof the curveshiftstowardthebluecomparedtothemaximumin photopiccondition(Purkinjeshift).Forthisreason, intraoc-ularscattering ofblue light, especially in older subjects, acquiresmorerelevanceinmesopicconditions.Thismight explainthe positiverole of the Drive lenses inimproving BCVAmesopic ofthePAL group.Althoughitisexpectedboth areductionoftheintraocularscatteringandareductionof thechromaticaberrationoftheeyewiththeDrivelenses,it isreasonabletoassumethattheimprovementofBCVAmesopic ismainlyattributabletothereductionofthescattering.
In this work, the main improvement was found under glareconditions.BothSTDandPROshowedbetterBCVAglare performancesthanclear lensesandthe improvementwas statistically significant, about 0.05 logMAR, for both PAL group and SVL group. Concerning the direct comparison betweenthe two Drive lenses,no statistical evidence of differences in BCVAglare was found bothin PAL group and SVLgroup.Areasonableexplanationfortheimprovement ofBCVAglarebyablue-filteringlensisagaintheattenuation ofintraocularscattering,whichisknowntoplayarelevant roleunderglare.19---21,48Itisknownthatintraocular scatter-ingincreasesgraduallywithage.19---21 Asalreadydiscussed, the effects begin to manifest at the lowest wavelengths intheageperiod correspondingapproximatelyto theSVL group. In older subjects, the effect at the lowest wave-lengthsincreasesanditalsoextendstolongerwavelengths. ThezerotransmittanceoftheDrivelensesintheblueregion upto(426±2)nmattenuatesintraocularscattering.Since thisspectralrangecorrespondstoarerionofscatteringeven intheagerangebetweenabout30and50years,theDrive lensesarealsoeffectiveinreducingintraocularscattering intheSVLgroup,notonlyinthethePALgroup.AlsoMahjoob etal.9recentlyreportedthepositiveeffectofayellowfilter onvisualacuityunderglare,thoughthe improvementwas onlysignificantinsubjectsaged51---60years.However,the onlyinformationavailable aboutthe spectral characteris-ticsofthisyellowfilteristhetotallighttransmission(80%). Itisnotspecifiedwhetherthereductionintransmittanceis duetothepresenceofaspecificabsorptionbandcentred somewhereinthebluespectralregionortotheshiftofthe cutoffasoccursinlongpassfilters.
Notwithstand-ing this,itcannotbeexcludedthat onlyaminority chose theclearlensbecauseoftheorderinwhichthethreefilters wereworn.AsshowninFig.1,infact,alltheparticipants woretheclearlensforthefirstfifteendays.The optomet-ricdatawereacquiredagainattheendoftheprojectwith theclearlensandtherewerenodifferenceswithrespectto phase1,buttheordermayhaveinfluencedthesubjective choice.
Conclusions
Theeffectsofcoloredfiltersonvisualperformanceis depen-dent on the balance between the possible reduction of chromaticaberrationandintraocularlightscatteringvs.the undesirable though unavoidable reduction of transmitted lightintensity.STDandPRODrivelensesarelongpass trans-mittancefilterswithcutoffat(426±2)nm,shiftedtolonger wavelengthofabout20nmcomparedtoaclearcontrollens. TheonlydifferencebetweenSTDandPROisanadditional bandcentredatabout450nminthePROspectrum,inthe samespectralregionoftheabsorptionofthehumanmacular pigment.
Both Drive lenses are found to maintain or improve some visual functions compared to the clear lens. The improvementofphotopiccontrastsensitivityatsome angu-lar frequencies, mesopic visual acuity, and visual acuity underglareismainlyattributedtothereductionof intraoc-ular light scattering as a consequence of the total light attenuationinthebluespectralrangebelowthecutoff.The improvementisobservedinoldersubjects(agerange:46---73 years,PALgroup).Foryoungersubjects(agerange:26---55 years,SVLgroup),itisdetectableforallbutmesopicvisual acuity.
Conflicts
of
interest
Hoya Corporation Vision Care (Tokyo) partly funded this study.NataliaVlasakandSilvanoLarcherarefullyemployed inHoyaVisionCare.Alltheotherauthorsreportnoconflicts ofinterest andhaveno proprietaryinterestinany ofthe materialsmentionedinthisarticle.
Acknowledgements
ThiswasacollaborativeresearchsupportedbyHOYA Cor-poration, Tokyo,Japan.The authorsthankthe employees ofHoyawhoparticipatedinthecalculation,ordering,and manufacturingofthelenses.Co-authorsNataliaVlasakand Silvano Larcher provided spectacles and the employee of Hoya.
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