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Spectacles Lenses - Vision Express India
The document provides an overview of spectacle lens materials, highlighting their optical characteristics, advantages, and disadvantages. It covers different types of lenses, including mineral, organic, polycarbonate, trivex, and various treatments such as anti-reflective coatings and tints. Additionally, it explains specialized lenses like polarized and photochromatic lenses, along with their intended uses and benefits.
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Spectacles Lenses - Vision Express India
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- 2. Spectacle Lenses • SpectacleLensmaterials: Materialsforspectacle lensesmustcomplywiththe followingoptical characteristics: • Good optical homogeneity • Highluminoustransmission • Low scatteredlightcreation • Chemical resistance • Temperature resistance • Good mechanical resilience 1. Mineral / Glassmaterial Lenses: • Glasslensesare the oldestmaterial usedforspectacle lensesbutrarelyusedtodayasit isbrittle and heavy. • Theyhave excellentopticspropertiesandare scratchresistantbutunfortunatelytheyare approximately33 percentheavierthantraditional plasticlenses(CR39) andthe leastsafe forimpact resistance. Advantages: • Hightransparency • HighAbbe Value • Highlyscratch resistant • Good Optical Quality • Resistanttochemical fumesandtemperature fluctuation • Available inphotochromatic&sunglassoption Refractive Index: • Mineral 1.5
- 3. • Mineral 1.60:20% thinnerthanMineral 1.5 • Mineral 1.70: 30% thinnerthanMineral 1.5 • Mineral 1.80: 40% thinnerthanMineral 1.5 • Mineral 1.90: 50% thinnerthanMineral 1.5 Disadvantages: • Heavy • Easilybreakable 2. Organiclensmaterial lenses: Advantages: • Hightransparency • HighAbbe Value • PopularOptical material • Good Optical Quality • Resistanttochemical fumesandtemperature fluctuation • Available insunglassoption –photochromatic,tintandpolarised Refractive Index: • Organic1.50 (CR39): 40% lighterthanmineral lenses • Organic1.6 : 20% thinner&lighterthanorganic1.5 • Organic1.67 : 35% thinner&30% lighterthanorganic1.5 • Organic1.74 : 43% thinner&32% lighterthanorganic1.5 Disadvantages:
- 4. • Thickerthan glass •Gets scratchedwhennotcoated 3. Polycarbonate Material: Advantages: • 23% thinner&25% lighterthanOrganic1.50 • 12 timesmoreshatter-proof thanOrganic1.50 • Has a veryhighimpactresistance –ideal forprotective eyewearandsportsglasses • Has a veryhighmechanical resistance • Can be groundverythinly – verylight • Good optionforrimlessandkidsasit has highimpactresistance Refractive Index: • Available in1.6index only Disadvantages: • Has a tendencytogetstressinducedcracks • Low scratch resistance –is systematicallyproducedwithahard coating • Can be tintedtoa limiteddegree • Polycarbonate hasa lowerabbe numberleadingtoloweroptical image properties 4. Trivex Material: Advantages: • 20% thinnerthanOrganic1.50 • lightestlensmaterial
- 5. • Ideal forrimlessframes •12 timesmoreshatter-proof thanOrganic1.50 • Has almostthe same refractionindex asCR39 butcan be groundmore thinly • Has a veryhighimpactresistance–ideal forprotectiveeyewearandsportslenses • Is chemicallyresistanttosolvents • Has verygood optical characteristics • Is with1.11 g/m3the lightestmaterial forlenses • Is toughand hard-wearing–easytodrill,groove andcut • Providesanalternative toOrganic1.50 as a standardlensbecause itislighterandtougher • Is systematicallyproducedwithahard coating • Trivex hasbetteroptical image propertiesthanpolycarbonate. Refractive Index: • Available in1.53index only • Anti-reflectionCoating: • To improve boththe visionthroughthe lensesandthe whole appearance of the glasses,ananti- reflectivecoatingcanbe appliedtothe lenses.ARcoatingsmake the lensesclearertolookatand through. • Theyconsistof several layersof metal oxidesappliedtothe frontor back lenssurfaces.Because of the layeringeffect,ARcoatingssometimeshave ahintof greenorpurple colour,dependingonthe individualmanufacturer’sformula. Eachlayerisscientificallycalculatedtoblockreflectedlight.The resultisthat you’ll see areductioninglare,annoyingreflectionsandhalosaroundlightswhilewearing the lenses.Thisisagreat safetybenefitwhenyou’re drivingatnight. • Anti-reflectivecoatingreducesbothinternal andexternalreflectionsonthe lensesthemselves, creatinga nicercosmeticappearance.Internal reflectionsappear,asringsthat make lenseslookthick. External reflectionsmaskyoureyesfromaclear,complete view whensomeone islookingatyou.So withan anti-reflective coating,lensesappearthinornon-existent,andyoureyeslookmore natural.
- 6. • Anyone onTVor whose photo istakenoftenbenefitstremendouslyfromthe betterappearance of ARcoated lenses,butreally,all eyeglasswearerswouldbenefitfromananti-reflective coatingfroma cosmeticpointof view.If youhave a strongprescription,youcanuse the AR coatingin conjunctionwith high-index orthinnerlensestomake yourglasseslookandfeel asthinaspossible. • Tints: • While some peoplethinkcolouredcontactlensesare merelycosmeticfunctions,the righttint can enhance visionandcomfortat specific tasks,frominthe office infrontof a computerscreen,to outdooractivitiessuchasgolf or skiing.Tintscome insolids,gradientsordouble gradients,andcanbe a fununique touchto yourlenses. • Pinkor Rose: • Thistint hasbeenknowntohelpreduce eyestraininbrightly-litoffices.Thistintisoften recommendedforcomputerwearers. • Yellow: • Oftenknownasblue blockers,yellow tintsare afavorite of skiersandskeetshootersbecause theyprovide excellentdepthperceptionandlow light contrast. • Yellowlensesare notrecommendedwhenaccurate colorperceptionisnecessary. • Brown: • Similartothe yellowtint,browntintsprovideexcellentcontrastbecause theyfiltersome blue light,butnot as muchas the yellowtint. • Brown lensesare excellentgeneral purposelenses. • Green: • The human eye ismostsensitivetogreenlight.Because of this,greentintsgiveusthe highest contrast andgreatestvisual acuityof any tint. • Greentintscan enhance contrastin low-lightconditions.
- 7. • Gray: • Themost populartint,a gray tintprovidesgoodprotectionfromglare anddoesnotoverly distortcolors. • Gray tintedlensesare excellentforgeneral purpose andfordriving. • Purple: • A goodchoice for hunters,purple tintsallowsfornatural colorperceptionwhileofferingsome shade fromthe sun. • Blue: • Blue tintsare not recommendedforoutdooruse because itcanincrease glare.Itcan be usedas a fashiontintif usedinlightershades. • If blue colouredcontactlenses are desiredforoutdoorwear,be sure toconsiderthe optionof a brownor gray polarizedlenswithablue flashmirrorcoat • AsphericLenses: • The asphericlensdesignthatcan be usedinmost lensmaterials. • The designof the lenscreatesa flatter,thinnerandlessdistortedlensthantraditional designs. • In general itachievesthisbychangingthe radiusof curvature the furtherfromthe centerof the lens. • Asphericlensesare anexcellentchoice forpluspoweredlenses • Asphericscanbe alsocombinedwithhighindex materialsanditcreatesanexcellentdesignfor cosmeticandoptical purposes. • PolarizedLenses: • Polarizedlensesare usedforprescriptionsunglasses. • Polarised filtersare made of a chemical filmappliedtoatransparentplasticorglasssurface.
- 8. • The chemicalcompoundusedwill be composedof moleculesthatnaturallyaligninparallel relationtoone another. • Whenapplieduniformlytothe lens,the molecules create amicroscopicfilterthatabsorbsany lightmatchingtheiralignment. • Most of the glare that causesyouto wear sunglassescomesfromreflectionoff of horizontal surfaces,suchas wateror a highway. • Whenlightstrikesasurface,the reflected lightwavesare polarizedtomatchthe angle of that surface.So,a highlyreflective horizontal surface,suchasa lake or the sea,will produce alot of horizontallypolarizedlight. • The polarizedlensesinsunglassesare fixedatan angle thatonlyallowsverticallypolarizedlight to enterthe eye hence reducingthe glare. • PhotochromaticLenses: • Photochromiclensesare eyeglasslensesthatdarkenautomaticallywhenexposedtosunlight, thenfade back whenyoureturnindoors. • In mostcases, photochromic lensesare clear(ornearlyclear) indoorsanddarkentoa medium suntint outdoors.Butthere are exceptions. • Photochromiclensesare available innearlyall lensmaterialsanddesigns,includinghigh-index lenses,bifocalsandprogressive lenses. • An addedbenefitof photochromiclensesisthattheyshieldyoureyesfrom100 percentof the sun’sharmful UVA and UVB rays. • Because a person’slifetime exposuretosunlightandUV radiationhasbeenassociated withcataractslaterinlife,it’sagood ideatoconsiderphotochromiclensesforchildren’seyewearaswell as for eyeglassesforadults.