PHOTOCHROMATIC LENSES. BY OPTOM. JITHIN JOHNEYpdf

Discover the transformative technology behind photochromatic lenses and how they enhance vision in varying light conditions. This presentation dives deep into the science, benefits, and applications of photochromatic lenses, making it an essential resource for optometrists, eyewear professionals, and anyone interested in advanced optical solutions. Learn about the mechanisms that enable these lenses to adapt to changing light, the types of photochromatic materials used, and the latest innovations in the field. Whether you're looking to educate clients or expand your knowledge, this PPT offers comprehensive insights into photochromatic lenses.


Photochromatic lenses
Adaptive eyewear
Light-responsive lenses
Optical technology
UV protection
Vision enhancement
Eyewear innovation
Lens materials
Optometry
Eyecare professionals

1. PHOTOCHROMIC LENSES
JithinJohney, Assistant professor, Optometry

2. ▪Aphotochromiclensisanopticallensthatdarkensonexposuretolightof
sufficientlyhighfrequency,mostcommonlyultraviolet(UV)radiation.
▪Intheabsenceofactivatinglight,thelensesreturntotheirclearstate.
▪Photochromiclensesmaybemadeofpolycarbonate,oranotherplastic.
▪Glasslensesusevisiblelighttodarken.
▪Theyareprincipallyusedinglassesthataredarkinbrightsunlight,butclear,or
morerarely,lightlytintedinlowambientlightconditions.

3. Glass Photochromic Lenses
▪Forglasslenses,thedarkeningprocessoccursasaresultofsilverhalidecrystals
withintheglassthatareactivatedbyUVandshortvisibleradiationof
wavelengthsbetween300and400nm.
▪Thephotochromicprocessissimilartothatwhichtakesplacewhenlightstrikes
photographicfilmemulsions,alsocontainingsilverhalidecrystals.
▪Withthecrystals“trapped”intheglass,however,thedarkeningprocessis
reversible.
▪Theglassphotochromiclenswillnotwearoutwithrepeateddarkeningand
lighteningcycles,althoughovertimethelensesdonotlightenindoorsliketheydo
whennew.
▪Withinayearindoorlighttransmissionpercentageisinthelow70s.

4. Plastic Photochromic Lenses
▪Photochromic lenses are now predominantly plastic.
▪Plastic photochromicsare available in a variety of brands and colors.
▪Instead of using an inorganic material, such as the silver halide crystals used for
glass lenses, plastic photochromicsuse organic dyes.
▪Plastics are more sensitive to light and reacts better than glasses.
▪Reaction time is very less comparing with glass material.

5. How Plastic PhotochromicsAre Made?
Plastic photochromicscan be made in a variety of ways. These include,
1)Imbibition
2)In Mass
3)Multimatrix
4)Dip Coating
5)Front Surface Coating
6)Transbonding
At the time of this writing, the first two methods are the most commonly used

6. 1).ImbibitionSurfaceTechnology.
▪Theprimaryexampleofthelenstypemadeusingimbibitionsurfacetechnology
istheTransitionsphotochromiclens.
▪Transitionslensesaremadebystartingwithaclearplasticlens.
▪ItcanbeplasticmaterialverymuchlikeCR-39orotherorganiclenses.
▪Eachlensmanufacturerisresponsibleformakingtheirownlensusingcompatible
lensmaterials.

7. ▪Theselensesarethensenttoafacilitywhere
theirsurfacesareinfused(imbibed)with
photochromicmaterialusingaproprietary
manufacturingprocess.
▪Theevenlydistributedphotochromicmaterial
resultsinanevencolordensityovertheentire
lensasitdarkens.

8. 2). In-Mass Technology.
▪In-masstechnologymixesthephotochromicdyesintotheliquidlensmaterial
beforethelenshasbeenformed.
▪Thishasbeenthestandardtechnologyforthemanufactureofglasslenses.
▪Thedisadvantageinglassisthatthephotochromicmaterialreactsthroughoutthe
lens.
▪Thiscausesthethickeredgesofaminuslenstodarkenmorethanthethinner
centerdoes.Butwithplasticmaterial,primarilyonlythephotochromicmaterial
positionednearthesurfaceofthelensreacts.

9. ▪Ahigh-minusglassphotochromiclensmaygiveaveryslight“bull’s-eye”effect.
▪Ahigh-minusplasticphotochromiclensdoesnotproducethesameeffect.
▪Theorganicdyeswearoutnearthesurfaceanddonotdarkenasfully,thedye
slightlydeeperinthelensisthenactivatedbythenowenteringUVrays.
▪Thedeeperdyestakeoverthedarkeningfunction,thusextendingthe
photochromiclifeofthelens.
▪CorningSunSensorsandRodenstockColorMaticlensesareexamplesofalens
madewiththistypeofmanufacturingtechnology.

10. 3). Dip Coating:A lens may be dip coated and then cured with a heat process.
4).Front-Surface Coating:Another method is to coat the front surface of the lens.
5). Transbonding:is used with polycarbonate and high-index lenses. This process
uses surface treatments in combination with a series of ophthalmic grade layers.
6).Multimatrix.
▪Kodak Insta-Shades photochromic lenses use a process they refer to as
Multimatrix.
▪This process begins with a clear lens that has a 1-mm layer bonded to it.
▪The bonded layer contains the photochromic dye.

11. Advantages and Disadvantages of
Photochromic Lenses
▪Overtimeplasticphotochromicswearoutandglassphotochromicsfailtofully
lightenintheirfadedstate.
▪Themorethelensiswornoutdoors,especiallyduringhighsunlightconditions,the
fasteritwillwearout.Thiscausesproblemswhenonlyonelensneedstobe
replaced.
▪Itisnotadvisabletoreplaceonelenseveniftheotherlensislessthan1yearold
becausethetwolenseswillagedifferently.
▪Photochromicsarebecomingmoreabletoperformlikeasunlensintheir
darkenedstate,theystillarenotabletoreplacesunglasslenses.

12. Factors Influencing Photochromic Performance
▪Thereareseveralvariablesthatinfluencephotochromictransmissionand
darkeningspeed.Someaffectonlyglassphotochromicsandothersbothglassand
plastic:
1)Lightintensity(bothglassandplastic)
2)Temperature(bothglassandplastic)
3)Previousexposures(exposurememory)(glass)
4)Lensthickness(glass)

13. Light Intensity
▪AlthoughexposuretoUVandvisiblelightistheconditionthatinfluences
photochromiclenstransmissionmost,severalotherfactorscontributetolightening
anddarkening.
▪Aphotochromiclensismadetoreturntoitslighterstatebyexposuretoredlight
orIRradiation.
▪Thisisreferredtoasopticalbleaching.

14. Temperature
▪Heatwillalsobleachthelens.Thisisreferredtoasthermalbleaching.
▪Asaconsequence,photochromiclensesdonotdarkenasmuchonhotdaysasthey
dooncolddays.

15. Exposure Memory
▪Thelenseshaveexposurememory,meaningtheyrespondtolightinproportionto
accumulatedtotalrecentexposures.
▪Putawayunusedforlongperiodsoftime,aglassphotochromiclenswillloseits
exposurememoryandhavetobebrokeninagaintoobtainrapid,complete
cycling.
▪Forthisreason,awell-usedglassphotochromiclenswilldarkenatafasterrate
thananidentical,newlens.
▪Whenonlyonelensisbeingreplacedinapairofglasses,thiscanpresentarather
curiouseffect.

16. Lens Thickness
▪Transmissionofglassphotochromicsisalsoinfluencedbylensthickness.
▪APhotoGrayExtralenswilldarkendownto22%transmissionif2mmthick,but
cangetasdarkas11%if4mmthick.
▪Eventhoughthetransmissionvarieswiththickness,thenoticeablevariationfrom
edgetocenterfoundinhigh-plusorhigh-minustintedglasssunlensesisnot
present.

17. Photochromic UV Absorbing Properties
▪PhotochromiclensesaregoodabsorbersofUVradiation.
▪Intheirdarkenedstate,glassphotochromiclensesgenerallyabsorb100%ofUVB
radiationand98%ofUVAradiation.
▪PlasticphotochromicshaveeffectiveUVabsorptionpropertiesaswell

18. Colorsfor Photochromic Lenses
▪Photochromiclensescanbemadeinavarietyofcolors.
▪Mostphotochromiclensesbeginwithonecolorandchangetoadarkershadeof
thatsamecolor.
▪Itisalsopossibletomakeaphotochromiclensthatstartswithonecolorinthe
lightenedstateanddarkenstoadifferentcolor.
▪Theselenseshavebeenavailableinthepastandmayreappearinthefuture.

19. Thankyou