Contact Lenses Clinical Function and Practical Optics.

Contact LensesContact Lenses

Clinical Function and Practical Clinical Function and Practical OpticsOptics

OutlineOutline

Basic opticsBasic optics Soft LensesSoft Lenses RGP LensesRGP Lenses HybridHybrid Lens CalculationsLens Calculations

An optical An optical interlude……interlude……

The corneal reflex is brighter in a person with contacts- WHY?

The corneal reflex with a contact lens is a superimposition of reflections from the air/tear interface, the anterior and posterior tear/lens interfaces and the tear/corneal reflex. Because RGP lenses have a higher n, the reflex off of these will be greater (2.5% versus 2.3%).

R={n’-n/n’+n}2

Air/tear interface Tear/lens interface

CO

NTA

CT

LEN

S CO

RN

EA

AQ

UEO

US

AIR

Prelens tear film

Post-lens tear filmTear/epithelial interface

For practical purposesthink of each layer as a separate lens in air

Nuances of CL powerNuances of CL power

CLS are treated as CLS are treated as thick thick lenseslenses– Anterior and posterior surfacesAnterior and posterior surfaces– Center thickness Center thickness – Index of refractionIndex of refraction– Saggital depth/extreme curvaturesSaggital depth/extreme curvatures

Contacts are THICK Contacts are THICK LENSESLENSES (!)(!)

f

F

H H’

fFVP

fT

A1 A2

tF’

f’T

fBVP

n’n

Tx this way b/c curves are so great….

CL Optics – Effective CL Optics – Effective PowerPower Remember to consider vertex Remember to consider vertex

distance for all powers > +/- 4.00 distance for all powers > +/- 4.00 DD– Myopes need less power in clsMyopes need less power in cls– Hyperopes need more power in clsHyperopes need more power in cls

Also have to vertex the cylinder Also have to vertex the cylinder componentcomponent– Use optical crossesUse optical crosses

Vertex of toric Rx’sVertex of toric Rx’s

Rx: Rx: +4.00+3.00X180+4.00+3.00X180

Fsp= K/ (1+dK)-use this to convert to spectaclesWhere d= vertex distance in metersK= power at the cornea

K= Fsp/1-dFsp- use this to convert from specs to contacts

CL Optics- changes in CL Optics- changes in accommodative demandaccommodative demand

Hyperopes have more Hyperopes have more accommodative demand with accommodative demand with glassesglasses– Pre-presbyopes love cls! (more plus Pre-presbyopes love cls! (more plus

with CLS)with CLS) Myopes have less accommodative Myopes have less accommodative

demand with glassesdemand with glasses– Pre-presbyopes do not do well (more Pre-presbyopes do not do well (more

minus to overcome with CLS)minus to overcome with CLS)

CL optics –Changes in CL optics –Changes in accommodative convergenceaccommodative convergence

MyopesMyopes = increased accommodation = increased accommodation with cls , thus will use MORE with cls , thus will use MORE accommodative convergenceaccommodative convergence– An esophoric myope will have to use more An esophoric myope will have to use more

NEGATIVE fusional vergenceNEGATIVE fusional vergence HyperopesHyperopes= decreased accom with cls, = decreased accom with cls,

will use LESS accommodative will use LESS accommodative convergenceconvergence– An exophoric hyperope will have to use An exophoric hyperope will have to use

more POSITIVE fusional vergencemore POSITIVE fusional vergence

CL Optics- Prismatic CL Optics- Prismatic effectseffects

Correctly fitted cls are always centered Correctly fitted cls are always centered on the eye, where glasses induce on the eye, where glasses induce prismprism

Plus lenses induce BO prismPlus lenses induce BO prism

–An esophoric hyperope is at a disadvantage with cls b/c An esophoric hyperope is at a disadvantage with cls b/c

there is no prismatic effect to counterbalancethere is no prismatic effect to counterbalance

CL Optics- Prismatic CL Optics- Prismatic EffectsEffects

Minus lenses induce BI prismMinus lenses induce BI prism

–An exophoric myope is at disadvantage with cls b/c there is no prismAn exophoric myope is at disadvantage with cls b/c there is no prism

The lack of prism effect is a benefit for anisometropes.The lack of prism effect is a benefit for anisometropes.

Prescribing prism in Prescribing prism in clscls BD prism reduces rotation BD prism reduces rotation

--toric lensestoric lensesbifocal lensesbifocal lenses

The lens thickness is increased The lens thickness is increased toward the base w/o alteration in toward the base w/o alteration in surface curvature, thus power is surface curvature, thus power is more plus towards the basemore plus towards the base– Exploited in bifocal designs (rgps)Exploited in bifocal designs (rgps)

Lenses can alter the shape of the Lenses can alter the shape of the cornea (warpage)cornea (warpage)

Cornea can alter the shape of Cornea can alter the shape of lenses (soft cls)lenses (soft cls)

RGP lenses can mask corneal RGP lenses can mask corneal astigmatismastigmatism

CL Optics- cl/eye CL Optics- cl/eye systemsystem

CL optics- CL optics- Magnification EffectsMagnification Effects

Occurs because the cl is touching the Occurs because the cl is touching the corneacorneaThe power factor of SM formula includes the The power factor of SM formula includes the distance from lens to entrance pupil, distance from lens to entrance pupil, changing this to zero causes a change in changing this to zero causes a change in magnificationmagnificationMyopeMyope will get larger retinal image will get larger retinal image

Hyperope will get smaller retinal imageHyperope will get smaller retinal image

The opposite of what happens in The opposite of what happens in glassesglasses!!

Magnification EffectsMagnification Effects

Mag=Original power/vertex powerMag=Original power/vertex power What is change in RIS switching What is change in RIS switching

from glasses to cls for -5.00D at from glasses to cls for -5.00D at 12mm?12mm?

-5/1-.012(5)=-4.72 (vertex)-5/1-.012(5)=-4.72 (vertex) -5/-4.72=1.06-5/-4.72=1.06 %change is 6% larger with cl.

CL optics –aberrations CL optics –aberrations and field of viewand field of view CL wearers have greater field of viewCL wearers have greater field of view

– No glasses rim!No glasses rim! Spectacles suffer from oblique Spectacles suffer from oblique

astigmatism, curvature of field and astigmatism, curvature of field and distortiondistortion– CLS eliminate OA and CF because the CLS eliminate OA and CF because the

lenses are always centeredlenses are always centered– CLS eliminate D because they are directly CLS eliminate D because they are directly

on the eyeon the eye

Wavefront guided contacts are available now!

Visual Optics –Visual Optics –corneal transparencycorneal transparency

The air/tear interface has the most The air/tear interface has the most refractive power because of change in refractive power because of change in index, although optically the TF has no index, although optically the TF has no powerpower

The stroma The stroma isis optically significant optically significant The tear film, epithelium, Bowman’s The tear film, epithelium, Bowman’s

and Decemet’s are optically and Decemet’s are optically insignificant b/c of their CT and parallel insignificant b/c of their CT and parallel surfacessurfaces

Corneal TransparencyCorneal Transparency

200 lamellar sheets arranged in parallel, 200 lamellar sheets arranged in parallel, stacked in an anteroposterior direction.stacked in an anteroposterior direction.

Regular spacing 65nm apart in a latticeRegular spacing 65nm apart in a lattice Lattice theory states that the spacing Lattice theory states that the spacing

between collagen is sufficiently small between collagen is sufficiently small that light scattered by individual fibers is that light scattered by individual fibers is mutually destroyed by destructive mutually destroyed by destructive interferenceinterference

Loss of Corneal Loss of Corneal Transparency d/t CLSTransparency d/t CLS EdemaEdema InfiltratesInfiltrates MicrocystsMicrocysts Vacuoles Vacuoles CalciumCalcium LipidLipid Dry spots/ dellenDry spots/ dellen ScarringScarring Salzmann’s nodulesSalzmann’s nodules

VascularizationVascularization Dimple VeilDimple Veil Inclusions (epi)Inclusions (epi) TraumaTrauma

MechanicalMechanical ChemicalChemical ToxicToxic OsmoticOsmotic HypoxicHypoxic

Alterations to eye Alterations to eye opticsoptics Myopic creep –unexplained Myopic creep –unexplained

– edema (rgp < scl)edema (rgp < scl)– Steeper k’s and altered pachy readingsSteeper k’s and altered pachy readings– Lowered stromal n (more +)Lowered stromal n (more +)– endotheliumendothelium

Change in anterior corneal Change in anterior corneal curvaturecurvature– Spectacle blurSpectacle blur

Lens flexure and Lens flexure and warpagewarpage CLS in vivo variably conform to CLS in vivo variably conform to

the corneathe cornea Function of material, K’s and the Function of material, K’s and the

lens/cornea fitting relationshiplens/cornea fitting relationship

Flexure – soft lensesFlexure – soft lenses

The most extreme exampleThe most extreme example– As cornea steepens, net minus power As cornea steepens, net minus power

increases for all lenses increases for all lenses Topography shows inferior steepeningTopography shows inferior steepening

Soft lenses Soft lenses cannot cannot be assumed to provide be assumed to provide the labeled powerthe labeled power

– OR varies depending on flexureOR varies depending on flexure– Dehydration raises n, increasing powerDehydration raises n, increasing power– Steepens with dryness, increasing powerSteepens with dryness, increasing power– Cannot confirm power in officeCannot confirm power in office– Tear fluid Tear fluid

tonicity/pH/temperature/heat/humiditytonicity/pH/temperature/heat/humidity

Flexure RGPsFlexure RGPs

Flex to the steepest meridianFlex to the steepest meridian– Wtr cornea, lens steepens in the Wtr cornea, lens steepens in the

vertical and slightly flattens in the vertical and slightly flattens in the horizontal.horizontal.

– Measured as toricity with over-K’sMeasured as toricity with over-K’s– Calculated effect is to lessen the Calculated effect is to lessen the

minus power of the LL in the minus power of the LL in the steepest meridiansteepest meridian

OutlineOutline

Optics of Optics of contactscontacts

Soft LensesSoft Lenses RGP LensesRGP Lenses Bifocal LensesBifocal Lenses Fitting Fitting

proceduresprocedures

Types of soft lensesTypes of soft lenses

SphericalToric

truncatedprism ballastthin ballast

AphakicExtended wearBifocalBandage lensesHigh dK/l

Different polymersDifferent polymers– Ionic high waterIonic high water– Ionic low waterIonic low water– Non-ionic high waterNon-ionic high water– Non-ionic low waterNon-ionic low water

Newer silicone Newer silicone FDA proposal:FDA proposal:

Same as above plus Same as above plus sihi designationsihi designation

Types of soft lensesTypes of soft lenses

Conventional (sphere/toric)Conventional (sphere/toric)– Keep for a yearKeep for a year– BifocalsBifocals– Higher powersHigher powers

Disposable (sphere/toric/bifocals)Disposable (sphere/toric/bifocals)– QuarterlyQuarterly– MonthlyMonthly– Weekly or Two weekWeekly or Two week– DailyDaily

http://oculuseyehospital.com/images/toric.jpg

Some optical Some optical considerationsconsiderations

Fitted flatter than the corneaFitted flatter than the cornea– Parallels the periphery and drapes Parallels the periphery and drapes

over apexover apex– 1 or 2 radii of curvature (base 1 or 2 radii of curvature (base

curves) only per type of lens are curves) only per type of lens are generally availablegenerally available

Why/Why not soft Why/Why not soft lenses?lenses? AdvantagesAdvantages

– ComfortableComfortable– AvailableAvailable– Easy to fitEasy to fit– Good for social Good for social

useuse– Better for internal Better for internal

cylcyl

DisadvantagesDisadvantages– More risk of infectionMore risk of infection– Dry outDry out– Prone to rotation Prone to rotation

(toric)(toric)– Get dirty quicklyGet dirty quickly– NoncomplianceNoncompliance– Poor Oxygenation Poor Oxygenation

(older lenses)(older lenses)– GPCGPC

Bifocals – soft lensesBifocals – soft lenses

D

N

N

D

D

N

ISimultaneous vision

aspheric

Soft CL problemSoft CL problem

Patient’s Rx is -4.00 -1.00 x 090 Patient’s Rx is -4.00 -1.00 x 090 all cyl is cornealall cyl is cornealPatient cannot afford toric lenses- Patient cannot afford toric lenses-

what do you prescribe?what do you prescribe?

Soft CL problemSoft CL problem

Patient’s Rx: -6.50+2.00x045Patient’s Rx: -6.50+2.00x045 K readings: 45.00/46.00@135K readings: 45.00/46.00@135

-What power CL?-What power CL? - What bc? (choice is 8.7 or 8.2)- What bc? (choice is 8.7 or 8.2) - Say CL OR is -1.00 – 0.50 x 040 what do - Say CL OR is -1.00 – 0.50 x 040 what do you do? you do? - what if lens is rotating 20 degrees nasal- what if lens is rotating 20 degrees nasal (lars)(lars) - what if the OR is -1.00-1.00 x 090?- what if the OR is -1.00-1.00 x 090?

OutlineOutline

Optics of Optics of contactscontacts

Soft LensesSoft Lenses RGP LensesRGP Lenses Bifocal LensesBifocal Lenses Fitting Fitting

proceduresprocedures

Rigid Gas PermeableRigid Gas Permeable

SphereSphere ToricToric

– BitoricBitoric– Front surface toricFront surface toric– Back surface toricBack surface toric

BifocalsBifocals– AsphericAspheric– SegmentedSegmented– ““Pinhole”Pinhole”

Anatomy of RGP CLAnatomy of RGP CL

RGP why/why not?RGP why/why not?

AdvantagesAdvantages– More OxygenMore Oxygen– CheaperCheaper– Less surface areaLess surface area– Better for dry eyeBetter for dry eye– Masks corneal cylMasks corneal cyl– ComplianceCompliance– Rare sleepingRare sleeping– Rare infectionRare infection– Superior opticsSuperior optics

DisadvantagesDisadvantages– AdaptationAdaptation– Chair timeChair time– MisconceptionMisconception

Lacrimal LensLacrimal Lens

An rgp interacts with the An rgp interacts with the tearstears– Has less effect on the curvature of Has less effect on the curvature of

the cornea (unless poor fit)the cornea (unless poor fit)– As long as rgp maintains it’s bc, the As long as rgp maintains it’s bc, the

interface between the lens and the interface between the lens and the tears is spherical (elimiates tears is spherical (elimiates astigmatism)astigmatism) Rgp does not affect internal Rgp does not affect internal

astigmatism!!astigmatism!!

Lacrimal LensLacrimal Lens

Steeper contact creates a + power LL

Flatter contact creates a – power LL

For every BC change, and equal and opposite change of power is needed .05mm=0.25D

Lacrimal Lens ProblemLacrimal Lens Problem

CL parameters:CL parameters:

7.50/-6.00/957.50/-6.00/95

Need to steepen Need to steepen BC .5D what is new BC .5D what is new power?power?

Need to flatten BC Need to flatten BC by .75D what is new by .75D what is new power?power?

Fitting PhilosophiesFitting Philosophies

Lid AttachmentLid Attachment– Fit is under the lidFit is under the lid– Moves with blinkMoves with blink– More comfortableMore comfortable– Less GPCLess GPC

InterpalpebralInterpalpebral– Wide eyesWide eyes– Must have good recoveryMust have good recovery

Fluorescein PatternsFluorescein Patterns

Next >>More Fluorescein Patterns: 1 2 3Making Lens Design ChangesFitting Pearls

Next >>More Fluorescein Patterns: 1 2 3Making Lens Design ChangesFitting Pearls

Alignment pattern

Even pattern centrally with slightly

greater clearance peripherally

Spherical BC on 3D WTR

astigmatic cornea

Horizontal bearing and excessive

vertical pooling is observed

Alignment pattern




astigmatic cornea



Alignment pattern




astigmatic cornea



Observe apical clearance andinsufficient peripheral clearance

On K 95/84

More alignmet with greaterPeripheral clearance

On K 95/76

Good edge, bit narrow

Bicurve design with a10.0mm PCR; .5mm wide

An increase in edge clearancecan be observed

Bicurve design with a10.0mm PCR; 1.0mm wide

Insufficient edge clearancecan be observed

Bicurve design with a9.0mm PCR; .8mm wide

Observe greater clearance

12mm PCR, .8mm wide

RGP ProblemRGP Problem

Rx:Rx: -8.50DS -8.50DS K: K:

44.50/[email protected]/46.00@78 What power?What power? What BC?What BC?

RGP ProblemRGP Problem

Rx: Rx:

-3.00 + 6.00 X 090-3.00 + 6.00 X 090 K:K:

42.50/[email protected]/47.75@1800

What bc?What bc? What power?What power?

Therapeutic RGP fitsTherapeutic RGP fits

Use topography and SLE to assess Use topography and SLE to assess KK

Goal is to fill in irregular part with Goal is to fill in irregular part with tearstears

Pick steepest K as starting pointPick steepest K as starting point Just fit the lens and then OR to Just fit the lens and then OR to

get powerget power

Bifocal RGPBifocal RGP

aspheric

n

d aspheric

http://www.hroptical.com/images/bifocal-contact-design.jpg

Bifocal RGP fittingBifocal RGP fitting

Many different Many different brandsbrands

Proprietary v Proprietary v customcustom

Fitting is specific Fitting is specific to brand/ typeto brand/ type

Many potential Many potential changeschanges

Set realistic Set realistic expectationsexpectations

Acknowlegde Acknowlegde time investmenttime investment

THE BASICSTHE BASICS

Details of previous cl wearDetails of previous cl wear What are the problems?What are the problems? When/how do you wear them?When/how do you wear them? Careful refraction (vertex over +/-4D)Careful refraction (vertex over +/-4D) Keratometry or topographyKeratometry or topography Examination of the cornea, lids, lashesExamination of the cornea, lids, lashes Dryness…..?Dryness…..? Pupil size (dim/light)Pupil size (dim/light) Palpebral Apeture/ characteristics –tight/loose Palpebral Apeture/ characteristics –tight/loose

etc.etc. Iris DiamterIris Diamter

The BasicsThe Basics

Technicians are key to Technicians are key to profitabilityprofitability

Insertion/removal trainingInsertion/removal training Lens hygiene teachingLens hygiene teaching Patient follow up- phone callsPatient follow up- phone calls

FOLLOW UP IS IMPERATIVE…FOLLOW UP IS IMPERATIVE…

Seriously? Yes, pretty Seriously? Yes, pretty common so check!common so check!

Contact Lenses Clinical Function and Practical Optics.

Documents

Transcript of Contact Lenses Clinical Function and Practical Optics.