Refractive Errors and their Refractive Errors and their corrective optionscorrective options

Dr. Zia-Ul-MazhryDr. Zia-Ul-MazhryFCPS(Pak), FCPS(Pak), FRCS(Edin),FRCS(Edin),

FRCS(Glasgow), FRCS(Glasgow), CIC Ophth- (UK)CIC Ophth- (UK)

Associate ProfessorAssociate ProfessorCentral Park Medical College Central Park Medical College

Consultant Eye Surgeon Consultant Eye Surgeon & & Head, Department of Ophthalmology Head, Department of Ophthalmology

Wapda Hospital Complex Lahore.Wapda Hospital Complex Lahore.

Refractive SurgeryRefractive Surgery• DefinitionDefinition

•A group of procedures performed on eyes with A group of procedures performed on eyes with refractive errors or presbyopia to finish or minimize refractive errors or presbyopia to finish or minimize dependency on glasses and contact lensesdependency on glasses and contact lenses

Discussion PlanDiscussion Plan• Eye as an Optical SystemEye as an Optical System• Refractive Errors and their correctionRefractive Errors and their correction• Refractive Surgery OverviewRefractive Surgery Overview• SummarySummary

Cornea and scleraCornea and sclera

The cornea and sclera form a The cornea and sclera form a

spherical shell which makes up spherical shell which makes up the outer wall of the eyeballthe outer wall of the eyeball. .

Cornea and scleraCornea and sclera• The sclera is The sclera is :: - - principally collagenous,principally collagenous, - - avascular (apart from some vessels on its avascular (apart from some vessels on its

surface)surface) - - relatively acellular. relatively acellular. It is perforated posteriorly by the optic nerve, and It is perforated posteriorly by the optic nerve, and

by sensory and motor nerves and blood vessels to by sensory and motor nerves and blood vessels to the eyeball. the eyeball.

The cornea and sclera merge at the corneal edge The cornea and sclera merge at the corneal edge (the limbus).(the limbus).

The chief functions of the The chief functions of the corneacornea• are protection against invasion of are protection against invasion of

microorganisms into the eye, and the microorganisms into the eye, and the transmission and focusing transmission and focusing (refraction) of light.(refraction) of light.

Cornea Cornea

• EpitheliumEpithelium• Bowman Bowman

membranemembrane• StromaStroma• Descemet Descemet

membrane membrane (posterior limiting (posterior limiting layer of cornea)layer of cornea)

• EndotheliumEndothelium

Cornea and scleraCornea and sclera• Retraction of light occurs because of the Retraction of light occurs because of the

curved shape of the cornea and its curved shape of the cornea and its greater refractive index compared with greater refractive index compared with air. air.

• The cornea is transparent because of the The cornea is transparent because of the specialised arrangement of the collagen specialised arrangement of the collagen fibrils within the stroma, which must be fibrils within the stroma, which must be kept in a state of relative dehydration.kept in a state of relative dehydration.

Sagittal section of the eyeSagittal section of the eye

• Fibrous tunic Fibrous tunic of eyeof eye

• ChoroidChoroid

• RetinaRetina

Eye as an optical systemEye as an optical system•Focusing Lenses

– Cornea•Fixed power 43D

– Lens•Variable power 10-

20D•Axial Length

– Fixed 22-24mm

f=1/Df=1/D• D = power in diopters & f=focal length cmD = power in diopters & f=focal length cm

EmmetropiaEmmetropia

Refractive ErrorsRefractive Errors

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REFRACTIVREFRACTIVE ERRORSE ERRORSMyopia Myopia Hyperopia Hyperopia Astigmatism Astigmatism

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MYOPIAMYOPIA

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Nearsightedness or myopia, occurs when light Nearsightedness or myopia, occurs when light

entering the eye focuses in front of the entering the eye focuses in front of the retina retina instead instead

of directly on it. This is caused by a of directly on it. This is caused by a corneacornea that is that is

steeper, or an eye that is longer, than a normal eye. steeper, or an eye that is longer, than a normal eye.

Nearsighted people typically see well up close, but Nearsighted people typically see well up close, but

have difficulty seeing far away.   have difficulty seeing far away.  

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HYPEROPIAHYPEROPIA

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FarsightednessFarsightedness or or hyperopichyperopic, occurs when light , occurs when light

entering the eye focuses behind the entering the eye focuses behind the retinaretina, instead , instead

of directly on it. This is caused by a of directly on it. This is caused by a corneacornea that is that is

flatter, or an eye that is shorter, than a normal eye. flatter, or an eye that is shorter, than a normal eye.

Farsighted people usually have trouble seeing up Farsighted people usually have trouble seeing up

close, but may also have difficulty seeing far away close, but may also have difficulty seeing far away

as well. as well.

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ASTIGMATISMASTIGMATISM

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AstigmatismAstigmatism means that the means that the corneacornea is oval like a is oval like a

football instead of spherical like a basketball. Most football instead of spherical like a basketball. Most

astigmatic corneas have two curves – a steeper curve astigmatic corneas have two curves – a steeper curve

and a flatter curve. This causes light to focus on and a flatter curve. This causes light to focus on

more than one point in the eye, resulting in blurred more than one point in the eye, resulting in blurred

vision at distance or near. Astigmatism often occurs vision at distance or near. Astigmatism often occurs

along with nearsightedness or farsightednessalong with nearsightedness or farsightedness

Correction of Refractive Correction of Refractive ErrorsErrors• SpectaclesSpectacles• Contact Contact

LensesLenses• Ref- SurgeryRef- Surgery

– CornealCorneal– LenticularLenticular

Desire to see clearly Desire to see clearly lead to invention of spectacle lead to invention of spectacle

lenslens

SpectaclesSpectacles• we do not know yet whom to we do not know yet whom to

thank for this invention. thank for this invention. • Marco Polo, journeying to Marco Polo, journeying to

China in 1270, observed China in 1270, observed elderly Chinese using elderly Chinese using spectacles. spectacles.

• The Chinese themselves claim The Chinese themselves claim that spectacles originated in that spectacles originated in Arabia in the 11th century.Arabia in the 11th century.

• Between 1725 and 1750, a Between 1725 and 1750, a London optician designed the London optician designed the first temple specsfirst temple specs

• Ben Franklin invented bifocalsBen Franklin invented bifocals

History Corneal ProceduresHistory Corneal Procedures• 1800 crude RK for high 1800 crude RK for high

astimatism astimatism • 1983 Trokel and co workers 1983 Trokel and co workers

used ArF to etch corneaused ArF to etch cornea• The first laser eye treatment The first laser eye treatment

using the PRK (Photorefractive using the PRK (Photorefractive Keratektomy) method was Keratektomy) method was performed in 1986. performed in 1986.

• LASIK has established itself LASIK has established itself since the early 1990s.since the early 1990s.

• 1992 Waring in USA 1992 Waring in USA PRK (Photorefractive Keratectomy)

• The so-called LASEK method The so-called LASEK method has been available since 1999has been available since 1999

No Spectacles? Any remedy No Spectacles? Any remedy other than glasses?other than glasses?

•Desire to get rid of specs was Desire to get rid of specs was probably born with the spectaclesprobably born with the spectacles

Contact LensesContact Lenses• SoftSoft

– Daily wearDaily wear– Extended Extended

wearwear– DisposableDisposable

• Rigid or Rigid or hardhard– SphericalSpherical– ToricToric– BifocalBifocal

Types of Refractive SurgeryTypes of Refractive Surgery• Corneal (Keratorefractve Corneal (Keratorefractve

Procedures)Procedures)• Surgical keratotomy(RK,AK,TK)Surgical keratotomy(RK,AK,TK)• Photorefractive keratectomy(PRK)Photorefractive keratectomy(PRK)• Laser insitu keratomileusis(LASIK)Laser insitu keratomileusis(LASIK)• Laser subepithelial keratomileusis(LESEK)Laser subepithelial keratomileusis(LESEK)• Intra Stromal ringsIntra Stromal rings• Conductive keratoplasty(CK)Conductive keratoplasty(CK)

• LenticularLenticular• Cataract surgeryCataract surgery• Clear lens exchangeClear lens exchange• Phakic IOLPhakic IOL• Accomodative IOLAccomodative IOL• Piggyback IOLPiggyback IOL

Excimer LASERExcimer LASER

– Excimer means Excimer means “excited dimer” “excited dimer” of Argon Fluorideof Argon Fluoride

– Wavelength is Wavelength is 193 nm 193 nm

– Excimer Laser etches the cornea to give the eye the required power for emmetropia

•Photorefractive keratectomy(PRK )•LASER in situ keratomileusis(LASIK)•Laser Subepithelial Keratomileusis(LASEK)

SublimationSublimation• Tissue is directly converted into gas/plumesTissue is directly converted into gas/plumes

How Does it WorkHow Does it Work• Surface Ablation of the Cornea in Surface Ablation of the Cornea in

order to decrease its convexity. order to decrease its convexity. • Mean corneal thickness is 500uMean corneal thickness is 500u• Removal of 10 u of tissue Removal of 10 u of tissue

corrects one diopter of myopiacorrects one diopter of myopia• Laser fires a 7 pulses per secondLaser fires a 7 pulses per second• 40 pulses removes 40 pulses removes

approximately 10 u of tissueapproximately 10 u of tissue

Pre LASER ConsiderationsPre LASER Considerations• Base input refraction on manifest refraction Base input refraction on manifest refraction

(not auto refraction or glasses). Manifest (not auto refraction or glasses). Manifest refraction should be the refraction should be the leastleast minus to see 6/6 minus to see 6/6

• Offer monovision to presbyopic patientsOffer monovision to presbyopic patients• Council presbyopic patients carefully about Council presbyopic patients carefully about

loss of near vision after surgeryloss of near vision after surgery• Check IOP once before surgeryCheck IOP once before surgery

Pre LASER ConsiderationsPre LASER Considerations– Consider correcting one Consider correcting one

eye first for patients eye first for patients above age forty - Many above age forty - Many patients choose only to patients choose only to have one eye have one eye performedperformed

– Council patients with Council patients with consideration to level of consideration to level of pre-operative myopiapre-operative myopia• hazehaze• visual outcomevisual outcome• time to visual recoverytime to visual recovery

We are treating a We are treating a normal seeing eyenormal seeing eye

Corneal topographyCorneal topography

PRK (Photorefractive Keratectomy)•Epithelium is scraped

away•Excimer Laser ablates

the cornea to give the eye the required power for emmetropia

•Healing response varies in patients

PRK and Low MyopiaPRK and Low Myopia• AdvantagesAdvantages

• Technically Easy to PerformTechnically Easy to Perform• None Serious Complications with significant visual lossNone Serious Complications with significant visual loss• Good predictabilityGood predictability

– 80% 20/20 uncorrected80% 20/20 uncorrected– 98% 20/40 or better uncorrected98% 20/40 or better uncorrected

• DisadvantagesDisadvantages• Slow visual recoverySlow visual recovery

– 20/40 uncorrected at one week20/40 uncorrected at one week– Continued visual improvement over 3-4 weeksContinued visual improvement over 3-4 weeks– Final visual result at 3-4 monthsFinal visual result at 3-4 months

• Continued need for corticosteroidsContinued need for corticosteroids• Pain / Irritation for 2-3 days following surgeryPain / Irritation for 2-3 days following surgery

LASIK (Laser Assisted Insitu Keratomilieusis)• Instead of the epithelium being scraped

away, there is a flap that is created consisting of epithelium and anterior stroma (120-180um)

• Excimer Laser ablates the cornea to give the eye the required power for emmetropia

LASIKLASIK •LASIK - AdvantagesLASIK - Advantages•Quick rehabilitation periodQuick rehabilitation period•No necessity for prolonged No necessity for prolonged corticosteroidscorticosteroids•Little post-op painLittle post-op pain•Final visual outcome at 2 weeks Final visual outcome at 2 weeks after surgeryafter surgery•No chance of corneal hazeNo chance of corneal haze•Preservation of Bowman’s Preservation of Bowman’s membranemembrane

•LASIK - DisadvantagesLASIK - Disadvantages•Surgically complexSurgically complex•Steep learning curveSteep learning curve•Machinery ExpensiveMachinery Expensive

–MicrokeratomeMicrokeratome–BladesBlades

LASIK - ComplicationsLASIK - Complications– Flap IrregularityFlap Irregularity

• FoldsFolds• DislocationDislocation• SeveredSevered

– Epithelial IngrowthEpithelial Ingrowth– Aborted CutsAborted Cuts– Ground CapsGround Caps– LASIK - ComplicationsLASIK - Complications– Intraocular PenetrationIntraocular Penetration– Debris in InterfaceDebris in Interface– Flap DislocationFlap Dislocation

LASEK•Epithelium is disrupted with alcohol

and then scraped off and hinged•Laser is applied to the stroma•The epithelium is then reapplied to

the treated stroma•Similar to PRK in many respects

LASIK vs. LASIK vs. LASEKLASEK

• Quick visual rehab.Quick visual rehab.• Less PainLess Pain• less Steroid Useless Steroid Use• Surgically ComplexSurgically Complex• Keratome dependentKeratome dependent• Complications more Complications more

severesevere

•Slower visual rehab.Slower visual rehab.•More painfulMore painful•Prolonged Steroid Prolonged Steroid UseUse•Surgically SimpleSurgically Simple•mannualmannual•No severe No severe complicationscomplications

Custom LASIKCustom LASIK•Wavefront

technology•Takes higher

order aberrations into consideration

•Results tend to be better and more accurate

LASIK VIDEOLASIK VIDEO

Femtosecond LASERFemtosecond LASER

– used in Femto-LASIK instead of the microkeratome used in Femto-LASIK instead of the microkeratome – sends ultra-short light pulses 0f 100 fs. (1 fs = a sends ultra-short light pulses 0f 100 fs. (1 fs = a

millionth of a billionth second). millionth of a billionth second). – photo disruption severs the tissue. photo disruption severs the tissue. – A complete cut in a level is achieved .A complete cut in a level is achieved .– The cornea lid, thus created, can be lifted up with The cornea lid, thus created, can be lifted up with

a precision instrument.a precision instrument.

Video flap creation by Video flap creation by femtosecond laser femtosecond laser

PRK: LASEK: LASIKPRK: LASEK: LASIK• LASIK attains quicker vision recovery, with less

discomfort however it weakens the cornea.• Surface ablation (LASEK and PRK), reduces the

biomechanical weakening of the cornea.• LASEK achieves better-defined edges than PRK,

with a faster epithelial recovery.• LASEK reveals a technique with higher

satisfaction levelthan PRK, because of faster visual recovery and less postoperative discomfort.

PresbyopiaPresbyopia• Presbyopia, Greek for "aging eye" is a Presbyopia, Greek for "aging eye" is a

progressive condition that causes near vision progressive condition that causes near vision to fade with age.to fade with age.

• it affects most people by the age of 40 and it affects most people by the age of 40 and everyone by the age of 51.everyone by the age of 51.

Conductive keratoplasty(CK)Conductive keratoplasty(CK)– Using a probe thinner than Using a probe thinner than

a strand of human hair, CK a strand of human hair, CK applies radio waves in a applies radio waves in a circular pattern on the circular pattern on the outer cornea to shrink outer cornea to shrink small areas of collagen. small areas of collagen.

– This shrinkage pattern This shrinkage pattern creates a constrictive creates a constrictive band (like the tightening band (like the tightening of a belt), of a belt),

– Thus increasing the Thus increasing the overall curvature of the overall curvature of the cornea to bring near-cornea to bring near-vision back into focus vision back into focus

CK AdvantagesCK Advantages• uses controlled radio waves, uses controlled radio waves,

instead of a laser or scalpelinstead of a laser or scalpel• is laser-free no cutting and is laser-free no cutting and

no removal of tissue.no removal of tissue.• is minimally invasive and is minimally invasive and

painless.painless.• is fast: under three minutes.is fast: under three minutes.• is easy to undergo: topical is easy to undergo: topical

treatmenttreatment

Video CKVideo CK

Refractive lens exchangeRefractive lens exchange• refractive lens exchange (RLE) refractive lens exchange (RLE)

and cataract surgery removes the and cataract surgery removes the eye's natural lens and replace it eye's natural lens and replace it with an artificial lens implant. with an artificial lens implant.

• This lens implant can be either This lens implant can be either – monofocal (which means it focuses monofocal (which means it focuses

at a single distance), at a single distance), – multifocal (which means it has multifocal (which means it has

multiple focal points) or multiple focal points) or – accommodating (which means it can accommodating (which means it can

change its focal point).change its focal point).

Refractive Lens ExchangeRefractive Lens Exchange

Ref- Lens Exchange- Ref- Lens Exchange- ProblemsProblems• glare, halos and night vision difficulties ( can glare, halos and night vision difficulties ( can

be considered severe in 5% of patients)be considered severe in 5% of patients)• no guarantee of freedom from spectaclesno guarantee of freedom from spectacles• surgeon cannot predict exact near point surgeon cannot predict exact near point

distance for best near visiondistance for best near vision• surgeon may choose to place regular surgeon may choose to place regular

monofocal IOL at the time of surgery if he monofocal IOL at the time of surgery if he has concern the IOL may not center well in has concern the IOL may not center well in the eyethe eye

Video Ref- lens exchangeVideo Ref- lens exchange

Accommodative IOLAccommodative IOL

To see dreams you need To see dreams you need specs onspecs on

SummarySummary• In Optical system of the eye length In Optical system of the eye length

is fixed, only power of the lenses is fixed, only power of the lenses i.e cornea and crystalline lens can i.e cornea and crystalline lens can be modified or manipulatedbe modified or manipulated

Add a lensAdd a lensSpecs,CL,phakiSpecs,CL,phakic lensc lens

Modify a lensModify a lensRK,Excimer,CKRK,Excimer,CK

Replace a lensReplace a lensRef- lens exchangeRef- lens exchange

Summary-Refracrtive Summary-Refracrtive ProceduresProcedures• CornealCorneal

– CentralCentral• SurfaceSurface

– PRKPRK– LASEKLASEK– EpiLASIKEpiLASIK

– Stromal(flap)Stromal(flap)• Microkeratome LASIKMicrokeratome LASIK• Femto LASIKFemto LASIK

– PeripheralPeripheral• CKCK

• LenticularLenticular– Phakic IOLPhakic IOL– Ref- Lens ExchangeRef- Lens Exchange

• SimpleSimple• ToricToric• AccommodativeAccommodative

Refractive Surgery: Refractive Surgery: Elective surgeryElective surgery

• MyopiaMyopia– -1D to –6D-1D to –6D

• LASEK, LASIK, PRKLASEK, LASIK, PRK– -7D to –12D-7D to –12D

• LASEK, EpiLASIKLASEK, EpiLASIK– -10D to –20D-10D to –20D

• Phakic IOLPhakic IOL• Ref- Lens ExchangeRef- Lens Exchange

• Myopic AstigmatismMyopic Astigmatism– -1D to –6D-1D to –6D

• LASEK, LASIK, PRKLASEK, LASIK, PRK

• HyperopiaHyperopia– +1D to +4D+1D to +4D

• CK, LASEK, LASIKCK, LASEK, LASIK– +5D to +15D+5D to +15D

• Phakic IOL, Ref- Lens Phakic IOL, Ref- Lens ExchangeExchange

• PresbyopiaPresbyopia– (+1d to+3D)(+1d to+3D)

• CK CK – blended/mono visionblended/mono vision

Individualized & Individualized & Tailored Tailored DecisionsDecisions• Age LimitationsAge Limitations• Type of Refractive ErrorType of Refractive Error• Refractive StabilityRefractive Stability• Life Style, Profession & Life Style, Profession &

MotivationMotivation• Expected OutcomeExpected Outcome• Limitations and RisksLimitations and Risks

New DevelopmentsNew Developments–Custom LasikCustom Lasik–Femto LASIKFemto LASIK–Epi LASIKEpi LASIK–Bifocal LASIKBifocal LASIK–Accommodating Accommodating IOLIOL

Femto LASIKFemto LASIK

Thank you Thank you for your attentionfor your attention

Kab nazar main aai gee bay dagh sabzay kee baharKab nazar main aai gee bay dagh sabzay kee baharKhoon kay dhabay mitain gay kitni barsatoon kay baadKhoon kay dhabay mitain gay kitni barsatoon kay baad