INTRAOCULAR LENSES

OVERVIEW

• HISTORICAL ASPECTS• PRESENT DAY IOLs– Classification – Design– Material

• ASPHERIC IOLs• MULTIFOCAL, ACCOMODATIVE, TORIC IOLs• PHAKIC IOLs• IOL IMPLANTATION IN SPECIAL SITUATIONS• COMPLICATIONS RELATED TO IOLs• RECENT ADVANCES AND THE FUTURE• IOL POWER CALCULATIONs• MANUFACTURING PROCESS

HISTORICAL ASPECTS

The Evolution of Intraocular Lenses*

*Yanoff & Duker: Ophthalmology, 3rd ed. Table 5-2-1, pg 394

HISTORY

• First IOL implantation– Sir Harold Ridley• November 29, 1949 at St. Thomas Hospital, London• 49 year woman• ECCE with in-the-bag placement• Biconvex perspex (Transpex 1) disc; 138 mg • Rayners Optical Company, Brighton• Substantial post op myopia (-24.0 Ds/ +6.0 Dcyl X 30 degrees)• IOL exchange in February, 1950 • Revealed only in 1951 at the Oxford Ophthalmic Congress

8.5 mm diameter, 2.4 mm thick, 108 mg

In 1795, Casamata implanted glass IOL which sank posteriorly.

– INSPIRATION• Inertness of intraocular plexiglass shards• A medical student, Steve Perry questioned him why was he not

replacing the lens after removal

– Approximately 1000 Ridley IOLs implanted in the next 12 years

– Complications*• Disclocation : approx 20%• Glaucoma : 10 %• Uveitis

– Went into disrepute• Strongly opposed by Sir Duke-Elders

*Ridley H: Intraocular acrylic lenses—past, present and future. Trans Ophthalmol Soc UK 1964;84:5–14

EARLY ANTERIOR CHAMBER IOLs• Rigid or semirigid AC-IOL– Baron, in France; May 13, 1952– Scharf and Strampelli

• Flexible or semiflexible AC-IOL– Open haptic loops – Closed haptic loops – Peter Choyce• Mark I to Mark VII

Strampelli Tripod AC-IOL (1953) Choyce Mark I AC-IOL(1956)

Dannheim AC-IOL with closed haptics (1952)Ridley Tripod AC-IOL (1957–60)

– Barraquer • Open-loop AC-IOL with J-haptics• Nylon haptics

– Complications• High vaulting

– Late endothelial atrophy, – Corneal decompensation, – Pseudophakic bullous keratopathy

• Uveal erosion– Uveitis-glaucoma-hyphema (UGH) syndrome

ADVANTAGES

• Less decenteration• Decreased reaction

DISADVANTAGES

• Corneal decompensation • Pseudophakic Bullous

keratopathy• Uveitis• Secondary glaucoma• UGH syndrome

IRIS-SUPPORTED LENSES

• Epstein, 1953 – Collar stud lens– Maltese cross lens– Copeland lens

• Iris pigment epithelial defects/atrophy, • Pigment dispersion glaucoma • Corneal complications

• Cornelius Binkhorst, – Iris clip lens; four-loop (1957)– Iridocapsular fixation; two loop (1965)

• Forerunner to capsular sac (in-the-bag) fixation of modern posterior chamber IOLs

• Fyodorov modification (1966)– Fyodorov I– Fyodorov II (Sputnik)

– Three haptics in front and three behind the iris

• Jan Worst (Holland)• Medallion IOL, mid-1970s

– Eliminating the anterior haptics while retaining the horizontally oriented posterior ones

– Prolene suture through the superior optic, securing it to the iris

– Hydrolytic biodegradation of the nylon stitches

Binkhorst 4-loop lens (1957/58), Fyodorov iris clip Sputnik lens (1968), Binkhorst 2-loop lens for iridocapsular

fixation (1965).

• Iris claw lens (lobster claw); by Worst in 1978– Artisan/Artiflex Lens– Slits in both haptics– Clamped into the mid-periphery

ADVANTAGES

• Away from angle structures • Rate of dislocation was less• Less contact with corneal

endothelium

DISADVANTAGES

• Iris chaffing• Pupillary distortion• Transillumination defects• Chronic inflammation• CME• Distortion on pupillary

dilatation• Endothelial

decompensation

INTERMEDIATE ACIOLs• Improved manufacturing techniques– Tumble polishing of IOLs

• Flexible loops with multiple point of fixation• More stable • Anterior-posterior vaulting characteristics • Elimination of sharp optic or haptic edges• Fixation elements – Spatula-like footplates– Small-diameter lens loops

• Closed • Open

Kelman multiflex AC-IOL (1982)Kelman flexible Tripod AC-IOL (1981),

Intermedics Inc Dubroff AC-IOL (1981), Modern, one-piece, flexible PMMA AC-IOL

(Kelman design) with Choyce foot plates (various manufacturers).

Azar 91Z AC-IOL (1982) ORC Inc Stableflex AC-IOL (1983)Surgidev Inc Style 10 Leiske ACIOL

(1978)

Mark VIII, Mark IX, flexible ACIOL, Kelman, Kelman flexible tripod, Kelman quadraflex,

Kelman multiplex 4 point fixation

• PHACOEMULSIFICATION• SOPHISTICATED MICROSURGERY• OPHTHALMIC VISCO-SURGICAL DEVICES• CONTINUOUS CURVILINEAR CAPSULORRHEXIS

– allows copious hydrodissection– stability of the capsular bag

• HYDRODISSECTION

• 1981 : FDA approval for IOL implantation following cataract surgery

IMPROVED PCIOLs

Charles Kelman

• Rigid tripod design (John Pearce)

• J-looped PCIOL (Steven Shearing)

• Modified J-looped PCIOL (Sinskey)

• C-looped PCIOL (Simcoe)

• One piece PCIOL (Eric Arnott)

ADVANTAGES OF IN-THE-BAG PLACEMENT• Proper anatomical site

• Symmetrical loop placement

• Intraoperative stretching or tearing of zonules is avoided

• Minimimal magnification (<2%); (20-30% aphakic glasses, 7-12% aphakic contact lens, ACIOL 2-5% )

• Low incidence of lens decentration and dislocation

• Maximal distance from the posterior iris pigment epithelium, iris root, and ciliary processes

• Loop material alteration is less likely

• Safer for children and young individuals

• Reduced posterior capsular opacification

MODERN IOLs

PRESENT DAY IOLs

• Classification • Design• Material

CLASSIFICATION

INTRAOCULAR LENS DESIGN• Single piece / monobloc• Plate haptic / open loop haptics• Angulated / planar haptics• Edge design• Optic design

ANGULATED HAPTICS ALLOW FOR ADEQUATE PUPILLARY CLEARANCE AND ADHESION TO THE POSTERIOR CAPSULE

• Square, truncated optic edge

HAPTIC DESIGN

• Plate haptic• Loop haptic– C-loop– J-loop– Modifies C-loop

• Plate-loop

LENS CHEMISTRY(Optic Materials)

• RIGID MATERIALS– PMMA

(Polymethylmethacrylate) – Water content <1%– Refractive index 1.49– Usually single piece– May be penetrated by

aqueous humor known as ‘glistenings’ (very rare)

• FLEXIBLE MATERIALS– Silicones – Acrylics

• Hydrophilic • Hydrophobic

– Hydrogels – Collamer

FLEXIBLE MATERIALS• Silicone– Polymers of silicone and oxygen– Since 1984; first material for foldable IOLs– Hydrophobic (contact angle with water of 99°)– 1.41 to 1.46– 3 piece– Thick optics (need larger incisons)– Handling is difficult; loading into injector – Bacterial adhesion– Anterior capsule rim opacifies quickly– Low PCO– Lowest threshold for YAG laser damage– Glistenings – Adherence of silicone droplets

HYDROPHOBIC ACRYLIC• Copolymers of acrylate and methacrylate• 1993 (Acrysof 3-piece lens)• Most successful IOLs today• Angle of contact with water is 73°• 3-piece or 1-piece designs• 1.44 to 1.55• Easy handling; prone to mechanical damage• At least a 2.2-mm incision• Low PCO rates• Good resistance to YAG laser• Photopsias • Glistenings • BSS packaging (reach 4% water content before implantation)

HYDROPHILIC ACRYLIC• Mixture of hydroxyethylmethacrylate (poly- HEMA) and hydrophilic

acrylic monomer• End of the 1980s• 1.43• 18 -26% water content • Contact angle with water is lower than 50°• Single piece• Easiest to handle; less mechanical/YAG laser damage• Sub-2-mm incisions• Higher PCO rate • Low resistance to capsular contraction• Calcium deposits

HYDROGEL

• Swell in water• 18% to 38% water content• Copolymers of methacrylate esters• Hydrophilic comonomer with a hydroxyl

functional group such as HEMA

COLLAMER

• STAAR Surgical• Hydrophilic • p-HEMA with 33% water and 0.2% porcine

collagen with a benzophenone UV blocker

UV ABSORPTION

• Additive• Chemical bonding– Hydroxybenzophenones– Hydroxyphenylbenzotriazoles

• UV-absorbing chromophore – Protective to macula– Interference with melatonin cycle

LENS CHEMISTRY(Haptic Material)

• PMMA• Polyimide (Elastimide)• Polyvinylidene fluoride (PVDF)– good material memory

ASPHERIC IOLS

ASPHERIC IOLs

• Human eye : Aspheric Optics

• Cornea : Positive spherical aberration

• Young crystalline lens : Negative spherical aberration

• Ageing crystalline lens : Increased positive spherical aberration

• spherical aberration ~ fourth power of the pupil diameter

Conventional IOL increasethe spherical aberration of the eye

HOW TO OVERCOME ?

• Strategy 1:– Lens with negative spherical aberrations to

balance the normally positive corneal spherical aberrations

• Strategy 2:– Lens with minimum spherical aberrations so that

no additional spherical aberration is added to the corneal spherical aberrations

• Anterior prolate surface– Tecnis, Advanced Medical Optics (AMO)

• Posterior prolate surface– Acrysof IQ, Alcon Laboratories

• Both Anterior and Posterior prolate surfaces– Akreos AO, SofPort AO and L161 AO, Bausch & Lomb

ASPHERIC IOLs• Need perfect centration

– Decentered IOLs can induce coma

• Decreased depth perception• More expensive• Need corneal topography for

optimal results• Not much difference in

photopic conditions and in older age group

• Not for previous hyperopic refractive surgery

• Better contrast sensitivity• Better mesopic vision• Night time driving

– AcrySof® IQ Aspheric IOL patients had an average increase of 130+ feet (vs the control lens) in which to stop after identifying a warning sign

• Better option for younger patients

PREMIUM IOLs

• MULTIFOCAL• ACCOMODATIVE• TORIC IOLs

RESTORATION OF ACCOMMODATION IN PSEUDOPHAKIA

METHODS

Monovision Multifocal IOLAccommodative

IOL

MULTIFOCAL IOLs

• Single IOL with two or more focal points

• Types – Refractive– Diffractive– Combination of both

• Hoffer in 1982• Patient with 6/6 vision in spite of an IOL that

was decentred by more than 50% of the pupillary area

• Dr. John Pearce, 1986; bull’s eye style• Pupil dependent

REFRACTIVE MULTIFOCAL IOLs• Bull’s eye lens– Concentric rings of different powers – Central addition surrounded by

distance optical power

• Annulus design– 3-5 rings– Central for distance vision– Near vision ring– Distance vision ring

12345

Bright light/ Distance dominant zoneLarge Near dominant zone

Low light/ Distance dominant zone

Distance zone

Near zone Aspheric transition

REFRACTIVE MULTIFOCAL IOLs

• Silicone MIOLs– Array multifocal IOL (AMO)– First FDA approved foldable MIOL

• 5 concentric zones on its anterior surface• 50% distance, 37% near, 15% for intermediate vision

• Acrylic MIOLs– ReZoom multifocal IOL (AMO)

• Zone 1,3 and 5 : distance• Zone 2 and 4 : near• 60% distance, 40% near and intermediate

• PREZIOL (Acrylic)(Care Group)– Manufactured by Indian company– Also available as non foldable PMMA lens

Multiple focal points of a refractive multifocal IOL

DIFFRACTIVE MULTIFOCAL IOLs• Anterior aspheric surface : basic

refractive power • Multiple grooves on posterior

surface : diffractive power

• 41% of light : distance• 41% : near vision• PMMA– 3M corp (3M diffractive MIOL)– Pharmacia 808,811E

• Pupil independent

DIFFRACTIVE MULTIFOCAL IOLs

Multiple focal points of a diffractive multifocal IOL

Based on the average corneal-surface

wavefront-derived spherical aberration

• Tecnis Multifocal IOLs (AMO)– ZM900 (Silicone)– ZA00 (Acrylic)

• Optic Diameter 6.0 mm• Optic Type– Modified prolate anterior surface– Total diffractive posterior surface– Diffractive Power +4.0 diopters of near addition

(+3.0 Diopters at spectacle plane)

• Acrysof IQ ReSTOR (Alcon)– Acrylic diffractive multifocal IOL with apodized design– Optic diameter- 6 mm– Refractive for distance, and a diffractive lens for near.– 16 rings distributed over central 3.6 mm– Peripheral rings placed closer to each other– Central rings : 1.3 µm elevated, near vision– Peripheral 0.2 µm elevated, distant vision– Anterior peripheral surface is modified to act as

refractive design – Near Addition +3.0 D at IOL plane (+2.5 D at spectacle

plane)

Apodization literally means "removing the foot“To remove or smooth a discontinuity at the edges

• Refractive lenses (pupil dependent) ideal for – Light to moderate readers– Drive mostly during the day. – Play sports, – Use a computer frequently,

or – Activities that rely heavily

on intermediate vision

• Diffractive IOLs (pupil independent)for – Spend a lot of time reading – Detailed craft-work– Scotopic activities

• Movies• Night time driving

PATIENT SELECTION FOR MfIOLs(most important factor)

• Strong desire to be spectacle independent• Functional & occupational requirements– Occupational night drivers (avoid)

• Pre-existing ocular pathologies• Hypercritical & demanding patients– strictly avoided

• > 1.0 D astigmatism; irregular astigmatism (avoid)• Individuals with a monofocal lens in one eye• History of previous refractive Surgery• Previous PK• Chances of IOL dislocation

INTRAOPERATIVE EXCLUSION

• Significant vitreous loss during surgery• Pupil trauma during surgery• Zonular damage• Capsulorhexis tear• Capsular rupture• Eccentric CCC

SPECIAL CONSIDERATIONS FOR MfIOLS

• Counselling (most important)• Accurate Biometry

– IOL master strongly recommended– immersion biometry better than applanation biometry

• Power Calculation– Plano to <+0.25– newer formulae

• Surgical Technique– Round, centered CCC completely overlapping the lens optic– Removal of all viscoelastic from behind the lens

MIXING AND MATCHING MULTIFOCAL IOLs

Stefan Pieh, MD; Herbert Weghaupt, Christian Skorpik MD; Contrast Sensitivityand glare disability with diffractive and refractive multifocal IOL. J Cataract and

Refract Surgery 1998; 24-659-662.

• Loss of contrast sensitivity• Glare and halos– scattering of light at the dividing line of the different

zones– improves with bilateral implantation, because of “a

bilateral summation” effect• Less satisfactory visualization of fundus- difficulty in

vitreo-retinal procedures• Requires Visual-Cortical Neuro-adaptation

ACCOMMODATIVE IOLs

• Monofocal IOL• Changes position inside the eye as the eye's

focusing muscle contracts• 1 mm of anterior movement of lens = 1.80 D

of accommodation• Mimicking the eye's natural ability to focus

• Silicone– Crystalens (Bausch & Lomb)– Only FDA approved IOL for correction of

presbyopia

• Hydrophilic Acrylic– BioComFold type 43E (Morcher GmbH) – 1CU (HumanOptics AG)– Tetraflex (Lenstec Inc.)

Akkolens IOL (Akkolens, Lumina IOL)

• Principle of the Alvarez lens

– Two sinusoidal optical surfaces slide across one another along the

horizontal axis

• Anterior element with a spherical lens

• Two cubic optical surfaces for varifocal effect

– fitted by spring-like haptics fused at the rim

– movement perpendicular to the optical axis

• Implanted in the sulcus

• 2 D to 5 D of near add power

Synchrony Dual-Optic IOL (Visiogen)

• One piece Silicon foldable IOL• Two optics – high plus anterior– posterior minus lens

• connected by spring like haptics.

• Zonular tension is released – compression of optic-spring haptic releases anterior optic forward.

TORIC IOLs

• 22% of patients undergoing cataract surgery have substantial corneal astigmatism

• >1.25 D

• Staar Surgical Intraocular Lens– First FDA approved (in 1998) toric IOL– 2.00 and 3.50D– Plate-haptic– Poor rotational stability– limited power range

• AcrySof IQ Toric IOL (Alcon Labs, USA)– September 2005– T3 to T9– posterior surface has added cylindrical power and axis

markings• Acri.Comfort 646TLC and Acri.LISA toric 466TD– Carl Zeiss Meditec– incision < 2 mm

• Rayner Sulcoflex toric 653T (Piggy back sulcus lens)

• CANDIDATES– > or = 1.0D regular corneal astigmatism

• AcrySof Toric IOL Calculator – compensates for surgically induced astigmatism

• Marking The Eye– reference marks at the 3- and 9-o’clock– sitting upright

• Aligning the Toric IOL with the Axis– Gross alignment, – Viscoelastic removal,– Final alignment

• Remove OVD from behind the IOL

• For every 1 degree of axis rotation, 3.3% of the lens cylinder power may be lost.

• At 30 degrees, all effect is lost

ROLLABLE IOLs

• Ultrathin ~100 µ• Hydrophilic material • Front surface curved• Back surface: series of steps with concentric rings• Open up gradually• Implanted by phakonit technique

• Acrismart • Thin Optx ultrachoice• Slimflex lens

IOL IMPLANTAION IN SPECIAL SITUATIONS• ABSENCE OF CAPSULAR SUPPORT

– Scleral fixation (suture/glue)– Iris fixated– ACIOLs

• PEDIATRIC AGE GROUP– Heparin coated– Multifocal IOLs

• DRUG ELUTING IOLs– Triamcinolone acetonide– Dexamethsone– Antibiotic– Diclofenac sodium (0.2 mg/mL)– Mitomicin C (0.2 mg/mL) – Colchicine (12.5 mg/mL) and 5-fluorouracile (10 mg/ml)– Anti-VEGF

ANIRIDIA IOLs

• Various designs

– Overall size = 12.5 to 14 mm

– Optic diameter = 3.5 to 5 mm

– Central clear optic

– Surrounding colored diaphragm

PHAKIC IOLs

PHAKIC IOLs

• Implantation of IOL without removing natural crystalline lens.

• ADVANTAGE: Preserves natural accommodation– Mostly used in Myopic eyes: -5 to -20 DS– Also used in Hyperopic eyes

• Concern in Hyperopes:– More chances of endothelial damage– Increased risk of angle closure glaucoma

– Life-long regular follow up required.

PHAKIC IOLs

• Posterior Chamber• Iris fixated• Angle fixated

PHAKIC IOLs

• Implantable collamer lens (ICL) (VISIAN; STAAR)• Phakic refractive lens (Mellennium)• Sticklens

• COMPLICATIONS:– Endothelial cell damage– Inflammation– Pigment dispersal– Elevated IOP– Cataract

Implantable Collamer Lens (ICL)

• Pre-crystalline lens made of silicone or collamer.

• Length of the lens = white-to-white limbal diameter - 0.5 mm– Overall size- 11-13 mm– Otical zone - 4.5-5.5 mm– Toric model also available

• COMPLICATIONS:– Constant contact pressure – Cataract– Ciliary body reactions– Prevent free passage of aqueous.- Iridectomy

required– SPINNAKER EFFECT: Blowing sail of a boat

IRIS FIXATED PHAKIC IOL• VERISYSE/ARTISAN (AMO/OPTECH)– Made of PMMA– convexo-concave– Length = 7.2 – 8.5 mm– Optic size = 5-6 mm– Haptics fixed to iris –claws

IRIS FIXATED PHAKIC IOL

• ADVANTAGES OVER ICL: – Customized smaller size possible– Easier examination from end-to-end

• COMPLICATIONS- – Early post op AC inflammation– Glaucoma– Iris atrophy on fixation sites– Implant dislocation– Decentration– Endothelial cell loss

ANGLE FIXATED PHAKIC IOL

• TWO TYPES – – 4 point fixation• Baikoff’s modification of Kelman type haptic design• NuVita MA20 (Bausch and Lomb)

– 3 point fixation• Vivarte (IOL Tech)• Separate optic and haptic

ANGLE FIXATED PHAKIC IOL

• COMPLICATIONS –– Endothelial cell loss– Irregular pupil– Iris depigmentation– Post-op inflammation– Halos and glare– Surgical induced astigmatism

PIGGYBACK IOLs• An intraocular lens that

“piggybacks” onto an existing intraocular lens or two IOLs are implanted simultaneously.

• First IOL is placed in the capsular bag.

• The second (piggyback) IOL is placed in the bag or sulcus.

• Easier to place 2nd IOL than to explant IOL & replace it– Lesser risk– More predictable– Can change power with time-by adding IOL or

explanting an IOL– Better image quality– Increased depth of focus

• COMPLICATIONS– Interlenticular opacification • (Interpseudophakos Elshnig’s pearls) • (RED ROCK SYNDROME)

– Unpredictable final IOL position

COMPLICATIONS RELATED TO IOLs

• MALPOSITIONS– Pupil capture– Decentration – Windshield wiper syndrome– Sunset syndrome

• PCO• Dysphotopsias – Positive : night time glare and halos– Negative : black ring more towards temporal field

• IOL material : acrylic > silicone• Refractive index : negative dysphotopsia more

with higher refractive indices• Smaller optic size • Square edge• Multifocal IOL• Iris-optic distance• Self resolving in a few weeks (cortical adaptation)

RECENT ADVANCES AND THE FUTURE

• LIGHT ADJUSTABLE IOL• TELESCOPIC IOLs• SMART IOLs

• ELECTRONIC IOLs

LIGHT ADJUSTABLE IOL

• Calhoun Vision• Silicone lens with two C-PMMA haptics• Photosensitive to the near-ultraviolet wavelength of

energy in a specific pattern– myopic adjustment : periphery of the lens

• Final irradiation step locks in the power change• ±2 D for sphere and 2.5 D for astigmatism at the

spectacle plane

• Sunglasses for about three weeks

IMPLANTABLE MINIATURE TELESCOPE

• Miniature implantable Galiliean telescope– Implanted in posterior chamber– Held in position by haptics loops– Contain number of microlenses which magnify

objects in the central visual field.– Improves central vision in ARMD.

• Telephoto system : 2-3 times magnification• Images in the central visual field – not be focused directly on the damaged macula– over other healthy areas of the central and

peripheral retina

• DRAWBACKS:– Surgically more challenging– Difficulty due to the size and

weight of the implant– Endothelial compromise– Blocked peripheral retinal visibility– Difficulty in future retinal laser

treatments– Loss of peripheral vision

TELESCOPIC IOL

• Next generation of implantable miniature telescopes.• Uses mirrors rather than glass lenses• 25 X magnification of central images• The LMI (Lipshitz Macular Implant)

– optics is 6.5mm – slightly thicker than a standard IOL

• Contains 2 miniature mirrors – 2.8 mm posterior doughnut shaped mirror that reflects light

anteriorly – 1.4 mm central retina–facing mirror which in turn focuses the

light on retina).• Does not affect peripheral vision.

SMART IOL

IOL POWER CALCULATIONS

• Before 1980s, – Best described as ‘educated guesses’• The IDEM lens (ideal emmetropia lens)

– +17.0 D for an AC lens, – +19.0D for an iris fixated lens – +21.0D for a posterior chamber lens

• The Standard lens– +1.25D added to the IDEM lens power

• The Emmetropia lens– (pre existing refractive error) X 1.25 + IDEM lens power

IOL POWER PREDICTION FORMULAE

• First Generation - SRK- 1 and Binkhorst formulae• Second Generation – SRK-2• Third Generation – SRK T, Hollday. Hoffer-Q• Fourth Generation – Hollday 2, HAIGIS

• Theoretical formulae• Regression formulae

• human eye functions as a dual lens system

• position of the cornea and the retina is fixed

• effective IOL power– Power of iol– Postion

• “in the bag” IOL is 21.0D• in the sulcus will

function as a 22.0 lens

THE ELPo

• Dr. Jack Holladay• Anatomical factors– axial length– steepness of the cornea– limbal white to white measurements– preoperative– anterior chamber depth– lens thickness

• position of the capsular bag equator from the corneal vertex : pre op ACD and 40% of the crystalline lens thickness

• IOL and surgery related factors– anterior angulation– material of the haptic– material of the optic– Asphericity

• Individual Surgeon’s Technique– CCC size and centration– inadequate removal of visco-elastic from behind the

IOL– Bag to Sulcus shift

MANUFACTURER’S LENS CONSTANT

• axial length of 23.5mm (applanation A scans)• central corneal power 43.86D (manual

keratometry)• limbal white to white diameter of 11.7mm• 22.0mm – 26.0mm• central corneal power of 41.0D – 46.0D

• The SRK formula– IOL power = A – 2.5 L – 0.9 K.– Donald Sanders, John Retzlaff and Kraff– mid 1980’s.– 6835 eyes– 22.0m – 24.5mm

• SRK 2 formula– Axial length 21-22mm, add 1 to A– 20-21 add 2– < 20 add 3– Over 24.5mm subtract 0.5

• SRK T Formula– third generation formula– 1990– John Retzlaff and Donald Sanders– combines theoretical and regression formulae– predicted post operative anterior chamber depth– retinal thickness– refractive indices of the cornea– regression element is used to optimize the ‘A constant

• The Hoffer-Q formula– Dr. Kenneth Hoffer in 1993– P = f (A, K, Rx, pACD)– short eye balls

• HAIGIS Formula– also called the

GOW 70 formula– Gernet, Ostholt

and Werner in 1970

• three ‘A constants’– a0 : manufacturers lens constant– a1 : pre operative ultrasonically measured ant

chamber depth (this has a default value of 0.4) – a2 axial length measurements (default value of 0.1)– enables customizationof each component– entire range of axial length values

• Holladay 2– 1998– Accurate estimation of the ELPo• Axial length.• Central corneal power (K)• Anterior chamber depth• Lens thickness measurement• Limbal white to white measurement• Age of the patient• Previous refraction of the patient

• Nine types’ of eyes model

• available as part of a package called the ‘Holladay IOL consultant

• entire range of axial lengths

IOL injectors

• Preloaded • Easy loading• Basic type• Autosert (alcon)

MANUFACTURING PROCESS

• MOLDING• LATHE CUT• TUMBLE POLISH

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