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Intraocular lens and

contact lens

Keerthi N S

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Intraocular lens

• Implanted lens in the eye.• Replaces the existing crystalline

lens, because:-

It has been clouded by cataract

Refractive surgery to change optical power

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History:-• Sir Harold Ridley was

the first to successfully implant an intraocular lens on November 29, 1949, at St Thomas' Hospital , London.

• That first intraocular lens was manufactured from Polymethylmethacrylate (PMMA.).

What would have made him think about the idea of implanting a lens in cataract surgery???

It is said that the idea of implanting an intraocular lens came to him

after an intern asked him

“ why he was not replacing the lens he had removed during cataract surgery”.

Why did he use acrylic plastic material???

The acrylic plastic material was chosen

because Harold Ridley noticed that it was inert,

after seeing RAF (Royal air Force) pilots of World War II with pieces of shattered canopies in their eyes.

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Parts of IOL

•Central part overlying the optic axis , called as optic and• peripheral arms, called haptics• use of haptics:•to hold the lens in place within the capsular bag inside the eye.

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Materials used for intraocular lenses

• Optic materials

• Non-foldable• Polymethyl

methacrylate

• Foldable• Silicone• Hydrophobic acrylic• Hydrophilic acrylic

• Haptic materials

• Polypropylene• PMMA• Acrylic

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Features of IOL

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• Rigidity :-• flexible or rigid• Optic size :-• 5-7mm• Shape:-• Round or oval• Spheric or aspheric• Plano convex or biconvex

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• Edge :-• Square or rounded

• Holes in the optic:-• Present or absent• To keep IOL in position

Different types of haptic angulation relative to the plane of optic:-

For posterior chamber lens:-100 anterior angulation to keep

the optic part away from the pupil.

For anterior chamber lens:-Posteriorly angulated lens to vault

the intraocular lens away from the pupil

Suitable position for implanting IOL in eye

• Best placed in posterior chamber in the capsular bag.

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Other positions:-

•Posterior capsule tear• zonular dialysis

In the ciliary sulcus

supported by the anterior

capsule.

•If posterior chamber is not feasible for implanting a lens

In anterior chamber

supported by the angle of

anterior chamber

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Power of intraocular lens

•To be calculated carefully to meet the visual requirements of individual patient.

Importance:-

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Power of intraocular lens• Calculated by various formula

Widely used formula

•Modified Sanders-Retzlaff-Kraff formula (SRK)

Modified Sanders-Retzlaff-Kraff formula

Based on the statistical correlation between

calculated and observed refractive error after ocular implantation.

Modified SRK Formula

E=A - 2.5L - 0.9KParameters used in the formula are

estimated by A-scan ultrasonographic

sonometry and keratometry

E=A - 2.5L - 0.9K

E:Emmetropic power of eye

A:Predetermined constant of IOL

L: Axial length

in mm

K:Average of

keratometry readings

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• Most IOLs fitted today are fixed monofocal lenses matched to distance vision.

CONTACT LENS

Contact lensis a thin optical lens worn on the eyeResting on the surface of cornea.Contact lenses are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons.

Adolf Fick

• In 1888, Adolf Fick was the first to successfully fit contact lenses, which were made from blown glass

Purpose of wearing contact lens

• . Aesthetics and cosmetics, to avoid wearing glasses

• For more visual reasons.

Uses of contact lens

Corrective contact lenses

To improve vision, by correcting refractive error

By directly focusing the light with the proper power for clear vision

Spherical contact lens :myopia and hypermetropia , aphakia

Aniseikonia; in unilateral aphakia

Toric contact lens has a different focusing power horizontally than it does vertically, astigmatism

Some spherical rigid lenses can also correct for astigmatism.

Presbyopia presents an additional challenge in the fitting of contact lenses.

Other types of vision correction: colour blindnessFor those with certain

color deficiencies, a red-tinted "X-Chrom" contact lens may be used.

Although the lens does not restore normal color vision,

it allows some colorblind individuals to distinguish colors better

Contact lens : In management of non-refractive disorders

Bandage contact lens protects:Bullous keratopathy,corneal edemaDry eyesCorneal abrasions and erosionKeratitisDescemetoceleCorneal ectasisMooren's ulcerAnterior corneal dystrophyNeurotrophic keratoconjunctivitis

Cosmetic contact lenses

To change the appearance of the eye.

Also correct refractive error.

Merits over spectacles

Typically provide better peripheral vision

Do not collect moisture such as rain, snow, condensation, or sweat.

This makes them ideal for sports and other outdoor activities.

Keratoconus and aniseikonia that are typically corrected better by contacts than by glasses.

Types of contact lens

• Hard• Soft• Rigid-gas permeable

Hard contact lens

1930-1970Made of PMMADo not allow enough oxygen to

reach the eye.Difficult to adaptBut visual clarity is goodUsed in astigmatic corneasLess acute infectiveIndications for use are now

restricted

Soft contact lens

Made from gel like plastic, hydroxy methyl methacrylate

Contains 79% waterBetter initial comfortBut prone to deposits;is disposables;15 hrsDifficult to keep clean and and to handle

Continuous wear soft contact lens

• Increased water content • Increased oxygen permeability• Allow up to 6 times more oxygen to cornea

than ordinary contact lens• Can be worn upto 30 nights and day• But has increased risk of infections than daily

wearing lenses.

Rigid gas permeable lenses

• Oxygen permeable lenses• Made from:firm,durable plastic that

transmits oxygen• A co-polymer of PMMA and silicone and

cellulate acetate butyrate• Do not contain water; resists deposits;

decreased risk of bacterial infections

• Easy to clean• Disinfect• Do not dehydrate• Last longer than soft lenses• Rigid; easy to handle than soft lenses• Retain their shape; provide sharp vision

Risks of cosmetic contact lensCarry risks of mild and serious

complicationsocular redness,painirritation, and infection.

Complications due to contact lens wear affect roughly 5% of contact lens wearers each year

Improper use of contact lenses may affect the eyelid, the conjunctiva, and the various layers of the cornea.

Poor lens care can lead to infections by various microorganisms including bacteria, fungi, and Acanthamoeba

Measures to be taken prior to use a contact lens

•Retinoscopy•keratometry

To measure anterior

curvature of lens

•Tear film and cornea examined under slit lamp

To rule out dry eye,blepharitis or

pre-existing keratopathy

•Trial lenses are evaluated under biomicroscope

Evaluation of Fitting

Tear film examination

• Fluorescein that Highlight tear film are useful in fitting rigid lens

• Ideal lens show a minimal , uniform film behind the contact lens

• Pooling of dye in centre denotes: a steep fit

• Absence of dye in centre: a flat fit

HARD CONTACT LENSES

SOFT CONTACT LENSES

RIGID GAS PERMEABLE LENSES

Oxygen delivery

Visual clarity

Use in astigmatism

Adaptation

Deposits

Durability

HARD CONTACT LENSES

SOFT CONTACT LENSES

RIGID GAS PERMEABLE LENSES

Oxygen delivery Poor High Moderate to high

Visual clarity Good Need to refocus after a blink

Clear vision

Use in astigmatism Possible Less suitable Possible

Adaptation Required Not required Required

Deposits Few Accumulate over time

Few

Durability May scratch Tend to tear Do not scratch or tear

Lens case to store contact lens