Post on 24-May-2015
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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