Download - Contact Lenses
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CONTACT
LENSES By
Sridevi Rajeeve2008 Batch
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What is a Contact Lens ?
Artificial device whose front surface substitutes the anterior surface of cornea.
Used for correction of: 1. Refractive errors 2. Irregularities on anterior surface of cornea
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Contact Lens pecifications
Diameter 1. Overall diameter [OD] - x mm 2. Optical zone diameter (OZ)
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Curves Base curve (BC) or central posterior curve (CPC) Peripheral curves : 1. intermediate (IPC) 2. peripheral (PPC) Central anterior curve (CAC) or front curve (FC) Peripheral anterior curve (PAC) Intermediate anterior curve (IAC)
Tear reservoir+ ski for lensmovements
Power
- Only in high power minus and plus lenses
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Edge Polished and blended union of the Peripheral
posterior curve & Peripheral Anterior curve of the lens
Power Central anterior curve curvature determines the
power of the lens Measured in terms of posterior vertex power. Unit: Diopters [D]
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Thickness Measured in the centre of the lens Varies depending upon the posterior
vertex power of the lens
Tint Color of the lens
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TYPES OF CONTACT LENSES
Depending upon nature of material used; Hard Lens Rigid Gas Permeable Lens Soft Lens
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HARD LENS
From PMMA (polymethylmethacrylate) High optical quality, stability, light weight,
nontoxic, durable & cheap Diameter of 8.5-10 mm Disadvantages: 1. Restricts the tolerance -
O2 impermeable
2. Corneal Abrasions 3. Stable tear film
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RIGID GAS PERMEABLE Lens
Material permeable to oxygen Popularized as Semi-Soft lenses Manufactured from a co-polymer of:
1. PMMA 2. Silicone containing vinyl
monomer 3. Cellulose acetate butyrate
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SOFT LENS
Material: HEMA (hydroxymethymethacrylate)
About 1-2 mm larger than corneal diameter
Advantages: 1. Comfortable
2. Well-tolerated
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Soft Lens Disadvantages: 1. Wettability 2. Proteinaceous deposits 3. Can get torn 4. Limited life 5. Inferior optical quality 6. Increased risk of corneal infections 7. Cannot correct astigmatism > 2D
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Soft Lens Types: ▪ Disposable or Non-Disposable ▪ Clear or Colored ▪ Spherical or Toric ▪ Extended Wear ▪ Multifocal
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Spherical Soft Lens A spherical contact lens is one in
which both the inner and outer optical surfaces are portions of a sphere
Corrects both short- and long- sightedness
Cheapest & most comfortable Easy to get in a disposable form
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Toric Soft Lens A toric lens is one in which either or
both of the optical surfaces have the effect of a cylindrical lens, usually in combination with the effect of a spherical lens
Corrects astigmatism Lens is specially weighted to conform
to irregular cornea More expensive than spherical Some are available in disposable
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Disposable Soft Lens Daily, two-weekly or monthly
replacement Very simple cleaning (no cleaning for
daily) Latest designs and materials Very popular
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Colored Contact Lens Handling tint
Useful when inserting or removing lens
Enhancing tint Makes light coloured eyes more vivid
Opaque tint Can change colour of eyes
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Colored Contact Lens
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Extended Wear Contacts Lens
New technology Made from silicone material which
transmits oxygen well Can wear for up to thirty days
without removing.
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MultiFocal Contacts Lenses Can have dual focus lenses New technology → More expensive Available as disposable lenses
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Indications for use Optical Therapeutic Preventive Diagnostic Operative Cosmetic Occupational
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Optical Indications Anisometropia Unilateral
Aphakia High Myopia Keratoconus Irregular
Astigmatism
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Advantage over spectacles
Can correct irregular corneal astigmatism
Normal field of vision provision No aberrations – peripheral /
prismatic Binocular vision in high
anisometropia No condensation of rain or fog Cosmetically more acceptable
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Therapeutic Indications Indications
Diseases of Cornea – Non-healing corneal ulcers, filamentary keratitis and recurrent corneal erosion syndrome.
Diseases of Iris – Aniridia, coloboma and albinism (avoid glare)
Glaucoma (vehicle for drug delivery) Amblyopia (Opaque lens - Occlusion) Bandage Soft Contact Lenses – Post-keratoplasty and microcornealperforation
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Preventive Indications Prevention of symblepharon and
restoration of fornices in chemical burns
Exposure keratitis Trichiasis
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Diagnostic Indications Gonioscopy Electroretinography Examination of fundus in case of
irregular corneal astigmatism Fundus photography Goldmann’s 3 mirror examination
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Operative Indications Goniotomy operation for congenital
glaucoma Vitrectomy Endocular photocoagulation
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Cosmetic Indications Unsightly corneal scars (Coloured
lenses) Ptosis (Haptic lenses) Cosmetic scleral lenses in phthisis
bulbi
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Occupational Indications Indications
Sportsmen Pilots Actors
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ComplicationsEyelid PtosisConjunctivaGiant papillary conjunctivitisSuperior limbic keratoconjunctivitisCorneaEpithelium
Corneal abrasionCorneal erosionContact lens acute red eye (CLARE)KeratitisCorneal ulcer
Corneal stroma Corneal neovascularisationCorneal oedemaCorneal infiltrates
Corneal endothelium Endothelial polymegathism
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ContraIndications Mental Incompetence/Poor Motivation Chronic Dacryocystitis Chronic Blepharitis and Recurrent Styes Chronic Conjunctivitis Dry-Eye Syndrome Corneal Dystrophies and Degenerations Recurrent diseases like Episcleritis,
Scleritis & Iridocyclitis
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THANK YOU!