Contact lens -Dr Ferdous

DR MD FERDOUS ISLAMDEPT OF OPHTHALMOLOGY

CMH,DHAKA

Contact Lens

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

Contact Lens Specifications Diameter 1. Overall diameter [OD] - x mm 2. Optical zone diameter (OZ)

Curves Base curve (BC) or posterior central curve (PCC) Peripheral curves : 1. intermediate (IPC) 2. peripheral (PPC) Central anterior curve (CAC) or front curve (FC) Peripheral anterior curve (PAC) Intermediate anterior curve (IAC)

- Only in high power minus and plus lenses

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]

Thickness Measured in the centre of the lens Varies depending upon the posterior vertex

power of the lens

Tint Color of the lens

Types Of Contact LensesDepending upon nature of material used;

Hard Lens Rigid Gas Permeable Lens Soft Lens

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

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

Soft Lens Material: HEMA

(hydroxymethymethacrylate) About 1-2 mm larger than

corneal diameter Advantages: 1. Comfortable 2. Well-tolerated

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 > 2.00D

Soft Lens Types: ▪ Disposable or Non-Disposable ▪ Clear or Colored ▪ Spherical or Toric ▪ Extended Wear ▪ Multifocal

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

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

Disposable Soft Lens Daily, two-weekly or monthly

replacement Very simple cleaning (no cleaning for

daily) Latest designs and materials Very popular

Colored Contact Lens Handling tint

Useful when inserting or removing lens

Enhancing tintMakes light coloured eyes more vivid

Opaque tintCan change colour of eyes

Colored Contact Lens

Extended Wear Contacts Lens New technology Made from silicone material which

transmits oxygen well Can wear for up to thirty days without

removing.

MultiFocal Contacts Lenses Can have dual focus lenses New technology → More expensive Available as disposable lenses

Indications For Use Optical Therapeutic Preventive Diagnostic Operative Cosmetic Occupational

Optical Indications Anisometropia Unilateral

Aphakia High Myopia Keratoconus Irregular

Astigmatism

Advantage Over Spectacles Can correct irregular corneal astigmatism No fall off,break Reducing aberrations. Reducing aniseikonia. Field of vision. Image magnifications. No distortion of image. No aberrations – peripheral / prismatic Binocular vision in high anisometropia No condensation of rain or fog Cosmetically more acceptable

Disadvantages When the pupil is dilated rigid contact

lens may produce a halo. Eye strain in presbyopic myopes.

Therapeutic 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

Preventive Indications Prevention of symblepharon and

restoration of fornices in chemical burns Exposure keratitis Trichiasis

Diagnostic Indications Gonioscopy Electroretinography Examination of fundus in case of irregular

corneal astigmatism Fundus photography Goldmann’s 3 mirror examination

Operative Indications Goniotomy operation for congenital

glaucoma Vitrectomy Endocular photocoagulation

Cosmetic Indications Unsightly corneal scars (Coloured

lenses) Ptosis (Haptic lenses) Cosmetic scleral lenses in phthisis bulbi

Occupational Indications Indications Sportsmen Pilots Actors

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

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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