CONTACT LENSES By Sridevi Rajeeve 2008 Batch
Jun 01, 2015
CONTACT
LENSES By
Sridevi Rajeeve2008 Batch
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 pecifications
Diameter 1. Overall diameter [OD] - x mm 2. Optical zone diameter (OZ)
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
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 LENSES
Depending 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 > 2D
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 tint Makes light coloured eyes more vivid
Opaque tint Can 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
Normal field of vision provision No aberrations – peripheral /
prismatic Binocular vision in high
anisometropia No condensation of rain or fog Cosmetically more acceptable
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
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
THANK YOU!