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Contact lenses
Contact lenses are artificial devices that correct refractive errors and ocular irregularities by replacing the cornea's anterior surface. They come in various types, including hard, rigid gas permeable, and soft lenses, each with distinct advantages and disadvantages related to comfort, durability, and optical quality. Indications for use extend across optical, therapeutic, cosmetic, and preventive reasons, while contraindications include certain chronic eye conditions and mental incompetence.
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Contact lenses
- 2. What is aContact Lens? • Artificial device whose front surface substitutes the antr. surface of the cornea • Used for correction of: 1. Refractive error 2. Irregularities on front surface of cornea
- 3. Contact Lens Specifications Diameter 1.Overall diameter (OD) 2. Optic zone diameter (OZ)
- 4. Curves • Base curve(BC) or central postr. curve (CPC) • Peripheral curves 1.intermediate (IPC) 2.peripheral (PPC) • Central antr. curve (CAC) or front curve (FC) • Peripheral antr. curve (PAC) • Intermediate antr. curve (IAC)
- 5. Edge • Union ofthe Peri.Postr.C & Peri.Antr.C of the lens Power • Central anterior curve determines the power of the lens • Measured in terms of posterior vertex power in diopters
- 6. Thickness • Measured inthe centre of the lens • Varies depending upon the postr. vertex power of the lens Tint • Color of the lens
- 7. Types of ContactLenses Hard Lens Rigid Gas Permeable Lens Soft Lens
- 8. Hard Lens • FromPMMA (polymethylmethacrylate) • High optical quality, stability, light weight, nontoxic, durable & cheap • Diameter of 8.5-10 mm • Disadvantages: 1. restricting the tolerance 2. corneal abrasions 3. stable tear film
- 9. Rigid Gas PermeableLens • Material permeable to oxygen • Hard, but called as semisoft lenses • Manufactured from: 1. Copolymer of PMMA 2. Silicone containing vinyl monomer 3. Cellulose acetate butyrate
- 10. Soft Lens • HEMA(hydroxymethymethacrylate) • About 1-2 mm larger than corneal diameter • Advantages: 1. comfortable 2. well tolerated
- 11. 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
- 12. Soft Lens • Types: ▪Disposable or Non-Disposable ▪ Clear or Colored ▪ Spherical or Toric ▪ Extended Wear ▪ Multifocal
- 13. 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
- 14. 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
- 15. Disposable Soft Lens •Daily, two-weekly or monthly replacement • Very simple cleaning (no cleaning for daily) • Latest designs and materials • Very popular
- 16. 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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- 18. Extended Wear ContactLens • New technology • Made from silicone material which transmits oxygen well • Can wear for up to thirty days without removing
- 19. MultiFocal Contact Lenses •Can have dual focus lenses • New technology → More expensive • Available as disposable lenses
- 20. Indications • Optical • Therapeutic •Preventive • Diagnostic • Operative • Cosmetic • Occupational
- 21. Optical Indications • Anisometropia •Unilateral Aphakia • High Myopia • Keratoconus • Irregular Astigmatism
- 22. Advantage Over Specs •Can correct irregular astigmatism • Normal field of vision • No aberrations • Binocular vision in high anisometropia • No condensation of rain or fog • Cosmetically more acceptable
- 23. Therapeutic Indications • Diseasesof Cornea • Diseases of Iris • Glaucoma • Amblyopia • Bandage Soft Contact Lenses
- 24. Preventive Indications • Preventionof symblepharon and restoration of fornices in chemical burns • Exposure keratitis • Trichiasis
- 25. Diagnostic Indications • Gonioscopy •Electroretinography • Examination of fundus in case of irregular corneal astigmatism • Fundus photography • Goldmann’s 3 mirror examination
- 26. Operative Indications • Goniotomyoperation for congenital glaucoma • Vitrectomy • Endocular photocoagulation
- 27. Cosmetic Indications • Unsightlycorneal scars • Ptosis • Cosmetic scleral lenses in phthisis bulbi
- 28. Occupational Indications • Sportsmen •Pilots • Actors
- 29. ContraIndications • Mental Incompetence/PoorMotivation • 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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