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Spectacles and contact lenses1

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  • 1. Spectacles and contact lenses
  • 2. Spectacles
    • Optical appliances comprising of lenses and a frame, with sides extending towards the ears
  • 3. Spectacles
    • Optical correction for refractive errors
    • Lens materials:
      • Transparent
      • Impact resistant
      • Low weight
      • Scratch resistant
      • Easy to manufacture
      • Inexpensive
  • 4. Materials:
    • Glass :
      • crown glass of refractive index 1.52.
      • Provide optimum visual clarity
      • Heavy / break easily
    • Plastic : eg PMMA, CR-39 (RI: 1.49)
      • lighter than glass,
      • does not shatter but can easily get scratched
      • Polycarbonate:
      • lighter, thinner and stronger.
      • high refractive index (1.58)
      • Unbreakable
  • 5.
    • High index glasses :
    • Used for high refractive errors
    • Have a high refractive index of 1.56-1.67, as compared to 1.52 for crown glass
    • These lenses, therefore, are thinner, flatter and lighter
    • Eg flint glass (1.62)
  • 6. Frames:
    • Durable
    • Non allergic
    • Resistant to corrosion
    • Inexpensive
    • Non inflammable
  • 7.
    • Metal
    • Plastic
    • Nylon
    • Combination
    • Tortoise shell
  • 8. Lens shapes
    • Meniscus lenses :
    • Small to moderate degree of refractive errors
    • The standard lenses are ground with base curves
    • + lens uses negative base curve
    • - lens uses positive base curve
    • The prescription is ground onto the other ‘combining surface’
  • 9.
    • Lenticular form:
    • Used for high refractive errors
    • The central portion of the lens is corrective and the peripheral surfaces are parallel to each other
  • 10.
    • Aspheric lenses:
    • - Lens curvature flattens peripherally thereby reducing aberrations and hence providing better peripheral vision
  • 11. Single vision and multiple power lenses
    • Single vision lenses (monofocal):
    • Lenses having the same refractive power over the entire surface
    • Used to correct myopia, hypermetropia, astigmatism, presbyopia
  • 12.  
  • 13.  
  • 14.
    • Multifocal, varifocal or progressive advancement lenses:
  • 15. Tinted, coated and photochromatic lenses
    • Tinted:
      • tints prevent damaging UV rays from entering the eyes
      • reduce the amount of light entering the eye thereby making the patient more comfortable in bright sunlight
  • 16.
    • Photochromatic lens
      • Lenses that darken on exposure to UV rays
      • Once UV is removed (eg. Walking indoors), the lenses become clear
      • Silver halide
  • 17.
    • Anti reflective coating:
      • Destructive interference
      • Prevents annoying reflexes from anterior / posterior surfaces of the lens
      • Driving at night, working at the computer
  • 18. Contact lenses
    • An artificial device substituting the anterior surface of the cornea
    • Concept of contact lenses
  • 19. Types
    • Hard contact lenses
    • Soft contact lenses
    • Rigid gas permeable lenses
  • 20. Hard contact lenses
    • Made of PMMA (poly methyl-methacrylate)
    • Comfort:
      • Do not allow enough oxygen to reach the eye
      • Therefore patients find it difficult to adapt to them
    • Quality of vision:
      • visual clarity is good
      • can be used in astigmatic corneas
    • Deposit formation:
      • Relatively resistant
  • 21. Soft contact lenses
    • Made from HEMA ( hydroxyethyl-methacrylate)
    • Contain ~ 70% water
    • Comfort: better
    • Prone to formation of deposits.
      • discomfort may occur on long term use. Therefore disposable contact lenses ( daily, weekly or monthly) have been introduced
  • 22. Oxygen permeable or Rigid gas permeable lenses (RGP)
    • Made of copolymer of PMMA, silicone and CAB ( cellulose acetate butyrate )
    • This polymer transmits oxygen
    • Deposit formation: resist deposit formation and less likely to cause infection
    • Quality of vision: retain shape better and provide sharper vision
    • Easy to clean and disinfect, last longer than soft C Ls
  • 23. Types: wear time
    • Daily wear
    • Extended wear
    • Continuous wear
  • 24. Type: frequency of replacement
    • Daily disposables
    • Monthly
    • Quarterly
    • Annual / conventional
  • 25. Indications
    • Optical: refractive errors(I huka)
      • Irregular astigmatism
      • High myopia
      • U/L aphakia
      • Keratoconus
      • Anisometropia
  • 26. Advantages
    • Less alteration of image size
    • Less aberrations
    • Retain binocular vision in case of high anisometropia
    • Cosmetically more acceptable
    • Normal field of vision
  • 27.
    • 2. Therapeutic
      • Recurrent epithelial erosions, exposure keratitis,
      • Drug delivery system-pilocarpine
      • Aniridia –absence of iris
    • 3. Diagnostic
      • Gonioscopy
      • Fundus examination
  • 28.
    • 4. Cosmetic
      • Color
      • Disfigured cornea
  • 29. Complications
    • Corneal
      • Epithelial oedema
      • Abrasions
      • Superficial punctate keratitis
      • Neovascularisation
      • Corneal ulcerations
  • 30.
    • Conjunctival:
      • Allergic conjunctivitis
      • Giant papillary conjunctivitis
      • Superior limbic keratoconjunctivitis
  • 31.
    • Contact lens related
      • Scratch / tear
      • Discoloration
      • Lens deposits
      • Loss of lens