Aphakia and its corection  4
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Aphakia and its corection 4

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Aphakia and its corection  4 Aphakia and its corection 4 Presentation Transcript

  • Aphakia and its correction
  • Aphakia
    • Def: Absence of crystalline lens from the patellar fossa
    • Produces a high degree of hypermetropia and loss of accomodation
  • Causes
    • Congenital absence of crystalline lens
    • Surgical aphakia after cataract extraction
    • Post-traumatic absorption of lens
    • Traumatic extrusion of lens
    • Posterior dislocation of lens
  • Optics of an aphakic eye
    • High hypermetropia
    • Total power of the eye reduced to +44 D
    • Aphakic eye consists of a curved surface, ie. cornea , separating two media of different refractive indices, air (1) and aqueous and vitreous humor (1.33)
    • Anterior focal point becomes 23.2 mm in front of the anterior surface of the cornea
    • Posterior focal point lies 31 mm behind the anterior surface of the cornea
    • Total loss of accomodation
  • Clinical features
    • Symptoms: defective vision for near and far
    • Signs:
    • Limbal scar may be seen in case of surgical aphakia
    • Deep anterior chamber
    • Jet black pupil
    • Iridodonesis
    • Purkinje image test: 3 rd and 4 th images are absent
    • Fundus examination: small hypermetropic disc
  • Treatment
    • Optical treatment:
    • Spectacles:
    • Standard aphakic glass- +10D
    • Exact power to be determined by retinoscopy
    • Advantages: safe, easy and inexpensive method of correcting aphakia
  • Treatment
    • Difficulties encountered in correcting aphakia with the use of spectacles:
    • - Image magnification of ~30% (cannot be used to correct unilateral aphakia as it will result in diplopia)
    • Spherical aberrations resulting in “pin-cushion” effect
    • Lack of physical coordination
  •  
    • “ Jack in the box” phenomenon- “roving ring” scotoma due to prismatic effects at the edges of the lens
    • Prismatic errors resulting from displaced optical centres of lenses
    • Reduced visual fields and poor eccentric acuity
    • Physical inconvenience and cosmetic deficiency of heavy spectacle lenses
    • Contact lenses:
    • Advantages:
    • Less image magnification
    • Elimination of aberrations and prismatic effects of thick glasses
    • Better field of vision
    • Cosmetically more acceptable
    • Suitable for unilateral aphakia
    • Disadvantages of contact lenses:
    • Costly
    • Cumbersome to use esp in children and elderly
    • Associated corneal complications
    • IOL implantation: best available method of correcting aphakia
    • Refractive corneal surgery:
    • Keratophakia- lenticule prepared from donor cornea is placed between patient’s corneal lamellae
    • Epikeratophakia: a lenticule prepared from the donor cornea is sutured to the surface of patient’s cornea after removing the epithelium
    • Hyperopic LASIK