Aphakia and its corection 4

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Aphakia and its corection 4

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

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