Aphakia – Causes, Optics, Clinical features and Treatment

  • Aphakia literally means absence of crystalline lens
  • From an ophthalmological point of view, aphakia is the absence of the lens in the pupillary area

Causes of aphakia

  • Congenital aphakia
  • Surgical aphakia – removal of lens as in cataract extraction
  • Aphakia due to absorption of lens – sometimes seen in children after trauma
  • Traumatic extrusion of lens
  • Posterior dislocation of lens into the vitreous causes optical aphakia

Optics in aphakia

  • The lens is important in refraction and hence its removal results in considerable decreased in the refractory power of the eye
  • The eye becomes highly hypermetropic
  • The power of eye decreases from +60D to +44D
  • The power of accomodation lost
  • The posterior focal point lies behind the eyeball

Clinical features

  • Symptoms
    • Defective vision – due to high hypermetropia and loss of accomodation
    • Erythropsia and cyanopsia – due to entry of infrared and ultraviolet rays in the absence of the crystalline lens
  • Signs (anterior to posterior)
    • Limbal scar in case of surgical aphakia
    • Deep anterior chamber
    • Iridodonesis – tremulousness of the iris due to loss of support of lens
    • Jet Black pupil
    • Loss of 3rd and 4th purkinje images
    • Fundus examination reveals a small hypermetropic fundus
    • Retinoscopy shows high hypermetropia

Treatment:

  • Spectacles
    • Spectacles should be prescribed with about +10D lens for correction of aphakia
    • It should also include correction for surgical astigmatism and +3-4D for near vision
    • Nowadays spectacles are not preferred for use in aphakia due to its many disadvantages
    • Advantages of using spectacles in aphakia
      • Cheap
      • Easy to use
      • No complications
    • Disadvantages
      • The images are magnified – about 30% – hence not useful in unilateral aphakia as it causes diplopia
      • The field of vision in decreased considerably
      • Spherical and chromatic aberration of high power lenses
      • Roving ring scotoma (Jack in the box phenomenon)
      • Prismatic effect of the thick lenses
      • High power are cosmetically not acceptable
  • Contact lenses
    • Advantages over spectacles:
      • Produces less magnification
      • Better field of vision
      • Less chromatic and spherical aberration
      • No prismatic effect
      • Cosmetically more acceptable
    • Disadvantages
      • Costly
      • More care in required usage of contact lenses – may not be suitable for use in young children and elderly
      • Complications related to use of contact lenses
  • Intraocular lens implantation
    • This is the preferred method nowadays
    • The lens can be implanted in the capsular bag or in the anterior chamber
    • It eliminates most of the disadvantages associated with the use of spectacles or contact lenses
    • Disadvantage include the complications associated with surgery
  • Refractive surgery – This is a newly emerging treatment for aphakia
    • Keratophakia
      • a lenticule prepared from the donor cornea is placed within the lamellae of the patient’s cornea
    • Epikeratophakia
      • a lenticule prepared form the donor cornea is stitched to the patients cornea after removing the epithelium
    • Hyperopic Lasik
3 Comments

Add a Comment

Your email address will not be published. Comments will be displayed only after moderation.