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