Aphakia  Symptoms, Causes , Diagnosis and Unknown Facts
Aphakia is a disorder of structure or function in a human, animal, or plant, especially one that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury.


What is Aphakia ?



Aphakia is a condition in which crystalline lens of the eye is not present in its normal position of pupillary area. Either there is no crystalline lens inside the eye or the lens is subluxated or luxated. This induces a refractive state which is not a refractive error in true sense. An emmetropic (normal refraction) eye or one having low grade ametropia (refractive error) becomes extremely hypermetropic after cataract surgery. A previously emmetropic eye requires a correction of about 10 to 11 dioptres (D) in spectacle when worn in the usual position.

Replacement of the crystalline lens with a spectacle lens causes the image on patient’s retina to be roughly 25% larger than the image formed with the crystalline lens. The exact magnification is determined by the power of the aphakic spectacles. There is about 2 % of magnification for each dioptre of power in the spectacles.

Aphakia comes from two Greek words (a means none and phacos means lens). It refers to both an anatomical and an optical condition.

Von Helmholtz (1855) worked on the optics of aphakia. Benito Daza De Valdes (1623) suggested that aphakia may be corrected with spectacles.




 

Aphakia Symptoms



Aphakia causes symptoms such as

  • Diminution of uncorrected vision.
  • Inability to focus (due to loss of accommodation caused by aphakia).



Aphakia Causes



Causes of aphakia are

  • Surgical aphakia: Surgical aphakia is the commonest type and is produced after removal of the crystalline lens.
  • Congenital absence of lens: There may be congenital absence of lens. It is a rare condition.
  • Absorption of lens matter: Rarely, absorption of lens matter may be seen after trauma in children.
  • Traumatic extrusion of lens: Rarely, there may be traumatic extrusion of lens from the eye leading to aphakia.
  • Posterior dislocation of lens: Posterior dislocation of lens in to the vitreous may cause optical aphakia.
  • Heritable disorders associated with dislocated lenses: These may be

-       Marfan’s syndrome.

-       Weil-Marchesani syndrome.

-       Homocystinuria.

-       Sulphite oxidase deficiency.

  • Heritable disorders reported with subluxated lenses: These include

-       Aniridia.

-       Ehlers- Danlos syndrome.

-       Craniofacial dysostosis.

-       Alport’s syndrome.

-       Megalocornea.

  • Ocular diseases which may lead to subluxated lenses: It includes

-       Hypermature cataract.

-       Buphthalmos.

-       Exfoliation syndrome of lens.

-       Intraocular tumours.

 

 

Optics of aphakia:

  • Optical changes: Optical changes seen after removal of crystalline lens are

-       The eye is highly hypermetropic with total power of about 44 D (power of eye with crystalline lens is about 60 D).

-       The anterior and posterior focal points are about 23 mm and 31 mm, respectively.

-       The two principal points are close to each other near anterior surface of cornea.

  • Image formation: The size of image varies in spectacle- corrected aphakia and contact lens- corrected aphakia.

-       Spectacle- corrected aphakia: There is magnification of about 25 % with aphakic spectacle correction.

-       Contact lens- corrected aphakia: There is less magnification (6-8%) as compared to spectacle correction.

  • Visual acuity: Visual acuity in spectacle- corrected aphakia seems better due to large size of the image. The recorded vision is theoretically better than the actual visual acuity.
  • Binocular vision: Aniseikonia (unequal size of retinal image) less than 5 %, is compatible with binocular vision. Aniseikonia is harmful to the development of normal binocular function.
  • Diplopia (double vision): Adult patients who have normal vision in un-operated eye find it difficult to attain binocular single vision and may suffer with diplopia.
  • Suppression amblyopia: Monocular aphakic children usually develop suppression amblyopia. It may lead to deviation of the operated eye.
  • Accommodation: Absence of crystalline lens leads to total loss of accommodation. Therefore, a patient needs bifocal, progressive or separate pair of glasses.


                                                                                                                                      

Aphakia Diagnosis


Diagnosis depends upon the symptoms and signs of aphakia.

Signs of aphakia:

  • Retinoscopy: Retinoscopy shows high hypermetropia.
  • Purkinje’s image: There are only two Purkinje’s images coming from the cornea. Images from the lens surface are missing.
  • Scar at limbus: Surgical aphakia may show scar at the limbus.
  • Anterior chamber: Anterior chamber is deep due to absence of lens from the eye.
  • Pupil: The pupil appears jet black in the absence of lens.
  • Iridodonesis: Iridodonesis or tremulousness of iris is present due to lack of support being provided by the lens.
  • Fundus: Examination shows hypermetropic fundus and the optic disc appears small.
  • Unexplained weight loss