Aphakia

Aphakia

APHAKIA

Aphakia literally means absence of crystalline lens from the eye. However,from the optical point of view,it may considered a condition in which  lens is absent from pupillary area. Aphakia produces high degree of hypermetropia.

CAUSES
1. Congenital absence of lens.
2. Surgical aphakia occuring after removal of lens is commonest presentation.
3. Aphakia due to absorption of lens matter is noticed rarely after trauma in children.
4. Traumatic extrusion of lens from eye.
5. Posterior dislocation of lens in vitreous causes optical aphakia.

OPTICS of APHAKIC EYE
1. Eye becomes highly hypermetropic.
2. Total power of eye is reduced to about +44D from +60D.
3. Anterior focal point  becomes 23.2 mm in front of cornea.
4. Posterior focal point is about 31 mm behind the cornea.
5. There occurs total loss of accomodation.

CLINICAL FEATURES
Symptoms
1. Defective vision. Main symptom in aphakia is marked defective vision for both far and near due to high hypermetropia and absence of accommodation.
2. Erythropsia and cyanopsia. Seeing red and blue images. This occurs due to excessive entry of ultraviolet and infrared rays in absence of crystalline lens.

Signs
1. Limbal scar may be seen in surgical aphakia.
2. Anterior chamber is deeper than normal.
3. Iridodonesis. Tremulousness of iris can be demonstrated.
4. Pupil is jet black in colour.
5. Purkinje's image test shows only two images.
6. Fundoscopy examination shows hypermetropic small disc.
7. Retinoscopy reveals high hypermetropia.

Treatment
Modalities for correcting aphakia include..
1. Spectacles prescription has been the most commonly employed method of correcting aphakia.
Advantages- it is cheap,easy and safe method.
Disadvantage- 1. Image is magnified by 30 percent, so not useful in unilateral aphakia.
2. Problem of spherical and chromatic aberrations of thick lenses.
3. Field of vision is limited
4. Prismatic effect of thick glasses
5. Roving ring scotoma
6. Cosmetic blemish.

2. Contact lenses.
Advantages-
1. Less magnification of image.
2. Elimination of aberrations and prismatic effect of thick glasses.
3. Wider and better field of vision.
4. Cosmetically more acceptable.
5. Better suited for uniocular aphakia
Disadvantages
1. More cost
2. Cumbersome to wear.
3. Corneal complications.

3. Intraocular lens implantation. It is commonest modality being employed.

4. Refractive corneal surgery.
1. Keratophakia.
2. Epikeratophakia
3. Hyperopic lasik.