WHAT IS APHAKIA ?

Aphakia literally means absence of crystalline lens from the eye.

However, from the optical point of view, it may be considered a condition in which the lens is absent from the pupillary area.

Aphakia produces a high degree of hypermetropia.

Causes

1. Congenital absence of lens. It is a rare condition.

2. Surgical aphakia occurring after removal of lens is the commonest presentation.

3. Aphakia due to absorption of lens matter is noticed rarely after trauma in children.

4. Traumatic extrusion of lens from the eye also constitutes a rare cause of aphakia.

5. Posterior dislocation of lens in vitreous causes optical aphakia.

Optics of aphakic eye

Following optical changes occur after removal of crystalline lens:

1. Eye becomes highly hypermetropic.

2. Total power of eye is reduced to about +44 D from +60 D.

3. The anterior focal point becomes 23.2 mm in front of the cornea.

4. The posterior focal point is about 31 mm behind the cornea i.e., about 7 mm behind the eyeball.

5. There occurs total loss of accommodation.

Clinical features

Symptoms.

1. Defective vision. Main symptom in aphakked defective vision for both far and near due to high hypermetropia and absence of accommodation.

2. Erythropsia and cynopsia i.e., seeing red and blue images.

This occurs due to excessive entry of ultraviolet and infrared rays in the absence of crystalline lens.

Signs of aphakia include:

1. Limbal scar may be seen in surgical aphakia.

2. Anterior chamber is deeper than normal.

3. Iridodonesis i.e., tremulousness of iris can be demonstrated.

4. Pupil is jet black in colour.

5. Purkinje's image test shows only two images

6. Fundus examination shows hypermetropic small disc.

7. Retinoscopy reveals high hypermetropia.

Treatment

Optical principle is to correct the error by convex lenses of appropriate power so that the image is formed on the retina.

Modalities for correcting aphakia include:

(1)spectacles,

(2) contact lens,

(3) intraocular lens, and

(4) refractive corneal surgery.

1. Spectacles prescription has been the most commonly employed method of correcting aphakia, especially in developing countries.

Presently, use of aphakic spectacles is decreasing. Roughly, about +10 D with cylindrical lenses for surgically induced astigmatism are required to correct aphakia in previously emmetropic patients.

However, exact number of glasses will differ in individual case and should be estimated by refraction. An addition of +3 to +4 D is required for near vision to compensate for loss of accommodation.

Advantages of spectacles.

It is a cheap, easy and safe method of correcting aphakia.

Disadvantages of spectacles.

(i) Image is magnified by 30 percent, so not useful in unilateral aphakia (produce diplopia).

(ii) Problem of spherical and chromatic aberrations of thick lenses.

(iii) Field of vision is limited.

(iv) Prismatic effect of thick glasses.

(v) 'Roving ring Scotoma' (Jack in the box phenomenon).

(vi) Cosmetic blemish especially in young aphakes.

2. Contact lenses.

Advantages of contact lenses over spectacles include:

(i) Less magnification of image.

(ii) Elimination of aberrations and prismatic effect of thick glasses.

(iii) Wider and better field of vision.

(iv) Cosmetically more acceptable.

(v) Better suited for uniocular aphakia.

Disadvantages of contact lenses are:

(i) more cost

(ii) cumbersome to wear, especially in old age and in childhood

(iii) corneal complications may be

associated.

3.Intraocular lens implantation is the best available method of correcting aphakia. Therefore, it is the commonest modality being employed now a days.

4. Refractive corneal surgery is under trial for correction of aphakia. It includes:

i. Keratophakia.

In this procedure a lenticule prepared from the donor cornea is placed between the lamellae of patient's cornea.

ii. Epikeratophakia.

In this procedure, the lenticule prepared from the donor cornea is stitched over the surface of cornea after removing the epithelium.

iii. Hyperopic Lasik

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