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.
Agarwal Sunita, Agarwal Athiya, Apple David J, Buratto Lucio, Aliό Jorge L, Pandey Suresh K, Agarwal Amar. Textbook of Ophthalmology Vol 1. Jaypee Brothers Medical Publishers (P) Ltd 2002. P 170- 173.
Helmholtz von H. Uber die Akommodation des Auges. Graefe Arch Ophthalmol. 1855; 1: 1- 89.
Helmholtz von H. Handbuch der Physiologishen Optik Third Edition Vol 1, Menasha, Wisconsin: The Optical Society of America, 1909.
Aphakia causes symptoms such as
Causes of aphakia are
- Marfan’s syndrome.
- Weil-Marchesani syndrome.
- Sulphite oxidase deficiency.
- Ehlers- Danlos syndrome.
- Craniofacial dysostosis.
- Alport’s syndrome.
- Hypermature cataract.
- Exfoliation syndrome of lens.
- Intraocular tumours.
Optics of aphakia:
- 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.
- 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.
Diagnosis depends upon the symptoms and signs of aphakia.
Signs of aphakia:
Management should be carried out under medical supervision.
Medical optical therapy:
Optical therapy of aphakia comprises of prescribing appropriate convex lenses. The convex lenses may be prescribed in the form of
- Magnification of image: The size of the image is magnified by about 25 %. Spectacles produce diplopia in cases of unilateral aphakia. The larger image of an object is interpreted to be closer to the eye. It requires efforts to coordinate between eyes and hand due to magnification. It produces difficulty in climbing stairs as well.
- Prismatic aberrations: It produces roving ring scotoma, usually described as Jack-in-the-box phenomenon. The prismatic effect is produced by the peripheral part of the correcting lens. It produces a ring scotoma. When patient sees an object and turns the eye towards it, the scotoma may shift inwards to occlude the object. On shifting the eye from the object, the scotoma shifts again and the object becomes visible.
- Spherical aberrations: When the objects are viewed through the periphery, the objects look enlarged, proximal, and elongated in radial direction. Pin-cushion effect produces distortion and it is the property of all plus lenses proportional to their diopteric power. This distortion makes a square look like a pincushion- the corners of the square have a stretched out appearance, and the sides are pushed in. The world becomes parabolic which continuously change its shape with eye movement. The objects appear to move faster. Driving a motor vehicle thus becomes very difficult.
- Field of vision: Monocular as well as binocular field of vision is markedly reduced. The actual field of view through the spectacles is reduced by 25 %, which makes it impossible to see that much of peripheral field.
- Coloured vision: There may be coloured hue in the vision. It occurs due to absence of natural filter of a crystalline lens. Removal of the crystalline lens increases blue and ultraviolet transmission of light.
- Thick glasses: The glasses are very thick and heavy. Bifocal glasses are especially difficult to adjust with and may require separate pair.
- Provides wider and better field of vision.
- There is less magnification of the image since the contact lenses are close to the cornea.
- More suited for uniocular aphakia.
- It eliminates spherical aberration and prismatic effect.
- It is cosmetically more acceptable.
However, there may be lack of dexterity in older patients and intolerance owing to a foreign body sensation.
Surgical therapy includes
- Minimal after- care of patients.
- Rapid return of binocular vision.
- Minimal aniseikonia (different image size seen by the eyes).
- Normal peripheral vision.
- Keratophakia: A lenticule obtained from donor cornea is placed in between the lamellar layers of the cornea of the patient.
- Epikeraophakia: A lenticule obtained from donor cornea is stitched over the surface of cornea after removing the epithelium. Epikeraophakia has the advantage that it may be done in patients where, because of age or ocular condition, a secondary or even primary IOL is not feasible. Since the eyeball is not entered, many complications can be avoided. Also, this procedure may be repeated.
- Hypermetropic Laser assisted in-situ keratomileusis (LASIK).
Prognosis for aphakia is generally good, unless there are complications like corneal oedema, cystoid macular oedema or secondary glaucoma.
However, aphakia increases the risk of retinal detachment, especially in high myopes and if the posterior capsule is ruptured.