What is aphakia?
An eye from which a lens is removed, whether after a cataract, dislocation or injury is termed an aphakic eye (Greek: a=without; phakos=lens).
In a normal person, what is the power of the eye lens?
The eye lens has a power of almost 17 dioptres. However, a lower power is needed in a spectacle frame since it is further away from the centre of the eye—usually the power of the spectacle lens is +10 to +12.
What is the age group of aphakic patients?
Since the most common reason for removal of a lens is cataract, patients of the age of 40 and above constitute the aphakic age group.
What problems are faced in correcting aphakia with glasses?
The correction of aphakia entails the use of high powered plus lenses. It is these high powered lenses which cause the problems listed below and not the surgical effects of aphakia as is commonly thought.
(A) Magnification effect
An aphakic eye corrected with spectacle lenses sees an image which is almost 30% larger than the normal eye. In essence, on a road, one would see a large bus inside which a smaller bus would be moving, the smaller image being the vision of the normal eye. Similarly walking on the road or crossing it and getting on the pavement would show two levels of the kerb, the operated eye showing the closer level.
It can be most confusing and a serious fall may result.
This magnification effect also causes a distortion in estimation of distances in space (spatial orientation). On trying to open a door, the door knob will appear closer than it actually is; ‘thus the aphakic patient will seem to be fumbling in air. This problem causes even more bizarre situations to develop at meal times.
(B) Curvature effects
The distortion induced by the spectacle lens makes straight lines appear curved. A door would thus seem to bulge in the middle and to narrow at the top and bottom. There is thus a great deal of distortion in perspective. An architect for example, would find the distortion intolerable.
(C) Reduced visual field
There is a marked reduction in field, since the optics of a thick spectacle lens completely cut off the peripheral vision. Thus an aphakic cannot see objects coming from the sides and tends to bang into objects. Driving may prove a hazardous manoeuvre.
There is in addition another distracting phenomenon; objects seem to pop in and pop out of the visual field like a jack-in-the-box. This is due to the prism induced in the edges of a thick plus lens.
(D) Critical near focus
Reading and near work raise momumental problems. The focus tends to be critical and the reading material has to be brought to the exact focus and held almost completely stationary.
Can the visual problems of aphakics be solved?
Yes. Since the visual problems are purely of an optical nature, due to the spectacle lens, any method whereby spectacles are not used could correct the problem.
Perhaps the simplest way is to wear a contact lens. With a contact lens the magnification factor is very low, there is no spherical aberration and the visual field is full.
As a matter of fact, in many advanced countries, an aphakic stands to lose his driving licence unless he wears contact lenses or has an implant.
The second method, the implant, is the simplest of all, simply the replacement of a human lens by a plastic lens places inside the eye. The lens can neither be felt nor seen and the patient has the advantage of normal vision. Though implants are regularly done in many countries, they are still new in India.
Do the problems of spectacles go away in an aphakic?
No, the problems are always there. However, the mind adapts to the problems, given time. It is simpler when both eyes have been operated as adaptation is quicker and more rapid.
However, some patients can never really adapt to the inherent problems, and for them alternative methods have to be provided.
Do bifocals cause more problems in aphakics?
Yes. The thick glasses induce problems and require a high precision for an exact fit. Undoubtedly, given time, one can adapt to a bifocal.
Usually, separate glasses for distance and near are prescribed for the first 6 months following surgery, to permit the patient to first adapt to the high power. Then, subsequently, once adaptation is completed, one can never revert to a bifocal.