Cataracts on the eye: what is it?
Cataract has nothing to do with the outer lens of the eye (the cornea), nor is it a ‘skin’ growing over any part of the eye. Cataract is a clouding or whitening of the internal focusing lens of the eye (the crystalline lens). This lens is situated behind the colored iris of the eye and light reaches it through the pupil.
Cataract is the result of changes in the orderly arrangement of the transparent fibers from which the lens is made.
The term ‘cataracts’ arose from the imaginative notion that the appearance of whiteness, seen in cases of dense lens opacity, was caused by a cataract or waterfall descending from above.
Some degree of loss of lens clarity is present in almost everyone over the age of about 60.
Usually this is patchy, and worse in the edges of the lenses, so that there is little effect on vision.
But the deterioration almost always progresses steadily with age, and most people over 75 have some measurable loss of sharpness of vision from lens opacity. Few people in their 80s are free from appreciable visual loss from this cause.
Symptoms of cataracts
The main symptoms of cataracts are:
- blurry vision;
- being dazzled easily by lights;
- faded color vision.
Progressive hardening of the center of the lens (nuclear sclerosis) is common in cataract. This often leads to a special form of short sight (index myopia) in which the bending power of the lens increases.
Index myopia can progress steadily to high degrees, so that many changes of glasses may be needed if correction is desired. It is the reason why old people often stop using their reading glasses after years of wear. However, this is a passing stage in the development of cataract, and vision is likely to get worse.
People with index myopia who can read without glasses will, of course, need ordinary short-sight glasses for vision in the distance.
Cataract usually causes a change in the appearance of colors. Reds, yellows and orange are accentuated at the expense of blue, but, because of the very gradual nature of the change, this may remain unnoticed. Patients may be surprised at the brilliance of blues after cataract operations.
Cataracts are irregularly opaque which causes some rays of light entering the eye to be scattered while some are not. This may occur even at an early stage, and may be very annoying. The effect is particular noticeable when the headlights of approaching cars shine in the eyes while driving at night.
Many people otherwise barely affected find they have to avoid night driving because of this.
Cataract never causes complete blindness in the sense of total absence of the ability to see light. People with dense cataracts can still usually distinguish an open from a closed door and will always see windows in daytime. But as the transparency of the lenses is gradually lost, image clarity slowly declines.
Perception of detail becomes less and less until eventually the vision is completely clouded.
Contrary to what many people think, cataracts are not usually visible by other people. It is only the occasional and exceptionally mature cataract that shows as a white pupil.
Causes of cataracts
Most cataracts are age-related and can be considered as a normal ageing effect, rather like the whitening of the hair. Some experts believe that undue exposure to sunlight can cause old-age cataracts, but this is not certain.
In diabetic people, cataracts tend to come on about ten years earlier than in non-diabetic people, but the form of the cataracts is the same.
Cataract in younger people is almost always the result of an identifiable cause, and there are many of these. They include:
- Cataract present at birth (congenital cataract) caused by German measles (Rubella) in the mother early in pregnancy, or, less often, by drugs taken by the mother during the early weeks when the eyes of the fetus were developing
- Down’s syndrome
- Various rare hereditary conditions
- Some severe skin problems, all fortunately rare
- Severe childhood diabetes, with high blood sugar levels
- Galactosaemia, a condition in which the infant is unable to break down galactose into simpler sugars, so that it accumulates in the body. Unless a galactose-free diet is given, cataract is inevitable.
Here are some other moments, that can cause cataract:
People taking large doses of steroids over a long period, or those using steroid eye drops for many months, are liable to develop cataract.
Various toxic chemicals, such as naphthalene, dinitrophenol or ergot, can cause cataract. Dinitrophenol had a vogue as an aid to slimming in the early twentieth century, but was abandoned when it was found that many of the young women taking it developed cataracts.
Injury to the eye is an important cause of cataract. A sudden blunt force such as from a flying stone or high-speed squash ball, a sharp poke from a finger or a severe blow to the face may cause cataract even without any external injury to the eye.
Penetrating wounds of the eye are even more likely to cause cataract, especially if the lens capsule is punctured or torn. In such cases, water immediately enters the lens substance, and within a matter of hours or days a dense cataract will develop.
Cataract can be diagnosed by an eye specialist using an examining microscope with intense illumination (slit lamp) and opthalmoscope to examine the eye. The opaque areas will be identified and their position in the lens noted. At the same examination, the clarity of vision (visual acuity) in each eye is measured, and an attempt is made to see past the opaque areas so that the retina can be examined. The pressure of fluid in the eye is also measured.
Treatment of the cataract
There is no possible way to restore transparency to a lens suffering from cataract other than cataract surgery. This is a most successful operation, and so long as the eye is otherwise healthy, excellent results can be expected.
Cataracts present at birth can be prevented by ensuring immunity from rubella by vaccination. Galactose cataracts can be prevented by early diagnosis and a galactose-free diet.
But there is probably no way of avoiding old-age cataracts. Some ophthalmologists believe that protection of the eyes from bright sunlight may help.