What Is A Cataract?
A cataract is a clouding of part of the eye called the lens, sufficient to reduce vision. Vision becomes blurred or dim because light cannot pass through the clouded lens to the back of the eye.
The lens
In a normal eye, the lens is clear, lying behind the iris (the coloured part of the eye) allowing the passage of light rays through it. The lens also contributes to the bending of light rays onto the retina (the light sensitive part at the back of the eye).
The lens can also change its shape to focus objects at different distances. If images are not focused onto the retina properly then vision is affected. Thus, if the lens is cloudy as in cataracts, light cannot pass through it.
Consequently, light images do not reach the retina, thus impairing vision. The first image below illustrates light rays passing through the lens and onto the retina of a normal eye, the second shows a cloudy lens (cataract) which is blocking light from reaching the retina.
An eye without a cataract.
An eye with a cataract.
How can cataracts affect my vision?
An opacity in the lens of the eye...
- causes a gradual painless loss of vision. (You may notice that some things seem blurred round the edges, or that your glasses seem dirty or scratched.)
- causes glare, particularly in bright light. (You may find that bright light or very sunny days make it more difficult to see.)
- may cause haloes to be seen.
- may alter the degree of long or short-sightedness.
- may cause double vision. (The cloudiness in the lens may occur in more than one place, so that the light rays reaching the retina are split, causing a double image.)
- may alter colour vision. (As the cataract develops its centre becomes more and more yellow, giving everything you see a yellowish tinge.)
Patients may have difficulty in recognising faces, reading or achieving the standard of vision required for driving. Both eyes can be affected simultaneously, but usually one eye worsens quicker than the other.
How does the doctor know that I have a cataract?
Using a special instrument to look at the eye called an ophthalmoscope, opacities, if present, can be seen. Similarly, the exact location of a cataract within the lens itself can be determined using another special piece of equipment known as a slit-lamp.
An example of vision with cataracts.
What causes cataracts?
Most cataracts develop slowly as a result of ageing. 65% of people aged 50 to 59 have lens opacities and all of those aged over 80 years.
The formation of a cataract occurs more rapidly in patients with a history of eye injury, inflammation of the eye, or diabetes - clinical studies strongly suggest that lens opacities are positively related to poorly controlled and unrecognised diabetes. Certain drugs, particularly steroid tablets and eye drops can increase the chance of cataract formation; however, there are still many individuals who do not develop cataracts following prolonged steroid administration. Similarly, certain occupations impose a greater risk for the development of cataracts including those who have worked with x-rays, microwaves, explosives, dyes and pesticides. Recent studies have also shown that smoking increases the chance of opacities developing in the lens.
Treatment of cataracts
As of yet, there is no way of preventing the development of cataracts due to old age - no diets or drugs have been shown to stop the development of cataracts. Similarly there is no medical drug treatment that can be given to benefit patients who have cataracts. Thus, the only successful means of dealing with a cataract is to remove the cloudy lens by surgery. You should be reassured that in the correct hands this is a safe and short procedure which I perform routinely.
As far as modern cataract surgery is concerned, there is no specific level of lens opacity (cloudiness) or visual loss that indicates surgery. Surgery can be performed at any stage. Indications for cataract surgery are :-
- Visual improvement - to improve the patient's quality of life (see below).
- Medical indications - when the presence of a cataract can hamper the treatment of a co-existing eye disease as the cataract prevents the ophthalmologist's view of the other problem (eg diabetic retinal disease).
However, the main criterion for removing an adult cataract is as follows:-
The removal of a cataract is indicated if the reduction in vision interferes with the patient's quality of life. For example, if visual impairment interferes with your ability to read, work, drive, or do the things you enjoy, then you will probably want to consider surgery.