A cataract is a condition in which the lens of an eye becomes cloudy and affects vision. Most commonly, cataracts occur in older people, and they usually develop gradually.
Cataracts can usually be treated with a day-case operation, where the cloudy lens is removed and is replaced with an artificial plastic lens. However, in developing countries where this treatment is not available, cataracts are a major cause of total loss of vision (severe sight impairment).
What are cataracts?
Cataracts are cloudy (opaque) areas that develop in the lens of the eye. The lens should normally be clear. However, with cataracts, the affected lens becomes like frosted glass.
The lens of the eye sits just behind the pupil, which is the opening in the coloured part of the eye (iris). The lens is held in place by a ring of supporting tissues. Its job is to focus the image of what you see on to the back of your eye.
The lens is made of water and protein, and is normally clear because of the way the protein is arranged. With ageing and other causes of cataract, some of the protein can ‘clump together’ and this starts to cloud the lens. Over time, this makes it harder to see. Things are made worse by a gradual tendency for the lens to discolour with age, acquiring a brownish tinge which can affect colour vision, and can also make reading less clear.
A cataract is a gradual change, which starts inside the lens. There are three different patterns of cataract formation:
Who develops cataracts and how common are they?
Age-related cataract (senile cataract)
This is by far the most common type, and it affects older people, becoming more common with increasing age. In the UK about 1 in 3 people over the age of 65 have at least one cataract. Men and women are equally affected. Often both eyes are affected but one eye is typically worse than the other.
Most age-related cataracts take many years to form, and at first there will be no symptoms. Many people with an early cataract do not realise they have it as there is very little cloudiness. For most, therefore, the cataract will be diagnosed at a routine eye check before symptoms ever develop.
For some people, the cataract never becomes bad enough to impair vision. However, in many cases, vision becomes gradually worse over the years.
Congenital cataracts (present at birth)
These are uncommon, but important to diagnose early, and must be removed as early as possible after birth. This is because vision and seeing have to be learnt very early in infancy. A cataract that is present at birth stops the eye from learning to see. It can cause total loss of vision (severe sight impairment) which may then persist even if the cataract is removed later in life. Doctors examine the eyes of babies for cataracts as part of routine baby checks both at birth and at 6-8 weeks of age.
Other types of cataract
There are some uncommon causes of cataracts.
What causes cataracts?
The cataract begins with a change to the structure of the proteins in the lens. Some of the proteins clump together in places within the lens. This causes tiny areas of cloudiness. Each tiny area of cloudiness blocks a bit of light getting through to the retina. The severity of the cataract depends on the number of areas of cloudiness that develop in the affected lens.
Most affected people develop a cataract for no apparent reason. Factors that may increase the chance of developing cataracts include:
What are the symptoms of cataracts?
At first you may notice your vision becoming a bit blurred. With time, you may notice some of the following:
Depending on the severity of the cataract, the effect on your sight can range from vision being slightly blurred to complete loss of vision in the affected eye.
How is a cataract diagnosed?
A cataract can usually be seen easily by a doctor or optician (optometrist) when they examine your eyes. This may be done because you have noticed a problem with vision, or during a routine eye check.
Do I need treatment for cataracts?
An early cataract may not cause any noticeable problem. The rate of decline in vision varies considerably from person to person.
Most people opt to have their cataract treated at an early stage when the cataract is just beginning to affect ability to function normally. For example, you might be offered surgery if you are having problems reading the paper, watching TV, driving, or cooking. Treatment is usually successful.
What is the treatment for cataracts?
When symptoms begin to appear, you may be able to improve your vision for a while by using new glasses, magnification, appropriate lighting or other visual aids.
There are currently no medicines, eye drops or lasers that treat cataracts, although research in this area is going on. For now, the only way of treating cataracts is with surgery.
The operation involves removing the cloudy lens and replacing it with an artificial plastic lens (an intraocular implant). It usually takes 10-20 minutes, and is often done as a day case.
The majority of people who have cataract surgery experience a marked improvement in their vision.
The decision on whether or not to have cataract surgery is a personal one which you should make after talking with your doctor or eye specialist. It will be affected by factors such as your general health and fitness, your wish to read or drive and the presence of any other eye problems which might mean that removing the cataract will not restore your vision.
What happens during a cataract operation?
The operation is usually done under local anaesthetic, so you are awake during the operation. The operation should be painless, as local anaesthetic eye drops are used to numb your eye. (Occasionally, local anaesthetic injections are also used around the eye.) Normally one eye is operated on at a time.
The operation is performed, using a microscope, through a very small opening in the eye. When the eye is numb, the surgeon makes a tiny hole in the front of the eye at the edge of the cornea. Then, the surgeon removes the inside of the lens. He/she may first break up the lens with ultrasound to allow it to be extracted through a smaller incision (this technique is called phacoemulsification).
A clear plastic lens is placed within the lens capsule. Usually no stitches are needed. You may have to wear a pad over your eye after the operation.
The standard plastic lens can’t change its focus – to look at near objects versus distant objects, for example. So, if you have a standard plastic lens inserted you will probably still need to wear glasses or contact lenses (assuming that you did before the operation).
It is sometimes possible to have an accommodating lens inserted which allows focusing on near as well as distant objects. Multifocal lenses which are even more versatile are now also available. Your surgeon will be able to discuss with you whether these are suitable for you, although these types of lens are not usually available on the NHS.
What are the possible complications of cataract surgery?
In the vast majority of cases, the operation is successful and vision improves immediately. In a small number of cases, complications occur. These may include
These are all uncommon and can usually be treated. However, they are very occasionally serious enough to cause permanent visual problems.
Complications which can occur some time after surgery include: