A cataract is an eye condition in which the lens of the eye becomes cloudy. This causes vision to worsen, making it especially difficult to see fine details clearly. Some people’s vision is only slightly affected, whereas others might lose their eyesight very quickly. How it progresses will depend on things like the exact type of cataract. The word “cataract” comes from the Greek word for “waterfall” because in the past it was believed that the blurring was caused by a fluid in the eye.
Cataracts mostly affect people over 50, and the risk increases with age: About 20 out of 100 people between the ages of 65 and 74 have a cataract. And more than 50 out of 100 people over the age of 74 are affected.
Cataracts are the main cause of blindness in developing countries. The number of people who go blind from cataracts is considerably lower in industrialized countries due to the availability of effective surgery. Cataract surgery involves removing the cloudy eye lens and replacing it with an artificial lens. It is one of the most common surgical procedures performed in Germany, where about 800,000 people have cataract surgery every year.
Vision loss due to cataracts is usually very gradual. This gradual loss of vision is the only symptom. Cataracts are not painful and do not cause burning or other similar symptoms. Vision becomes increasingly blurry and dull: Things appear as if seen through a veil or fog. Contrasts and colors become less clear as time goes on. Some people become very sensitive to the glare of the sun or other bright lights. Driving becomes more difficult, particularly at night. Poor vision increases the risk of falling and getting hurt. Spatial vision is affected as well.
But cataracts may have surprising effects too: Sometimes people who wear glasses can suddenly see better without them. This is because the refractive power of their eye changes, affecting their ability to focus on objects at different distances. Improved vision without glasses does not last long, though.
Causes and risk factors
About 90% of people who have a cataract have what is called a "senile" cataract. Here, the gradual clouding of the lens is caused by aging. Normally, the lens bends light and focuses it onto the retina (the back of the eye) to create sharp images. This makes it possible to see objects clearly, both close and far away. Cataracts affect this ability.
Some people are born with a higher risk of developing cataracts. Ultraviolet light (UV light) and smoking are believed to increase the risk. Cataracts are more common in people who have diabetes too. In developing countries they are often caused by malnutrition and poor living conditions, and many people are already affected earlier in life.
Cataracts can also develop following an inflammation or injury to the eye. Eye surgery and some steroid medications can lead to cataracts too.
Cataracts cause your vision to gradually worsen. At first you become more short-sighted. As mentioned above, people who used to be far-sighted might then find that they can see better without glasses for a short while. But their vision will gradually become more cloudy and blurred. If left untreated, cataracts can lead to blindness but this does not always happen. Both eyes are usually affected. The condition might progress more quickly in one eye than in the other, though.
Its natural course can vary quite a bit. It can lead to quite sudden vision loss in some people, but hardly affect vision in others. The type and progression of symptoms depends on various things, including what area of the lens is cloudy. There are three main types of cataracts:
- Cortical cataracts: Apart from causing blurred vision, this type of cataract leads to problems with glare in particular, for instance when driving at night.
- Posterior subcapsular cataracts: This type of cataract is more common in younger people and progresses relatively quickly.
- Nuclear cataracts: These cataracts affect your ability to see things in the distance more than your ability to see nearby objects. Vision is sometimes affected only a little, and the condition progresses relatively slowly.
There are many reasons why your vision may get worse over time. Because of this, other possible causes need to be ruled out before cataracts can be diagnosed. Your eye doctor (ophthalmologist) will first ask you about your symptoms and your general medical history. You will have a few eye tests done to find out how much your eyesight is affected and what might be causing the symptoms.
The lens of the eye is examined using a slit lamp (a microscope with a light). The doctor looks at the eye through the microscope with the help of a line – or slit – of light that shines onto your eye. This makes it possible to take a close look at the lens and the parts of the eye behind the lens. This examination is not painful.
In order to look at the back of the eye, doctors usually use medication to dilate (widen) your pupils. The pupils stay dilated for a few hours. During this time it is difficult to focus properly and you will be more sensitive to light and glare. For this reason, you should not drive a car for the next four to five hours. This effect can last longer in some people. If you're not sure whether your eyes have returned to normal, it's better not to drive.
There are no known scientific studies showing that particular preventive measures lower the risk of developing cataracts.
It is thought that smoking increases the risk and that quitting smoking could therefore lower the risk. Stopping smoking has a lot of health benefits anyway. People who are exposed to a lot of UV light can protect their eyes from the sun, for instance by wearing sunglasses.
Some steroid medications can increase the risk of developing cataracts. It might be possible to switch to a different medication.
Dietary supplements are often claimed to be able to prevent eye diseases, but research has shown that this is not the case for cataracts.
Some people can compensate for the vision loss, temporarily or even in the longer term, by wearing glasses or contact lenses. There are no medications for the treatment of cataracts.
The only effective treatment is surgery. Cataract surgery involves removing the cloudy lens and replacing it with a new, artificial lens. The lens capsule – an elastic membrane surrounding the lens of the eye – is left in the eye during surgery. Only the inner core and the outer cortex of the lens are broken up into small pieces using ultrasound. The pieces are then sucked out of the eye through a small cut. This procedure, called phacoemulsification, is the standard technique in Germany and some other countries. Once the lens has been removed, an artificial lens is implanted into the lens capsule.
Whether and when surgery is an appropriate treatment option is very much a personal decision. The extent to which vision loss is affecting someone’s life will play a very important role. Another factor to consider is the presence of other (eye) conditions, which could affect the outcome of cataract surgery.
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Allen D, Vasavada A. Cataract and surgery for cataract. BMJ 2006; 333(7559): 128-132.
American Academy of Ophthalmology. Prefered Practice Pattern Guidelines. Cataract in the adult eye. San Francisco: AAO; 2011.
Asbell PA, Dualan I, Mindel J, Brocks D, Ahmad M, Epstein S. Age-related cataract. Lancet 2005; 365(9459): 599-609.
Jacobs S. Cataract in adults. UpToDate 2016 (online).
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