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Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-.

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Overview: Cataracts

Created: ; Last Update: June 4, 2013.

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A cataract is an eye condition where the lens of the eye becomes cloudy and affects people’s eyesight, particularly their ability to see fine details. 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 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.

You can find more information on this topic in our feature.

Cataracts usually develop later in life: most people are over the age of 50 when their cataracts develop. 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. This is one of the most common surgical procedures in Germany, where it is carried out about 800,000 times per 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 symptoms. People’s vision becomes increasingly blurred and cloudy, as if they are looking through 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 also increases the risk of falling and getting hurt. Spatial vision is affected too.

Cataracts can have unexpected temporary effects too: for example, some people who wear glasses suddenly see better without glasses. This is because the refractive power of their eye changes, changing their ability to focus on objects at different distances. But this improved vision without glasses does not last long.

Causes and risk factors

About 90% of all people who have cataracts have age-related cataracts (senile cataracts): here the lens of the eye gradually becomes cloudy as part of the aging process. The lens usually bends light and focuses it on the retina (the back of the eye) to create clear images. This makes it possible to see both close and far away objects clearly. Cataracts affect this ability. You can find out more about the function of the eye in our information “How does the eye work?”

Some people are born with a higher risk of developing cataracts. Ultraviolet light (UV light) and smoking are believed to be risk factors. Cataracts are more common in people who have diabetes too. Malnutrition and poor living conditions are common causes of cataracts in developing countries, where many people are already affected by this eye condition at an early age.

Cataracts can also develop following an inflammation or injury to the eye. Eye surgery and some steroid medications can lead to cataracts too.

Course of the condition

The vision of people who have cataracts gradually gets worse and worse. At first they might see things that are closer better than before. As mentioned above, people who used to be far sighted might then find that they can see better without glasses for a short while. Their vision gradually becomes more cloudy and blurred. If the cataract is not treated, they might go blind, 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.

Cataracts are different in different people. They lead to quite sudden vision loss in some people, and hardly affect the vision of 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 the ability to see objects in the distance more than the ability to see nearby objects. They sometimes only affect people’s vision a little, and usually progress relatively slowly.


There are many reasons why people’s vision may get worse over time. Because of this, before cataracts can be diagnosed, other possible causes must be ruled out first. The eye doctor (ophthalmologist) will ask you about your symptoms and how they developed. Various eye tests and examinations will be 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. A line – or slit – of light is shone onto the eye. This makes it possible to take a close look at the lens and the parts of the eye behind the lens. The examination of the front of the eye, including the lens, does not hurt. In order to look at the back of the eye, doctors usually use medication to dilate (widen) the pupils. The pupils stay dilated for a few hours. During this time people are not able to focus properly and they are more sensitive to light and glare. For this reason they should not drive a car soon after the eye examination.


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.

Although dietary supplements are often claimed to prevent eye diseases, research has shown that this is not true for cataracts. You can read more about the research in this area in our information “Cataracts: Can vitamin supplements help save your vision?”


Some people can overcome their vision losses using glasses or contact lenses, temporarily or even in the longer term. 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 phacoemulsificiation, is the standard technique in industrialized 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. You can read more about the various surgical procedures, their chances of success and the associated risks in our fact sheet on cataract surgery.

Published by the Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

Next planned update: June 2016. You can find out more about how our health information is updated in our text "Informed Health Online: How our information is produced."


  • IQWiG health information is based on research in the international literature. We identify the most scientifically reliable knowledge currently available, particularly what are known as “systematic reviews.” These summarize and analyze the results of scientific research on the benefits and harms of treatments and other health care interventions. This helps medical professionals and people who are affected by the medical condition to weigh up the pros and cons. You can read more about systematic reviews and why these can provide the most trustworthy evidence about the state of knowledge in our information “Evidence-based medicine.” We also have our health information reviewed to ensure medical and scientific accuracy.
  • Allen D. Cataract. Clinical Evidence 2011; 02: 708. [PMC free article: PMC3275311] [PubMed: 21718561]
  • Allen D, Vasavada A. Cataract and surgery for cataract. BMJ 2006; 333: 128-132. [Full text] [PMC free article: PMC1502210] [PubMed: 16840470]
  • American Academy of Ophthalmology. Preferred Practice Pattern Guidelines. Cataract in the adult eye. San Francisco: AAO; 2011. [Full text]
  • Asbell PA, Dualan I, Mindel J, Brocks D et al. Age-related cataract. Lancet 2005; 365: 599-609. [PubMed: 15708105]
  • Jacobs S. Cataract in adults. UpToDate 2012 (online).
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