Cataract (gray star)

A cataract (gray star) gradually turns the lens of the eye cloudy. This makes the vision increasingly blurred, as though looking through fog. Sometimes the person’s vision is only slightly impaired, while in other people the deterioration is worse. In the long term, only an operation will help.

At a glance

  • A cataract is an eye disease in which the lens of the eye becomes clouded.
  • The vision of people with a cataract becomes increasingly blurred, as if looking through a veil or fog.
  • Sometimes the person’s vision is only slightly impaired, while in other people the deterioration is worse.
  • The clouded lens can be removed during an operation and replaced by an artificial lens.
  • Cataracts usually occur in the over-50s.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

Cataract: older woman with grayish blue eyes looking into the distance.

What is a cataract?

A cataract is an eye disease in which the lens of the eye becomes increasingly clouded. This impairs the vision. Minor details, in particular, can then no longer be seen clearly. An older popular term for cataract is “gray star”.

The disease is called “gray star” because the lens is gray and those affected more severely often develop a stare. In some people with a cataract, vision is only slightly affected. In others the impairment is worse and they lose their sight quickly. How the disease progresses depends, for one thing, on the type of cataract.

Cataracts usually occur in the second half of a person’s life, i.e. they generally affect the over-50s. The risk increases over time: around 20 of every 100 people aged between 65 and 74 have cataracts. In the case of over-74s the figure is over half.

People over 50 are most likely to have a cataract.

Cataracts are the main cause of blindness in developing countries. In industrialized countries, far fewer people go blind as an operation can often save the person’s sight. In this procedure, the clouded lens is removed and replaced by an artificial one.

What are the symptoms of cataracts?

With a cataract, the person’s vision gradually disappears. The sight loss is the only symptom: there are no other ill effects. The sight of people with a cataract is always more blurred and less clear, as if looking through a veil or fog. Over time, images lose their contrast and colors fade. Some people develop great sensitivity to glaring light, for example from the sun or other bright light sources. Driving also becomes more troublesome, especially at night. The impaired vision increases the risk of falling and injury. The person's spacial vision also declines.

A cataract sometimes also has unexpected effects: some spectacle wearers can suddenly see better without their glasses. This is because the disease changes the focal power of the eye and, thus, the ability to clearly see things that are at different distances. However, this effect does not last long.

What causes a cataract?

Around 90 percent of all those affected suffer from age-related cataracts. Doctors then speak of a senile cataract. The reason for the gradual clouding of the lens of the eye in these cases is the aging process.

In some people, the risk of suffering from a cataract is greater for hereditary reasons. The disease is very rarely congenital. It may be, for example, that a child is born with a cataract when the mother has been infected with measles or rubella during the first weeks of pregnancy.

There is evidence that certain factors can increase the risk of cataracts. These include, for example, UV light and X-rays, but also smoking. Diabetes sufferers are also affected more often.

The disease can also be the consequence of eye inflammations or eye injuries. Eye operations can also result in a cataract. The same applies to certain medications, for example cortisone, if it is used for lengthy periods.

Factors that increase the risk of having a cataract include malnutrition, age, an inflammation or eye injury, medication, smoking, diabetes and UV light.

How does a cataract develop?

The sight of a person who gets a cataract gets gradually worse. The impairments initially show up as short-sightedness. Then people who used to be far-sighted (hyperopic) spectacle wearers can briefly see better without glasses. As the disease progresses, the sight of sufferers becomes increasingly clouded and blurred. If left untreated, a cataract can lead to blindness. However this does not need to be so. Both eyes are usually affected. However, a cataract can progress more rapidly in one eye than the other.

Cataracts progress in different ways. Some sufferers lose their vision quite quickly. Others find that their sight is hardly affected at all. Depending on the location of the blurriness, differentiation is made between the following types:

  • Cortical cataract: someone affected by this type does not just have blurred vision, but also reacts more sensitively to glaring light, for example when driving at night.
  • Posterior subcapsular cataract: this type most frequently affects younger people. It progresses relatively quickly. The blurriness starts at the back of the lens.
  • Nuclear sclerotic cataract: the far-sightedness of people with a nuclear sclerotic cataract is more impaired than their near vision. The inside of the eye lens is clouded. Sometimes the person's vision is only slightly impaired. This type of cataract only deteriorates rather slowly.

How can cataracts be prevented?

There is no scientific evidence to show that particular preventive measures reduce the risk of a cataract. It is thought that smoking increases the risk. If the person stops smoking, the risk could fall back again.

Rays such as UV light could also possibly increase the risk of a cataract. People who spend a lot of time in the sun can take care to properly protect their eyes against UV light, for example by wearing sunglasses with a UV filter. Persistently taking certain medications containing cortisone can also increase the risk of a cataract. A person using this type of product can check whether they can switch to another medication.

The advertising for certain dietary supplements sometimes claims that they can prevent eye diseases. However, studies show that dietary supplements have no effect on cataracts.

How is a cataract diagnosed?

There are many possible reasons for gradual sight loss. To diagnose a cataract, the eye specialist will first exclude other possible causes. To do this the patient will be asked about their symptoms and their medical history. Eye tests and eye examinations are used to determine how badly the vision is affected and what the cause could be.

The examination involves assessing the lens of the eye with a slit lamp. With this special light microscope the specialist can see into the eye. The eye is lit up with a slit-shaped beam of light so that the specialist can assess the lens and other parts of the eye such as the vitreous humor and the retina. This examination is pain-free.

To have the rear sections of the eye examined, patients are usually administered a drug that dilates the pupils. This drug can cause the person to see less clearly and be more easily dazzled for a couple of hours. Driving should therefore be avoided for four to five hours afterwards. As the drug’s effects can sometimes last longer though, it is best to avoid driving in the event of doubt.

How is a cataract treated?

Some people with a cataract can compensate for their impaired vision for some time, or even over the long term, by wearing glasses or contact lenses. Cataracts cannot be treated with medication.

The only effective treatment option is an operation. In this procedure, the clouded lens is removed and replaced by an artificial lens. The operation takes about 20 to 30 minutes and is usually performed on an outpatient basis. Patients can be collected and taken home a few hours after the operation.

Whether and when an operation is a good idea depends very much on how badly the loss of vision affects the sufferer's life. Another factor is whether someone has other (eye) diseases that could affect the operation.

For more information, for example on the operation for a cataract, please visit

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG).

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