Cataracts are cloudy areas in the lens inside the eye - which is normally clear. They are said to be the leading cause of vision loss in people over the age of 40.
Cataracts can develop in one or both eyes. If they develop in both eyes, one will be more severely affected than the other. A normally clear lens allows light to pass through to the back of the eye, so that the patient can see well-defined images.
If a part of the lens becomes opaque light does not pass through easily and the patient's vision becomes blurry - like looking through cloudy water or a fogged-up window. The more opaque (cloudier) the lens becomes, the worse the person's vision will be.
There are two types of cataracts:
- Age related cataracts - they appear later in life and are the most common form of cataracts.
- Congenital cataracts (childhood cataracts) - these may be present when the baby is born, or shortly after birth. Cataracts may also be diagnosed in older babies and children - these are sometimes referred to as developmental, infantile or juvenile cataracts. Researchers from the University Zurich were the first to identify the chromosomal location and exact molecular defect in the coding region of the gene responsible for a childhood cataract.
The rest of this article focuses just on age-related cataracts.
A cataract is a clouding of the lens inside the eye.
A patient with cataracts will eventually find it hard to read, or drive a car - especially during the night. Even seeing people's facial expressions becomes difficult. Cataracts are not usually painful. The patient's long-distance vision is more severely affected at first.
As cataracts develop very slowly most people do not know they have them at first. However, the clouding progresses and vision will gradually get worse. Stronger lighting and eyeglasses can help improve vision. Nevertheless, eventually the vision impairment affects the patient's ability to carry out everyday tasks. At this point the individual will need surgery. Fortunately, cataract surgery is usually a very effective and safe procedure.
Cataracts cause more vision problems globally than any other eye condition or disease - especially in developing countries, where they are much more common among poor people, according to a study carried out in Kenya, The Philippines, and Bangladesh.
Some studies indicate that cataracts are more common among elderly people further down the socioeconomic ladder in the USA - prevalence of cataracts causing significant visual problems appears high among older U.S. Hispanics who also often encounter barriers to access to care (in the USA "Hispanics" refers to Americans of Latin American origin, not people who originate from Spain).
Both men and women are affected equally.
According to the National Health Service (NHS), UK, approximately one third of people aged 65 or over have cataracts in one or both eyes.
Risk factors for cataracts
We are all at risk of developing cataracts because we will all get old one day - the greatest risk factor is age. In the USA approximately 50% of people aged 65 or more have some degree of lens clouding. 70% of Americans aged 75 or more have their vision significantly impaired by cataracts.
Researchers at the Wilmer Eye Institute at The Johns Hopkins Medical Institutions, Baltimore predicted in 2004 that the number of people in the USA affected by cataracts will rise to 30.1 million people within 20 years, an increase of 50 percent, because people will live longer.
The following factors may increase a person's chances of developing cataracts:
- Close relatives who have/had cataracts (family history)
Ionizing radiation exposure - airline pilots have an increased risk of nuclear cataracts compared with non-pilots, and that risk is associated with cumulative exposure to cosmic radiation, scientists from the University of Iceland reported.
- Statins - researchers from the University of Waterloo, Canada, reported in the journal Optometry and Vision Science that people who take statins have a higher risk of developing age-related cataracts.
- Long-term exposure to bright sunlight
- Long-term use of corticosteroids - many people with asthma rely on inhaled, and sometimes oral, steroids, as do people with chronic obstructive pulmonary disease. A study conducted by the Centre for Vision Research, University of Sydney, Australia, revealed that cataract risk is higher for patients taking these medications.
- Previous eye inflammation
- Previous eye injury
- Exposure to lead - lifetime lead exposure may increase the risk of developing cataracts, scientists from the National Institute of Environmental Health Sciences, USA revealed.
- Crystallins loss of function - A specific type of protein (crystallins) begins to lose function as the eye ages. As the protein loses function, small peptides, made of 10 to 15 amino acids, start forming and accelerate cataract formation in the eye, a study revealed.
On the next page we look at the symptoms of cataracts and how cataracts are diagnosed. On the final page we discuss the available treatments, prevention and the possible complications caused by cataracts.