Clouding of the lens of the eye, causing loss of vision
- More common after the age of 75 but may be present from birth
- Sometimes due to an abnormal chromosome
- Contact sports and frequent exposure to the sun are risk factors
- Gender is not a significant factor
If you have a cataract, the normally transparent lens of the eye is cloudy as a result of changes in protein fibres in the lens. The clouding affects the transmission and focusing of light entering the eye, reducing clarity of vision.
If cataracts are present from birth, total loss of vision (see Congenital blindness) may result. However, cataracts do not usually affect children or young adults. Most people over the age of 75 have some cataract formation, but visual loss is often minimal as only the outer edges of the lens are affected.
Cataracts usually develop in both eyes, but generally one eye is more severely affected. A cataract in the central part of the lens or one that affects the whole lens can cause loss of clarity and detail in vision. However, the affected eye will still be able to detect light and shade.
What are the causes?
All cataracts occur as a result of structural changes to protein fibres within the lens. These changes cause part or all of the lens to become cloudy.
Changes in the protein fibres are a normal part of aging, but cataracts that develop in young adults may be the result of an eye injury or prolonged exposure to sunlight. They may also develop due to diabetes mellitus, uveitis, or long-term treatment with corticosteroids. Cataracts are a common disorder in people with the chromosome disorder Down’s syndrome.
What are the symptoms?
Cataracts usually develop over a period of months or years. In most cases, they are painless and usually cause only visual symptoms, such as:
Blurred or distorted vision.
Star-shaped scattering of light from bright lights, particularly at night.
Altered colour vision: objects appear reddish or yellow.
In longsighted people, temporary improvement in near vision.
A severe cataract may make the pupil of the eye appear cloudy.
What might be done?
The doctor will examine your eyes with a slit lamp (see Slit-lamp examination) and an ophthalmoscope (see Ophthalmoscopy). If your vision is affected significantly, he or she may recommend that the cataract is removed surgically and an artificial lens put in the eye (see Cataract surgery). If there is no other reason for your visual deterioration, your sight should improve greatly after the operation. However, you may still need to wear glasses afterwards.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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