what is a cataract

The human eye contains a translucent lens inside it. This lens focuses the rays of light entering the eye on to the retina (the neurological lining of the eye) rather like rays of sunshine being focused by a magnifying glass. The retina converts this light into neurological messages that are then transmitted to the brain by the optic nerve. If this ocular lens becomes cloudy or hazy it is called a cataract. The light focused on the retina is then no longer sharply focused, and the patient's vision becomes blurred in this eye. Cataract sufferers may notice other symptoms, too, such as glare in bright light (or difficulty in driving at night) difficulty in distinguishing colours clearly, or distortion of the visual image.

Cataract surgery has a claim to be the world's oldest operation, having its origins in India and being introduced to the West by the conquests of Alexander the Great.

For specific examples of cataract, please refer to the section at the bottom of this page.

Cataractous changes in the ocular lens can occur at any age, but are more common in older people. They are sometimes associated with conditions such as diabetes, steroid drugs or injuries to the eye, but in most people there is no other underlying problem apart from the cataract.

In times gone by, patients had to wait many years, gradually going blind, until the cataract was 'ripe' or 'mature' enough to be operated on. This is no longer the case, and a cataract can generally be removed when the visual symptoms are sufficiently troublesome to the patient to make surgery worthwhile. Unless there is a specific contraindication, which is very rare, a new lens (an 'implant' or 'intraocular lens') is inserted at the time of surgery. This is made of plastic and will remain in the eye for evermore. It does not wear out; nor does it have to be changed, except in the most unusual circumstances.

'Cataract' really means any opacity in the lens of the eye, and there are many different patterns and types.

Key to Cataract Types
Top Left This is a posterior subcapsular cataract. Such cataracts often cause difficulty in reading, and a disabling glare in bright light.	Top Right Cortical cataract as seen against the reflection of the retina. This is a very common type of cataract causing glare and blurring of vision.
Bottom Left Nuclear cataract is another common type. This is an opacity in the central nucleus of the lens which tends to cause refractive changes and blurring of vision.	Bottom Right A mature cataract. These are now rare in developed countries.

What is Cataract?

What is a Cataract?