Cataract is an opacity in the crystalline lens in the eye. The lens resides behind the pupil, the dark part through which the light enters the eye. It focuses the light, although it does so more effectively when we are young as it can change in focus. It is a remarkable piece of biologic engineering. Most tissue is opaque but the lens manages to stay clear for a great number of years by virtue of a high level of organisation in its structure. Any loss of that organisation, either with cross-linking of proteins, or water seeping into the lens, or disorganisation of cells, produces opacity in the lens, which we call a cataract.
 

In many ways, the question should be not ‘what causes cataract’ but ‘why does the lens remain clear for as long as it does?’
Cataracts are related to family history, they are also related to injury, to inflammation in the eye, to illness in the rest of the body, particularly diabetes, and medication use such as steroid. Although, mostly they are due to having birthdays, and it is probably that most of us will get one.

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Whilst cataract is inevitable, some forms of cataract really do not bother the eye and person too much. Cataracts come in different types, although the exact type does not alter the way we deal with them.