What causes a cataract to form?

A cataract is a cloudiness in the natural lens of the eye.  The natural lens of the eye usually remains clear for many years due to some amazing biologic engineering. Most tissues in the body are opaque, but the lens manages to stay clear for decades due to its organisation and structure.  Many things can alter this structure of the lens, causing it to become cloudy.  

The most common cause of cataract is ageing. Age-related cataracts develop as a result of exposure to ultraviolet light, which causes a build-up of protein within the lens.  A very dense age-related cataract can be seen in the image below.  The pupil has been dilated in this image, allowing us to see the dense cloudy cataract.

Some cataracts may also result from the use of certain medications such as steroids (cortisone) or some diseases, such as diabetes.  Smoking may speed up the progression of certain types of cataract.  Occasionally an injury or blow to the eye may cause a traumatic cataract.  Sometimes cataracts run in families and a small number of babies are born with congenital cataracts.

Although cataract is inevitable, some forms of cataract do not bother the eye or person too much. Cataracts come in different types, although the exact type does not alter the way we treat them.

The cloudiness or opacity in the lens can involve the surface of the lens, called a cortical cataract, or may only involve the centre of the lens, called a nuclear cataract.  Rarer types of cataract include those that only affect the back surface of the lens, a posterior subcapsular cataract, or only affect the front surface of the lens, an anterior subcapsular cataract.  Rarer still are posterior polar cataracts, Christmas tree cataracts, and Morgagnian cataracts.  Most cataracts are a combination of different types.

Fortunately, most cataracts can be successfully removed and vision restored with modern microsurgery techniques.