Cataract definition

The natural lens of the eye is in the front of the eye. It has an important function to focus light entering the eye from varying distances onto the retina.

Lens position in the eye

The lens of the eye is in the front of the eye (blue structure on the right in diagram). Credits: AAO

A cataract is a clouding of this natural lens of the eye. When we are born, the lens of the eye is usually clear. As we get older, the lens becomes cloudier.


Top: Clear lens when born. Bottom: Brown lens in older eyes. Credit: AAO

There are different types of cataract. The main 3 types are nuclear sclerotic, cortical and posterior subcapsular. If the entire lens is involved by cataract, it is called a mature cataract.

Mature white cataract

Mature cataract: the entire lens has become involved by the cataractous change and become white

The main cause of cataract is ageing. Other common causes include injury to the eye, long term steroid use, radiation exposure and prolonged ultraviolet light exposure. Diabetics tend to develop cataract earlier. Previous eye surgery or eye inflammation may lead on to cataracts too.

The symptoms of cataract include blurring of vision, dulling of colors, glare, change in spectacle power and eye pain (lens- induced glaucoma).

To prevent cataracts, protection from ultraviolet light is suggested e.g by wearing sunglasses.  Early cataracts may be initially treated by changing glasses or contact lenses. The treatment of more significant cataracts is by cataract surgery. Evidence is lacking that eyedrops can prevent cataract worsening. Some eyedrops like glaucoma eyedrops can cause cataracts with prolonged use.