A cataract is a clouding of the natural lens of the eye. The natural lens is a fine, transparent object suspended behind the pupil, black circular opening of the eye, and is normally clear. When light enters the eye it passes through the pupil and the lens. The lens focuses the light rays onto the retina at the back of the eye which in turn sends a message to the brain. However, when cataracts develop, the light is distorted and cannot focus clearly on the retina causing reduced vision.

Almost everyone who lives a long life will develop cataracts. The most common cause of a cataract is natural age-related changes, however other causes are trauma, inflammation, radiation damage, metabolic and nutritional defects, or birth defects.

Some common symptoms of a developing cataract are: objects appear yellowed, haziness, appearance of dark spots or shadows, increased need for more light to see clearly, halos or coloured rings around lights, increased nearsightedness, and double vision.

This varies from person to person. Some cataracts may develop slowly over the years while others may progress rapidly within a few months. A cataract does not spread from one eye to another but will usually develop in both eyes at some time.