Cataracts are a condition where the lens (a part of the eye that focuses light) becomes cloudy. The lenses in the eyes are normally clear or transparent, but with age, the structure or chemical makeup of the lens changes, causing them to "cloud over." This causes a gradual and painless loss of vision, which can eventually lead to blindness. Fortunately, the process can almost always be corrected with surgery.

Cataracts are very common. In fact, they are the most common cause of blindness worldwide. They usually begin to appear after age 50, and about half of people aged 75 are affected. While we're all at risk of getting them as we age, some things make cataracts more likely, including cigarette smoking, lack of vitamins, sun exposure, and certain medications (see below).

The lenses of your eyes are mostly made up of neatly arranged proteins. Sometimes these proteins stick together, breaking formation and losing transparency. This causes the lenses to become cloudy. The world becomes hazy, darker, and less colourful. Untreated, the cloudy area may spread, progressively impairing vision in that eye.

A few people are born with congenital cataracts, which usually affect both eyes. These don't always affect vision. Traumatic cataracts refer to a condition that may appear immediately following an eye injury, or it may occur years later. Secondary cataracts are caused by certain chronic diseases. Diabetes is the most common cause of secondary cataracts.

Aging is the most common cause of cataracts. These cataracts have previously been called senile cataracts, but this term has fallen out of favour.

The following factors can add to the risk of developing cataracts:

• Exposure to sunlight increases the risk of senile cataracts. Radiation from the sun, especially ultraviolet B (UVB) rays, damages the proteins in the lens.
• Cigarette smoke damages the proteins in the lens.
• Alcohol use.
• Lack of some vitamins and other antioxidants such as vitamins C and E, selenium, beta-carotene, and lycopene has been shown by research to be linked to cataracts. Antioxidants protect the body from oxidants, also known as free radicals. Free radicals react with your cells, effectively "rusting" them. If you're not getting enough antioxidants in your diet, such as vitamins C and E, you might be putting yourself at risk for cataracts.
• Poorly controlled diabetes and high blood pressure.

Certain medications can also cause cataracts, including:

• Chlorpromazine*, a sedative
• Amiodarone, a heart medication
• Phenytoin, an antiseizure medication used in Epilepsy
• Lovastatin, a cholesterol-lowering medication
• corticosteroids such as Prednisone that are used to reduce inflammation

Cataracts cause a gradual, painless loss of vision. In older people who wear glasses for reading, close-up vision may actually improve at first. This is because they are going from Farsightedness to Nearsightedness. Double vision may also appear temporarily early on in the course of the disease.

Other symptoms include:

• frequent changes in your glasses or contact lenses
• cloudy or blurred vision
• dull, faded colour and difficulty with distinguishing dark blue from black
• poor night vision
• odd visual effects around lights, such as glare or halos

Cataracts can't jump from one eye to the other. But people who get one often end up developing it in the other eye.

If you've noticed any of the symptoms described above, see your primary doctor or an eye care specialist. Your primary doctor can find cataracts by shining a special light into your eye to look for cloudiness. You might then be sent to an eye specialist (ophthalmologist), who will use special instruments to learn more about your cataracts and any other eye problems you might have.