A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil.

Cataracts are the most common cause of vision loss in people over 40 and is the principal cause of blindness in the world. Today, cataracts affect more than 22 million Americans age 40 and older. And as the U.S. population ages, more than 30 million Americans are expected to have cataracts by the year 2020.

The risk of cataract increases as you get older. Other risk factors for cataract include:

• Certain diseases (for example, diabetes).
• Personal behavior (smoking, alcohol use).
• The environment (prolonged exposure to ultraviolet sunlight).

Types of cataracts include:

• Subcapsular cataract: occurs at the back of the lens. People with diabetes or those taking high doses of steroid medications have a greater risk of developing a subcapsular cataract.
• Nuclear cataract: forms deep in the central zone (nucleus) of the lens. Nuclear cataracts usually are associated with aging.
• Cortical cataract: is characterized by a white, wedge-like opacity that starts in the periphery of the lens and works its way to the center in a spoke-like fashion. This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus.

Cataracts usually form slowly. You may not know you have them until they start to block light. Then you might notice:-

• Vision that’s cloudy, blurry, foggy, or filmy
• Nearsightedness (in older people)
• Changes in the way you see color
• Problems driving at night (glare from oncoming headlights, for example)
• Problems with glare during the day
• Double vision in the affected eye
• Trouble with eyeglasses or contact lenses not working well