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A cataract is a clouding of the lens of the eye that can impair vision. More than half of all Americans age 65 and older have cataracts in their eyes.

What Causes Cataracts?

The eye functions much like a camera. Light rays enter through the front of the eye, passing through the cornea, the pupil, and the aqueous humor -- transparent fluid in the front of the eye -- onto the lens. The lens then bends light rays to focus objects onto the retina in the back of the eye. From there, the retina, the optic nerve, and the brain process the images and form vision.

Cataracts occur when there is a buildup of protein in the lens that makes it cloudy. This prevents light from passing through a normally clear lens, causing some loss of vision. No one knows what causes the buildup of protein responsible for clouding the lens. The cataract is a lens that has become clouded.

What Are the Symptoms of Cataracts?

Cataracts often form slowly and cause few symptoms. When symptoms are present, they can include:

• Vision that is cloudy, blurry, foggy, or filmy
• Sudden nearsightedness
• Changes in the way you see color, especially yellow
• Problems driving at night because oncoming headlights are distracting
• Problems with glare
• Double vision
• Sudden temporary improvement in close-up vision