cataract is a clouding of the lens in the eye which leads to a decrease in vision.[1] Cataracts often develop slowly and can affect one or both eyes.[1] Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night.[1] This may result in trouble driving, reading, or recognizing faces.[6] Poor vision caused by cataracts may also result in an increased risk of falling and depression.[2] Cataracts are the cause of half of blindness and 33% of visual impairment worldwide.[3][7]

Cataracts are most commonly due to aging but may also occur due to trauma or radiation exposure, be present from birth, or occur following eye surgery for other problems.[1][4] Risk factors include diabetessmoking tobacco, prolonged exposure to sunlight, and alcohol.[1] Either clumps of protein or yellow-brown pigment may be deposited in the lens reducing the transmission of light to the retina at the back of the eye.[1] Diagnosis is by an eye examination.[1]

Prevention includes wearing sunglasses and not smoking.[1] Early on the symptoms may be improved with glasses.[1] If this does not help, surgery to remove the cloudy lens and replace it with an artificial lens is the only effective treatment.[1] Surgery is needed only if the cataracts are causing problems and generally results in an improved quality of life.[1][8] Cataract surgery is not readily available in many countries, which is especially true for women, those living in rural areas, and those who do not know how to read.[4][9]

About 20 million people are blind due to cataracts.[4] It is the cause of approximately 5% of blindness in the United States and nearly 60% of blindness in parts of Africa and South America.[9] Blindness from cataracts occurs in about 10 to 40 per 100,000 children in the developing world, and 1 to 4 per 100,000 children in the developed world.[10] Cataracts become more common with age.[1] 

(Ref : wikipedia.org)