Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Cataract ?
    ### Response:
    A cataract is a clouding of the lens in your eye. It affects your vision. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.    A cataract can occur in either or both eyes.
    