A cataract is a clouding of the lens in the eye, which can lead to blurred or dim vision. It often develops slowly and can affect one or both eyes. Common symptoms include difficulty seeing at night, sensitivity to light, and seeing halos around lights. Cataracts are most commonly associated with aging, but they can also result from factors like diabetes, smoking, and prolonged exposure to ultraviolet light. Treatment typically involves surgery to remove the cloudy lens and replace it with an artificial one, restoring clearer vision.