CataractCataract is when the lens inside the eye becomes cloudy or opaque. Usually to see clearly the lens inside the eye needs to be clear so that light is focused through to the back of the eye. If the lens becomes cloudy as with cataract, vision becomes blurry. How blurry the vision is, depends on how cloudy the lens becomes. Imagine looking through a camera that has a dirty or cloudy lens. The photo would be blurry until you cleaned the lens. The same applies with the lens clouding. Except to clean the lens inside the eye, the person needs to undergo cataract surgery. A new plastic lens is inserted in its place and visual clarity can be restored.
Below is an image of a television screen. The first picture is crisp and clear, whereas the second is an example of what it would be like to look through a lens that has moderate cataract.