A cataract forms on the lens of the eye with age. It turns the natural lens cloudy and starts to interfere with the patient's vision.
Far-sightedness is when the patient's cornea is a bit too flat to focus rays of light properly onto the retina. This flatness leads to blurred near vision and in some cases intermediate and distance vision.
Near-sightedness is when rays of light are not properly focused on the retina because of how the cornea bends the rays. Near-sightedness results in blurred vision, trouble with distance vision and problems seeing at night.