Most people have poor vision because of the shape of the cornea.
It is the shape of the cornea that effects the way the eye focuses light onto the retina. Myopia, most commonly known as nearsightedness, is the result of a cornea that is too steep and focuses light in front of the retina. Hyperopia, or farsightedness, focuses light beyond the retina due to a cornea that is too flat. Astigmatism focuses light in several places because the cornea is irregular or more football-shaped. Refractive procedures alter the shape of the cornea so that it may focus light directly on the retina to achieve better vision.