The cornea or window of the eye is normally shaped like a basketball. In an eye with astigmatism, the eye is shaped more like a football, with two different curvatures, one steeper than the other. The eye therefore has two different focal points, one corresponding to each curvature. The image may not only be blurred, but may be seen as a doubled or overlapping image. This effect is also termed a ghost image. Despite the fact that astigmatism causes blurry vision, it is different than nearsightedness or farsightedness because of this doubling effect and the fact that it blurs distance and reading vision. Astigmatism can occur along with myopia or hyperopia and can be corrected with glasses or contact lenses. Astigmatism is most effectively corrected with hard or gas permeable contact lenses. With glasses, larger amounts of astigmatism may result in distorted images. With soft contact lenses, the vision may not be quite as good as with glasses unless custom astigmatic lenses are used. Laser vision correction procedures such as LASIK or PRK can correct up to 6 diopters of astigmatism.