Understanding your vision
Vision is the result of the eye refracting incoming light onto the back of the eye, called the retina. By normal vision the light rays are bend by the cornea, the front part of the eye exactly in one point directly on the retina, forming a clear image.
If the curvature of the cornea is not regular or the proportions of the eye are not exact, the light cannot be brought into sharp focus at the back of the eye. This causes a blurry, unfocused vision.