What causes extreme myopia & farsightedness?
In extreme nearsightedness, the cornea is excessively steep and/or the eye is extremely long so light rays are focused in front of the retina. The eye cannot focus properly, especially on objects in the distance. In extreme farsightedness, the eye is extremely short and/or the cornea is excessively flat. When light rays enter the eye they are focused behind the retina giving blurred vision. The blur is even worse when looking at near objects.