Some evidence supports the theory that nearsightedness is hereditary.
There is also growing evidence that nearsightedness may be caused by the stress of too much close vision work. It normally first occurs in school age children. Since the eye continues to grow during childhood, nearsightedness generally develops before age 20. An individual that has myopia has trouble seeing clearly at a distance. With myopia, the center of the cornea is thinned, like cutting the hole in a donut.