New research supports the theory that the refractive errors known as nearsightedness and farsightedness are primarily inherited. The group also identified the probable location—on the long arm of chromosome 5—of genes that help determine axial length, a key factor in these refractive errors. Axial length is a specific measurement from the front to back of the eye; this distance is longer than normal when a person is nearsighted and shorter than normal in a farsighted person.