Substantial evidence has emerged over the past decades for a role of genetics in the development of human refractive error. There is also an emmetropization mechanism that uses visual signals to match the axial length to the focal plane. There has been little discussion of how these two important factors might interact. We explore here ways in which genetic factors driving axial growth may interact with the emmetropization mechanism, mostly to produce emmetropic eyes but often to produce myopia. An important factor may be a normal, yet reduced ability of juvenile eyes to use myopia to restrain genetically driven axial elongation. Reduced ability to respond to myopia by slowing axial elongation may contribute to the development of myopia in cases where genetics alone would make the axial length longer than the focal plane. Copyright © 2011 American Academy of Optometry.