Myopia occurs when light rays are focused in front of the retina and a person is unable to see distant objects.  This condition is also known as nearsightedness.  It affects 25% of the adult population in the United States and 75% or more of the adult population in Asian countries such as Taiwan. Our research group has constructed a theory that explains the underlying mechanism of myopia development.  Briefly, the theory states that in addition to the genetically-predetermined component, the rate of axial elongation is modulated by the rate of change in retinal-defocus area (i.e., rate of change of the size of the blur circle corresponding to a point source).  this in turn leads to a cascade of neuro-biomechanical processes, resulting in a corresponding change in the rate of axial elongation (Fig. 1).   For example, a decrease in retinal-defocus area, as can occur during a time increment of genetically-preprogrammed growth, results in a decrease in the rate of release of neuromodulators, such as dopamine, by the amacrine cells in the retina.   This in turn leads to a decrease in the rate of proteoglycan synthesis, a precursor of the scleral matrix material.   The reduction in scleral matrix material decreases the integrity of the scleral tunic, thus resulting in an increase in axial growth rate relative to normal, and in turn the development of myopia (Fig. 2).  It can be shown that excessive reading results in the same process above that leads to myopia. 

Fig. 1

Fig. 2