Emmetropization in the primate eye

A theory to explain the mechanism of emmetropization of the human eye is reviewed and updated. The theory is probably also valid for the primate eye. It is proposed that the ciliary muscle-choroid layer behaves like a solid sheet of smooth muscle, so that it is able to resist part of the intraocular pressure and to regulate scleral stretch in the growing eye. It is suggested that the autonomic nervous system and stress play a role in the development of ametropia and that interference with the cortical-subcortical control of the ciliary muscle may prevent emmetropization.