We propose three sets of studies on experimental myopia: First, there is clear evidence from several laboratories that the eye enlargement and myopia produced by form deprivation in chicks is associated with increased growth of the posterior sclera. Furthermore, when form vision is restored to these animals the rate of scleral growth falls to less than normal, thereby reducing the relative elongation of the eye until it reattains normal shape and refraction. We propose in vitro studies utilizing this bidirectional modulation of growth to answer refraction. We propose in vitro studies utilizing this bidirectional modulation of growth to answer three questions: Is the altered scleral growth the consequence of the cells being continuously stimulated or inhibited or is it a consequence of a change in state of the cells? Can we show by conditioned medium experiments that the retina or other ocular tissues secrete factors that alter the growth of the scleral cells? Does the sclera secrete paracrine growth-modulating substances that differ depending on the visual circumstances? Second, we propose two questions to be addressed by in vivo studies of deprivation myopia: Because retinal dopamine levels are lower in chicks wearing diffusers, and dopamine agonists ameliorate deprivation myopia and eye elongation, do the agonists of dopamine act specifically to reduce the excessive growth associated with form deprivation or do they simply reduce eye growth in general? As the form-deprivation myopia shown in tree shrews is similar to that of chickens, is it also attributable to increased growth of the posterior sclera? Third, we propose several studies on the issue of to what extent can the eye use growth modulation to guide it toward emmetropia, if adequate vision is present. This situation has the advantage of being more similar to the one in which myopia develops in humans in that the eyes have unrestricted vision. Recently we have discovered a new process involved in emmetropization: The choroid can dramatically change its thickness by as much as 0.5mm and thereby compensate for refractive errors up to 8 diopters. We need to know what contribution to emmetropization is attributable to these choroidal changes and what is attributable to changes in growth of the globe (i.e. sclera).
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