It has been found that some animal species become myopic when an eye is exposed to visual deprivation during postnatal development. This environmentally-produced alteration in ocular development can provide information about the mechanisms that normally act to produce emmetropic and ametropic eyes. Studies ar proposed in the present application on a mammalian animal model, thee shrew, to answer several questions: 1) Are there active regulatory mechanism that produce emmetropia? 2) What is the role of accommodation in any regulatory mechanism? 3) Are there local retinal control mechanisms within the eye that do not require a feedback loop through central visual structures? 4) When an eye becomes myopic as a result of environmental manipulations, is the axial elongation due to growth or stretch? Experiment 1 will determine whether rearing with + or - power goggles will result in shorter or longer eyes. In addition, we will explore whether recovery from experimentally-induced myopia can occur after small amounts of myopia have been produced early in the sensitive period. Experiment 2 will determine whether experimentally-induced myopia can develop after removal of accommodation by lesions of either the Edinger-Westphal nucleus or the ciliary ganglion. Experiment 3 will determine whether local retinal control mechanisms exist that can regulate the development of the eye. In these experiments, we will test whether local myopia can result from partial visual field deprivation, whether exposure to strobe-light flashes will prevent lid-suture myopia, and whether lid-suture myopia develops during blockage of afferent visual information with intravitreal tetrodotoxin. Experiment 4 will examine whether the axial elongation in lid-suture myopia occurs through stretch of the sclera as suggested by preliminary data using lathyritic agents to enhance the experimentally-induced myopia. It will also provide a needed dark-rearing control for the lathyritic studies. If the experiments support scleral stretch as a mechanism, in Experiment 5 we will reduce intraocular pressure to determine whether this will decrease the amount of lid-suture myopia. These experiments will significantly advance our understanding of the mechanisms that affect ocular development. If we can learn the mechanisms that produce emmetropia and ametropia in tree shrews, a species closely related to primates, it will then be reasonable to ask whether similar mechanisms control ocular development in humans.
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