The main goal of the proposed project is to increase the understanding of the hereditary and environmental factors which underlie the normal emmetropization process and which may produce abnormal growth of the eye eventuating in myopia in school-age children. Despite the high prevalence of myopia and its prominence as a public health problem, little is known about its etiology. Much evidence, including some from our 20-year longitudinal study of refraction and visual development, suggests that myopia has a genetic component. Hereditary susceptibility, however, cannot be the sole factor determining myopia since both animal research and human epidemiological studies implicate environmental conditions. In order to determine the roles of these factors in emmetropization and its failure, as in myopia, this project has five specific aims: 1) To determine if the eyes of infants at risk for myopia (based on familial incidence) are elongated early in life and/or undergo a different course of emmetropization than the eye of infants not at risk. Growth rates of ocular components will be compared to changing refractive error in children from infancy to 5 years. (2) To establish the pedigrees of families of children with known refractive histories from our longitudinal sample and to access their relatives in order to perform genetic linkage analysis. (3) To delineate the course of development of coordinated accommodative responsiveness, convergence and pupillary response (constriction for near targets) and relate it to the development of myopia. Anomalies in the linkage of these functions have been reported to be related to myopia onset in older children and adults. (4) To test the hypothesis that chronic blurring of the retinal image during close work, such as reading, results in continued growth of the eye and consequent myopia in susceptible children. The myopigenic effects of chronic blur have been established in animal models and in some human pathologies. Among sources of blur is the deficit of accommodation of recently myopic children previously reported by this laboratory. (5) To construct predictors of who, when, and by how much children will become myopic, by combining the above measures using a variety of statistical techniques. Increased knowledge of the etiology of myopia will aid in the identification of at-risk individuals so that preventive measures can be applied selectively.
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