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David Troilo; The role of accommodation in emmetropization and the development of myopia: Evidence from animal studies. Journal of Vision 2005;5(12):8. doi: 10.1167/5.12.8.
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The relationship between near work (particularly reading), accommodation, emmetropization, and the development of myopia has been the subject of much interest and debate. In this talk I will summarize several experimental studies with animals that examine how ciliary muscle activity affects emmetropization, and others that describe how experimental manipulations of eye growth and refractive state affect accommodation. I will also describe our recent studies on accommodative behavior under free-viewing near work conditions in animals and humans.
The results of these experiments lead to several conclusions and working hypotheses: (1) The action of the ciliary muscle is probably not directly involved in the regulation of eye growth and the development of myopia. (2) Low accommodative stimulus-response gain in myopes appears to be a consequence of the developing myopia itself. The alternative hypothesis - that low gain increases susceptibility to developing myopia - is not supported by our data. (3) Accommodation to near-targets under free-viewing conditions is not tightly sustained, suggesting that the temporal pattern of accommodative behavior is important for understanding the visual control of eye growth. (4) During reading by adult human subjects, although the average accommodative response is steady, there is considerable variability in the response, the degree of which is proportional to the subject's myopia, suggesting that the variability of accommodation during near vision may be an important factor in the relationship between near work and myopia.
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