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F. Thorn; Mathematical Models of Refractive Distributions Suggest Different Underlying Mechanisms in Chinese and Western Myopes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1025.
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Young infants have a broad Gaussian distribution of refractive errors. This suggests uncontrolled and relatively independent development of refractive components. Subsequent leptokurtotic narrowing of the distribution suggests feedback control driving eyes toward emmetropia. In this study, the nature of subsequent refractive distribution changes that occur in highly myopic populations are analyzed to elucidate the processes underlying human myopia development.
Mathematical models have been developed to describe refractive data from preschool, illiterate, and highly educated populations. The combination of mean, variance, leptokurtosis, and skew is used to infer hypothetical mechanisms.
Refractive data from preschool children and illiterate adult populations show similar narrow, unskewed, highly leptokurtotic refractive distributions with an emmetropic mean. In contrast, refractive distributions from highly educated populations of European and ethnic Malaysian descent are leptokurtotic and highly skewed toward myopia but with little change in the peak value of the distribution. The refractive distribution of highly educated Chinese populations approaches bimodality. Half the subjects show a distribution that is similar to Europeans and Malaysians. However, the other half of the highly educated Chinese population has a broad Gaussian distribution with a mean of about -4 diopters and SD of 2.5 to 3.0 diopters.
Leptokurtotic refractive distributions in European and Malaysian populations indicate the presence of refractive feedback control, although a highly myopigenic environment compromises this control in many individuals. The bimodality of Chinese refractive distributions suggests two response mechanisms to a strong myopigenic environment, one similar to Europeans, the other half using a very different mechanism. The most parsimonious explanation of these results is that most eyes have a genetic predisposition with variable penetrance levels for resisting strong myopigenic factors. However, the refractive control response to strong myopigenic factors follows a different path in half the Chinese eyes.
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