57 Gene-Environment Interactions in the Aetiology of Myopia

Overall, parental myopia appears to be more viable as a surrogate measure of genetic background and susceptibility than ethnicity, but there is currently no convincing evidence of gene-environment interactions.

Conclusion

Clearly much more data need to be collected for rigorous testing of hypotheses. But, at this stage, putting to one side the clearly genetic high familial myopias and hyperopia of >2D, there is little evidence for a genetic basis to variations in refractive error, particularly of common myopia. Strong evidence for gene-environment interactions in the statistical genetic sense is lacking, although there is clear evidence for an impact of environmental exposures on refractive outcomes independent of genetic background. Thus, since the evidence for gene-enviroment interactions was reviewed in 2000,55 there has been little progress, and better definition of genetic contributions to school myopia and rigorous analysis of gene-environment interactions are still necessary.

When we reviewed the etiology of myopia in 2005,5 we concluded that there was abundant evidence of environmental impacts on the prevalence of myopia, but little evidence of significant genetic contributions to myopia, apart from high myopia. The genetic evidence obtained since then has not substantially changed this conclusion, although there are now a few cases of potential genetic associations with some forms of mild to moderate myopia, which provide the basis for looking at gene-environ- ment interactions in the future. The use of ethnicity or parental myopia as surrogate measures of genetic factors has not provided evidence of geneenvironment interactions.

Overall, we conclude that the evidence still favors the idea that myopia is predominantly a disorder caused by abnormal environmental exposures, and that the marked differences in prevalence associated with ethnicity or educational attainments represent cases of simple environmental effects, rather than cases of genetic determination or geneenvironment interactions. We, therefore, suggest that school myopia is not primarily due to some sort of genetically determined failure of emmetropization, but represents a case in which environmental exposures that promote axial elongation, simply push the emmetropization mechanism too far.

58 I.G. Morgan and K.A. Rose

Acknowledgments

This work was supported by a grant from the Australian Research Council to the ARC Centre of Excellence in Vision Science (COE956320).

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