Epidemiological studies on multiple risk factors for myopia in Taiwan: Gene-environment interaction

Myopia is a hyperendemic eye disease in Taiwan showing a rapid increase in prevalence since the early 1950s. In a recent national survey of schoolchildren, the prevalence of myopia was found to increase from 12% at age 6, 54% at age 12 to 85% at age 18. The prevalence was higher in females than males for all age groups. There was a striking difference in myopia prevalence in areas with different degrees of urbanization. Children in rural areas had a lower prevalence than those in urban areas. There was a significant familial aggregation of myopia. Children whose parents were affected with myopia had a higher prevalence of myopia than those without affected parents. The higher the proportion of siblings affected with myopia, the higher the risk of being affected with myopia. There were significant associations with myopia in a dose-response relationship for duration of near-work and sleeping, distance of studying and watching television as well as rank of academic achievement in class. Two twin studies were carried out to differentiate the relative importance of genetic and environmental components in the determination of myopia. Monozygotic (MZ) twins were found to have a higher concordance in myopia than dizygotic (DZ) twins. The concordance in ocular refraction, corneal curvature and axial length was higher in MZ twins than DZ twins. The heritability of the parameters was estimated to range from 0.16 to 0.31. MZ and DZ cotwins with similar studying and reading habits had a higher concordance in myopia than MZ and DZ twins with different studying and reading habits. A significant gene-environment interaction in the determination of myopia has also been observed. However, the etiological mechanism for the development of myopia remains to be elucidated.