Purpose: The etiology of myopia has been attributed to both genetic and environmental factors. The purpose of this paper is to attempt to distinguish between genetic and environmental factors in three generations of subjects from three locations.
Methods: Noncycloplegic autorefraction and distance visual acuity were measured in 3131 Chinese children 7 to 17 years old from Hong Kong, Tianjin, and Ban Chau. Data on the refractive status of the parents and grandparents were collected using questionnaires. Myopia was defined operationally as spherical equivalent refractive error (SER) of at least -1.00 D and uncorrected vision worse than logMAR 0.18 (6/9).
Results: The odds of having myopia for the grandparents', parents', and children's generations were 0.06, 0.26, and 0.35, respectively. Having myopic parents increased the odds ratio for having myopia (odds ratio 1.85 for children's generation and 6.71 for parents' generation), showing a genetic influence. However, the odds of having myopia also increased in offspring of nonmyopic parents between generation 2 and 3, suggesting an environmental influence. Results of prevalence and odds ratios from the three locations also demonstrated an environmental effect on development of myopia.
Conclusion: We propose that myopic development in Chinese follows a multifactorial and polygenic model in which the genetic input has remained constant while the environmental influence has increased over the last three generations.