Both appear to contribute to myopia development.
It is also established that myopia tends to run in the family. For example, if both parents suffer from severe myopia, it is likely that all their children will encounter the same problem.
Although myopia is passed down as a genetic trait, environmental factors can and do play an important part in its onset and development. For example, the increase in myopia prevalence rates in Singapore are not just restricted to the Chinese race but has occurred across the board for the other races as well. Consider also the recent rapid and severe increases in myopia prevalence rates in Singapore, Taiwan, Hong Kong and Japan. These have been analysed to be too rapid and severe to be attributed solely to genetic factors and instead point to environmental factors as the predominant causes.
Much research has been done and is still being done to understand the various genetic and environmental factors that affect myopia onset, development and progression. Environmental factors are generally the predominant causes of mild myopia. Moderate myopia probably results from equal contribution of both genetic and environmental factors while for severe myopia, genetic factors are usually the predominant causes.
Presently, there is not much that can be done to modulate genetic factors beyond being cautious and taking extra care if there is strong genetic predisposition, such as where both parents suffer from high myopia. Hopefully, this may change in the future with the advances being made in the field of gene therapy and the completion of the human genome mapping project.The good new is that there is really quite a lot that can be done with respect to modulating environmental factors. And this will be the main focus of the strategies to be outlined.