Posted: December 28th, 2015

the rapid increase of myopia prevalence is not due to genes, it must be due to changes in environmental factors and finding out which factors are the important ones is then the crucial issue.

the rapid increase of myopia prevalence is not due to genes, it must be due to changes in environmental factors and finding out which factors are the important ones is then the crucial issue.

There are various ways to structure the argument. One way is to outline what people believed (ie genetic determination through these points; heritability and twin studies, parental myopia, myopia among families and siblings, myopia among ethnic groups and myopia resulting from some syndromes or diseases), and the reasons that they believed in this. (I’ll upload a review helps you in this)

You will need to fill those points in with a paragraph or two about each point. You will need to note that it is the twin study part, which led to the idea of almost total genetic determination, and you therefore need to spend some time on the limitations of twin studies, and why even 90% heritability does not necessarily mean almost total genetic determination.

You then need to give the reasons why this old view has to be discarded. This is where the changes in prevalence come in. They are simply not compatible with the old ideas of genetic determination.

There is another reason why the old idea has to be discarded, and that is that modern genetic analysis (GWAS and other gene linkage studies) have not found anything like the amount of associated genetic variation to account for the variations seen in most populations. This is what is known as missing heritability. Here, a devout geneticist will argue that given enough time, and a large enough population, and virtually unlimited funding, they will be able to explain everything, but we already know that this is not true, at least for some populations, because of how much change has been observed.

You probably also need to deal with issues of ethnicity in a bit more detail, because there are still some who argue that different ethnic groups are more of less susceptible to environmental risk factors. But the arguments are also pretty clear here. In Singapore, Indians are almost as myopic as the Chinese, and more myopic than the Malays. But the Chinese and Malays are closer genetically. It is particularly important that the Indians are much closer to the populations of the Middle East and Europe, so if they can be so affected by the environment, we would expect that people from the Middle East and Europe would be too.