Myopia: Where genetics and schooling interact

In June 2022, we started an article on the role of genetics in myopia development with a question about whether myopia is a product of nature or nurture.[1] It's an ongoing debate which affects so many aspects of our development. And often, the answer boils down to 'a bit of both.'

For instance, when it comes to myopia, studies have revealed that parental myopia can increase the risk of a child developing the condition. But studies have also shown that lifestyle factors such as too much close screen time, a lack of outdoor activities, and poor nutrition play their part.

A lot of research exists investigating the effect of myopia (some dating as far back as 1928!), yet there isn't a clear answer on whether near work indeed causes myopia or is instead just associated with developing it. Part of the problem with various types of studies is that a lot of the research is at risk of Recall Bias (e.g. when adults have to recall how many hours they used to read per day) and differences between studies on what counts as "near work", etc.

The CLEERE study (2010) [2] stated that near work did not cause or increase the risk of developing myopia. A study in 2007 by Guggenheim et al. [3] analysed 315 children who also participated in the SCORM study. The study involved two main components: a cross-sectional study which showed that those children who read more than two books per week had longer axial lengths. They also performed a longitudinal analysis (2005) over three years, which (frustratingly) determined that near work and axial length were not associated.

The Sydney myopia study [4] was a longitudinal study that compared two groups of children: younger children (6yr olds) and older children (12yr olds). It compared the risk of developing myopia depending on the child's time spent outdoors vs how long they spent doing near work.

It is evident from this study that it is not enough to mention just near work or time spent outdoors, but instead, try to influence both behaviours. It was shown that those who spent the most time doing near work and the least time outdoors had the highest risk of developing myopia.

Figure 1 Sydney study showing the varying impact of near work and outdoor activity on the likelihood of developing myopia within the 6-year-old cohort

Figure SEQ Figure \* ARABIC 1 Sydney study showing the varying impact of near work and outdoor activity on the likelihood of developing myopia within the 6-year-old cohort The Sydney study [4] demonstrated that spending high amounts of time outdoors reduced the impact of high levels of near work on the likelihood of developing myopia but most notably illustrated a disproportionately increased likelihood of developing myopia if a child spends low amounts of time outdoors but increased amount of time doing near work.

Verhoeven et al. (2013) [5] included data from the Rotterdam Studies (two large cohorts of n=5,256 and n=3,938 European adults). They found that the most significant rate of myopia was in people with a high genetic risk AND the highest education levels. The inference being those with the highest level of education also spent the most extended time reading and doing near work.

Interestingly, in disproportionate results that are very similar to those of the Sydney Myopia study, Verhoeven's study raises the question of whether having a high genetic predisposition to myopia amplifies the impact of near work on developing myopia (see figure 2). Those with high genetic risk but with lower levels of education had a lower risk of developing myopia than those with low genetic risk with a higher education level.

Tedja et al., in their study [6], "Genome-wide association meta-analysis highlights light-induced signalling as a driver for refractive error", report no significant differences in myopia-associated genes between East Asian and European ethnic groups (n=11,595). In this study, they stated that genetics accounted for only a small variance in refractive error in their East Asian cohort.

Although this cohort sample was relatively small, their study indicates that the differences in environmental factors influence the refractive outcome more than differences in genetic makeup. Whatever the results of this further research, one thing is clear; the more that the genetics of myopia is understood, the greater the chance of targeting appropriate myopia management techniques for individuals.

A report issued at the end of 2022 has taken this nature versus nurture aaproach one step further, investigating whether certain genes could increase the likelihood of myopia developing in individuals exposed to certain lifestyle risk factors.[7]

According to the report’s authors, more than four hundred and fifty genetic variables have been linked to an increased risk of myopia, the nature end of the equation.

Rather than examine all of these genes, for this initial research, the report's authors decided to focus on individuals who had received some form of higher education and whose myopia may have partly been caused by a significant amount of close study time in education.

Using data gleaned from the UK Biobank, the researchers identified twenty-five specific genetic variants which they say are linked to an increased risk of myopic development for those who spend time in higher education. Five of these, in particular, were shown to deliver an increasing risk of myopia in line with increasing time in education.

However, the researchers were careful to point out that further research is required before establishing a direct causal link. For example, they suggest that those in extended periods of education may spend more time in close work or less time outdoors and that either of these could also trigger myopia. It should also be noted that the people studied were all born between 1940 and 1990, so their conclusion of how genetics are more influential might not be as applicable to a generation who undertake higher-level education and who use digital devices much more or who have a much more near-work-involved upbringing.

In the meantime, the best advice remains to eat a balanced diet, limit the distance and duration of near activities, and spend much more time outdoors (ideally 2+ hours per day).

The importance of having a regular eye check also cannot be underestimated as the sooner that a tendency towards myopia is identified, the quicker that management plans can be introduced.

Evidence exists that not correcting or under-correcting a child's myopia can worsen the progression of their myopia [8], so the sooner it's corrected, the better.

If you're a parent whose child has been diagnosed with myopia or if they are struggling with their distance vision, we hope you found MyopiaFocus helpful. Please join our community or sign our petition to get the government and NHS to recognise myopia as an ocular disease/severe ocular condition and fund myopia management for children.