Myopia, also known as nearsightedness, is a refractive mistake that occurs at the opposite end of the spectrum to hypermetropia. Nearsightedness is a more common name for myopia. This refractive error results from ocular expansion. An increasing ‘epidemic of myopia, which is characterised by an increased prevalence and a shift towards younger-onset and greater severity in the population, is now a major public safety problem. As a consequence, more people are at risk from the potentially blinding consequences if myopia severity increases, as seen in Asia but less in Europe.
Study: TEvidence from the UK Biobank Study: Observations on trends in myopia severity, frequency and type in the UK. Image Credit: Shidlovski/Shutterstock
Myopia severity (childhood vs. adult onset) is closely linked. Childhood-onset myopia often progresses into adulthood and is often more severe.
Although it offers the opportunity to explore the relative importance and nature of environmental risk factors and genetic predisposition, onset is rarely taken into account in myopia research. Onset is an opportunity to expand the current focus on aetiological and preventive public health interventions regarding the role of education experience and intensity in childhood.
Even though severity is always measured in research, it is more common for it to be used as an intermediate rather than a final measure because the latter can only be assigned in middle/late adulthood.
In this study, PLoS ONE, a team of researchers used the UK Biobank Study to investigate whether changing environmental factors are causing an increase in myopia. The UK Biobank Study, a unique sample of contemporary adults, has been underwent a thorough ophthalmic examination. Its members were all born in the last three decades. This allows the examination of ‘historical” cohorts that span a period of significant sociodemographic and economic change in the United Kingdom. From which emerging and current trends can be identified.
The study
The overall prevalence rate of primary myopia in the UK Biobank was 26.9%. There were 4.0% with high myopia and 9.5% with moderate myopia. 13.3% had low myopia. Overall, 45.6% of the subjects were emmetropic, while 27.6% were hypermetropic. The findings show that starting with a baseline overall myopia frequency of 20.0% in cohort 1 (1939–44), there was an increase in subsequent birth cohorts, peaking in cohort 4 (1955–54) and then plateauing.
Nevertheless, the prevalence of childhood-onset myopia peaked at 17.8% in cohort 3, two decades earlier than the prevalence of adult-onset myopia peaked at 15.0% in cohort 5 (1960–1964). While moderate myopia was more common than half of childhood-onset myopia in all cohorts, it drove the most significant relative increase in MSE in high myopia.
Fully adjusted analysis to model associations between myopia and sociodemographic factors revealed that later year of birth was associated with a lower likelihood of myopia overall, but this was driven by a progressive decline in the likelihood of childhood-onset myopia across all cohorts, resulting in a roughly 30% reduction in risk of childhood-onset myopia to those born after the 1960s compared to the baseline cohort 1 (born between 1939 and 1944).
Females were at a higher risk of myopia overall, but this included a 24% increased risk of childhood-onset myopia and a 12% lower risk of adult-onset myopia. An increase in myopia risk due to Chinese heritage was 90%. However, there was a 19% increase in adult-onset myopia and a 240% higher risk of childhood-onset myopia than with White ethnicity. All other ethnicities were considered ‘protective’. A clear relationship between ‘dose response’ and education level was found to strongly link the highest education level to an increased risk for childhood-onset myopia. Adult-onset myopia showed a similar gradient, but smaller effect sizes.
Both types had the largest effects on educational attainment associations after 18 years. Males had a larger effect size. This is consistent in the finding that school experience/highest educational intensity was a ‘trajectory effect’ or a ‘threshold effect regarding myopia risk. An increased risk of adult myopia was associated with higher socioeconomic status. There was a gradient between the categories. However, myopia was not associated with childhood-onset in those who had the highest socioeconomic status.
Implications
This illustration of complex temporal trends shows that the United Kingdom has a dynamic mix in environmental risk factors as well as cohort effects in gene–environment interactions. This is visible only by separating adult-onset myopia from childhood.
Historical evidence has shown that frequency plateauing can be stabilised or reversed. Evidence showing a differential impact of educational experience/intensity on childhood-onset and high myopia and its amplification through time indicates that the frequency of childhood-onset myopia will continue to rise in the future, regardless of educational intensity/experience.
But, focusing on myopia’s severe public health consequences in childhood-onset will not solve the problem. While adult-onset myopia may be less severe than that of childhood myopia in the UK, it is still a serious problem and can cause significant hardship for both individuals and society. To expand our understanding of modifiable risks across life and how to address them, a mixed economy of research is needed.
