Taking a close look at short-sightedness

Myopia, or short-sightedness, is a significant global health problem estimated to affect 1406 million people (about 23% of the world’s population) as of 2000. And if you get the sense that there are more and more people experiencing this disease these days, a new study led by researchers from University College London (UCL) and the UK Biobank Eye and Vision Consortium suggests you’re right.

The study used a large dataset from the UK Biobank, which has collected samples and health information from half a million adults living in the UK and born between 1939 and 1970. Analysing health and sociodemographic data from more than 100,000 people, the researchers established an increased prevalence of myopia in the UK over time, from 20% prevalence in the oldest cohort (born 1939–1944) to 29.2% in the youngest cohort (born 1965–1970).

However, the researchers didn’t stop there.

“The breadth of information and sample size offered by the [UK] Biobank allowed us to do something very unusual but important to us – that is to analyse childhood-onset and adult-onset myopia separately,” says senior author Jugnoo Rahi, a professor at UCL.

By doing so, the researchers were able to differentiate that while childhood-onset myopia had peaked in the cohort born in the early 1950s, the frequency of adult-onset myopia peaked in the cohort born a decade later. A trend of increasing myopia severity over time was seen only for childhood-onset disease.

“When all myopia is lumped together, important differences in risk factors are missed,” says Rahi.

Line graph demonstrating the myopia epidemic changing myopia frequency by birth year
Frequency of myopia (all, childhood-onset and adult-onset), by year of birth as 5-year bands. Figure from Cumberland et al., 2022, PLOS ONE, CC-BY 4.0.

The study also explored environmental and sociodemographic factors that could be shaping the changing prevalence and severity of myopia.

“Myopia is a condition that arises when the usually very tightly controlled process of eye growth is derailed by environmental triggers in genetically ‘susceptible’ people,” Rahi explains.

For example, higher current socio-economic status was associated with increased risk of adult-onset myopia.

A related major factor of interest was education level, as eyesight researchers are interested in the relationship between myopia risk and “near viewing” (looking at nearby objects) and “distance viewing” (looking at distant objects).

More years or intensity of formal education is associated with more time spent near viewing – for example, at books or computer screens – while distance viewing, especially outdoors, is thought to protect against myopia. Rahi points out that, within the study period, UK society experienced increases in school-leaving age and higher education, and decline in time spent outdoors – all of which may have affected the balance of near and distance viewing.

In fact, higher educational attainment was associated with myopia in the study – but this relationship varied across ethnic groups. Adult-onset myopia was associated with higher educational attainment in people whose ethnicity was reported as White or Asian, but not Black, while people of Chinese ethnicity and highest educational qualifications were at the highest risk of both child- and adult-onset myopia. The researchers suggested that these findings may provide indirect evidence of gene-environment interaction shaping myopia risk.

By identifying such potentially modifiable risk factors, the researchers hope to offer a way to halt the trend of increased myopia in younger generations – for example, by increasing children’s access to distance-viewing activities.

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