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While myopia, or nearsightedness, has been thought to progress mostly in children and adolescents, a new study suggests the condition can progress in more than a third of adults as well.

Of patients without myopia at ages 18-22, 14% (95% CI 11.5%-17.4%) proceeded to develop myopia after 8 years, reported Samantha Sze-Yee Lee, PhD, of the Lions Eye Institute in Perth, Australia, and colleagues. Of those without high myopia initially, 0.7% (95% CI 0.3%-1.2%) developed it within 8 years.

Overall, 37.8% of the included participants had a "myopic shift" -- i.e., a change of 0.5 diopters or greater -- in at least one eye and 22% had a myopic shift in both eyes, the researchers noted in .

"With younger generations increasingly pursuing postgraduate education, we may expect more at-risk young adults to develop myopia in their 20s or early 30s," the team wrote. "Even in non-university students or graduates, individuals are likely to start their first full-time occupation in or just prior to their 20s, and the rise in indoor occupations will inevitably result in the development or progression of myopia in a substantial proportion of the population."

Previous studies on myopia in young adults have been conducted mostly in university students. As such, the data on myopia development or progression in young adults are limited and selective, the investigators said. "A main strength of the current study is the large sample of community-based young adults, rather than recruiting participants from universities or myopic cohorts, as has been done in previous studies on young adults."

The new study was conducted with participants from the , a cohort of patients who were born in Perth and were followed from the neonatal period into adulthood.

The findings, however, are in contrast to those in a , which suggested that myopia stabilizes at around age 15-16.

In both univariate and multivariate analyses, myopia incidence was significantly associated with parental myopia and East Asian race, consistent with on race and myopia incidence.

Myopia incidence was also associated with less sun exposure, which was quantified using conjunctival ultraviolet autofluorescence (CUVAF) area, Lee and co-authors said. " have noted a protective effect of increased time outdoors against myopia, but findings on whether it reduces myopia progression have been conflicting."

Women in the study were also more likely to develop myopia than men. "This difference between young men and young women may reflect the modern societal push for higher education in girls and women, as reflected by the increasing proportion of women with higher education than men, and a tendency for women to work in indoor-based occupations in Australia," the team wrote.

The association between female sex and myopia progression was still significant after adjusting for education level and sun exposure, the study authors noted. Higher education level was not significantly associated with myopia incidence or progression.

In the U.S., over 150 million Americans, or nearly one-half of the U.S. population, have refractive errors including myopia, according to the .

The Australian study followed participants of the Raine study, whose birth mothers were recruited from 1989 to 1991; a total of 2,868 children were born in the cohort.

A 20-year follow-up eye examination, considered as a baseline, took place from 2010 to 2012, and 1,344 participants attended, with data obtained from 1,328.

A 28-year follow-up took place from 2018 to March 2020, when it was cut short by the pandemic. In this follow-up exam, 801 participants attended, and data were obtained for 783. Slightly more males than females did not attend the follow-up visit, the researchers noted. At baseline, 698 participants were without high myopia and 516 had no myopia, and the progression analysis included a total of 691 individuals.

Both exams included CUVAF photography, ocular biometry, post-mydriatic autorefraction/keratometry, and lens thickness measurement.

Study limitations, the researchers said, included that the findings may not be generalizable to recent immigrants to Western Australia, which includes a higher proportion of people of East Asian descent compared with the cohort recruited 30 years earlier. In addition, a significant proportion of the baseline cohort did not attend the 28-year eye exam, in part due to the COVID-19 pandemic.

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