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HomemifeatureSummary of Risk Factors for Developing Myopia

Summary of Risk Factors for Developing Myopia

The topic of myopia goes beyond its impact on a person’s eye health, because myopia also has significant impacts on public health in general. If not managed, nearsightedness can lead to many eye problems, some of which include serious sight-threatening diseases.

This makes continued research into myopia critical. When we understand the genesis and progression of myopia, governments, academics, and practitioners can shape public health policies, medical interventions, and societal behaviours to minimise its prevalence. Additionally, the public can be educated and encouraged to make better choices about its eye health.

Orthoptist Luke Seesink provides an overview of what we currently know about myopia: the predominant factors that instigate its emergence, potential treatment strategies, and preventative methods to manage and reduce progression.

GENETIC AND ENVIRONMENTAL FACTORS

Hereditary components have been hypothesised as contributors to myopia, evidenced by its propensity to manifest more commonly within familial lineages and its pronounced occurrence among monozygotic twins versus dizygotic twins.1 Among mainland Chinese school children, the incidence of myopia was 7.6% for those with no myopic parents, 14.9% for those with one myopic parent, and 43.6% for those with two myopic parents.2 Advanced genomic investigations have revealed over two dozen genomic regions affiliated with myopia and identified distinct gene mutations, including ARR3, BSG, and ZNF644, that are precursors to high myopia.3

Prominent genome-wide association studies, notably by the Consortium for Refractive Error and Myopia (CREAM), have unearthed a multitude of genetic locations associated with the refractive anomalies and the age-specific onset of myopia across large cohorts.3 Cumulatively, these genetic markers encompass a proportion of the variability observed in myopia manifestations. They not only indicate susceptibility but also shape the progression trajectory and severity gradient of the condition. These genes are intricately woven into a gamut of biological processes pivotal to ocular health, ranging from neurotransmission to ion dynamics and even ocular morphogenesis. Recent scientific studies have hinted at correlations between myopia predisposition and specific ocular anomalies, diurnal patterns, pigmentary characteristics, and molecular signalling routes.4 Such genomic revelations provide invaluable insights into potential therapeutic avenues and contribute to the understanding of the fundamental processes underlying myopia.

The growth of a child’s eye towards emmetropia is influenced by environmental factors and is mainly complete by age seven to nine years. The cornea, lens, and axial length grow towards an emmetropic state during this time so that clear vision can be attained by the eye for both near and distant objects. For this reason, unless the child is highly myopic and at risk of developing amblyopia, it is not recommended to correct small amounts of refractive error before age five.

High myopia in very young children and infants can be caused by retinopathy of prematurity (ROP) or an interaction of genetic and environmental factors.5 Retinal dystrophies and connective tissue disorders of genetic origin, like Marfan syndrome or Stickler syndrome, may contribute to high myopia in very young children.5 These can cause malformations in the lens and/or the cornea.

Typically, myopia first emerges in school-age children. With the advent of genome-wide association studies (GWAS), nearly 200 genetic locations have been linked with myopia and refractive errors.3 Most of these carry a minor risk and are present in many people. Those with high combined genetic risk can have up to a 40-fold increase in myopia risk.3 While most genes linked with specific myopia syndromes haven’t been connected to general nearsightedness, there’s some overlap. However, these genes account for only about 8% of the variability in myopia, suggesting that environment plays a significant role.3 This is reinforced by the sharp rise in myopia over the past half-century, which can’t be explained by genetics alone.

One of the major environmental risk factors is education. Higher education levels, academic performance, and education-focussed countries correlate with increased myopia risk.6 The precise cause isn’t certain, but extended reading and writing periods are likely contributors.

Spending more time outside seems to prevent myopia, but it is unclear if outdoor time slows myopia progression once it has started.1 One theory suggests outdoor brightness might release dopamine, which stops the eye from growing too long.1

Children with nearsighted parents tend to develop myopia, but whether this is due to genes, environment, or both isn’t clear.

Gender’s influence on myopia risk varies; older studies found males more at risk,6 while newer ones indicate females are.6 Differences also exist among ethnic groups, with East and Southeast Asian populations showing higher myopia rates, possibly due to environmental factors.6

A recent study from China linked staying up late with higher myopia risk.4 However, why this occurs remains unknown. Other potential risk factors include birth order, height, physical activity, intelligence, socio-economic status, diet, and housing.6,7 More research is needed to confirm these links and understand their roles in myopia development.

When children transition into high school and later into adulthood, the progression of myopia usually slows down, settling over time. While there aren’t a lot of studies on older groups, the research shows that by age 15, about half of the myopia cases stabilise, 77% by age 18, and by the age of 21, it’s 90% of cases.8 Although uncommon, people can become myopic in adulthood. This is especially seen in people in academic environments or jobs that involve a lot of near work.6 Adult onset myopia does not typically progress as quickly as it does in younger people.8

SCREEN TIME AND DIGITAL DEVICES

The worldwide impact of the COVID-19 pandemic led to a rise in online learning, increasing the time children spent on screens while decreasing their time spent outside. Studies have theorised that these behavioural changes may have increased the risk of myopia in children. Looking at studies from this time gives us insight into the risks9 of near tasks and limited outdoor time. However, it is important to realise that only some of the studies undertaken used solid testing methods. Overall, the quality was average, and there is a clear need to improve research methods, use better testing tools, and study a wider range of people.

OUTDOOR TIME AND NATURAL LIGHT

A growing body of research has highlighted the benefits of outdoor engagements and sunlight exposure in countering the advance of myopia.10 These findings resonate with an age-old understanding of the human body’s intrinsic relationship with the natural environment. The therapeutic effects of natural light, combined with the physiological benefits of outdoor activities, may play a role in safeguarding ocular health.

When discussing the protective attributes of sunlight, it is worth noting its potential role in stimulating the production of dopamine in the retina, a neurotransmitter believed to slow down the elongation of the eye1 – a primary factor in myopia’s development. Moreover, outdoor activities often involve a balance of near and distance vision tasks, which can provide a more diverse range of visual stimuli compared to the often static, near-focus tasks indoors.

During childhood, when the eye undergoes significant developmental changes, consistent exposure to a range of visual stimuli outdoors may be important in setting a trajectory away from myopia. This emphasises the need to encourage young individuals, especially those in urban environments where interaction with nature may be limited, to spend more time outdoors.

Furthermore, given the genetic predisposition that some cohorts possess, proactive measures become even more crucial. Families with a history of myopia should be particularly vigilant in ensuring that children experience ample outdoor time from a young age. This can be facilitated through play, sports, and educational activities.

TAKING A MULTIDIMENSIONAL APPROACH

Having examined the numerous factors influencing myopia progression, it is clear that a singular intervention strategy to mitigate its rising incidence will be inadequate.

Instead, the multifaceted nature of myopia’s determinants – ranging from genetic predispositions to environmental exposures – necessitate a multidimensional approach. Only by integrating multiple strategies and tailoring interventions based on an individual’s specific risk factors will we address the complex interplay of elements driving the prevalence of myopia.

This must encompass early diagnosis, evidence-based interventions, public awareness campaigns, and perhaps even societal structural changes that prioritise ocular health. Furthermore, it requires the interdisciplinary collaboration of geneticists, ophthalmologists, educators, urban planners, and policymakers to foster environments that not only mitigate the risk of myopia but also promote overall visual health.

Finally, it is imperative that we remain agile, adapting our strategies to leverage new knowledge and technologies.

In essence, while the challenge of myopia is multifaceted and formidable, armed with knowledge, we can create a future where myopia’s impact is significantly diminished, and vision health is prioritised. The collective endeavour towards this goal will not only benefit those directly affected by myopia but will also contribute to a broader societal benefit of reduced cost of preventable blindness.

Luke Seesink B.Appl.Sci. (Orthoptics)(Hons) is a Senior Clinical Research Manager at the Brien Holden Vision Institute. He has worked for almost 20 years as a qualified orthoptist and in a variety of different clinical research roles within ophthalmology.

References

  1. Baird, P.N., Saw, S.M., He, M., et al., Myopia. Nat Rev Dis Primers. 2020 Dec 17;6(1):99. DOI: 10.1038/S41572-020- 00231-4. PMID: 33328468.
  2. Lim, L.T., Gong, Y., Yu, S., et al., Impact of parental history of myopia on the development of myopia in mainland China school-aged children. Ophthalmol Eye Dis. 2014 Jun 24;6:31-5. DOI: 10.4137/Oed.S16031. PMID: 25002817; PMCID: PMC4076205.
  3. Tedja, M.S., Haarman, A.E.G., Meester-Smoor, M.A., et al., IMI – Myopia Genetics Report. Invest Ophthalmol Vis Sci 2019;60(3):M89-M105. DOI: 10.1167/Iovs.18-25965.
  4. Liu X.N., Naduvilath, T.J., Wang, J., et al., Sleeping late is a risk factor for myopia development amongst school-aged children in China. Sci Rep 2020;10(1):17194. DOI: 10.1038/ S41598-020-74348-7.
  5. Ghoraba, H.H., Ludwig, C.A., Moshfeghi, D,M., Biometric variations in high myopia associated with different underlying ocular and genetic conditions. Ophthalmol Sci. 2022 Oct 25;3(1):100236. DOI: 10.1016/J. Xops.2022.100236. PMID: 36545263; PMCID: Pmc9761849.
  6. Morgan, I.G., Wu, P.C., Ostrin, L.A., et al,. IMI – Risk factors for myopia. Invest Ophthalmol Vis Sci 2021;62(5):3. DOI: 10.1167/Iovs.62.5.3.
  7. Yu, M., Hu, Y., Bi, H., et al., Global risk factor analysis of myopia onset in children: A systematic review and meta-analysis. PLOS One. 2023 Sep 20;18(9):E0291470. Doi: 10.1371/Journal. POne.0291470. PMID: 37729320; PMCID: PMC10511087.
  8. Bullimore, M.A., Lee, S.S., Schmid, K.L., et al., IMI – Onset and progression of myopia in young adults. Invest Ophthalmol Vis Sci 2023;64(6):2. DOI: 10.1167/Iovs.64.6.2
  9. Lau, J., Koh, W.l., Koh, V., et al., How can we better evaluate paediatric progression of myopia and associated risk factors? Lessons from the COVID-19 pandemic: A systematic review. Acta Ophthalmol. 2023 Oct 3. DOI: 10.1111/Aos.15773. Epub ahead of print. Pmid: 37786939.
  10. Sánchez-Tocino, H., Villanueva, Gómez A., GalindoFerreiro, A., et al., The effect of light and outdoor activity in natural lighting on the progression of myopia in children. J Fr Ophtalmol. 2019 Jan;42(1):2-10. DOI: 10.1016/J. Jfo.2018.05.008. Epub 2018 Dec 17. PMID: 30573292.