The Reality

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Myopia has become a significant global health and socio-economic problem. It is estimated that by 2050, half the world’s population will be myopic, and nearly 1 billion people will suffer from high myopia (Holden, 2016). Most cases of myopia are considered benign because vision can be corrected with spectacles or contact lenses. However, about a quarter of patients with high myopia develop pathological myopia, which places the eyes at risk of irreversible vision impairment and blindness. Myopia develops in childhood; therefore, early intervention is the best approach to reduce the burden of pathological myopia later in life. In this section, we examine the prevalence of myopia in children, the role inheritance plays, and the risks that uncontrolled myopia can pose in adulthood.

Prevalence of Myopia in Children

‍ ‍Myopia became an escalating problem in parts of East Asia starting in the 1990s. Population surveys of 12-year-old children showed over half were myopic in cities like Singapore, Hong Kong, and Guangzhou, China, whereas the range was 11-20% in countries like the United States, the United Kingdom, and Australia. Myopia starts quite young too; prevalence among preschoolers in Taiwan was 3% at age 3 and 12% by age 6 (Lai, 2009).

Longitudinal studies are interesting in that they show how myopia is trending. A nationwide myopia survey in Taiwan showed that the prevalence of myopia among 7-year-olds increased from 6% in 1983 to 21% in 2000. At 12 years old, that number was 37% in 1983, increasing to 61% in 2000; corresponding figures for 15-year-olds were 64% and 81%, respectively (Lin, 2004). There are fewer such studies in the West, but a notable one from Minnesota, USA, showed the prevalence of myopia in adults rose from 34% in the 1960s to 57% in the 2010s. More concerning is that the prevalence of high myopia also increased, almost tripling in the same period (Tailor, 2024).

There is therefore a generational difference in the prevalence of myopia and high myopia. Researchers found a strong association between education and high myopia in children, but not so in older adults (Jonas, 2016). They therefore concluded that the higher prevalence of myopia in this generation of children was mainly driven by environmental factors and not by genetics, unlike in the older generation.

An unexpected natural experiment in environmental change threw further light on myopia prevalence in children. Researchers from Hong Kong found an abrupt rise in their cohort of children during the COVID pandemic, the most significant of which was a doubling in prevalence in 6-year-olds (Zhang, 2023). Authors cite “reduced time spent outdoors, increased near-work time, and increased screen time” as potential factors involved. The magnitude of change in the youngest age group studied is noteworthy, as early-onset increases the likelihood of developing high myopia.

Myopia is Not Always a Benign Condition

The World Health Organization estimates that 12.8 million children aged 5–15 worldwide are visually impaired from uncorrected myopia, hyperopia, and astigmatism (Sharma, 2012). With myopia prevalence increasing, this number is likely to climb further. Although optical correction seems straightforward, barriers to treatment include the availability of a trained eye care workforce, the affordability of vision aids in lower-income economies, and the acceptability of wearing glasses; some cultures believe wearing them will harm children’s eyes, for example. School-aged children with vision impairment also experience lower levels of educational achievement and self-esteem than their normally sighted peers (WHO, 2019).

The true cost, however, is the association of high myopia with potential complications that may lead to irreversible blindness. High myopia is defined by most studies as a prescription of -6.00 D or over. It is estimated that about a quarter of these will go on to develop pathological myopia (PM). PM is a term used to describe structural changes in the back of the eye resulting from high myopia. Essentially, the rear portion of the eye becomes so stretched that most of its structure becomes thin and fragile.

The macula is the small central part of the retina, the lining of the eye that senses light, which gives the clearest vision. Imagine it to be a high-resolution sensor of a digital camera. In PM, the components can become so thin that they start to lose function. This is called macular atrophy. The thinning can also lead to cracks in the macula, causing new abnormal blood vessels to form within these defects. This is called choroidal neovascularization and can also lead to vision loss.

Stretching of the outer regions of the retina can lead to holes and tears forming within it. The retina may then separate from its underlying support structures, leading to retinal detachment. Scar-like tissue can also form in highly myopic eyes, and when it contracts, it can pull on the retina, causing it to detach. Both situations can result in an abrupt loss of vision, and prompt treatment is required to preserve vision.

People with high myopia have an increased risk of glaucoma, which slowly damages the optic nerve. The optic nerve carries visual signals to the brain. It seems to become more vulnerable to damage with high myopia. The vision loss from glaucoma is slower and may not be noticeable at first. In late stages, it causes tunnel vision and severe vision loss.

Preventing childhood myopia is therefore very important, as the earlier the onset, the greater the chance of developing high myopia. When the eyeball becomes too long, the risk of sight-threatening complications is also increased. Because these complications rarely appear until adult life, the significance of good myopia control in childhood can easily be overlooked.

The Genetics of Myopia

There is a risk of myopic parents producing myopic children. The Hong Kong Children Eye Study showed how strong this link is (Tang, 2020). Recruiting children with no myopic parents as the control group, the study showed that a child with one myopic parent is about twice as likely to develop myopia, and a child with two myopic parents is roughly three times as likely.

However, if myopia were caused by genes alone, there would not be such a dramatic rise in numbers seen over a relatively short period, especially in East Asia. Evolutionary change in human DNA cannot happen this quickly. As prevalence studies have shown, what has changed during this time is children’s lifestyle: more years of schooling, more prolonged reading and screen use, and less outdoor time. Therefore, inheritance might create susceptibility, but the environment influences how strongly it is expressed.

Unlike classic single-gene diseases like cystic fibrosis, myopia is usually polygenic, meaning various genes each contribute a small amount to a child’s risk rather than one gene acting alone. There are forms of extreme myopia that have a strong inherited pattern in some families, but this is very rare and different to the common type of myopia seen in school children. There is an ongoing research effort to identify all candidate genes, and each gene may control different parts of eye development. What this means in practice is that there is no single gene test currently available that can determine the risk.

If there is a family history of myopia, then it is advisable to schedule eye examinations early in childhood. Early adoption of lifestyle changes listed in the section “The Context” is recommended. There are now treatments available to slow down myopia progression, and these are discussed in the last section, “The Response”.

Next: The Science‍ ‍

References

Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, et al. Global prevalenceof myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology. 2016;123(5):1036–42.

Jonas JB, Xu L, Wang YX, Bi HS, Wu JF, Jiang WJ, et al. Education-related parameters in high myopia: adults versus school children. PLoS One. 2016;11(5):e0154554.

Lai YH, Hsu HT, Wang HZ, Chang SJ, Wu WC. The visual status of children ages 3 to 6 years in the vision screening program in Taiwan. J AAPOS. 2009;13(1):58–62.

Lin LL, Shih YF, Hsiao CK, Chen CJ. Prevalence of myopia in Taiwanese school children: 1983 to 2000. Ann Acad Med. 2004;33(1):27–33.

Sharma A, Congdon N, Patel M, Gilbert C. School-based approaches to the correction of refractive error in children. Surv Ophthalmol. 2012 May-Jun;57(3):272-83.

Tailor PD, Xu TT, Tailor S, Asheim C, Olsen TW. Trends in Myopia and High Myopia from 1966 to 2019 in Olmsted County, Minnesota. Am J Ophthalmol. 2024 Mar;259:35-44.

Tang SM, Kam KW, French AN, Yu M, Chen LJ, Young AL, Rose KA, Tham CC, Pang CP, Yam JC. Independent Influence of Parental Myopia on Childhood Myopia in a Dose-Related Manner in 2,055 Trios: The Hong Kong Children Eye Study. Am J Ophthalmol. 2020 Oct;218:199-207.

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Zhang XJ, Zhang Y, Kam KW, Tang F, Li Y, Ng MPH, Young AL, Ip P, Tham CC, Chen LJ, Pang CP, Yam JC. Prevalence of Myopia in Children Before, During, and After COVID-19 Restrictions in Hong Kong. JAMA Netw Open. 2023 Mar 1;6(3):e234080.