Myopia Pathogenesis

In normal eye development, axial length starts at approximately 16-17 mm at birth, reaches ~23 mm by age 3 after a rapid growth phase, then slows to stabilize at ~23.5 mm by the end of adolescence. This process is known as "emmetropization": the eye grows toward a length matched to its optical power.

In myopia, this balance breaks down: the eyeball continues to elongate disproportionate to its optical power. Each 1 mm of axial elongation corresponds to approximately −2.5 D of myopia. Light focuses in front of the retina rather than on it, causing distant objects to appear blurred.

Axial elongation is irreversible. Treatment does not reduce existing myopia; it aims to slow or halt further elongation. This is why early intervention is critically important.

Myopia has a strong heritable component. Genome-wide association studies (GWAS) have identified over 200 myopia-associated gene loci (Tedja et al. 2019, IMI Genetics).

According to Morgan et al. (2012, Lancet): children with no myopic parents have baseline risk; those with one myopic parent have ~2-3× increased risk; those with two myopic parents have ~6× increased risk.

However, genetics only determines susceptibility, not the epidemic. The rise of myopia prevalence in East Asia from ~20% to 80-90% since the 1960s (within just 2-3 generations) proves the decisive role of environmental factors. Gene-environment interaction (GxE) models show that genetically predisposed children are more sensitive to environmental risk factors.

The myopia epidemic correlates strongly with fundamental changes in modern lifestyle. Three main environmental risk factors stand out:

1. Reduced Outdoor Time

He et al. (2015, JAMA), a randomized controlled trial of 1,903 children in China: adding 40 minutes of outdoor activity during school hours reduced myopia incidence by 23% over 3 years. A similar protective effect was shown in Rose et al.'s (2008) Sydney study. While the mechanism is not fully understood, sunlight is thought to slow axial elongation by increasing retinal dopamine release.

2. Increased Near Work

According to Huang et al.'s (2015) meta-analysis, each additional hour of near work per week increases myopia risk by 2%. Working distance shorter than 30 cm and prolonged uninterrupted reading further increase risk. Rising digital device use and educational intensity amplify this factor.

3. Urbanization and Educational Intensity

In Williams et al.'s (2015) European study, each additional year of education significantly increases myopia risk. Myopia prevalence in urban areas is 2-3× higher than rural areas. This difference is explained by increased indoor time and decreased outdoor time.

Myopia prevalence shows dramatic variation between regions:

• East Asia (China, South Korea, Japan, Taiwan): 80–90% of young adults (IMI 2021)
• Southeast Asia (Singapore, Malaysia): 40–60%
• Europe: 30–40% (Williams et al. 2015)
• North America: 30–35%
• Middle East and Turkey: 25–30% (Hashemi et al. 2018)
• Africa: 10–15% (Kobia-Acquah et al. 2022)

These differences reflect both genetic background and differences in education systems, urbanization levels, and lifestyle. The high prevalence in East Asia correlates strongly with intensive educational pressure and indoor lifestyle. The fact that myopia prevalence changes in individuals of the same ethnic group after migration to different environments supports the decisive role of environment.

Myopia is not merely a refractive error. Particularly in high myopia (≤ −6.00 D or AL ≥ 26 mm), the risk of serious ocular complications increases exponentially:

• Retinal detachment: risk increased 5-6× in high myopia (Saw et al. 2005)
• Myopic maculopathy: the most common cause of vision loss in pathological myopia (Ohno-Matsui et al. 2015, META-PM classification)
• Open-angle glaucoma: risk increased 2-3× in myopes
• Early cataract: 2-5× increased risk in high myopia
• Choroidal neovascularization: 5-10% incidence in pathological myopia