Risk factors for myopia: Putting causal pathways into a social context
- Publisher:
- Elsevier
- Publication Type:
- Chapter
- Citation:
- Updates on Myopia: A Clinical Perspective, 2020, pp. 133-170
- Issue Date:
- 2020
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| Filename | Description | Size | |||
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| chapter.pdf | Published version | 1.08 MB |
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© The Editor(s) (if applicable) and The Author(s) 2020. Myopia is often described as resulting from a complex set of interactions between genetic and environmental risk factors. Rare forms of strongly familial myopia account for myopia in around 1% of any population. “School myopia”, the most common form in most modern societies, is also influenced by genetic factors, but changes in environmental risk factors appear to be responsible for the major increases in the prevalence of myopia in some parts of East and Southeast Asia. Two major environmental risk factors have been identified-intensive schooling and limited time outdoors, with educational pressures high and time outdoors particularly limited in the parts of East and Southeast Asia afflicted by an epidemic of school myopia. Several other “independent” risk factors for myopia have been reported. The effects of many of these may be mediated by modulation of the two major risk factors, and in future studies on risk factors, mediation analysis needs to be used systematically. In the case of school myopia, we argue that there are two major environmental risk factors, with a limited role for genetic variation and minimal interactions. We propose a method for comparing the impact of identified genetic risk factors with the cumulative effects of environmental exposures. This suggests that genetic risk factors associated with more myopic refractions generally lead to myopia only when combined with exposures to environmental risk factors. The predominant role played by increased educational pressures and limited time outdoors suggests strategies for controlling the current epidemic of myopia by directly reducing educational pressures, perhaps by limiting homework and rote learning in the early school years, combined with increases in time spent outdoors in schools. Identification of distal environmental factors, such as early onset of competition for selective academic streams and schools, and the use of after-school tutorial classes also suggest strategies for reducing the current epidemic through changes at the school system level. When combined with clinical techniques for controlling the progression of myopia, these measures have the potential to markedly reduce the current high prevalence rates of both myopia and sight-threatening pathological high myopia.
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