IMI Risk Factors for Myopia
Ian G. Morgan (1,2), Pei-Chang Wu (3,4), Lisa A. Ostrin (5), J. Willem L. Tideman (6-8), Jason C. Yam (9-11), Weizhong Lan (12-15), Rigmor C. Baraas (16), Xiangui He (17-19), Padmaja Sankaridurg (20,21), Seang-Mei Saw (22-24), Amanda N. French (25), Kathryn A. Rose (25), Jeremy A. Guggenheim (26)
- Research School of Biology, Australian National University, Canberra, ACT, Australia
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Centre, Sun Yat-Sen University, Guangzhou, China
- Department of Ophthalmology, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan
- Chang Gung University College of Medicine, Kaohsiung, Taiwan
- College of Optometry, University of Houston, Houston, Texas, United States
- Department of Ophthalmology, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands
- Department of Epidemiology, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands
- The Generation R Study Group, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands
- Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China
- Hong Kong Eye Hospital, Hong Kong, China
- Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong, China
- Aier School of Ophthalmology, Central South University, Changsha, China
- Aier School of Optometry, Hubei University of Science and Technology, Xianning, China
- Aier Institute of Optometry and Vision Science, Aier Eye Hospital Group, Changsha, China
- Guangzhou Aier Eye Hospital, Jinan University, Guangzhou, China
- National Centre for Optics, Vision and Eye Care, Faculty of Health and Social Sciences, University of South-Eastern Norway, Kongsberg, Norway
- Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Centre, Shanghai Eye Hospital, Shanghai, China
- Department of Ophthalmology, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China
- Shanghai Key Laboratory of Ocular Fundus Diseases, National Clinical Research Centre for Eye Diseases, Shanghai, China
- Brien Holden Vision Institute Limited, Sydney, Australia
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
- Saw Swee Hock School of Public Health, National University of Singapore (NUS), Singapore
- Singapore Eye Research Institute, Singapore
- Duke-NUS Medical School, Singapore
- Discipline of Orthoptics, Graduate School of Health, University of Technology Sydney, Sydney, Australia
- School of Optometry & Vision Sciences, Cardiff University, Cardiff, United Kingdom
Date: Apr 2021
Reference: Morgan IG, Wu P-C, Ostrin LA, et al. IMI Risk factors for myopia. Invest Ophthalmol Vis Sci. 2021;62(5):3 [Link to open access article]
Analysis of the risk factors for myopia is important for determining intervention possibilities. However, interpreting research has often been made more complex from confounding elements, and establishing definitive causal links has proved difficult.
Proposed risk factors for myopia include non-modifiable influences such as parental myopia, gender and ethnicity; modifiable risk factors are behaviour-driven such as sleep patterns, near work and time spent outdoors. The rate of increase in prevalence seen in East and South East Asia has suggested that genetics alone cannot be the primary cause and as such, there is an increasing need to discover the influence of environmental exposures on the onset and progression of myopia and high myopia, and what prevention methods exist.
This paper reviewed the strength of evidence for risk factors for myopia and assessed if associations had direct causal relationships or were related to other variables.
Strong causal links between myopia and increased education and limited time outdoors have been identified. The underlying mechanism for each has yet to be discovered, although elements of extended near work and reading - such as close reading distance and long durations of reading - have been shown by meta-analysis studies to be contributing factors. Increased near work is also synonymous with reduced time outdoors and where increased time outside has been shown to have a protective effect, this becomes a see-saw risk factor. Meta-analyses have found a strong association between reduced myopia and increase time outdoors.
Children are increasingly using computers and smartphones which may be replacing book reading as a dominant near work activity. Although there has been limited evidence to suggest a causal link of screen and near work with myopia, countries such as China and Taiwan have introduced formal measures to limit screen time for children in an attempt to control this as a risk factor.
The focus of future research should be on myopia development during school years, due to the association of axial myopia and education. To achieve this, demonstrations of causal relationships should be shown using Mendelian randomisation or randomised clinical trials, cycloplegic refraction should be adopted as a gold standard approach in studies, and measurements of the risk factors needs to be as accurate as possible, ideally using objective measuring devices. The increasing use of objective wearable devices will measure near working distance and time spent accurately in future studies and guide intervention advice.
The validity of causal risk factors will shape the evidence-based intervention advice that can be offered to patients and parents.
What does this mean for my practice?
- Increasing time outdoors and reducing time spent on near work tasks have been cited as intervention methods to help balance potentially myopigenic lifestyles, particularly if parental myopia is also present.
- We can assess the collective risk factors for each patient and discuss the changes they could make to reduce each modifiable risk factor.
What do we still need to learn?
Currently, there are uncertainties over:
- Whether continuous near work or the working distance is more important than the total time spent on near work, and what age-specific differences this may provide due to reduced plasticity of the visual system with age
- If electronic devices have simply served as a replacement to reading and writing or if they are a risk factor in their own right
- The role of retinal dopamine release as a mechanism for the protective effect of outdoor time. Other factors such as lighting levels, vitamin D, seasonal variations and differing spatial frequencies of the outdoor environment also warrant further investigation.
Title: IMI Risk Factors for Myopia
Authors: Ian G. Morgan, Pei-Chang Wu, Lisa a. Ostrin, J. Willem L. Tideman, Jason C. Yam, Weizhong Lan, Rigmor C. Baraas, Xiangui He, Padmaja Sankaridurg, Seang-Mei Saw, Amanda N. French, Kathryn A. Rose, Jeremy A. Guggenheim
Risk factor analysis provides an important basis for developing interventions for any condition. In the case of myopia, evidence for a large number of risk factors has been presented, but they have not been systematically tested for confounding. To be useful for designing preventive interventions, risk factor analysis ideally needs to be carried through to demonstration of a causal connection, with a defined mechanism. Statistical analysis is often complicated by covariation of variables, and demonstration of a causal relationship between a factor and myopia using Mendelian randomization or in a randomized clinical trial should be aimed for. When strict analysis of this kind is applied, associations between various measures of educational pressure and myopia are consistently observed. However, associations between more nearwork and more myopia are generally weak and inconsistent, but have been supported by meta-analysis. Associations between time outdoors and less myopia are stronger and more consistently observed, including by meta-analysis. Measurement of nearwork and time outdoors has traditionally been performed with questionnaires, but is increasingly being pursued with wearable objective devices. A causal link between increased years of education and more myopia has been confirmed by Mendelian randomization, whereas the protective effect of increased time outdoors from the development of myopia has been confirmed in randomized clinical trials. Other proposed risk factors need to be tested to see if they modulate these variables. The evidence linking increased screen time to myopia is weak and inconsistent, although limitations on screen time are increasingly under consideration as interventions to control the epidemic of myopia.
Ailsa Lane is a contact lens optician based in Kent, England. She is currently completing her Advanced Diploma In Contact Lens Practice with Honours, which has ignited her interest and skills in understanding scientific research and finding its translations to clinical practice.