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Claire McDonnell explores the links between myopia development, progression and time spent outdoors
One of the earliest and most cited studies into the association between time spent outdoors and myopia development is from 2007. This was a retrospective study that examined data previously collected from 514 children in the Orinda Longitudinal Study of Myopia. The authors of this study concluded that more time spent outdoors decreased a child's likelihood of becoming myopic1. Since then, there have been enough studies on this topic to generate several systematic reviews. In 2022, an overview of seven systematic reviews investigating the relationship between time outdoors and myopia development and progression was published2. In this overview, the authors concluded that time spent outdoors did appear to help prevent the onset of myopia, but that it did not appear to slow its progression once established. The authors do note, however, that all seven reviews had serious flaws and that five of the reviews had a high risk of bias. Studies do not seem to show that time outdoors can help to slow the progression of myopia. A Chinese study carried out between 2012 and 2016 examined changes in myopia progression in six to seven year old children who were put on a programme of 30 minutes of outdoor jogging every school day for at least one year3. After one year, the children who had been jogging showed significantly less myopia progression and axial length elongation than the control group. Unfortunately, once the programme ended the children in the jogging group showed a rebound of myopia within the following three years. This was a relatively small study with only 157 children in the treatment group, but it would suggest that any slowing of myopia progression from time spent outdoors may not be ultimately sustainable. A 2008 study compared children of Chinese ethnicity living in Singapore with those living in Sydney4. The prevalence of myopia in the children in Sydney was far lower than that of the children living in Singapore. The authors noted that the lower prevalence in Sydney was strongly associated with increased outdoor time. The mean number of hours that the Sydney children spent on outdoor activities per week was 13.75 hours. Based on the Sydney-Singapore study, the Ministry of Education in Taiwan initiated the Tian-Tian 120 programme in 2010, whereby children were encouraged to spend 120 minutes per day outdoors both at school and at home. This was not made compulsory, but was very strongly promoted, with the idea being that if a child achieved 120 minutes per day of outdoors time that would equate to 14 hours per week. A retrospective review of the data from the children of Taiwan showed that, from 2011 to 2015, the prevalence of children with reduced visual acuity (taken as a proxy measurement of myopia prevalence) started to decrease, whereas in the preceding 10 years it had been continuously increasing5. The research would suggest that two hours a day spent outdoors can help prevent susceptible children (e.g. those with parents with myopia) from developing myopia4,5. While those who are already myopic may not gain the same ocular benefits from outdoors time, it is still beneficial for those children (and indeed adults) to spend time outdoors as research has shown numerous other physical and mental health benefits to time spent outdoors6.Does time spent outdoors help to prevent the development of myopia in the first instance?
Once myopia has developed, does time outdoors help to slow the progression of myopia?
How much time outdoors is optimum?
Conclusion
References
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