The current trend of increased adoption of digital technologies by younger generations suggests that the future is likely to be promising for light therapies such as those used at home or that are wearable. However, at present, the most cost-effective and effective way to control myopia’s growing prevalence is to encourage children to spend more time in natural outdoor environments.
Children today are engaging in fewer outdoor activities compared to their predecessors from several decades ago due to the advancement of digital technology and the need for higher education; this shift towards an indoor lifestyle has been correlated with an increase in the prevalence of myopia. Outdoor light exposure has been suggested to provide a protective effect against myopia development since the late 18th century, with multiple factors attributed to this effect, including high-intensity ambient light, spectral content, pupil miosis, relaxed accommodation, and increased high spatial frequency. Furthermore, hypotheses have been suggested that link light exposure, circadian rhythm, melatonin levels, and ocular growth to the protective effect of outdoor light.
Light Exposure and Eye Health
Recent research has mainly focused on the effects of light intensity and wavelength on ocular growth. Studies have shown that short-term exposure to moderate to high-intensity light can slow axial elongation in humans. Additionally, one hour of exposure to blue or violet light has been found to be protective against myopia. Low-level red-light exposure has also been seen to have a positive effect on myopia control in children. Furthermore, daily morning light therapy with a wearable device has been proposed as a non-invasive treatment for ocular growth control. However, further clinical trials and validation are needed before these treatments can be recommended.
Indoors versus Outdoors
The differences in light intensity and spectral content between outdoor and indoor locations are considerable. Outdoors, the light intensity can range from as low as 11 lux to as high as 9000 lux, while indoors, light intensity typically ranges from <1000 lux. Additionally, the spectral content of ambient light varies across different outdoor and indoor locations.
Studies have conclusively demonstrated the value of outdoor time in delaying or preventing the onset of myopia. However, its effectiveness in slowing down the progression of myopia has been unclear. A recent review by Dhakal et al. (2022) reported that in children who are already myopic, outdoor light exposure does not seem to control myopia progression. Even so, spending time outdoors is beneficial for general health, and it has the additional effect of reducing near work. A recent laboratory experiment showed that when children are outside, performing near work in an outdoor environment can lead to an increase in axial length compared to a distant viewing task in an outdoor area. Therefore, it is recommended that children be encouraged to engage in activities/sports that require distant viewing while outside, instead of focusing on digital devices or near-work activities.
Guidelines for Outdoor Time
Despite the extensive research into outdoor light exposure and myopia, many questions remain highly contested. What are the factors that contribute to the protective effects of outdoor time? Is it the intensity or type of light, or something else? What is the most beneficial time of day to be outdoors, morning or evening? How will increased indoor illumination in classrooms impact the development of myopia?
It appears that the most effective and economical approach to managing myopia’s increasing prevalence is advocating for children to spend more time in outdoor environments. However, there are no definitive guidelines for this, so it would be beneficial to recommend specific locations (e.g. open playgrounds/parks), times (e.g. during the day), and duration (e.g. two hours per day) of outdoor activities. As digital technologies continue to advance and young people become more tech-savvy, at-home and wearable light therapies may become viable solutions in the future.