A study led by Tongji University in Shanghai shows that a combination of time outside and exposure to moderately bright light could help delay or postpone myopia, also known as near-sightedness or short-sightedness, in young children.
Using smart watches to monitor the activity of a group of children for a year, the study showed that a minimum of 15 minutes outside a day at a light intensity of 2,000 lux or more, equivalent to a moderately bright but overcast day, were needed to have a positive impact on the progression of nearsightedness.
Myopia is a very common eye condition where people affected have problems with distance vision and need corrective glasses or contact lenses. It is particularly common in Asian populations, where up to 90% of young people with 12–13 years of education have myopia versus around 42% of the U.S. population.
“Previous studies have demonstrated that spending more time outdoors is an effective intervention for myopia. The findings from randomized clinical trials revealed that children who engaged in increased outdoor activities exhibited a significantly lower incidence of myopia and experienced less myopic shift,” write co-lead author Xiangui He, Shanghai Eye Hospital, School of Medicine, Tongji University, and colleagues in JAMA Network Open.
“Animal studies involving chicks and rhesus monkeys have established that the intensity, duration, and frequency of light exposure impacted myopic shift … Recently, a myopia intervention study reported a dose-response association between outdoor light exposure and myopia incidence. The previous findings emphasized the impact of daily time outdoors and sunlight intensity … indicating a potential collaborative association between time outdoors and sunlight intensity in preventing the onset of myopia.”
The current study included 2,976 students aged 7 years on average, who lived in the Shanghai area on enrollment. The children were not nearsighted at enrollment, wore a smartwatch during the day for at least 6 hours during the study, and took part in the study for at least 90 days in a 1-year period.
Using smartwatch data to monitor the children’s activity, the researchers found that the average time spent outside was 90 minutes at an average light intensity of 2,345 lux. Looking at different patterns of time spent outside and light intensity, the investigators found that children who spent at least 15 minutes outside a day at a minimum light intensity of 2,000 lux experienced less myopic shift than those who spent less time outside and were exposed to less intense light.
“Although animal studies have suggested that shorter duration and higher frequency of light exposure might effectively slow down myopic shift, the current study suggests that outdoor exposure patterns with short durations may have minimal effects on myopic shift in humans,” write He and team.
“One of the possible explanations for this discrepancy is that the near-work time among humans is much longer than that for other species. Another explanation is related to the oxygen saturation in choroid vessels. The blood density would decrease after intense near work and longer outdoor exposure with stronger light levels could facilitate the recovery of blood intensity in choroid vessels efficiently.”
