The following article is presented to you by Pablo Sanz and Miguel García
Disclaimer: For all the general public and specialists, some technical knowledge might be required.
Let en-light our blog, pick our sunglasses and let´s talk about the influence of outdoor time on the onset, development as well as progression of myopia. Besides, as far as 100 years ago (1), some studies started to conjecture about ambient light and its impact on the development of the eye. Starting to be considered as plausible public action to stop myopia prevalence increase, especially in those areas with high risk of development such as East Asia, the topic triggered interest again.
For more in-depth treatment of the issue of outdoors effect we should keep in mind different terms such as time exposure and light intensity, because many factors could contribute to this “shielding effect“.
During the last years a large number of research studies investigated the hypothesis that time spent outdoors protects against the development and progression of myopia.
Since the beginning of this hypothesis, all researches pointed to this direction. Earlier, it was shown in chickens (2) and children that ambient light plays an important role at compensation of myopic defocus and onset of myopia. While at early stages in humans, it was though that physical activity could have a major input, Rose et al (3) showed that light conditions where the key.
To get a better overview on this matter we should introduce the sentence scientific evidence.
But what´s evidence?
In a scientific environment, there is no place for believes, and the evidence relies in the studies published and their repeatability. If we want to grade the evidence they give, we do so according to the type of article, as following pyramid illustrates.
As pointed out by the pyramid, meta-analysis are the highest source of evidence in science. And a recent meta-analysis from Xiong et al, 2017 (4), analyzed over 25 studies and they concluded that time outdoors prevent the development, but has no effect on slowing progression of eyes that are already myopic.
Other studies that looked into the possible use of longer outdoor hours to prevent myopia (5) as public policies, concluded that an extra hour could have greater impact on the onset and development of myopia in children between 5 to 8 years. Similar recommendation were given by He et al 2015,(6) where they claimed that 45 min of outdoor activities for schools in China could prevented myopia onset.
“Although research about understanding the exact mechanism is still underway, based on current results approximately 3 hours of outdoor activity during a day may be considered protective against myopia.”
– Verkicharla, 2016 (7)