The great outdoors and myopia
Last month there was an excellent article in Contact Lens Spectrum by David Berntsen in which the author summarized the recent studies that have demonstrated the protective effect of outdoor time against the onset of myopia. Over the past 10 years a multitude of studies have clearly shown that spending more time outdoors reduces the incidence of new cases of myopia.
Why is this? The answer is that we are not really sure. Two possible explanations include smaller pupils when outside in a bright environment providing an increased depth of focus and less near tasks in an outdoor setting reducing accommodative demand. Other research suggests that the outdoor effect is due to dopamine, in that higher (outdoor) light levels stimulate dopamine release, which is known to slow eye growth (and hence possibly the onset of myopia).
Given that spending time outdoors helps to protect against the onset of myopia, one would possibly expect that increasing outdoor time will also help to slow the progression of myopia. Interestingly, this does not appear to be the case. Although it has been shown in one recent study that there is faster progression of myopia in winter months and slower progression in summer months, to date there is no definitive evidence that increasing outdoor time helps to slow myopia progression in children who are already myopic.