Time outdoors and the prevention of myopia

Abstract

Recent epidemiological evidence suggests that children who spend more time outdoors are less likely to be, or to become myopic, irrespective of how much near work they do, or whether their parents are myopic. It is currently uncertain if time outdoors also blocks progression of myopia. It has been suggested that the mechanism of the protective effect of time outdoors involves light-stimulated release of dopamine from the retina, since increased dopamine release appears to inhibit increased axial elongation, which is the structural basis of myopia. This hypothesis has been supported by animal experiments which have replicated the protective effects of bright light against the development of myopia under laboratory conditions, and have shown that the effect is, at least in part, mediated by dopamine, since the D2-dopamine antagonist spiperone reduces the protective effect. There are some inconsistencies in the evidence, most notably the limited inhibition by bright light under laboratory conditions of lens-induced myopia in monkeys, but other proposed mechanisms possibly associated with time outdoors such as relaxed accommodation, more uniform dioptric space, increased pupil constriction, exposure to UV light, changes in the spectral composition of visible light, or increased physical activity have little epidemiological or experimental support. Irrespective of the mechanisms involved, clinical trials are now underway to reduce the development of myopia in children by increasing the amount of time they spend outdoors. These trials would benefit from more precise definition of thresholds for protection in terms of intensity and duration of light exposures. These can be investigated in animal experiments in appropriate models, and can also be determined in epidemiological studies, although more precise measurement of exposures than those currently provided by questionnaires is desirable.

Prevalence and associated factors of myopia among primary and middle school-aged students: a school-based study in Guangzhou

“…Similarly, some previous studies among Chinese children also showed that there was no significant association or weak association between outdoor activity and myopia. 7,[37][38][39] The different results may be related to 40,41 Consistent with previous findings showing that parental myopia was significantly related to myopia, and illustrating an increased risk of myopia in children with increasing numbers of myopic parents, 13,17,24,28 the current study demonstrated that there was a trend for higher myopia prevalence among children with a parental myopia history. Both male and female students with one myopic parent or two myopic parents were at a higher risk of myopia than those without myopic parents.…”

Genetic and environmental effects on myopia development and progression

“…In a recent study, 41 the authors discussed possible mechanisms of this protective effect, and suggested that increased light intensity outdoors results in lightstimulated release of the retinal transmitter dopamine, which is known to be able to reduce axial elongation.…”

Rola aktywności zewnętrznej w rozwoju krótkowzroczności u dzieci w wieku szkolnym

“…However, during visual work indoors we tend to look at close objects and require more accommodative power, and therefore the refractive error progresses [1,27,28,29].…”