There is strong evidence from both cross-sectional and longitudinal
data that children who spend more time outdoors are less
likely to be or become myopic. This finding is supported by evidence
from studies in a number of different locations and ethnic
groups, including those with high prevalences of myopia. Although
a small number of studies failed to find a significant association
between time outdoors and myopia, it is likely that the population
characteristics affected the ability of these studies to detect significant
effects. Overall, it is clear that time spent outdoors is
important for normal refractive development in children, and that
deficits in time spent outdoors are reflected in higher prevalences
of myopia. It is currently unclear if time outdoors also slows progression
in existing myopes, but the fact that it prevents incident
myopia opens up the possibility of preventing the development of
myopia, for all but the very low percentage who affected by myopia
of clearly genetic aetiology. The effects of time outdoors are large
enough to make investigation of its use in prevention worthwhile