Aveneu Park, Starling, Australia

The et al. 2013), a similar finding

The concept that spending more time
outdoors would prevent the progression of myopia has a long history, the first
remarkable evidence came from  a
longitudinal study, which suggested that children who spent more time on outdoors
activity were less likely to progress myopia, initially the effect was noted
only in male gender (Pärssinen
O et al. 1993). Somewhat later, a cross-sectional study showed that time
spent on sports was associated with less myopia but the effect was not
significant (Mutti et al.
2002). Recently, the protective
effect of time outdoors have been reported from several studies including a cross
sectional data from the Sydney Myopia Study (SMS) measured both outdoors
activities and near work simultaneously and shown that near work had little
impact on refraction, and that outdoor activity is a factor negatively
associated with myopia (
Rose KA et al. 2008: French AN et al. 2013:
Chia A et al. 2016)) , followed with a longitudinal data from Orinda
study and SMS (Jones LA et al. 2007: Morgan IG et al. 2013). The
Singapore Cohort Study of Risk Factors for Myopia (SCORM) and the Avon Longitudinal
Study of Parents and Children reported also similar finding (Dirani M et al. 2009: Guggenheim JA
et al. 2012), supported with several other studies (Khader YS et al.2006:
Sherwin JC et al. 2012: Wu LJ et al. 2015: Wu PCet al. 2015). In
contrast, a few studies have reported minor effect, probably due to
the low amounts of time spent outdoors ( Lin Z et al. 2014:  Zhou Z et al. 2015).

The Oriana study
reported that increasing  amounts of
sports outdoors prevent the additional risk of myopia correlated with parental
myopia (Jones LA et al. 2007) and  intensive near-work
(Rose KA et al. 2008), while the
Sydney Myopia Study has found that sports activities indoor have no effect on
myopia, which involves that increasing  time spent outdoors, are a fundamental
protective factor, rather than sport itself (French AN et al. 2013: Morgan IG et al. 2013), a similar finding in the
SCORM study (Dirani M et al.
2009), and  the Avon Longitudinal
Study also confirmed this concept (Guggenheim JA et al. 2012). Few studies have suggested that the
physical activities are a protective factor, but none have provided evidence
that this effect can be separated from the effect of time spent outdoors (Jacobsen N et al. 2008: Guggenheim
JA et al. 2012).

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The biological mechanism underlying
this protective effect remains equivocal, It is assumed that higher light
intensity outdoors could increase the depth of focus and reduce image blur due
to pupillary constriction (Rose
K et al. 2008: Fujiwara M et al. 2012). However, the hypothesis that the
accommodation reduced outdoors, it seems not reasonable because people outdoors
do not focus continuously on the horizon 
(Flitcroft DI, 2012).
In addition, the hypothesis that  the
spectral composition of the light outdoors, play a critical role ,rather than
the intensity of light (Mehdizadeh
M et al. 2009), and that the exposure to ultraviolet rays outdoors might
be the key factor (Prepas SB,
2008: Mutti Do et al. 2011) , Further the increase  of dopamine level in the retina due to intensive
light stimulation, which can slow the eye growth by dopamine agonists (Witkovsky P, 2004: Rose KA et al. 2008: Feldkaemper M, Schaeffel F, 2013).  Although
there is a correlation between vitamin D level in the blood and myopia (Choi JA et al. 2014: Tideman JW et
al. 2016), itemized
studies reported that this relation is not causation, the exposure  to daylight prevent myopia and increase
vitamin D level equivalently (Guggenheim JA et al. 2014).

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