Review of existing literature on myopia (2012)

Myopia
Prof Ian G Morgan PhD , Prof Kyoko Ohno-Matsui MD , Prof Seang-Mei Saw PhD 

The Lancet, Volume 379, Issue 9827, Pages 1739 - 1748, 5 May 2012

The authors of this article searched the Medline and Online Mendelian Inheritance in Man (OMIM) databases for research on myopia.  They note that there's is not enough epidemiological support for the idea that intense near work is related to myopia development; that environmental conditions (such as increased study indoors) might play a stronger role than genetics in many cases of school myopia ;  that peripheral defocus might be be a consequence rather than a cause of myopia,  and that orthokeratology might not work long term.   Here are some passages that seemed particularly interesting or informative to me:

From the text:
On myopia development:
"Most children are born hyperopic, with a normal
distribution of refractive errors.7 During the fi rst year or
two after birth, the distribution narrows,8 with a mean in
the hyperopic range of +1–2 dioptres (D). This change
indicates that there is an active process shaping the
distribution of refraction, known as emmetropisation.
After that period, the cornea stabilises,9 but refraction
can become more myopic as axial length can continue to
increase for another two decades. By contrast, lens power
decreases substantially up to the age of about 12 years,10
with slower decreases for most of adult life.9 Myopia
generally develops during the early to middle childhood
years, but significant myopia can also develop in the late
teenage years or early adulthood.11 Axial length is the
most variable factor during development, with the
strongest correlation with refractive status, with longer
eyes more likely to be myopic than shorter eyes.12 Control
of the axial elongation of the eye during development is
thus crucial for achieving normal vision, and therefore is
a primary site for prevention."


"Increased accommodation due to intensive near
work, such as reading and writing, could mediate the
association of myopia with schooling, but epidemiological
support for this idea is not strong. Although Saw and
colleagues31 showed that Singaporean children who read
more than two books per week were more likely to have
higher myopia than those who read less, the Sydney
Myopia Study showed that near work per se was a weak
factor, but that children who read continuously or at a close
distance were more likely to be myopic.32 Results from the
US Orinda Longitudinal Study of Myopia33 showed weak
albeit signifi cant eff ects of increased hours of near work,
and the authors of this study argued that the evidence did
not support a signifi cant effect of near work.27"



"A consistent finding is that children with myopic
parents have a higher prevalence of myopia,33,52,53 but the
relative risk varies substantially, and is lower in locations in which the prevalence of myopia is high, such as in east
Asia. No consistent relation with number of myopic
parents exists. At this stage, the impact of parental
myopia might be evidence of genetic effects. Differences
in family behaviour associated with myopic parents seem
less likely, but cannot be excluded at this time."



"The development of peripheral hyperopia now seems
to be a consequence, rather than a cause of myopia,
because it seems to appear in parallel with the
development of myopia, rather than before.90 Peripheral
hyperopia nevertheless could contribute to myopic
progression, and this perspective does not preclude the
use of localised manipulation of defocus to control
myopia, whatever the developmental mechanisms."



"Preliminary reports have also suggested overnight
orthokeratology contact lenses, which correct refractive
errors by physically flattening the cornea, might also
protect against myopic progression,96 and it has been
proposed that this might due to peripheral myopic
defocus imposed by the distorted cornea. However, the
eff ects might not be permanent and there might be
a rebound of progression rates of the cessation of
orthokeratology treatment."

Link to abstract:
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60272-4/abstract