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. 2013 Oct 24;98(1):6–12. doi: 10.1136/bjophthalmol-2013-304225

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Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions

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Flow chart showing numbers of studies included and excluded. CCT, controlled clinical trial; PICO, Population, Intervention, Comparator, Outcome; SR, systematic review.