Funding for this research was provided by:
Queen Elizabeth Diamond Jubilee Trust coordinated through the Commonwealth Eye Health Consortium - United Kingdom (ITCRZC6812)
Text and Data Mining valid from 2018-11-07
Received: 16 February 2018
Accepted: 17 October 2018
First Online: 7 November 2018
Change Date: 30 April 2019
Change Type: Correction
Change Details: Following publication of the original article , the authors reported an error in Fig. 4 in the PDF version. Figure 4 is the duplicate image of Fig. 3 and the correct figure is missing. The authors would like to apologize for this error. The correct figure is shown below.
Ethics approval and consent to participate
: Ethics approval was obtained from Research Ethics Committee of London School of Hygiene and Tropical Medicine, UK.
: The authors provided an approval for publication in BMC Systematic Review.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.