affiliation not provided to SSRN, affiliation not provided to SSRN, affiliation not provided to SSRN, affiliation not provided to SSRN, Fondation Botnar, affiliation not provided to SSRN, London School of Hygiene and Tropical Medicine, affiliation not provided to SSRN, Universidad Peruana Cayetano Heredia - Unit for Environmental Development, Health and Environment, affiliation not provided to SSRN, Centre Suisse de Recherches Scientifiques en Côte d’Ivoire, Johns Hopkins University, Rwanda International Institute of Ophthalmology, University of Basel - Swiss Tropical and Public Health Institute, University of Cape Coast, University of Nairobi, affiliation not provided to SSRN, University of Basel - Swiss Tropical and Public Health Institute, University of Basel - Swiss Tropical and Public Health Institute, affiliation not provided to SSRN, University of Basel - Swiss Tropical and Public Health Institute, Institute for Health Policy, Aravind Eye Hospital, University of New South Wales (UNSW) - School of Optometry and Vision Science, affiliation not provided to SSRN, Lao Tropical Public Health Institute, affiliation not provided to SSRN, University of Basel, affiliation not provided to SSRN, affiliation not provided to SSRN, University of Basel - Swiss Tropical and Public Health Institute and University of Basel - Swiss Tropical and Public Health Institute