1. 1Centre de Recherche en Santé de Nouna, Burkina Faso;
2. 2Centre de Recherche et Interventions en Santé Publique, Niamey, Niger;
3. 3Francis I Proctor Foundation, University of California, San Francisco, California;
4. 4Department of Ophthalmology, University of California, San Francisco, California;
5. 5Department of Epidemiology and Biostatistics, University of California, San Francisco, California