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