1. Public Health Research Group, University of Alicante, Campus San Vicente del Raspeig, Ap. 99 CP 03080, San Vicente del Raspeig, Alicante, Spain.
2. International Centre for Eye Health, London School of Hygiene & Tropical Medicine, London, England.
3. Regional Educational Direction of Apurimac, Abancay, Peru.
4. ONCE Foundation for Solidarity with Blind People in Latin America, Madrid, Spain.
5. Universidad Peruana Los Andes, Lima, Peru.