1. From the London School of Hygiene and Tropical Medicine, London, United Kingdom; the 2Medical Research Council Laboratories, Fajara, The Gambia; and
2. the Medical Research Council Laboratories, Fajara, The Gambia; and
3. From the London School of Hygiene and Tropical Medicine, London, United Kingdom;
4. the National Eye Care Programme, Banjul, The Gambia.