1. From the Institute of Ophthalmology, University College London, United Kingdom; the
2. Medical Statistics Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom; the
3. Department of Biostatistics, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland;
4. Keyl Associates, East Sandwich, Massachusetts; and the
5. Dana Center for Preventive Ophthalmology, Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland.