1. Department of Community Medicine, West Virginia University School of Medicine, Robert C. Byrd Health Sciences Center,1 Medical Center Drive, P.O. Box 9190, Morgantown, WV 26505, USA
2. Singapore Eye Research Institute, Singapore National Eye Centre, 11 Third Hospital Avenue #05-00, Singapore 168751
3. Department of Medicine, University of Washington, Seattle, WA 98195, USA
4. Center for Healthy Aging Research, School of Social and Behavioral Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis OR 97331, USA