1. Wilmer Eye Institute, Johns Hopkins University School of Medicine , Baltimore, Maryland , USA
2. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Johns Hopkins University , Baltimore, Maryland , USA
3. Division of Geriatrics, University of Mississippi Medical Center , Jackson, Mississippi , USA
4. Division of Neurology, University of Mississippi Medical Center , Jackson, Mississippi , USA
5. Department of Epidemiology, School of Public Health, University of Colorado , Denver, Colorado , USA
6. Department of Ophthalmology, School of Medicine, University of Colorado , Denver, Colorado , USA