1. University of Nebraska Medical Center; Stanley M. Truhlsen Eye Institute; 985540 Nebraska Medical Center Omaha Nebraska USA 68198-5540
2. Johns Hopkins Bloomberg School of Public Health; Department of Epidemiology; 615 N. Wolfe Street Baltimore Maryland USA 21205
3. Johns Hopkins University; 3400 N. Charles Street Baltimore Maryland USA 21218
4. Clemenceau Medical Center; Affiliated with Johns Hopkins International Beirut Lebanon
5. Johns Hopkins University School of Medicine; Wilmer Eye Institute; 550 North Broadway, 9th floor Baltimore Maryland USA 21205-2010
6. Kresge Eye Institute; Department of Ophthalmology; Wayne State University School of Medicine 4717 St. Antoine Boulevard Detroit Michigan USA 48201