1. University of Nebraska Medical Center; Stanley M. Truhlsen Eye Institute; 3902 Leavenworth Street Omaha Nebraska USA 68105
2. University of Nairobi; Department of Ophthalmology; P.O Box 347, KNH Nairobi Kenya 00202
3. Johns Hopkins University; 3400 N. Charles Street Baltimore Maryland USA 21218
4. Johns Hopkins University School of Medicine; Wilmer Eye Institute; 550 North Broadway, 9th floor Baltimore Maryland USA 21205-2010