1. Department of Ophthalmology, University of Iowa, College of Medicine, Veterans Administration Hospital, Iowa City, Iowa, United States
2. Department of Neurology, University of Iowa, College of Medicine, Veterans Administration Hospital, Iowa City, Iowa, United States
3. Department of Biostatistics, College of Public Health, University of Iowa, Iowa City, Iowa, United States
4. School of Health Professions, Peninsula Allied Health Centre, Plymouth University, Plymouth, Devon, United Kingdom