1. Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas.
2. Departments of Cellular and Structure Biology, University of Texas Health Science Center, San Antonio, Texas.
3. Department of Neurology, University of Texas Health Science Center, San Antonio, Texas.
4. Department of Ophthalmology, University of Texas Health Science Center, San Antonio, Texas.
5. Research Division, South Texas Veterans Health Care System, San Antonio, Texas.