1. Department of Ophthalmology, Spencer Center for Vision Research, Byers Eye Institute, Stanford University, Palo Alto, California 94304, United States
2. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
3. Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States
4. VA Palo Alto HealthCare System, Palo Alto, California 94304, United States