1 Department of Ophthalmology and Visual Sciences, Washington University in St. Louis, School of Medicine, St. Louis, MO, USA. Electronic address: ferguson@vision.wustl.edu.
2 Department of Cell Biology, University of Virginia, Charlottesville, VA, USA; Department of Ophthalmology, University of Virginia, Charlottesville, VA, USA. Electronic address: gwl6s@virginia.edu.