1. From the Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, Pennsylvania; the
2. Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, University of Toronto, Toronto, Canada;
3. Howard Hughes Medical Institute and the4Department of Ophthalmology, University of Iowa Hospitals and Clinics, Iowa City, Iowa; the
4. Departments of Ophthalmology and Visual Sciences and6Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan.