1 Division of Ophthalmology, Alpert Medical School, Brown University, Providence, RI.
2 Department of Quantitative Health Sciences, University of Massachusetts Medical School, Worcester, Mass.
3 Departments of Ophthalmology and Public Health Sciences, Penn State College of Medicine, Hershey, Pa.
4 Division of Ophthalmology, Alpert Medical School, Brown University, Providence, RI; Section of Ophthalmology, Providence Veterans Affairs Medical Center, Providence, RI. Electronic address: paul_greenberg@brown.edu.