1. Department of Ophthalmology; Massachusetts Eye and Ear Infirmary and Harvard Medical School; Boston Massachusetts 02114
2. Department of Physiology; University of Oklahoma Health Sciences Center; Oklahoma City Oklahoma 73104
3. Department of Ophthalmology; Medical University of South Carolina; Charleston South Carolina 29425
4. Department of Biochemistry, NCMLS; Radboud University Nijmegen Medical Centre; 6525 HP Nijmegen The Netherlands