1. Department of Propedeutics of Internal Diseases, Medical Faculty, Medical University of Plovdiv, 4000 Plovdiv, Bulgaria
2. Second Department of Internal Diseases, Medical Faculty, Medical University of Plovdiv, 6000 Plovdiv, Bulgaria
3. Department of Special Surgery, Medical Faculty, Medical University of Plovdiv, 6000 Plovdiv, Bulgaria
4. Department of Otorhynolaryngology, Medical Faculty, Medical University of Plovdiv, 6000 Plovdiv, Bulgaria
5. Department of Ophthalmology, Faculty of Medicine, Medical University of Plovdiv, 4000 Plovdiv, Bulgaria
6. University Eye Clinic, University Hospital, 4000 Plovdiv, Bulgaria