Proliferative diabetic retinopathy - pathogenesis, classification, indications to laser surgery and its incidence in the materials of Wrocław University Eye Clinic - Niżankowska, Maria Hanna; Łukasik-Czerek, Anna; Oficjalska-Młyńczak, Jolanta (Klinika Oczna / Acta Ophthalmologica Polonica, 1995)