Boehm, B.O., Lang, G., Feldmann, B., Kurkhaus, A., Ro-singer, S., Volpert, O., et al. (2003) Proliferative Diabetic Retinopathy Is Associated with a Low Level of the Natural Ocular Anti-Angiogenic Agent Pigment Epithelium-Derived Factor (PEDF) in Aqueous Humor. A Pilot Study. Hor-mone and Metabolic Research, 35, 382-386.