von Willebrand factor and early diabetic retinopathy: no evidence for a relationship in patients with Type 1 (insulin-dependent) diabetes mellitus and normal urinary albumin excretion - Stehouwer, C DA; Zellenrath, P; Polak, B CP; Baarsma, G S; Nauta, J JP; Donker, A JM; den Ottolander, G JH (Diabetologia, 1992)