Correlation of Flicker Induced and Flow Mediated Vasodilatation in Patients With Endothelial Dysfunction and Healthy Volunteers.

Inclusion Criteria: Patients with diabetic retinopathy: * Men and women aged \> 18 years. * Normal findings in the medical history unless the investigator considers an abnormality to be clinically irrelevant. * Inclusion criteria of patients are insulin dependent diabetes mellitus (IDDM) with non or mild non-proliferative diabetic retinopathy. Patients with no signs of diabetic retinopathy (level 1) or patients with one or more microaneurysms (level 2) will be included. Level of diabetic retinopathy will be assessed according to the criteria defined in the AREDS-study.(1991) * serum cholesterol \< 250 mg/dl (treated or untreated) Patients with mild hypertension and/or hypercholesterinemia: * Men and women aged \> 18 years. * mild essential hypertension defined as a blood pressure meeting the criterion of hypertension grade 1 of the World Health Organisation blood pressure classification * systolic blood pressure between 140 and 159 mmHg and diastolic blood pressure between 90 and 99 mmHg and/or * serum cholesterol \> 250 mg/dl * blood pressure will be measured at two different occasion in a sitting positions Healthy subjects: * Men and women aged \> 18 years. * Normal findings in the medical history unless the investigator considers an abnormality to be clinically irrelevant * normal ocular findings * serum cholesterol \< 200 mg/dl * systolic blood pressure between 110mmHg and 140mmHg * diastolic blood pressure \< 90 mmHg Exclusion Criteria: * Abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study * Symptoms of a clinically relevant illness in the 3 weeks before the first study day * Blood donation during the previous 3 weeks * other ocular pathologies than diabetic retinopathy level 1 or 2 * History or family history of epilepsy * Ametropy greater or equal than 3 dpt * systolic blood pressure \< 100mmHg * diastolic blood pressure \< 75mmHg * pregnant or lactating women