Coupling of Neural Activity and Retinal Blood Flow in Diabetes

Inclusion Criteria: * Men and women aged over 18 years, nonsmokers * Normal findings in the medical history (except diabetes) and physical examination unless the investigator considers an abnormality to be clinically irrelevant * normal laboratory findings (except diabetes associated parameters) unless the investigator considers the abnormality to be clinically irrelevant * normal ophthalmic findings (except mild diabetic retinopathy), Ametropia less than 6 diopters * inclusion criterion of patients is type I diabetes with non or mild non-proliferative retinopathy Exclusion criteria Any of the following will exclude a healthy subject from the study: * Regular use of vasoactive drugs * 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 * History or presence of any ocular pathology * History or family history of epilepsy * Systemic hypertension defined as systolic blood pressure \>150mmHg, diastolic blood pressure \>90mmHg * Pregnancy Any of the following will exclude a subject with diabetes from the study: * Presence of non-insulin dependent diabetes, maturity onset diabetes of the young (MODY diabetes) * History or presence of any other diabetes induced vascular pathologies or any other ocular condition other then diabetic retinopathy * Best corrected visual acuity \<0.8 * Previous laser photocoagulation treatment * Systemic hypertension defined as systolic blood pressure \>150mmHg, diastolic blood pressure \>90mmHg * History or family history of epilepsy * 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 * Pregnancy