Choroidal Blood Flow Changes During Dark/Light Transitions in Patients With Insulin-dependent Diabetes Mellitus (IDDM)

Inclusion Criteria: For healthy control subjects: * Men and women aged over 18 years, matched in regard to age, sex and smoking status * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant * Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant * Normal ophthalmic findings, Ametropia \< 3 dpt for healthy control subjects For patients with IDDM: * Men and women aged over 18 years * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant * Long standing IDDM \> 10 years * Mild or moderate to severe non-proliferative diabetic retinopathy (defined according to the MAHC) * Ametropia \< 3 dpt Exclusion Criteria: Any of the following will exclude a healthy subject from the study: * Regular use of vasoactive medication with may interfere with the study procedure, 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 Any of the following will exclude a patient with IDDM from the study: * Evidence of any relevant retinal or choroidal disease (Glaucoma, age related macula degeneration, cataract, history of central retinal artery obstruction or central retinal vein thrombosis) * Ophthalmological surgery (history of photo laser coagulation, including argon laser trabeculoplasty (ALT), trabeculectomy, deep sclerectomy) * History of intravitreal injection with anti-proliferative therapy * Need for dialysis * Non-treated systemic hypertension (SPB\>150, DBP\>95) * Evidence of coronary heart disease, cardiomyopathy, stenocardia, congestive heart failure, peripheral occlusive vascular disease, cardiac autonomic neuropathy * Symptoms of a clinically relevant illness in the 3 weeks before the first study day * Blood donation during the previous 3 weeks