A variety of studies demonstrate that ocular blood flow is altered in diabetes and retinal perfusion abnormalities have been proposed to contribute to the pathogenesis of diabetic retinopathy.

Various animal and human studies have demonstrated that retinal and optic nerve blood flow increase in response to diffuse luminance flicker. Based on studies with ERG, this effect has been attributed to augmented activity in the retinal ganglion cells and associated axons indicating a coupling mechanism between neuronal activity and retinal blood flow. Whereas a variety of studies describe the effects of flickering light on retinal and optic nerve head blood flow, the knowledge about this coupling in the diabetic retina is sparse.

In view of the fact that neural activity and blood flow are strongly coupled in the human retina, one could hypothesize that neurodegenerative changes in the retina could contribute to the vascular dysregulation and in turn lead to changes of ocular perfusion. The investigators set out to investigate whether the coupling of neural activity and blood flow is impaired in patients with early stage diabetic retinopathy compared to those in healthy volunteers.

Inclusion Criteria:

• Men and women aged between 20 and 50 years
• Normal findings in the medical history and physical examination 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 retinopathy. Patients with no signs of diabetic retinopathy (level 1) or patients with one or more microaneurysms (level 2) will be included. Duration of Diabetes is between 5 and 20 years
• Men and women will be included in equal parts. A pregnancy test will be performed at screening
• Ametropia of less than 3 diopters and anisometropia of less than 1 diopter

Exclusion Criteria:

• Non insulin dependent diabetes
• Maturity onset diabetes of the young (MODY diabetes)
• Any sign of non diabetes induced vascular pathologies, systemic hypertension (defined as systolic blood pressure > 150 mm Hg and diastolic blood pressure > 90 mm Hg.)
• Presence of intraocular pathology other than diabetic retinopathy
• History or family history of epilepsy
• Pregnancy

50 Patients with Diabetes Type 1 50 Healthy Control Subjects