RETINAL DISORDERS Diabetic patients with retinopathy show increased retinal venous oxygen saturation Martin Hammer & Walthard Vilser & Thomas Riemer & Aleksandra Mandecka & Dietrich Schweitzer & Uta Kühn & Jens Dawczynski & Fanny Liemt & Jürgen Strobel Received: 2 December 2008 / Revised: 20 February 2009 / Accepted: 26 March 2009 / Published online: 29 April 2009 # Springer-Verlag 2009 Abstract Background Longstanding diabetes mellitus results in a disturbed microcirculation. A new imaging oximeter was used to investigate the effect of this disturbance on retinal vessel oxygen saturation. Methods The haemoglobin oxygen saturation was mea- sured in the retinal arterioles and venules of 41 diabetic patients (65±12.3 years) with mild non-proliferative through proliferative diabetic retinopathy (DR). Twelve individuals (61.3±6.2 years, mean ± standard deviation) without systemic or ocular disease were investigated as controls. Measurements were taken by an imaging oximeter (oxygen module by Imedos GmbH, Jena). This technique is based on the proportionality of the oxygen saturation and ratio of the optical density of the vessel at two wavelengths (548 nm and 610 nm). Results Whereas there were no significant differences in the arterial oxygen saturation between controls and diabetic retinopathy at any stage, the venous oxygen saturation increased in diabetic patients with the severity of the retinopathy: controls 63±5%, mild non-proliferative DR 69±7%, moderate non-proliferative DR 70±5%, severe non-proliferative DR, 75±5%, and proliferative DR 75±8%. Conclusions The increase of retinal vessel oxygen satura- tion in diabetic retinopathy points to a diabetic microvas- cular alteration. This may be due to occlusions and obliterations in the capillary bead and the formation of arterio-venous shunt vessels. On the other hand, hyperglycaemia-induced endothelial dysfunction, with sub- sequent suppression of the endothelial NO-synthase and disturbance of the vascular auto-regulation, may contribute to retinal tissue hypoxia. Keywords Diabetic retinopathy . Blood flow . Oxygen saturation Introduction Retinal oxygen tone is tightly controlled by autoregulation of the vessel diameters [29]. Any imbalance in the autoregulation may result in a disturbance of the microcir- culation and, finally, in diabetic microangiopathies which can be critical for the maintenance of retinal structure and function by capillary occlusion and poor distribution of blood to the retina [7]. Diabetic retinopathy (DR) seems to be linked closely to disturbances in the vascular system. Thus, a variety of studies have investigated the retinal blood flow, i.e. the product of flow velocity and vessel cross section. The results, however, have been somewhat Graefes Arch Clin Exp Ophthalmol (2009) 247:1025–1030 DOI 10.1007/s00417-009-1078-6 Walthard Vilser and Thomas Riemer have proprietary interests in the Vessel Map software. All primary data are under full control of the authors. M. Hammer (*) : D. Schweitzer : U. Kühn : J. Dawczynski : J. Strobel Department of Ophthalmology, University of Jena, Bachstr. 18, 07740 Jena, Germany e-mail: martin.hammer@med.uni-jena.de W. Vilser : T. Riemer Imedos GmbH, Jena, Germany A. Mandecka Department of Internal Medicine III, University of Jena, Jena, Germany F. Liemt University of Applied Sciences Jena, Jena, Germany