Optical coherence tomography (OCT) is an interferometric method for the analysis of refractive media. The expansion of this technique to Doppler OCT allows the measurement of velocities via the Doppler effect. This work describes the development and application of a novel dual beam Doppler Fourier Domain optical coherence tomography system for the measurement of the total retinal blood flow. Blood flow measurements are of interest for medical reasons: a number of ocular diseases can be correlated with changes of the retinal perfusion. The presented system differs from previous systems in that it has two orthogonal detection planes, allowing to record the blood flow in vessels with arbitrary orientations. Moreover, a commercially available Dynamic Vessel Analyzer, yielding precise data on the vessel diameter, was included in the system. Thus, the blood flow can be measured in absolute values. The absolute blood flow values reported in this work lie within the range of values reported in literature. Moreover, the results reported in this thesis show a high degree of conformity between the flow in the arteries and veins, which further corroborates the measurements' validity. The system is capable of measuring the arterial as well as the venous flow in vessels with diameters down to about 30 microm. Thus, it is possible to measure the dependence of the flow on the vessel diameter for a very large range of values. For vessels with diameters of above 60 microm, these measurements yield a log-log correlation coefficient close to three, which would be expected according to Murray's law. For smaller diameters, however, a clear divergence from this relationship can be found. Owing to the high measurement sensitivity, the large possible measurement range, and the reliable results, the system has a high potential to be of use in the investigation of ocular perfusion. Thus, it may further our understanding of ocular diseases which go hand in hand with changes in the retinal blood flow.