Resonant Doppler Fourier Domain Optical Coherence Tomography is a functional imaging modality for quantifying fast tissue flow. The method profits from the effect of interference fringe blurring in spectrometer-based FDOCT in the presence of sample motion. If the reference path length is changed in resonance with the Doppler frequency of the sample flow the signals of resting structures will be suppressed whereas the signals of blood flow are enhanced. This allows for an easy extraction of vascularization structure. 3D images of blood vessels at the human optic nerve head are obtained with high axial resolution of 8 mu m in air and an imaging speed of 17.400 depth profiles per second. An electrooptic modulator allows controlled reference phase shifting during camera integration. A differential approach is presented for the quantification of fast flows that are un-accessible via standard phase sensitive Doppler analysis. Flow velocity analysis extracts only the axial component which is dependent on the orientation of the vessel with respect to the optical axis. 3D information of the segmented vessel structure is readily used to obtain the flow velocity vectors along the individual vessels and to calculate the true angle-corrected flow speed.