Optical coherence tomography (OCT) is a three-dimensional imaging modality using the interferometric principle to probe transparent or translucent samples non-invasively, at high-speed and with high resolution. Conventional OCT instruments employ a single imaging channel to obtain real-time cross-sectional images of micrometer scale resolution in vivo. However, the addition of supplementary imaging channels proved successful for a variety of OCT sub-modalities or extensions. Ophthalmology, and in particular retinal imaging, rapidly evolved into OCTs most distinguished medical field of application. Since its introduction in the early 1990s, ophthalmic disease detection and monitoring of treatment response both experienced a revolutionary surge of advancement. Within this doctoral thesis, existing multi-channel approaches for retinal OCT are improved and expanded as well as novel concepts developed. The presented multi-channel OCT prototypes are primarily applied for extensions beyond purely morphologic imaging, i.e. for Doppler OCT (DOCT) and directional OCT. The first instrument, a three-channel swept source OCT system, was developed for retinal blood flow (RBF) measurements using DOCT. Besides the integration of recent light source technology, the instrument features a so-called active-passive approach in terms of signal detection. Only one of the three probing channels is employed for sample illumination (one active, two passive). 3D velocity vector measurements in a flow phantom and RBF measurements in the eyes of healthy human volunteers are demonstrated. The second prototype features another approach for multi-channel sample illumination. By the integration of high-speed fiber optical switches in the sample arm of the instrument, the technique of time encoding is introduced for multi-channel OCT. The three channels are not illuminating the sample simultaneously but sequentially in extremely short succession. The channel switching interval is increased to the A-scan rate of the tunable light source (inter-A-scan switching) and beyond (intra-A-scan switching). Again, primarily DOCT flow measurements are demonstrated this time, using alterations of the switching schemes for the purpose of extending the range of unambiguous absolute velocity measurements. The third project focuses on the introduction of a novel multi-channel OCT contrast extension multi-directional OCT. Directional OCT investigates the angular scattering properties of samples from different illumination orientations using consecutive measurements. Multi-directional OCT, however, enables visualization and contrasting of directionally reflective structures within a single acquisition. Using this new technique, specific retinal layers/areas exhibiting directional scattering are investigated qualitatively as well as quantitatively. Three journal articles (two peer-reviewed, one in peer-review at present) build the foundation of this thesis, while technological and medical background information is provided along.