Up to now, a variety of coherent optical techniques have been proposed and extensively studied for diagnostics of the retinal blood flow. These techniques are mainly based on dynamic laser light-scattering phenomena such as the laser Doppler effect and the laser speckle fluctuation. This paper reviews, first, spectral reflectance properties of the ocular fundus tissue layers and, then, principles of the techniques with the comparison of the Doppler and the speckle methods. Some physical phenomena are also discussed in the origin of the techniques such as heterodyne and homodyne beatings, and time-varying speckles. Developing processes of each technique are briefly outlined. Peculiarities of blood flow measurements at the retina are finally examined from the methodological point of view. © 1999 Society of Photo-Optical Instrumentation Engineers.