Assessment of ocular blood flow using laser based instruments is a rapidly emerging area of ophthalmic diagnosis. In this article, six specific laser based instruments are described and compared in terms of appropriate target vasculature and measured hemodynamic parameters. Described are retinal laser Doppler instruments, laser Doppler instruments for assessment of the optic nerve head microcirculation, and laser speckle instruments. © 1998 Society of Photo-Optical Instrumentation Engineers.