The theory underlying the development of laser Doppler instrumentation for the measurement of retinal blood flow is framed in terms of (a) the enunciation of the Doppler principle; (b) the invention of the laser; and (c) the invention of the technique known as optical mixing spectroscopy. The features of the instrumentation, beginning with the first prototype in 1972 and culminating with the introduction of the Canon Laser Blood Flowmeter in 1998 are presented in detail. Results from seven separate studies reporting on the reproducibility of retinal blood flow measurements using the Canon instrument, as well as a review of 12 separate presentations made at the 2004 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) using the Canon instrument in studies involving retinal circulatory physiology and associated clinical research are also presented.