We present results of an investigation into the visualization and measurement of retinal blood flow distribution by means of single-exposure laser-speckle fundus photography. The technique relies on the speckle effect produced when laser light is scattered at a diffusing structure and on the fact that the speckle will be averaged out to some extent when the structure concerned is moving and/or decorrelating. We discuss two alternative techniques used to process the specklegrams obtained from the retina. The first technique uses an analog optical spatial filtering procedure to enhance the resulting variations in speckle contrast. Although first results have shown the basic usefulness of this technique, it suffers from fundamental disadvantages. In the second technique we digitize the specklegram and use digital image processing techniques to (1) convert contrast variations in the fundus photography into color variations and (2) obtain the blood flow of the vessels with a reasonably low statistical error.
A. F. Fercher,
"Visualization And Measurement Of Retinal Blood Flow By Means Of Laser Speckle Photography," Optical Engineering 25(6), 256731 (1 June 1986). https://doi.org/10.1117/12.7973897