A new method has been developed to evaluate the retinal blood flow using laser speckle phenomena. A He-Ne laser illuminates the ocular fundus by means of a standard fundus camera. The laser light scattered from the fundus generates the speckling phenomenon in the detecting plane which fluctuates due to red blood cells moving in the retinal vessels. This speckle intensity fluctuation is detected by a photomultiplier and analyzed to obtain the power spectrum. The retinal blood-flow rate is estimated from the distribution of the power spectrum.
In the present method, the size of the probe region at the fundus is defined to be large (3mm φ) in comparison with the diameter of the blood vessels. Then, the analysis of output signals gives the overall estimation of various blood flows existing in the probe region, rather than the absolute determination of both the blood-flow velocity and its direction in a single vessel.
The method is used to evaluate the retinal and choroid blood flows of a rabbit. The experimental results show the usefulness of the method for evaluation of the retinal blood flow.