2-DIMENSIONAL MAPPING OF RETINAL AND PAPI LLARY MICROCIRCULATION BY SCANNING LASER-DOPPLER FLOWMETRY

Purpose To present clinical applications of a new non-invasive method imaging in a high-definition the topography of perfused retinal vessel s. Method By a combination of a laser Doppler flowmeter with a scannin g laser system the perfusion of the retina and the optic nerve head is visualized and quantified. The principles of measuring blood flow by Laser Doppler Flowmetry are based on the optical Doppler effect: laser light scattered by a moving particle is shifted in frequency by an am ount delta f. Our data acquisition and evaluation system is a modified laser scanning tomograph. The technical data are: retinal area of mea surement 2.7 mm x 0.7 mm, 10 degrees-field with 256 points x 64 lines, measurement accuracy 10 mu m, wavelength 670 nm and 790 nm, light pow er 100 mu W, data acquisition time 2048 s. Every line is scanned 128 t imes by a line-sampling rate of 4000 Hz. By performing a discrete Fast Fourier Transformation over 128 intensities of each retinal point the laser Doppler-shift is calculated for each retinal point. With these data a 2-D map with 256 x 64 points of the retinal perfusion is create d. The brightness of the picture-point is coded by the value of the Do ppler shift. We estimated the reliability and the validity of the meth od. Perfusion-pictures of the superficial retinal layer and in the opt ic nerve head were presented. Results The reliability-coefficients r(1 ) of ''Flow'', ''Volume'' and ''Velocity'' were 0.85, 0.83, and 0.85 r espectively. The blood flow measurements by the presented method (''Sc anning Laser Doppler Flowmetry'') in an artificial capillary gave a li near relationship (r-value 0.973, p < 0.00001) between defined blood v elocities and the measured blood flow. By the confocal technique, depe ndent on the focus, capillaries of the retinal superficial vasculature of the optic nerve head became visible with a high resolution. Offlin e the blood flow of areas of 110 mu m x 110 mu m were calculated in te rms of laser Doppler flowmetry. Conclusion ''Scanning Laser Doppler Fl owmetry'' facilitates the visualisation of perfused retinal capillarie s and vessels in high resolution. The representation of the function o f the retinal circulation of SLDF leads to an image similar to the ana tomical situation. The 2-dimensional mapping of local blood flow leads to a physiological picture of the retinal perfusion with visible vess els and capillaries.