2-DIMENSIONAL MAPPING OF RETINAL AND PAPILLARY 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 vessels. Method By a combination of a laser Doppler flowmeter with a scanning 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 amount delta f. Our data acquisition and evaluation system is a modified laser scanning tomograph. The technical data are: retinal area of measurement 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 power 100 mu W, data acquisition time 2048 s. Every line is scanned 128 times 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 created. The brightness of the picture-point is coded by the value of the Doppler shift. We estimated the reliability and the validity of the method. Perfusion-pictures of the superficial retinal layer and in the optic nerve head were presented. Results The reliability-coefficients r(1) of ''Flow'', ''Volume'' and ''Velocity'' were 0.85, 0.83, and 0.85 respectively. The blood flow measurements by the presented method (''Scanning Laser Doppler Flowmetry'') in an artificial capillary gave a linear relationship (r-value 0.973, p < 0.00001) between defined blood velocities and the measured blood flow. By the confocal technique, dependent on the focus, capillaries of the retinal superficial vasculature of the optic nerve head became visible with a high resolution. Offline the blood flow of areas of 110 mu m x 110 mu m were calculated in terms of laser Doppler flowmetry. Conclusion ''Scanning Laser Doppler Flowmetry'' facilitates the visualisation of perfused retinal capillaries and vessels in high resolution. The representation of the function of the retinal circulation of SLDF leads to an image similar to the anatomical situation. The 2-dimensional mapping of local blood flow leads to a physiological picture of the retinal perfusion with visible vessels and capillaries.