[Measurements of blood flow velocity in human retinal veins using laser speckle flowgraphy system]

We measured the blood flow velocity in human retinal veins using a laser speckle flowgraphy system. This system consists of a fundus camera, a diode laser, an image sensor and a personal computer system. The fundus is illuminated with a diode laser through a fundus camera and the laser speckle pattern is imaged onto the area sensor. From the time change of contrast of speckle pattern, normalized blur (NB) value, a quantitative index of tissue blood velocity, was calculated by means of a logistic board, and two-dimensional distribution of NB in the measurement field was displayed in a color display. In the in vitro experiment, the NB obtained from the blood flow in a glass capillary tube was correlated with the diameter of the tube, background NB value and the blood flow rate actually measured. In the in vivo experiment, the blood velocity in human retinal veins of approximately 50 microns in diameter was estimated in 16 normal eyes using nomograms based on the results of the in vitro experiment. Velocity averaged 11.1 +/- 0.6 mm/ sec (mean +/- standard deviation, n = 16) in retinal veins of 53 +/- 6 microns in diameter and the reproducibility index of the in vivo measurements was 2.5 +/- 0.9%.