Real-time blood velocity measurements in human retinal vein using the laser speckle phenomenon

Purpose: To measure the in vivo blood velocity in human retinal veins using a laser speckle system. Methods: The system consists of a fundus camera, a diode laser, an image se nsor, and a personal computer system. The fundus area, including a target r etinal vein, is illuminated with a diode laser through a fundus camera and the laser speckle pattern is imaged onto the area sensor. From the time cha nge of the contrast of the speckle pattern, the normalized blur (NB) value, a quantitative index of blood velocity, was calculated using a logic board . Results: In an in vitro experiment, the NB obtained from blood flow in 50-3 00 mu m internal diameter glass capillary tubes, used as an analogue of a r etinal vein, correlated with the diameter of the tube, the actual blood flo w rate, and the background NE value, which was used as an analogue of choro idal circulation. In the in vivo experiment, the blood velocity in human re tinal veins of approximately 50 mu m in diameter was estimated in 16 normal human eyes using nomograms based on the result of the in vitro experiment. Velocity averaged 11.1 +/- 0.6 mm/s (mean +/- SD, n = 16) in retinal veins 53 +/- 6 mu m in diameter. The coefficient of reproducibility of 5-minute interval measurements was 2.5 +/- 0.9%, and it took 63 +/- 15 seconds for o ne measurement. Conclusions: The present methodology is clinically valid for measuring bloo d velocity in retinal veins. Jpn J Ophthalmol 1999;43:186-195 (C) 1999 Japa nese Ophthalmological Society.