[An apparatus using the laser speckle phenomenon for non-invasive two-dimensional analysis of retinal...

A new instrument using the laser speckle phenomenon for non-invasive two-dimensional analysis of the retinal microcirculation was developed. The fundus was illuminated with an argon laser spot and its image speckle was detected with an area sensor. The difference between the average of output data (Imean) and output data for successive scannings of the image speckles at the sensor plane was calculated and integrated to give Dmean, and Imean/Dmean is defined as normalized blur (NB), which is a quantitative index of blood flow velocity. The results were displayed in color graphics showing the two-dimensional variation of the NB level in the area of interest. The NB had a good correlation with the speed of rotation of the ground glass in a range between 5 and 120 mm/sec. Using this instrument, the effect of intraocular pressure (IOP) on the microcirculation of the rabbit retina was studied. The coefficient of reproducibility was 9.2% when measured in the same area twice at 5-minute intervals. A stepwise reduction in the ocular perfusion pressure (OPP) was introduced by elevating the IOP manometrically. The NB in the retina was little affected by OPP change when OPP was above 50 mmHg, but below this value the NB decreased as the OPP decreased.