An application of laser speckle phenomenon for noninvasive two-dimensional evaluation of microcirculation in ocular...

A new instrument has been developed which uses the laser speckle phenomenon for noninvasive two-dimensional analysis of the microcirculation in the optic nerve head (ONH). The ONH is illuminated by a diode laser spot and its image speckle is detected by an area sensor. The difference between a pair of output data from successive scannings of the image speckles at the sensor plane is calculated and integrated for each pixel to obtain the average difference (AD) value, which is a quantitative index of blood flow velocity. The results are displayed in color graphics showing the two-dimensional variation of the AD value in the area of interest. In an in vitro model, the AD value correlated well with the speed of rotation of a ground glass in a range between 0 and 5 mm/second. Using this instrument, the effect of intraocular pressure (IOP) on the circulation was studied in the area of the rabbit ONH free of surface vessels. The coefficient of reproducibility was 4.7% when measured twice in this area at 5-minute intervals. A stepwise reduction in the ocular perfusion pressure (OPP) was introduced by elevating the IOP manometrically. The AD value was little affected by a change in OPP when the OPP was above 40 mmHg; while when the OPP was below 40 mmHg, a linear correlation was found between the AD value and the OPP. This finding agreed well with those of previous studies where the effect of the OPP on the ONH blood flow were studied using various invasive methods.(ABSTRACT TRUNCATED AT 250 WORDS)