NONCONTACT, 2-DIMENSIONAL MEASUREMENT OF RETINAL MICROCIRCULATION USING LASER SPECKLE PHENOMENON

Purpose. To report a new apparatus for noncontact, two-dimensional mea surement of retinal microcirculation using the laser speckle phenomeno n and to demonstrate that this apparatus can document known or expecte d changes in retinal blood flow. Methods. The rabbit fundus was illumi nated by an argon (blue) laser spot (0.62 X 0.62 mm), and its image sp eckle was detected with an image sensor. The difference between the av erage of the speckle intensity (I-mean) and the speckle intensity for successive scannings was calculated, and the ratio of I-mean to this d ifference was defined as normalized blur (NB), a quantitative index of blood velocity in the retinal microcirculation. The results were disp layed on a color monitor showing the two-dimensional variation of the NB level in the measurement area. Using this apparatus in the rabbit, the NB in the retinal field free of visible surface vessels was determ ined and compared with the retinal blood flow rate measured using the microsphere technique in the same eye simultaneously. In addition, the effect of the ocular perfusion pressure (OPP) on NB was studied. In t he above experiments, a stepwise reduction in OPP was introduced by el evating the intraocular pressure manometrically. Results. The relative decrease in the average NB (NBav) over the field measured, with the r eduction in OPP, showed significant correlation with the relative chan ge in the blood flow rate determined using the microsphere technique ( r = 0.59, P < 0.001). Although NBav in the retina was little affected by OPP change when OPP was greater than 50 mm Hg, NB decreased along w ith OPP at levels less than 50 mm Hg. Conclusions. The NBav showed sig nificant correlation with the retinal blood flow rate determined with microsphere technique. Retinal microcirculation under various conditio ns can be studied two dimensionally and noninvasively in the living ey e with the present apparatus.