NONCONTACT, 2-DIMENSIONAL MEASUREMENT OF TISSUE CIRCULATION IN CHOROID AND OPTIC-NERVE HEAD USING LASER SPECKLE PHENOMENON

A new apparatus has been developed using the laser speckle phenomenon for non-contact, two-dimensional analysis of tissue circulation in the choroid and optic nerve head (ONH). The fundus was illuminated by a d iode laser spot and its image speckle was detected by an image sensor. The difference between the average of the speckle intensity (I-mean) and the speckle intensity for successive scannings was calculated, and the ratio of I-mean to this difference was defined as normalized blur (NB), which is a quantitative index of blood velocity. The results we re displayed on color graphic monitors showing the two-dimensional var iation of the NE level in the measurement field. In the rabbit, this a pparatus was used to study the relationship between the results of NE measurement and the choroidal blood now determined by the microsphere technique, the relationship between NE obtained from the ONH tissue fr ee of Visible surface vessels and the ocular perfusion pressure (OPP) after a lethal injection of pentobarital, and the effect of intraocula r pressure (IOP) on the NB in the choroid or in the ONH. A stepwise re duction in the OPP was introduced by elevating the IOP manometrically. The relative decrease in the average NB over the field measured, NE(a v), in the choroid with the reduction in OPP showed a significant corr elation with the relative change in the blood flow rate determined usi ng the microsphere technique (r = 0.60, P < 0.001), NBav in the ONH ha d a good correlation with the OPP after a lethal injection of pentobar bital (r = 0.98, P < 0001). NE(av) in the choroid decreased with reduc tion in the OPP. Although NE(av) in the ONH was little affected by OPP change when OPP was above 40 mmHg, at OPP levels below 40 mmHg, NE(av ) in the ONR decreased along with a reduction in the OPP. These result s suggest that by using the present apparatus, the blood velocity in t he choroid or ONH under various conditions can be studied non-invasive ly in the living eye.