IN-VIVO MEASUREMENT OF IRIDIAL CIRCULATION USING LASER SPECKLE PHENOMENON

PURPOSE. To evaluate the use of the laser speckle phenomenon for nonin vasive in vivo consecutive measurement of the iridial circulation. MET HODS. A pigmented rabbit iris was illuminated using a diode laser, and the normalized blur of the resulting laser speckle pattern, NBiris. w as determined as a quantitative index of blood velocity in the iridial tissue. The authors compared data on positional variation, reproducib ility, and correlation to iridial blood velocity derived with this tec hnique with the blood flow rate simultaneously determined by the micro sphere technique. They also evaluated the effects on iridial circulati on of ocular perfusion pressure (OPP) change, rectus muscle excisions, and instillation of topical timolol or betaxolol. RESULTS. The NBiris increased gradually from the pupil margin to the periphery; the coeff icient of variation of NBiris was lowest at the center of this area. T he coefficient of reproducibility of two NEiris measurements at 5-minu te intervals was 8.8%; at 24-hour intervals, it was 14.1%. The NBiris correlated well with the microsphere technique measurements of blued f low rate at several intraocular pressures (IOP) (r = 0.61, P = 0.0002, n = 40) and with the comparison of preinstillation and postinstillati on unoprostone (r = 0.93, P = 0.0068, n = 8). The NBiris decreased wit h OPP reduction, decreased temporarily after excision of the superior or inferior rectus, and showed no significant change after excision of the medial or lateral rectus. Instillation of timolol caused a signif icant decrease in IOP but did not significantly change the NBiris. Top ically applied betaxolol decreased IOP and increased. NBiris at 2.5 ho urs after instillation in an ipsilateral eye. CONCLUSIONS. The laser s peckle method permits noninvasive, semiquantitative, consecutive measu rement of the iridial circulation, with reasonable reproducibility.