CONFOCAL SCANNING LASER-DOPPLER FLOWMETRY - EXPERIMENTS IN A MODEL FLOW SYSTEM

Purpose: We conducted this study toward validating confocal scanning l aser Doppler flowmetry (SLDF), a new noninvasive technique for measuri ng retinal and optic nerve head hemodynamics. Methods: We designed a m odel flow system using a glass capillary coupled to a microlitre syrin ge driven by an infusion pump. Eleven capillaries with parallel walls (internal diameters ranging 705 to 25 mu m) were used. The capillaries were perfused with skim milk over a range of pump flow rates. At each flow rate, measurements were made with the Heidelberg Retina Flowmete r (HRF) to study the relationship between HRF-measured flow and actual flow. The initial experiments (n = 2) were conducted to establish the approximate velocity operating range of the HRF with single HRF measu rements across a wide range of flow rates, whereas the subsequent expe riments (n = 9) were concentrated within this operating range with fiv e HRF measurements at each flow rate. Results: When pump flow rates we re converted to actual velocity at the measurement point far the initi al experiments, the velocity operating range of the HRF was similar to 0.08 to 1.0 mm/s. For velocities of >1 mm/s, HRF measured velocity wa s not linearly related to actual velocity. Within the operating range, there was a highly significant linear relationship between HRF-measur ed flow and actual flow (0.935 less than or equal to r less than or eq ual to 0.990, p < 0.001). When the curves of HRF-measured velocity ver sus actual velocity for the different experiments were plotted, they l argely superimposed. The variability of the HRF measurements was betwe en 3.57% and 4.05% and was independent of flow rate. Conclusions: SLDF measures reliably and linearly within a given operating range.