Variability in measurement of central retinal artery velocity using color Doppler imaging

The purpose of our study was to test the reproducibility of the central retinal artery velocity measurements as made by color Doppler imaging and pulsed Doppler spectral tracings and to define the optimal location for placement of the sample volume. We used the Siemens Quantum (Q 2000) with a 7.5 MHz linear array transducer to identify the central retinal artery and record its velocity. Eleven eyes from 11 normal subjects were evaluated for the peak systolic central retinal artery velocity in two positions, the first posteriorly in the optic nerve at an average of 3.56 mm from the surface of the optic disc and the second at an average of 1.76 mm from the surface of the optic disc. We then used a color-flow threshold to identify and record the point of maximal velocity. The range of systolic velocities in the 11 eyes was from 5.85 to 22.51 cm/sec. The peak systolic velocity posteriorly in the optic nerve averaged 8.16 cm/sec, whereas near the surface of the optic disc the velocity averaged 13.89 cm/sec (70.2% higher). Using the color flow threshold method, the maximal velocity was located at an average of 1.98 mm from the surface of the optic disc. Our data show that large differences exist in measured central retinal artery velocity that depend on the location of the measurement, and that color-flow thresholding is valuable in locating the optimal location for pulsed Doppler spectral recording.