PRINCIPLE, VALIDITY, AND RELIABILITY OF SCANNING LASER-DOPPLER FLOWMETRY

Purpose: The objective of this study is to present the reliability and validity of scanning laser Doppler flowmetry (SLDF) performing a high -definition topography of perfused vessels of the retina and the optic nerve head with simultaneous evaluation of blood flow. Methods: The e xamination of blood flow by SLDF is based on the optical Doppler effec t. The data aquisition and evaluation system is a modified laser scann ing device; the wavelength of the laser source is 670 nm, with a power of 100 mu W (Heidelberg Engineering, HRF). The reliability of SLDF wa s estimated by performing five seperate measurements in 10 eyes on 5 d ays. The validity of the method was tested by two experiments. First, in an experimental set-up, the capability of SLDF to measure the veloc ity of a moving plane in absolute units was estimated. Second, compara tive measurements were performed of retinal blood flow in 16 normal ey es and in 33 glaucomatous eyes with SLDF and a commercially available single-point laser Doppler flowmeter (Oculix). Results: We found SLDF to produce a high reliability. The reliability coefficients r(1) of fl ow, volume, and velocity were 0.82, 0.81, and 0.83, respectively. Comp arative measurements of the retinal blood flow by SLDF and a single-po int laser Doppler flowmeter of corresponding retinal points showed a l inear and significant relationship between flow (r = 0.83, p < 0.0001) , volume (r = 0.51, p < 0.0001), and velocity (r = 0.59, p < 0.0001). In the experimental set-up, SLDF was able to quantitatively measure ve locity in absolute units. Conclusions: SLDF enables the visualization of perfused vessels of the juxtapapillary retina and the optic nerve h ead in high resolution by two-dimensional mapping of the optical Doppl er shift and a reproducible evaluation of capillary blood flow.