Relative flow volume, a novel blood flow index in the human retina derived from laser speckle Flowgraphy

PURPOSE. We investigated the accuracy and reproducibility of relative flow volume (RFV), a novel index of blood flow in the human retina derived from laser speckle flowgraphy (LSFG). METHODS. Pre- and postbranch retinal RFV measurements were compared in 34 retinal venous bifurcations in 34 healthy volunteers (mean age, 49.0 6 14.8 years) to determine the accuracy of RFV. Next, the coefficient of variation (COV) of RFV was determined for 30 temporal retinal arteries in a second group of 18 healthy volunteers (mean age, 30.3 6 7.7 years). Finally, laser Doppler velocimetry (LDV) data were obtained from the same study population and compared to RFV data from the retinal vessels. RESULTS. A comparison of RFV measurements in a trunk vessel of the retina and the sum of its two daughter vessels revealed a strong correlation (r = 0.98, P < 0.001). Reproducibility analysis showed that the COV for RFV was 5.9% 6 3.6%. Linear regression analysis revealed that RFV was correlated significantly with LDV measurements of mean retinal blood velocity (ν_mean) and retinal blood flow (F_LDV, ν_mean, r = 0.61, P < 0.001; F_LDV, r = 0.51, P = 0.004, respectively), but not significantly correlated with ocular perfusion pressure (r = 0.04, P= 0.76). CONCLUSIONS. These results suggest that RFV values obtained with LSFG can be considered an accurate and reliable index of relative blood flow in the human retina. Thus, RFV, a novel LSFG-derived variable, has potential for assessing retinal blood flow alterations in ocular disease.