Non-invasive volumetric blood flow measurement in the orbit

We read with great interest the article of Orge and co-workers1 who claim a first ever solution to the problem of non-invasive volumetric blood flow measurement in the ophthalmic artery. This is a very important topic both from the clinical and scientific point of view, since blood supply is an important factor, for example, in glaucoma studies. However, to date for the orbital circulation only the blood velocity has been measurable; from this the resistivity indices can be calculated, but the volumetric flow cannot be determined because the small diameter of the orbital vessels does not allow the vessel diameter measurement, which is indispensable for such calculation. In spite of the novelty of the report and the extensive analysis of the authors on the possible sources of high variability of volumetric flow measurements, it appears to us that there are several points which need further consideration; some of these were analysed in the editorial by Hedges,2 but we would like to highlight two …