Quantification of total retinal blood flow via dual‐beam bidirectional Doppler optical coherence tomography for the assessment of neurovascular coupling

Abstract

PurposeIn recent years, the reliability of dual‐beam Doppler optical coherence tomography (DOCT), a method for measuring absolute retinal blood flow velocities, has been proven. A simultaneous determination of retinal vessel diameters allows calculating total retinal blood flow. The combined measurement of both parameters also offers the ability to quantify perfusion of the retina under different stimuli conditions and by this getting insight into the mechanisms of neurovascular coupling.MethodsTotal retinal blood flow was measured in four healthy subjects at baseline condition (constant illumination of the fundus) and 20 min after this during stimulation with diffuse luminance flicker light at 12 Hz.ResultsThe average increase in total retinal blood flow during flicker stimulation was about 40%, which is assumed to be caused by an increased firing rate of the retinal ganglion cells. However, when comparing the blood flow in single retinal vessels under both baseline condition and flicker stimulus, the individual increase varied vastly.ConclusionsWe think the observed phenomena are caused by resistance changes of the vasodilated vascular network which cause non‐linear flow changes in single vessels. Our results show that the measurement of a single retinal vessel alone is not adequate for assessing neurovascular coupling in the retina. To conclude, for gaining insight into the mechanisms and functioning of neurovascular coupling, total retinal blood flow must be assessed.