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Veronika Doblhoff-Dier, Gerold Aschinger, Leopold Schmetterer, Walthard Vilser, René M Werkmeister; Acquisition of the total retinal blood flow with a dual-beam FD-OCT system and an integrated dynamic vessel analyser. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4320.
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Abnormalities in the retinal blood flow can be a sign of ocular diseases. Determining absolute flow values with Doppler optical coherence tomography (OCT), validating the results, and gaining insight on flow properties can offer valuable information for the diagnosis of retinal diseases.
We present a novel setup of a dual beam Fourier-domain Doppler OCT system, integrating a commercially available Dynamic Vessel Analyzer (DVA) by Imedos Systems UG (Jena, Germany). As opposed to the simpler single beam systems, dual-beam systems have the advantage that the results do not depend on the usually unknown Doppler angle, thus allowing to measure absolute flow values. The system is equipped with rotatable detection planes, which allows measuring all vessels exciting and entering the eye. Integrating a DVA into the OCT system extends the system’s capability from measuring only the blood flow velocity to measuring the total flow, as velocity and vessel diameter can be determined concurrently. The setup allows measuring very small vessels (down to about 30 µm in diameter). OCT measurements were performed on four healthy subjects using a square scanning pattern around the optic nerve head. To average the velocity over several pulse periods, timelines were recorded during a measurement time of around five seconds at each position. Consequently, the presented system permits calculating the total retinal blood flow by measuring the blood flow velocity and the vessel diameter of both the eye’s arteries and veins.
Vessels with diameters from 30 to 190 µm were measured. The mean velocities were found to be in the range of 2-30 mm/s in the arteries and 2-15 mm/s in the veins. In accordance with Murray’s law, the log-log regression coefficient of blood flow and vessel diameter was found to be around 3 for vessels with diameters above 65 µm, but diverged to lower values for smaller vessels. The total arterial blood flow was calculated to be 35.7 ± 4.1 µl/min, the total venous flow to be 36.0 ± 4.5 µl/min.
The resulting blood flow values were in the range of previously reported data. Moreover, the venous and arterial flows for each subject were in good agreement, which corroborated the validity of the data. Hence, the system offers a high potential for examining retinal blood flow in patients with ocular disease.
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