Absolute retinal blood flow measurement with a dual-beam Doppler optical coherence tomography

Purpose. To test the capability of a novel dual-beam Doppler optical coherence tomography (OCT) technique for simultaneous in vivo measurement of the Doppler angle and, thus, the absolute retinal blood velocity and the retinal flow rate, without the influence of motion artifacts. Methods. A novel dual-beam Doppler spectral domain OCT (SD-OCT) was developed. The two probing beams are separated with a controllable distance along an arbitrary direction, both of which are controlled by two independent 2D optical scanners. Two sets of optical Doppler tomography (ODT) images are acquired simultaneously. The Doppler angle of each blood vessel segment is calculated from the relative coordinates of the centers of the blood vessel in the two corresponding ODT images. The absolute blood flow velocity and the volumetric blood flow rate can then be calculated. To measure the total retinal blood flow, we used a circular scan pattern centered at the optic disc to obtain two sets of concentric OCT/ODT images simultaneously. Results. We imaged two normal human subjects at ages of 48 and 34 years. The total retinal blood flow rates of the two human subjects were calculated to be 47.01 μL/min (older subject) and 51.37 μL/min (younger subject), respectively. Results showed that the performance of this imaging system is immune to eye movement, since the two sets of ODT images were acquired simultaneously. Conclusions. The dual-beam OCT/ODT system is successful in measuring the absolute retinal blood velocity and the volumetric flow rate. The advantage of the technique is that the two sets of ODT images used for the calculation are acquired simultaneously, which eliminates the influence of eye motion and ensures the accuracy of the calculated hemodynamic parameters.