To improve the scan quality of Doppler Optical coherence tomography for blood flow measurement, we investigate how to improve the Doppler signal for all vessels around optic disc. Doppler signal is depending on the Doppler angle, which is defined as angle between OCT beams and normal direction vessel. In this examination, we test the effect of different OCT beam direction on Doppler angles of all veins. We also test maximizing the Doppler angle by combining scans with different OCT beams direction. Three criteria were used to evaluate the overall quality, average Doppler angle, the percentage of vessels with Doppler angle larger than the optimize value, the percentage of vessel with Coefficient variance of Doppler angle less than the optimize value. The result showed that the best protocol is to maximize the Doppler angle from one scan with OCT beam through supranasal portion of pupil and other scan with OCT beam through infranasal portion of pupil.