| The normal function of the retina requires continuous delivery of nutrients and oxygen to the retina via the retinal circulation. Current approaches to measuring the retinal circulation are limited by resolution and/or the size of vessels that can be studied and thus involve tradeoffs. An AOSLO flowmeter system was designed and built to overcome those limitations and provide high resolution imaging and tracking of individual blood cells in the living human retina. The system is capable of searching for the target vessel in a wide field on the retina without asking the subject to change fixation, ensuring subject comfort and imaging efficiency. The high speed imaging functionality allows for tracking variations in blood flow within a heartbeat cycle, and thus to measure the pulsatility of retinal blood flow. The retinal blood velocity increases rapidly at the beginning of a heartbeat and decreases gradually afterwards. The system was used to measure both the maximum velocity and the spatial distribution of velocity within blood vessels. The blood velocity distribution across the vessel cross-section is flatter than the theoretical shape which applies to the flowing water velocity in a tube. Computerized presentation of visual stimuli has been used to investigate the retinal blood flow response to such neural activity. The retinal blood flow response to visual flicker is related with the size and location of the stimulus. |
