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Z. Zhong, H. Song, X. Qi, S. A. Burns; High Speed Imaging of Retinal Microvessels Using an AOSLO. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4773.
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© ARVO (1962-2015); The Authors (2016-present)
To increase the high speed imaging ability of the Indiana Adaptive Optics Scanning Laser Ophthalmoscope and use high speed imaging to study blood flow in retinal microvessels.
An 840 nm (center wavelength) SLD was used as the light source. The AO control of our system was maintained using a BMC MEMS deformable mirror and a Shack Hartmann sensor operating in closed loop at 8 Hz. The laser beam was steered by an 8 kHz horizontal scanner and a programmable vertical scanner to form an image frame. The imaging frame rate depends on the horizontal scanning frequency and how many lines a frame contains. We increased the imaging frame rate in two ways. First, since during each horizontal scan the imaging beam is swept across the same retinal location twice, we captured images for both directions of scan, displacing the vertical position between scans, generating a horizontal imaging frequency of 16 KHz; Second, we used the programmability of the vertical scanner to allow us to reduce the number of lines for each frame, producing a higher frame rate. To image blood flow in retinal micro-vessels, high resolution imaging frame rate of up to 180 fps were used. In the extreme case when each frame is a single line, all the line frames were collected from the same location in sequence with a frame rate of 16000 fps.
High resolution, high speed images of retinal micro-vessels were obtained. Individual RBC’s were visualized as light-scattering dots moving in a single file in retinal micro-vessels. The intensities of the RBC’s were changing quickly, presumably because an individual cell rotates axially as it moves through a vessel, influencing its light scattering property. Arteries and veins can be differentiated from each other by the direction in which RBC’s are moving. The moving cells appeared brighter in micro-arteries than in micro-veins, presumably because oxygenated blood scatters more light for our imaging wavelengh. The RBC velocity in micro-vessels (lumen diameter <20 microns) ranged from 1 mm/s to 10mm/s. As expected, the RBC velocity fluctuates with the subject’s cardiac cycle.
Imaging retinal structures with high resolution and high speed is possible via AOSLO. The RBC movements are traceable with the assistance of adaptive optics and high speed imaging. This technique is sensitive to the cardiac cycle of the subject. This technique has the potential to monitor the hemodynamic in retinal micro-vessels which are sensitive to retinal diseases.
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