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H. Song, X. Qi, T. Chui, S. A. Burns; High-Resolution in vivo Retinal Imaging of Glial Cell Endfeet. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4515.
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© ARVO (1962-2015); The Authors (2016-present)
To explore cellular structures in the living human retina using a high resolution Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO); to further establish the AOSLO as a valuable high resolution, in-vivo imaging tool by imaging different layers and cellular structures in the retina.
An 840 nm (center wavelength) SLD was used as the imaging light source. The adaptive optics control of the system was maintained by using a Boston Micromachines MEMS deformable mirror and Shack Hartmann sensor operating in a closed loop at 8 Hz. The imaging beam was steered by an 8k Hz horizontal scanner and a 15 Hz vertical scanner to sweep an imaging region of 1.8 x 1.7 degree on the retina. Real time video images were collected while focused on retinal veins and capillaries in 4 normal subjects. Images were aligned and averaged using post-processing. The size and morphology of observed structures related to the blood vessels was compared to published histology.
In live AOSLO video movies, the appearance of retinal vessels is dominated by the movement due to blood flow. However, along the blood vessels, at different depth relative to the never fiber layer, numerous stationary bright spots are also visible. And for vessels near the inner limiting membrane, other filamentous structures can be reliably imaged along the surface of blood vessels for all subjects. The size of the bright spots varies from 10um to 20um, which is comparable to the size of the endfeet of the retinal astroglia. The filamentous structures connect to the bright spots, and do not show evidence of blood flow in the live video images, suggesting that they are not capillaries but astroglial processes. These structures are smaller than the retinal nerve fiber bundles, which are readily observed. Repeat imaging in one of the subjects over 3 months indicates that the small structures are stable over time, and therefore not related to blood constituents.
We believe the bright structures along the surface of retinal blood vessel are the endfeet of astroglia because of their close similarity to histological data in terms of their location, size and morphology.
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