High-resolution in-vivo human retinal imaging using full-field OCT with optical stabilization of axial motion.
Mecê, P., J. Scholler, K. Groux, and C. Boccara.
Biomedical Optics Express 11, no. 1 (2020): 492-504.
Résumé: © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. Time-domain full-field OCT (FF-OCT) represents an imaging modality capable of recording high-speed en-face sections of a sample at a given depth. One of the biggest challenges to transfer this technique to image in-vivo human retina is the presence of continuous involuntary head and eye axial motion during image acquisition. In this paper, we demonstrate a solution to this problem by implementing an optical stabilization in an FF-OCT system. This was made possible by combining an FF-OCT system, an SD-OCT system, and a high-speed voice-coil translation stage. B-scans generated by the SD-OCT were used to measure the retina axial position and to drive the position of the high-speed voice coil translation stage, where the FF-OCT reference arm is mounted. Closed-loop optical stabilization reduced the RMS error by a factor of 7, significantly increasing the FF-OCT image acquisition efficiency. By these means, we demonstrate the capacity of the FF-OCT to resolve cone mosaic as close as 1.5o from the fovea center with high consistency and without using adaptive optics.
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Retinal Capillary Plexus Pattern and Density from Fovea to Periphery Measured in Healthy Eyes with Swept-Source Optical Coherence Tomography Angiography.
Lavia, C., P. Mecê, M. Nassisi, S. Bonnin, J. Marie-Louise, A. Couturier, A. Erginay, R. Tadayoni, and A. Gaudric.
Scientific reports 10, no. 1 (2020): 1474.
Résumé: Optical coherence tomography angiography is evolving towards wider fields of view. As single widefield acquisitions have a lower resolution, preventing an accurate segmentation of vascular plexuses in the periphery, we examined the retinal vascularisation from the macula to the periphery in all retinal quadrants, using 3 × 3-mm volume scans, to obtain montages with sufficient image resolution up to 11 mm from the foveal centre. Images were qualitatively and quantitatively analysed, using C- and B-scan approaches to calculate the capillary density (CD) and the interplexus distance (IPD). Three vascular plexuses (i.e., superficial vascular plexus: SVP, intermediate capillary plexus: ICP, and deep capillary plexus: DCP) were observed up to the mid-periphery in all sectors. The CD of the SVP decreased from about 5 mm of eccentricity, along with ganglion cell density decrease. The CD of the ICP progressively decreased from the fovea towards the periphery, along with the retinal thinning and then vanished from 8 to 9 mm of eccentricity, becoming undetectable beyond. This ICP disappearance resulted in an increased IPD between the SVP and the DCP in an area known to be frequently affected by capillary drop-out in diabetic retinopathy. The DCP only showed a slightly decreased CD towards the retinal periphery.
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Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography.
Puyo, L., M. Paques, M. Fink, J.A. Sahel, and M. Atlan.
Biomedical Optics Express 10, no. 10 (2019): 4942-4963.
Résumé: © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Laser Doppler holography was introduced as a full-field imaging technique to measure blood flow in the retina and choroid with an as yet unrivaled temporal resolution. We here investigate separating the different contributions to the power Doppler signal in order to isolate the flow waveforms of vessels in the posterior pole of the human eye. Distinct flow behaviors are found in retinal arteries and veins with seemingly interrelated waveforms. We demonstrate a full field mapping of the local resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their systolodiastolic variations. Finally we investigate the arterial flow waveforms in the retina and choroid and find synchronous and similar waveforms, although with a lower pulsatility in choroidal arteries. This work demonstrates the potential held by laser Doppler holography to study ocular hemodynamics in healthy and diseased eyes.
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Origin and role of the cerebrospinal fluid bidirectional flow in the central canal.
Thouvenin, O., L. Keiser, Y. Cantaut-Belarif, M. Carbo-Tano, F. Verweij, N. Jurisch-Yaksi, P.L. Bardet, G. van Niel, F. Gallaire, and C. Wyart.
eLife 9 (2020).
Résumé: © 2020, Thouvenin et al. Circulation of the cerebrospinal fluid (CSF) contributes to body axis formation and brain development. Here, we investigated the unexplained origins of the CSF flow bidirectionality in the central canal of the spinal cord of 30 hpf zebrafish embryos and its impact on development. Experiments combined with modeling and simulations demonstrate that the CSF flow is generated locally by caudally-polarized motile cilia along the ventral wall of the central canal. The closed geometry of the canal imposes the average flow rate to be null, explaining the reported bidirectionality. We also demonstrate that at this early stage, motile cilia ensure the proper formation of the central canal. Furthermore, we demonstrate that the bidirectional flow accelerates the transport of particles in the CSF via a coupled convective-diffusive transport process. Our study demonstrates that cilia activity combined with muscle contractions sustain the long-range transport of extracellular lipidic particles, enabling embryonic growth.
Mots-clés: central canal; cerebrospinal fluid; cilia dynamics; embryogenesis; fluid dynamics; long range transport; physics of living systems; zebrafish
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