Biology subjects

Mece, P.

Publications and source records attributed to Mece, P..

8 recordsLinked to original sources

bioRxiv2024

Adaptive Optics Rolling Slit Ophthalmoscope: Combining cellular-resolution, high-speed and large field-of-view in a multimodal retinal imager

Label-free optical imaging systems capable of monitoring dynamic biological processes over a large field-of-view (FOV) are essential for advancing our understanding of retinal and neurovascular health. However, existing imaging modalities often involve trade-offs between spatial resolution, contrast, FOV, and frame rate. In this study, we present the Adaptive Optics Rolling Slit Ophthalmoscope (AO-RSO), a novel imaging system that integrates the high-speed, wide-FOV capabilities of camera-based systems with the enhanced contrast and multimodal functionality of point-scanning techniques--without compromising resolution or speed. The AO-RSO utilizes line illumination synchronized with the rolling shutter of a high-speed sCMOS camera, enabling precise and dynamic spatial selection of detected photons: back-scattered photons for near-confocal bright-field imaging and forward-scattered photons for phase-contrast imaging of translucent retinal features. This system successfully visualizes diverse retinal structures, including cone and rod photoreceptors, nerve fiber bundles, red blood cells, vessel walls, and ganglion cells, across a wide retinal area (4.5{degrees}x 2.5{degrees}). With a large FOV and frame rates up to 200 Hz, the AO-RSO enables the quantification of blood flow, tracking of red blood cells within hundreds of capillaries, and evaluation of thousands of photoreceptors in the living human retina. This capability opens new opportunities for functional neuronal imaging, neurovascular coupling studies, and the early detection of retinal and neurodegenerative diseases.

bioengineering↗

bioRxiv2024

Measuring flicker induced vasodilation at a high spatial and temporal resolution in the human retina.

Neurovascular coupling (NVC) is a crucial process in which blood flow is dynamically adjusted to meet the metabolic demands of active neurons. In this study, we introduce an innovative method for in-vivo imaging of retinal blood vessel dilation in response to visible light stimulation, offering insights into the functional regulation of retinal blood flow. Using high-resolution, high-speed phase contrast imaging, we continuously monitored retinal vessel dynamics in eight healthy subjects, capturing precise temporal and spatial changes in vessel size under both stimulated and baseline conditions. We have measured a significant vessel dilation of 5.2% {+/-} 1.6% (4.4 {micro}m {+/-} 1.3 {micro}m) during flicker-stimulation compared to a dilation of 2.5% {+/-} 1% (2.1 {micro}m {+/-} 0.9 {micro}m) without stimulation. The flexibility of our method also allowed for the exploration of various acquisition and stimulation settings, broadening possibilities for investigating neurovascular coupling in the retina. This work not only enhances our understanding of neurovascular coupling but also has the potential to identify new biomarkers for vision-impairing conditions and neurodegenerative diseases. SignificanceNeurovascular coupling is a fundamental mechanism of the brain which locally regulates blood flow in response to changes in neuronal activity. Here, we present a new imaging technique that enables measuring vasodilation in response to visible light stimulation of the neurons at high spatial and temporal resolution in the living human retina. Owing to the unprecedented measurement precision of the presented technique, we provide new insights into the inner working of functional blood flow regulation in the retina. Clinically, this method holds promise for vascular dysfunction early detection, which can improve diagnosis of retinal and neurodegenerative diseases, as well as assist the development of new targeted therapies.

neuroscience↗

bioRxiv2023

Foveal drusen increase fixation instability: fixational eye movements as biomarkers for pre-symptomatic AMD

PurposeThis study aims at linking subtle changes of fixational eye movements (FEM) in controls and in patients with foveal drusen using adaptive optics retinal imaging in order to find anatomo-functional markers for pre-symptomatic Age-related Macular Degeneration (AMD). MethodsWe recruited 7 young controls, 4 older controls and 16 presymptomatic AMD patients with foveal drusen from the Silversight Cohort. A high speed research-grade adaptive optics flood illumination ophthalmoscope (AO-FIO) was used for monocular retinal tracking of fixational eye movements. The system allows for sub-arcminute resolution, high-speed and distortion-free imaging of the foveal area. Foveal drusen position and size were documented using gaze-dependent imaging on a clinical-grade AO-FIO. ResultsFEM were measured with high precision (RMS-S2S=0.0015{degrees} on human eyes) and small foveal drusen (median=60{micro}m) were detected with high contrast imaging. Microsaccade amplitude, drift diffusion coefficient and ISOline Area (ISOA) were significantly larger for patients with foveal drusen compared with controls. Among the drusen participants, microsaccade amplitude was correlated to drusen eccentricity from the center of the fovea. ConclusionsA novel high-speed high-precision retinal tracking technique allowed for the characterization of FEM at the microscopic level. Foveal drusen altered fixation stability, resulting in compensatory FEM changes. Particularly, drusen at the foveolar level seemed to have a stronger impact on microsaccade amplitudes and ISOA. The unexpected anatomo-functional link between small foveal drusen and fixation stability opens up a new perspective of detecting oculomotor signatures of eye diseases at the presymptomatic stage.

neuroscience↗

bioRxiv2022

Imaging the structure and dynamic activity of retinal microglia and macrophage-like cells in the living human eye

PurposeWe recently showed how a refined sequential detection pattern and image processing pipeline for multi-offset adaptive optics scanning light ophthalmoscopy (AOSLO) can increase the contrast of weakly scattering inner retinal structures, including microglia. However, sequential detection was still time-consuming, preventing dynamics from being monitored over short intervals (< 3 mins). Here we show that simultaneous fiber-bundle (FB) detection can overcomes this limitation to reveal the structure and dynamic activity of microglia and macrophage-like cells in healthy and diseased retinae. MethodsWe designed and implemented a custom 7-fiber optical FB with one central confocal fiber and six larger fibers for multi-offset detection in AOSLO at a single focal plane. We imaged the ganglion cell layer at several locations at multiple timepoints (from minutes to weeks) in 8 healthy participants and in 4 patients with ocular infections or inflammation, including ocular syphilis and posterior uveitis. Microglia and immune cells were manually segmented to quantify cell morphometry and motility. ResultsFiber-bundle detection reduced single acquisition time to 20-30 seconds, enabling imaging over larger areas and monitoring of dynamics over shorter intervals. Presumed microglia in healthy retinas had an average diameter of 12.8 m and with a spectrum of morphologies including circular cells and elongated cells with visible processes. We also detected the somas of putative macroglia, potentially astrocytes, near the optic nerve head. Microglia moved slowly in normal eyes (0.02m/sec, on average) but speed increased in patients with active infections or inflammation (up to 2.37m/sec). Microglia activity was absent in a patient with chronic uveitis that was quiescent but apparent over short intervals in an active uveitis retina. In a patient with ocular syphilis imaged at multiple timepoints during treatment, macrophage-like cells containing granular internal structures were seen. Decreases in the quantity and motility of these immune cells were correlated with improvements to vision and other structural and systemic biomarkers. ConclusionsFB-AOSLO enable simplified optical setup with easy alignment and implementation. We imaged the fine-scale structure and dynamics of microglia and macrophage-like cells during active infection and inflammation in the living eye for the first time. In healthy eyes we also detected putative glia cell near the optic nerve head. FB-AOSLO offers promise as a powerful tool for detecting and monitoring retinal inflammation and infection in the living eye over short response to treatment.

bioengineering↗

bioRxiv2022

Retinal axial motion analysis and implications for real-time correction in human retinal imaging

High-resolution ophthalmic imaging devices including spectral-domain and full-field optical coherence tomography (SDOCT and FFOCT) are adversely affected by the presence of continuous involuntary retinal axial motion. Here, we thoroughly quantify and characterize retinal axial motion with both high temporal resolution (200,000 A-scans/s) and high axial resolution (4.5 {micro}m), recorded over a typical data acquisition duration of 3 s with an SDOCT device over 14 subjects. We demonstrate that although breath-holding can help decrease large-and-slow drifts, it increases small-and-fast fluctuations, which is not ideal when motion compensation is desired. Finally, by simulating the action of an axial motion stabilization control loop, we show that a loop rate of 1.2 kHz is ideal to achieve 100% robust clinical in-vivo retinal imaging.

bioengineering↗

bioRxiv2020

Spatial frequency-based image reconstruction to improve image contrast in multi-offset adaptive optics ophthalmoscopy

Off-axis detection methods in adaptive optics (AO) ophthalmoscopy can enhance image contrast of translucent retinal structures such as cone inner segments and retinal ganglion cells layer neurons. Here, we propose a 2D optical model showing that the phase contrast produced by these methods depends on the offset orientation. While one axis provides an asymmetric light distribution, hence a high phase contrast, the perpendicular axis provides a symmetric one, thus a substantially lower contrast. We support this model with in-vivo human data acquired with a multi-offset AO scanning light ophthalmoscope. Then, using this finding, we provide a post-processing method, named Spatial frequency-based iMAge ReconsTruction (SMART), to optimally combine images from different off-axis detector orientations, significantly increasing the structural cellular contrast of in-vivo human retinal neurons such as conne inner segment, putative rods and retinal ganglion cells.

bioengineering↗

bioRxiv2020

Improvements to multi-offset adaptive optics scanning laser ophthalmoscopy for in vivo imaging of individual retinal ganglion cell layer neurons in humans

Previous work has shown that multi-offset detection in adaptive optics scanning laser ophthalmoscopy (AOSLO) can be used to image retinal ganglion cells (RGCs) in monkeys and humans. However, though images of RGCs in anesthetized monkeys with high light levels produced high contrast images of RGCs, images from humans failed to reach the same contrast due to several drawbacks in the previous dual-wavelength multi-offset approach. Our aim here was to design and build a multi-offset detection pattern for humans at safe light levels that could reveal the retinal ganglion cell layer neurons with a contrast, robustness and acquisition time approaching results only previously obtained in monkeys. Here, we present a new imaging system using only one light source, compared to the previous dual-wavelength used on monkeys. Our single-wavelength solution allows for increased light power and eliminates problematic chromatic aberrations. Then, we demonstrate that a radial multi-offset detection pattern with an offset distance of 8-10 Airy Disk Diameter (ADD) is optimal to detect photons multiply scattered in all directions from RGCs thereby enhancing their contrast. This new setup and image processing pipeline led to improved imaging of retinal ganglion cells using multi-offset imaging in AOSLO.

bioengineering↗

bioRxiv2020

Improvements to strip-based digital image registration for robust eye-tracking and to minimize distortions in images from scanned ophthalmic imaging systems

Retinal image-based eye tracking from scanned ophthalmic imaging systems, such as scanning laser ophthalmoscopy, has allowed for precise real-time eye tracking at sub-micron resolution. To achieve real-time processing rates, strip-based image registration methods for real-time applications have several constraints that limit their performance. This trade-off is acceptable for many imaging and psychophysical applications but when the objective is precise eye motion measurement over time, a high error tolerance can be consequential. Dropped strips in these applications can complicate FEMs quantification. Some light starved imaging applications, such as autofluorescence retinal imaging, also require the retention and registration of as much of the data as possible to increase the signal to noise ratio in the final integrated or averaged image. We show here that eye motion can be extracted from image sequences from scanned imaging systems more consistently when the constraints of real-time processing are lifted, and all data is available at the time of registration. This is enabled with additional image processing steps to achieve a more robust solution. Our iterative approach identifies and discards distorted frames, detects coarse motion to generate a synthetic reference frame and then uses it for fine scale motion tracking with improved sensitivity over a larger area. We demonstrate its application here to tracking scanning laser ophthalmoscopy (TSLO) and adaptive optics scanning light ophthalmoscopy (AOSLO). We show that it can successfully capture most of the eye motion across each image sequence, leaving only between 0.04-3.39% of non-blink frames untracked, even with low quality images, while simultaneously minimizing image distortions induced from eye motion. These improvements will facilitate precise FEMs measurement in TSLO and longitudinal tracking of individual cells in AOSLO.

bioengineering↗