Time-domain Full-Field OCT (FFOCT) acquires en-face images of a sample in a given depth. One of the biggest challenge to use FFOCT for in-vivo retinal imaging is the presence of retinal axial motion during image acquisition. To address this challenge, we previously proposed to couple a spectral-domain OCT (SD-OCT), where axial motion can be measured and later corrected by moving the FFOCT reference arm accordingly in a control loop fashion. However, due to the inherent temporal delay of the control-loop (typically 2-frame delay and 50Hz loop rate), the achieved precision was only around 10µm rms, against ideal 4µm rms (coherence gate of 8µm). Here, we propose to use learning-based prediction methods to enhance the precision of the axial retinal motion correction in real-time, thus improving the FFOCT robustness for in-vivo retinal imaging.
This work presents a clustering approach for Time-domain Full-field optical coherence tomography (TD-FFOCT) retinal images.TD-FFOCT is an efficient method for cellular-level analysis of retinal structures, with fast acquisition and wide field-of-view. However, clinical use faces challenges from involuntary axial retinal motion due to breathing, heartbeat, and pulsation. Despite real-time axial motion compensation, achieved precision is around 10µm rms, below the ideal 4µm for an 8µm coherence gate, impacting system robustness and image depth selection. One way to overcome this is to group together images featuring similar retinal structures and acquired at the same depth. We propose a comprehensive clustering approach using learning-based and non-learning-based methods for feature extraction and clustering. Results show that clustering can help mitigate the effects of motion on the acquired image data, improving imaging accuracy and robustness.
We presented a method to study the influence of static and dynamic ocular aberrations on FFOCT image quality when imaging the retina at high-resolution. The results presented here give important information to infer the best AO design to be used in FFOCT.
We presented the first clinical images generated with compact, clinical-adapted FFOCT. This was made possible thanks to the replacement of the former Adaptive Lens by a Woofer-Tweeter approach, combining a Variable Focal Lens for defocus correction, and the Phaseform’s Deformable Phase Plate for high-order aberrations correction, enabling to improve both SNR and lateral resolution when imaging patients.
We demonstrate the feasibility of a multimodal AO flood-illumination ophthalmoscope, able to provide both bright-field and dark-field images. The multimodality was made possible by integrating a digital micromirror device (DMD) at the illumination path to project a sequence of complementary high-resolution patterns into the retina. Owing to the given system, and the proposed acquisition/processing pipeline, we were able, at the same time, to: (1) obtain up to four-fold contrast improvement in bright-field modality when imaging highly scattered structures such as PRs and NFL; and (2) to visualize, through phase contrast images, translucent retinal features such as capillaries, red blood cells, vessel walls, ganglion cells, and PRs inner segment.
In this work, we implement an Adaptive Optics (AO) Time-Domain Full-Field OCT (TDFFOCT) system, giving the first successful application of sensor-based adaptive optics for wavefront correction in real-time in TDFFOCT. The results demonstrate enhanced resolution and SNR after AO correction, enabling high performance in foveal imaging and also inner retina layers in proximity to the ganglion cell layer (GCL) in a wide FOV (up to 5° x 5°) without any apparent anisoplanatism.
Adaptive optics imaging techniques are invaluable for cellular-level retina visualization. While AO Flood illumination ophthalmoscopes provide distortion-free, high-speed images, they lack contrast. On the other hand, AO scanning laser ophthalmoscopes offer highly contrasted images due to point by point illumination and spatial filtering but suffer from low pixel throughput and distortion artifacts. Our recent advancements, using a DMD integrated AO-FIO, show that we can illuminate and capture multiple spatially separated zones, achieving contrast close to the one of a confocal microscope. Our theoretical framework emphasizes that each zone must be smaller than 100μm in both directions or smaller than 10μm in only one direction to minimize the diffuse light component. Building upon these results, we developed a cutting-edge confocal rolling slit ophthalmoscope, able to achieve brightfield contrast similar to a confocal ophthalmoscope, along with phase contrast images. We utilize a classical sCMOS camera with a rolling shutter synchronized with the line source scanning of the field of view. The system makes use of all the incident photons that can be collected, whether singly, multiply scattered or absorbed. Easy digital switching between the darkfield and brightfield, as well as modification of the size and offset of the detection aperture, enhances the adaptability and versatility of this multimodal imaging system, allowing for fine-tuning of imaging modalities and comprehensive exploration of the retina.
In this work, we implement a pupil conjugated DM-based wavefront sensorless approach in our FFOCT setup. Given the high DM stroke and precision, as well as the Zernike mode-based wavefront optimization using the high-speed DONE algorithm, we showed that higher resolution can be achieved in foveal imaging, as well as obtaining an improved SNR when imaging photoreceptors and NFL when compared to our previous work. Thanks to this SNR improvement, we were able to visualize inner retinal features not previously observed in FFOCT.
We enhanced the capabilities of an Adaptive Optics Flood Illumination Ophthalmoscope to achieve multimodal imaging. The control of the illumination with a digital micromirror device, combined with a wide field of view and a light data processing, allows us to improve the brightfield contrast with a pseudo-confocal mode and to visualize transparent retinal structures with phase contrast imaging. We achieved to get from a single sequence of acquisition, four wide field images, each corresponding to one type of the following imaging modes: contrast-enhanced brightfield, darkfield, offset aperture and split-detection imaging.
KEYWORDS: Wavefronts, Retinal scanning, Optical coherence tomography, In vivo imaging, Eye, Signal to noise ratio, Sensors, Glasses, Image resolution, Cones
We propose a compact full-field OCT assisted by an adaptive lens positioned in front of the eye for wavefront correction, enabling to ally high resolution (2 μm × 2 μm × 8 μm) with a wide field-of-view (5°× 5°) for in vivo retinal imaging.
We present Optical Incoherence Tomography (OIT): a completely digital method to generate tomographic retinal cross-sections from en-face through-focus image stacks acquired by non-interferometric imaging systems, such as en-face adaptive optics (AO)-ophthalmoscopes. We show how to use OIT to guide focus position in cases where the user is “blind" focusing, such as auto fluorescence imaging of the Retinal Pigment Epithelium (RPE). We also demonstrate that OIT can produce distinctive cross-sectional views of the retina using back-scattered, multiply-scattered or even fluorescent light, making it a complementary technique to OCT.
Dynamic FFOCT allows us to record the intrinsic motion of biological samples in 3D, over hours. We performed scratch assays on primary porcine RPE and human induced pluripotent stem cells derived RPE cell cultures. We plotted motion maps from the optical flow. For wounds <40µm, the cell layer close the wound at different speeds depending on the type of RPE cells. For bigger wounds, the cell layer retract, mimicking degenerative diseases. Comparison between Dynamic FFOCT images and Immuno-chemistry images showed that mitochondria may contribute to the dynamic profile of cells. Dynamic FFOCT can be useful for the study of regenerative medicine.
The highest three-dimensional (3D) resolution possible in in-vivo retinal imaging is achieved by combining optical coherence tomography (OCT) and adaptive optics. However, this combination brings important limitations, such as small field-of-view and complex, cumbersome systems, preventing so far the translation of this technology from the research lab to clinics. Here, we mitigate these limitations by combining our compact time-domain full-field OCT (FFOCT) with a multi-actuator adaptive lens positioned just in front of the eye, in a technique we call the adaptive-glasses wavefront sensorless approach. Through this approach, we demonstrate that ocular aberrations can be corrected, increasing the FFOCT signal-to-noise ratio and enabling imaging of different retinal layers with a 2μm x 2μm x 8μm resolution over a 5° x 5° field-of-view, without major anisoplanatism influence.
Allying high-resolution with a large field-of-view (FOV) is of great importance in the fields of biology and medicine, but particularly challenging when imaging non-flat living samples such as the retina. Indeed, high-resolution is normally achieved with adaptive optics (AO) and scanning methods, which considerably reduce the useful FOV and increase the system complexity. Here, we introduce coherence gate shaping for FF-OCT, to optically shape the coherence gate geometry to match the retinal curvature, thus achieving a larger FOV than previously possible. Using this instrument, we obtained high-resolution images of photoreceptors close to the foveal center without AO and with a 1x1m² FOV. This novel advance facilitates the extraction of photoreceptor-based biomarkers and 4D monitoring of individual photoreceptors. We compare our findings with AO-assisted ophthalmoscopes, highlighting the potential of FF-OCT, as a compact system, to become a routine clinical imaging technique.
Retinal laser photocoagulation (LP) is commonly used to treat Diabetic Macular Edema. Yet, it is impossible with current lasers to prevent some degree of damage to healthy surrounding tissues. We evaluate through simulation the improvement in thermal confinement of the photocoagulation effects, using Adaptive Optics (AO), a technology that corrects eye’s aberrations in real-time, to assist LP system.
Based on experimental ocular aberrations data and realistic retinal diffusion model, we simulate the photocoagulation operation and compare LP thermal confinement in laser systems without and with AO correction. Resulting sizes of thermal damage show an improvement of depth confinement, from a 300μm extension with current systems, to a 70μm depth size (limited to therapeutic target) with AO corrected system.
These results underline the need of AO for focal LP to ensure thermal depth confinement and guarantee safe operation.
Dynamic FFOCT allows us to see the sub-cellular motion of biological samples. We are able to follow the evolution in the same plane of biological samples for hours thanks to an autofocus procedure. RPE cells are involved in the integrity of retina and vision. We performed a linear scratch assay in RPE cell culture with a surgical scalpel blade, inducing border cell migration at 20.8 µm/h to close the scratch. We also recorded motility of microvilli, thanks to rapid GPU computing. Quantitative live imaging of RPE cell culture with DFFOCT is useful in development of disease models of retinal degeneration.
To achieve 3D high-cellular resolution, a great effort, in the past years, was made to develop Adaptive Optics (AO)-OCT systems. However, such systems require quite complex, expensive and cumbersome hardware, making clinical transfer challenging. Moreover, conventional AO correction is limited to the retina isoplanatic patch (about 1deg), reducing the useful field of view (FOV). Recently, we showed the potential of Time Domain Full-Field-OCT (FF-OCT) to achieve 2deg FOV high-cellular-resolution in-vivo retinal imaging without using AO. Nevertheless, the technique was still facing some challenges in providing consistent and reproducible images (mainly due to axial eye motion), and it presented a reduced signal and FOV. Here, we present the new generation of FF-OCT system with axial eye motion tracking. We show new results and methods to minimize dispersion and coherence gate curvature enabling achieving 4deg (potentially 8deg) FOV high-cellular-resolution retinal images.
We present a filtering procedure based on singular value decomposition to remove artifacts arising from sample motion during dynamic full field OCT acquisitions. The presented method succeeded in removing artifacts created by environmental noise from data acquired in a clinical setting, including in vivo data. Moreover, we report on a new method based on using the cumulative sum to compute dynamic images from raw signals, leading to a higher signal to noise ratio, and thus enabling dynamic imaging deeper in tissues.
KEYWORDS: Adaptive optics, Eye, Optical coherence tomography, Signal to noise ratio, 3D image enhancement, 3D image processing, Retinal scanning, Glasses, In vivo imaging, Aberration correction
To achieve 3D high-cellular resolution, a great effort, in the past years, was made to develop Adaptive Optics (AO)-OCT systems. However, such systems require quite complex, expensive and cumbersome hardware, making clinical transfer challenging. Recently, we demonstrated that the use of spatially incoherent illumination in Time-Domain Full-Field (FF)-OCT offers a valuable advantage: the lateral resolution is almost insensitive to ocular aberrations that only affect the FF-OCT signal level. We took advantage of this property to image in-vivo photoreceptor mosaic without using an AO technique. Nevertheless, the FF-OCT technique was still facing some challenges in providing consistent and reproducible images, mainly due to axial eye motion and reduced signal level. Here, we present the Adaptive Glasses-assisted FF-OCT, where an adaptive lens is placed just in front of the eye, like spectacles, enabling correction of the first 10 Zernike polynomials, increasing the FF-OCT signal level.
KEYWORDS: In vivo imaging, Retinal scanning, Optical coherence tomography, Wavefronts, 3D image processing, Adaptive optics, Stereoscopy, 3D metrology, Sensors, Eyeglasses
Full-Field Optical Coherence Tomography (FF-OCT) offers aberration independent resolution. This inherent property makes FF-OCT a promising imaging modality for 3D high-resolution retinal imaging. Nevertheless, ocular aberrations affect signal reduction, imposing Adaptive Optics. Here we investigate the best strategy to compensate for ocular aberrations in our FF-OCT setup, in terms of wavefront measurement and correction. The use of wavefront sensorless approach based on the FF-OCT signal level is investigated. Moreover, a strategy of static wavefront correction in a non-conjugated pupil plane and next to the eye’s pupil, just like spectacles, favoring a compact and non-complex AO design, is also investigated. Additionally, the use of wavefront corrector devices such as an adaptive liquid lens (correcting to defocus and astigmatism) and multi-actuator adaptive lenses (correcting up to the 4th order Zernike polynomial) are evaluated. Finally, we expect the implementation of one or a combination of the studied strategies into our FF-OCT setup to lead to the first in-vivo retinal images obtained using AO-assisted FF-OCT, for different retinal layers with enhanced SNR and a 3D high-resolution.
We propose a study to better understand the impact of dynamic ocular aberrations in the axial resolution of nonconfocal adaptive optics (AO) ophthalmoscopes via a simulation of the 3D PSF in the retina for various AO-loop rates. We then use Optical Incoherence Tomography (OIT), a method enabling the generation of tomographic retinal cross-sections in incoherent imaging systems, to evaluate the benefits of a fast AO-loop rate on axial resolution and consequently on AO-corrected retinal image quality. We used the PARIS AO flood- illumination ophthalmoscope (FIO) for this study, where retinal images from different focal planes at an AO-loop rate of 10 Hz and 50 Hz were acquired.
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