CE19 - Technologies pour la santé

The EYE, a WINdow to neurovascular coupling – EyeWin

The EYE, a WINdow to neurovascular coupling

Neuro Vascular Coupling (NVC) is a mechanism by which the supply of oxygen and nutrients is adjusted to neural activity via blood flow regulation. Disruption of NVC in the brain is at the core of several pathologies. Extensive analysis of NVC has been performed on animals. Non-invasive technics are used on humans (OLD fMRI) but lack resolution. Retina offers access to NVC evaluation through non invasice optical techniques, provided that high spatial and temporal resolution is reached.

Goals and challenges of the Eyewin project

The goal of the EyeWin project is to provide an advanced clinical tool to probe neurovascular coupling in the retina at the micrometer and millisecond scale, so as to analyze NVC through high resolution stimulation and imaging of vascular response biomarkers. The Eyewin project aims therefore to explore NVC in various locations throughout the retina, at different temporal and spatial scales in order to better understand how NVC modulates circulation in the various retina layers at an unprecedented scale. Biomarker maps will be generated at each retinal zone. Areas of abnormality in these biomarker maps will be highlighted in image processing. This clinical NVC mapping will uncover the core mechanism of the principle diseases that impair vision and the neurovascular system. The foreseen impact goes beyond ophthalmology, because the eye provides a window to observe the neurovascular network of the brain.

The eyewin project relies on various tools:
- the Clovis3D bench, developped during a previous ANR to study and treat diabetic retinopathy and macular oedema with a revolutionary accuracy, thanks to an adaptive optics system ;
- th EcurOeil PAris Group pathfinder: this bench is installed in the 15-20 hospital and equipped with adaptive optics to realize state of the art retinal images. It allows testing various disrupting imaging concepts on patients
- the RTX1 commercial adaptive optics imager: that allows to image the retina on a large number of patients, though spatial and temporal resolution is lower than EcurOeil and Clovis3D, but allows to select the most relevant cases and to perform preliminar clinical analysis.
The eywin project is structured along 4 axis or workpackages:
1- analysis of the clinical needs and conditions for NVC study
2- adaptation of Clovis3D and EcurOeil benches for stimulation and development of the associated functional imaging features.
3- upgrade Clovis3D and EcurOeil up o clinical grade tools
4- realize a clinical investigation of NVC

A reliminary analysis of NVC has been performed yhanks to the RTX1 and has allowed to elaborate a specific strategy for clinical investigation of NVC with Clovis3D and EcurOeil, while identifying the necessary modifications of these tools.
This analysis has allowed to spot the limitations of these tools in particular robustness and performance issues. An optimization and robustification work has been thus started on the following points:
- high performance stabilisation of retinal imaging on Clovis3D : so as to ensure targeted stimulation and high resolution imaging with high contrast, a 1.5µm rms stabilization has been developped, working up to 85% of the time thanks to saccades handling. This brings Clovis3D stabilization to the state of the art.
- Optimization of full field imaging quality: Clovis3D adaptive optics corrected full field imaging is limited to 2°. A optical field corrector has been designed to increase this field to 4° so as to be able to evaluate NVC in wider areas.
- robustifying Clovis3D bench: so as to ensure use of the bench on patients, and in addition to the stabilisation function, an original method for wvaefront sensing with Shack Hartmann has been developped, ensuring robust analysis in degraded conditions.
- New ethod for high resolution imaging of the retina: so as to increase the contrast of retinal camra and thus the accuracy of vascular activity, an hybrid technic, between full field ophtalmoscope and scanning laser ophtalmoscope, has been proposed : the partial field illumination ophtalmoscope. This disruptive concept is tested on EcurOeil.
- Clovis3D and EcurOeil as clinical grade tools: both benches have been adapted to become clinical grade tools, based on an ANSM equest, evaluation and adjustment of eye safety, and evaluating the thermal effects at retinal and RPE levels.The ergonomy of the benches has been adapted.

The Clovis3 bench has now reached the robustness, the performance and the ergonomy required for NVC clinical investigation on patients, though in spite of various difficulties. The next steps of the project are thus:
- transfer of the clovis3D bench to the 15-20 hospital, planned during summer 2021
- start of the stimulation tests on EcurOeil and Clovi3D, using the specificities of each bench. Stimulation will first be investigated in a large field approach to validate the functional imaging and compare results with those obtained on RTX1, with similar stimulation strategies. Clovis3D and Ecuroeil will provide already higher spatial and temporal resolution. The partial field illumination ophtalmoscope shall improve the imaging on EcurOeil (higher contrast).
In 2022 will be performed:
- a NVC clinical study in large field stimulation or medium field stimulation on patients with the strategy validated in 2021.
- adjustment of Clovis3D to allow high resolution and targeted stimulation with investigation on patients.

It should be noted that the work done in eyewin has allowed to identify an original application: psychophysics, because the very accurate measurement of ocular micromovements is a biomarker of normal aging or of neurovascular network disruption, similarly as NVC. The evolutions of Ecuroeil, performed within Eyewin, have allowed to acquire unprecedented high quality data to characterize fine fixating movements.

- Preliminary analysis of NVC in the eye : D. Castro Farias Master report

- High performance stabilization : a method for fast and accurate stabilization based on correlation of retinal images with detection of saccades allowing to reach the world highest performance with a 1.5µm rms stabilisation, 85% of the time. Article currently being written.

- robustifying the Shack-Hartmann measurement of ocular aberrations: this work allows considering adaptive optics on patients with increased robustness. Article currently being written.

- Evaluation of thermo-optical effect of a confined laser beam on the retina: this work related to photo-thermal effects of a focused laser beam onto the retina is both valuable to ensure proper eye safety when performing stimulation and preparing laser photocoagulation with higher energy. Article currently being written.

These main results have been obtained in the framework of the PhD of A. Chen and have been presented in various oral presentations in national and international conferences.

- Partial illuminated ophtalmocope: this new thecnic shall increase the onctrast of retinal cameras for vascular imaging thanks to an hybrid approach. An article is currently under review.

- Validation of Clovis3D and EcurOeil as clinical grade tools by ANSM: this allows considering clinical tests in imaging. The procedure shall be extended to incorporate stimulation.

- Patents : 2 patents related to Clovis3D
Laser photocoagulation system of a retina
Method for optical incoherence tomography in ophthalmology

NeuroVascular Coupling (NVC) means that increased metabolic activity in neurons calls for increased blood supply. Disruption of NVC in the brain is at the core of several pathologies, including ischemic stroke, Alzheimer ‘s Disease (AD), and hypertension induced cognitive deficits. A precise characterization of NVC will provide biomarkers for the evolution of these diseases, and may ultimately lead to the development of therapies.
In humans, however, the only optical window to a neuro-vascular network in our body is the eye as the retinal neurovascular network is an integral part of the brain. As such, NVC is a core mechanism in the retina too, and NVC disruption is involved in the most common retinal diseases - Diabetic Retinopathy (DR), Glaucoma and Age-related Macular Degeneration (AMD). It can be assessed by illuminating photoreceptor neurons with flickering light, and measuring short-term blood flow evolution (over a few seconds) in response to the light stimulation. Many techniques have been used to document NVC in the retina but these methods lack spatial resolution both for stimulation and vascular imaging. A high spatial resolution in NVC observation is required as blood flow control in the retina is finely localized, DR and AMD start with focal lesions, and NVC affects the various layers of retinal microvessels differently.
The goal of the EyeWin project is to provide an advanced clinical tool to probe local neurovascular coupling in the retina at the micrometer and millisecond scale. NVC can be monitored by looking at changes in vessel caliber, blood flow and oximetry, in response to stimulation. The system will selectively stimulate pathological areas in the central retina (typically a few 100µm size) with a precision of a few micrometers, which represents an unprecedented resolution in NVC studies. Subsequent vascular response biomarkers will be imaged at the micrometer and millisecond scale.
The project will rely on an existing set-up, Clovis3D, developed for high resolution laser photocoagulation and embedding colocalized SD-OCT and AOFIO en-face imaging, thus representing a powerful tool for NVC investigation. Imaging will be performed in the infrared to prevent any stray light stimulation of the retina. Vessel caliber, blood flow or oxygen saturation maps will be generated at each retinal zone. Areas of abnormality in biomarker maps will be highlighted in image processing, to provide the clinician with a visual representation of areas of reduced retinal function, which he can then target for therapy. The efficacy of this therapy can then be monitored using the same method.
First, clinical needs will be assessed based on an existing image database and preliminary clinical tests on commercial devices, in order to define the most relevant biomarkers, as well as the optimal observation and stimulation parameters. These requirements will be translated into system specifications. Identified evolutions of the bench, required to adapt and optimize stimulation, will be performed. Novel vascular functional imaging techniques, based on latest developments on the PARIS Pathfinder, will be improved and implemented on EyeWin setup. To perform clinical trials in safe and ergonomic conditions, this setup will be brought up to a clinical grade tool, compliant with ANSM requirements. After validation of the final setup and associated softwares, a clinical campaign will be carried out on numerous patients to shine a new light on the retinal neurovascular network.
The project relies on a well-established partnership between clinicians (CIC1423), a research lab specialized in technology transfer (Onera) and an international market leader in industry (Quantel Medical), developed through various prior projects, including Clovis3D. Progress is expected in both diagnosis and therapy of pathologies associated with cerebrovascular dysfunctions with potentially high societal impact.

Project coordination

CYRIL PETIT (OFFICE NATIONAL D'ETUDES ET RECHERCHES AEROSPATIALES)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CIC1423 CIC des XV-XX
QLM QUANTEL MEDICAL
ONERA OFFICE NATIONAL D'ETUDES ET RECHERCHES AEROSPATIALES

Help of the ANR 483,801 euros
Beginning and duration of the scientific project: - 36 Months

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