Recent investigations in humans have shown that rod and cone outer segments (ROS and COS, respectively) elongate in response to visual stimuli. Specifically, in phase-based optoretinographic (ORG) the relative phases of backscattered light from photoreceptors' inner segment / outer segments (IS/OS) junction and the COS tips (COST), or ROS tips (ROST), is measured, which allows observation of stimulus-evoked, nanometer-scale changes in the OS length. In this manuscript, we used a cellular resolution AO-OCT system employing an FF-SS-OCT acquisition engine that allowed up to kHz volume acquisition rates, which greatly reduced retinal motion artifacts. ORG responses were recorded in two healthy volunteers, with photopigment bleaching levels in the range of 1-60 %, and modeled using an exponential sum. The proposed harmonic oscillator-based response model allowed us to describe the shape of the cone's ORG responses by amplitudes of deflection and relaxation times. The development of simple quantitative parameters describing the ORG response should benefit future clinical applications and help to track the progress of blinding diseases.
In this presentation we will evaluate the signal processing steps required to obtain stimulus-evoked nm-scale changes in the photoreceptor outer segment (OS) length using full field swept source optical coherence tomography (FF-SS-OCT). Evaluation of stimulus-evoked OS length changes is the basis of photoreceptor optoretinography (ORG), an emerging test of retinal function. To allow cellular resolution, an adaptive optics (AO) enhanced FF-SS-OCT system was constructed. This system allows up to kHz volume acquisition rates, which greatly reduce retinal motion artifacts. Specifically, the effects of wave number calibration, dispersion compensation, and application of short-time Fourier transform (STFT) on image quality metrics, SNR of individual OCT volumes, and extracted phase noise will be presented.
Cellular-resolution imaging of the living human retina requires continuous correction of blur caused by the eye’s dynamic, living optics. Over the past twenty-five years, dozens of labs have employed adaptive optics (AO) to measure and correct this blur in conjunction with retinal imaging modalities such as fundus imaging, scanning light ophthalmoscopy, and optical coherence tomography. While the benefits of AO have become more apparent, the costs of developing AO systems has not fallen substantially. A significant fraction of the cost of an AO system is development of control and analysis software. This software is typically developed by individual investigators, and represents a significant duplication of effort and grant support. Here we present an open-source AO control application and illustrate its performance in conjunction with off-the-shelf optical components.
Light-evoked functional retinal imaging is of great interest in clinical and experimental ophthalmology because the alterations in retinal function hold the promise of being potentially more sensitive for disease diagnosis than purely morphology-based assays. Recent progress in Optoretinography (ORG), a technique employing OCT to extract light-evoked functional response of retinal tissue, promises to provide the needed sensitivity to probe early alterations in retinal function. The most promising implementations of the ORG probing of photoreceptor function in clinical settings are using parallel OCT detection schemes such as Line Field and Full Field designs. Herein, we present the instrumentation scheme of a Full-Field-Swept-Source OCT (FF-SS-OCT) system incorporating a high-precision light stimulation channel for facilitating phase-based functional retinal imaging in mice. The assessment of the OCT signal phase errors and their correction using short-time Fourier transform (STFT) is detailed. The performance of the system is investigated using a model eye.
Optoretinography (ORG) is an emerging effort to noninvasively measure the functional responses of retinal neurons. We and other groups have previously shown that cellular-resolution coherent imaging of photoreceptors can reveal microscopic stimulus-evoked changes in the shape of photoreceptors. Such methods track the position of cellular features using phase differences among them. Here we present a novel method using low-cost OCT hardware that monitors the phase velocity of these features instead. The primary advantage of this system is elimination of the need to resolve and track single cells using costly and complicated optical and computational methods. This system may permit rapid, high-throughput measurement of retinal function healthy volunteers and patients.
Development of high resolution functional retinal imaging tools is of great interest to clinical and experimental ophthalmology because the alterations in retinal function, at cellular resolution, hold the promise of being more sensitive for disease diagnostic then the purely retinal morphology-based assays. In this work we present our initial design and implementation of mouse retinal imaging system that incorporates full-field (FF) swept- source (SS) optical coherence tomography (OCT) with dedicated light stimulation channel for high-speed measurements of light evoked responses in photoreceptors of mice. The Optoretinograpahy (ORG) results acquired with our FF-SS-OCT system are compared with those acquired with our standard raster scanning mouse ORG-OCT system.
The development of functional retinal imaging is of great interest to clinical and experimental ophthalmology, because it should provide more sensitive tools for ocular diseases diagnostic that would go beyond current gold standard of simple evaluation of the static retinal morphology. In this presentation we will review our recent progress in measurements and interpretation of OCT-based optoretinograms (ORG) i.e., the paradigm of using NIR OCT to measure in vivo bleaching-induced changes in retinal morphology (transient changes in volume of individual neurons, or thickness of retinal layers). Specifically, comparison between different instrumentations used to acquire ORGs and between results acquired using clinical (human) and experimental (animal) systems will be presented. Additionally, intensity-based and phase-based ORG extraction framework will be presented. Finally, we will discuss our findings in the context of current understanding of measured process, being a result osmotically driven water movements between the photoreceptors, and other retinal neurons and its surroundings.
KEYWORDS: Eye, Angiography, Optical coherence tomography, In vivo imaging, Image quality, Data acquisition, Wavefronts, Wavefront sensors, Visualization, Systems modeling
Accurate and reproducible OCT angiography (OCTA) measurements are highly dependent on the overall phase stability of the sample. Raster-scanning OCT systems are vulnerable to eye motion, which makes phase correlation impossible if the retinal displacement is too large. Numerical methods exist to correct components of phase shifts due to the axial movement, but that due to lateral movement bigger, then imaging spot are not generally correctable. Real-time eye tracking provides a method to reduce the phase shifts caused by lateral eye movement. Here we report the advancements on monitoring ocular metrics during OCTA acquisition and its effects on image quality.
In this work we present a retinal imaging system that incorporates full-field (FF) swept-source (SS) optical coherence tomography (OCT) with hardware adaptive optics (AO) correction operating in real time. We demonstrate that this configuration permits resolution of foveal cones, with volume rates adequate to measure light-evoked changes in photoreceptors. With the OCT reference arm blocked, the system is a high speed (kHz) AO flood illumination (FI) camera, supporting future studies of optoretinographic responses through common path interference. The characterization and demonstration of the system performance with in vivo human photoreceptor mosaic are presented.
In vivo functional imaging of human photoreceptors is an emerging field, with compelling potential applications in basic science, translational research, and clinical management of ophthalmic disease. Measurement of light-evoked changes in the cone photoreceptors has been successfully demonstrated using adaptive optics (AO) coherent flood illumination (CFI), AO scanning light ophthalmoscopy (SLO), AO optical coherence tomography (OCT), and full-field OCT with digital aberration correction (DAC). While the optical and computational principles of these systems differ greatly, and while these differences manifest in the resulting measurements, we believe that the approaches are all sensitive to light-evoked swelling of the cells. We describe a combined OCT-SLO with AO designed to measure this light-evoked swelling. In addition to OCT measurement of cone responses, we report their simultaneous OCT-SLO measurement as well as OCT measurement of rod photoreceptor function, neither of which, to our knowledge, have been reported before.
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