Coarse-scale optoretinography (CoORG) with extended field-of-view for normative characterization

Light-adapted flicker-optoretinography based on raster-scan optical coherence tomography towards clinical translation

Optoretinography (ORG) is a promising non-invasive and objective technique for assessing retinal function by measuring its response to light stimulation. Optical coherence tomography (OCT) has emerged as a promising tool for implementing ORG due to its three-dimensional imaging capabilities, high sensitivity to nanometer-scale changes induced by light stimulation, and clinical availability. Although ORG has proven feasible in laboratory settings, research-grade OCT systems lack satisfactory usability and cost-effectiveness to be clinically viable. Standard clinical raster-scan OCT systems, with their limited imaging speed, fall short of the requirements for measuring rapid ORG responses. To bridge this gap, we introduce a flicker-ORG modality based on a raster-scan OCT system that resembles standard clinical OCT. This system overcomes speed limitations through an innovative two-stage scanning protocol coupled with a 600 kHz swept source, enabling repeated volume imaging and precise retinal activity measurements over a finite area. Additionally, the light-adapted ORG strategy eliminates the need for dark adaptation, allowing examinations under photopic conditions and thus improving patient compliance. We tested this new ORG method by measuring flicker-induced photoreceptor responses in five healthy subjects. The results demonstrated high repeatability and revealed dependencies of the ORG response on flicker frequency and retinal eccentricity. These findings, combined with the system's utility, cost-effectiveness, and ease of integration into existing technologies, underscore its substantial potential for clinical application.

Optical Assessment of Photoreceptor Function Over the Macula

Purpose

The purpose of this study was to develop next-generation functional photoreceptor imaging using ultrahigh-speed swept-source optical coherence tomography (UHS-SS-OCT) and split-spectrum amplitude-decorrelation optoretinography (SSADOR) algorithm. The advancement enables rapid surveying of large retinal areas, promising non-contact, objective, and quantifiable measurements of macular visual function.

Methods

We designed and built a UHS-SS-OCT prototype instrument using a wavelength tunable laser with 1 MHz A-scan rate. The functional scanning protocol records 5 repeated volumes in 3 seconds. A flash pattern selectively exposes the imaged retina area. SSADOR quantifies photoreceptor light response by extracting optical coherence tomography (OCT) signal changes within the photoreceptor outer segment before and after the flash.

Results

The study prospectively enrolled 16 eyes from 8 subjects, demonstrating the ability to measure photoreceptor light response over a record field of view (3 × 3 mm2) with high topographical resolution (approximately 100 µm). The measured SSADOR signal corresponds to the flashed pattern, whose amplitude also correlates with flash strength, showing consistency and reproducibility across subjects.

Conclusions

The integration of high-performance UHS-SS-OCT and SSADOR enables characterizing photoreceptor function over a clinically meaningful field of view, while maintaining a workflow that can be integrated into routine clinical tests and trials. The new approach allows detecting changes in photoreceptor light response with high sensitivity and can detect small focal impairments.

Translational Relevance

This innovative advance can enable us to detect early photoreceptor abnormalities, as well as help to stage and monitor degenerative retinal diseases, potentially providing a surrogate visual function marker for retinal diseases and accelerating therapeutic development through a safe and efficient outcome endpoint.

Multimodal High-Resolution Imaging in Retinitis Pigmentosa: A Comparison Between Optoretinography, Cone Density, and Visual Sensitivity

Purpose

Retinitis pigmentosa (RP), the most common inherited retinal disease, is characterized by progressive photoreceptor degeneration. It remains unknown to what extent surviving photoreceptors transduce light and support vision in RP. To address this, we correlated structure and functional measures using adaptive optics scanning laser ophthalmoscopy (AOSLO), adaptive optics microperimetry, and adaptive optics optical coherence tomography (AO-OCT)-based optoretinograms (ORGs).

Methods

Four patients with RP were imaged with AOSLO across the visual field covering the transition zone (TZ) of normal to diseased retina. Cone density was estimated in discrete regions spanning the TZ. Visual sensitivity was assessed by measuring increment thresholds for a 3-arcmin stimulus targeted via active eye tracking in AOSLO. ORGs were measured at the same locations using AO-OCT to assess the cones' functional response to a 528 ± 20-nm stimulus. Individual cone outer segment (COS) lengths were measured from AO-OCT in each subject.

Results

Cone density was significantly reduced in patients with RP. Density reduction correlated with TZ location in 3 patients with RP, while a fourth had patches of reduced density throughout the retina. ORG amplitude was reduced in regions of normal and reduced cone density in all patients with RP. ORG response and COS length were positively correlated in controls but not in patients with RP. Despite deficits in cone density and ORG, visual sensitivity remained comparable to controls in three of four patients with RP.

Conclusions

ORG-based measures of retinal dysfunction may precede deficits in cone structure and visual sensitivity. ORG is a sensitive measure of RP disease status and has significant potential to provide insight into disease progression and treatment efficacy.

Line-field dynamic optical coherence tomography platform for volumetric assessment of biological tissues

Dynamic optical coherence tomography (dOCT) utilizes time-dependent signal intensity fluctuations to enhance contrast in OCT images and indirectly probe physiological processes in cells. Majority of the dOCT studies published so far are based on acquisition of 2D images (B-scans or C-scans) by utilizing point-scanning Fourier domain (spectral or swept-source) OCT or full-field OCT respectively, primarily due to limitations in the image acquisition rate. Here we introduce a novel, high-speed spectral domain line-field dOCT (SD-LF-dOCT) system and image acquisition protocols designed for fast, volumetric dOCT imaging of biological tissues. The imaging probe is based on an exchangeable afocal lens pair that enables selection of combinations of transverse resolution (from 1.1 µm to 6.4 µm) and FOV (from 250 × 250 µm2 to 1.4 × 1.4 mm2), suitable for different biomedical applications. The system offers axial resolution of ∼ 1.9 µm in biological tissue, assuming an average refractive index of 1.38. Maximum sensitivity of 90.5 dB is achieved for 3.5 mW optical imaging power at the tissue surface and maximum camera acquisition rate of 2,000 fps. Volumetric dOCT images acquired with the SD-LF-dOCT system from plant tissue (cucumber), animal tissue (mouse liver) and human prostate carcinoma spheroids allow for volumetric visualization of the tissues' cellular and sub-cellular structures and assessment of cellular motility.

Intensity-based optoretinography reveals sub-clinical deficits in cone function in retinitis pigmentosa

Introduction

Clinical tools have been widely used in the diagnosis, description, and monitoring the progression of retinitis pigmentosa (RP); however, many of these methods have inherently low sensitivity and specificity, and significant photoreceptor disruption can occur before RP progression has clinically manifest. Adaptive optics scanning light ophthalmoscopy (AOSLO) has shown promise as a powerful tool for assessing photoreceptor disruption both structurally and functionally due to its increased resolution.

Methods

Here we assess photoreceptor structure and function at the cellular level through AOSLO by acquiring intensity based optoretinography (iORG) in 15 individuals with no reported retinal pathology and 7 individuals with a prior clinical diagnosis of RP. Photoreceptor structure was quantified by calculating cone nearest neighbor distance (NND) across different retinal eccentricities from the AOSLO images. Cone outer segment length was measured across different retinal eccentricities using optical coherence tomography (OCT) derived longitudinal reflectivity profiles (LRPs). Finally, iORG measures of photoreceptor function were compared to retinal sensitivity as measured using the macular integrity assessment (MAIA) microperimeter.

Results

Broadly, participants with RP exhibited increasing cone nearest neighbor distances and decreasing cone outer segment length as a function of retinal eccentricity, consistent with prior reports for both controls and individuals with RP. Nearly all individuals with RP had reduced iORG amplitudes for all retinal eccentricities when compared to the control cohort, and the reduction was greater in eccentricities further from the fovea. Comparing iORG amplitudes to MAIA retinal sensitivity, we found that the iORG was more sensitive to early changes in photoreceptor function whereas MAIA was more sensitive to later stages of disease.

Discussion

This highlights the utility of iORG as a method to detect sub-clinical deficits in cone function in all stages of disease progression and supports the future use of iORG for identifying cells that are candidates for cellular based therapies.

Parafoveal cone function in choroideremia assessed with adaptive optics optoretinography

Choroideremia (CHM) is an X-linked retinal degeneration leading to loss of the photoreceptors, retinal pigment epithelium (RPE), and choroid. Adaptive optics optoretinography is an emerging technique for noninvasive, objective assessment of photoreceptor function. Here, we investigate parafoveal cone function in CHM using adaptive optics optoretinography and compare with cone structure and clinical assessments of vision. Parafoveal cone mosaics of 10 CHM and four normal-sighted participants were imaged with an adaptive optics scanning light ophthalmoscope. While acquiring video sequences, a 2 s 550Δ10 nm, 450 nW/deg2 stimulus was presented. Videos were registered and the intensity of each cone in each frame was extracted, normalized, standardized, and aggregated to generate the population optoretinogram (ORG) over time. A gamma-pdf was fit to the ORG and the peak was extracted as ORG amplitude. CHM ORG amplitudes were compared to normal and were correlated with bound cone density, ellipsoid zone to RPE/Bruch's membrane (EZ-to-RPE/BrM) distance, and foveal sensitivity using Pearson correlation analysis. ORG amplitude was significantly reduced in CHM compared to normal (0.22 ± 0.15 vs. 1.34 ± 0.31). In addition, CHM ORG amplitude was positively correlated with cone density, EZ-to-RPE/BrM distance, and foveal sensitivity. Our results demonstrate promise for using ORG as a biomarker of photoreceptor function.

Optical coherence tomography split-spectrum amplitude-decorrelation optoretinography

This pilot study reports the development of optical coherence tomography (OCT) split-spectrum amplitude-decorrelation optoretinography (SSADOR) that measures spatially resolved photoreceptor response to light stimuli. Using spectrally multiplexed narrowband OCT, SSADOR improves sensitivity to microscopic changes without the need for cellular resolution or optical phase detection. Therefore, a large field of view (up to 3 × 1 mm² demonstrated) using conventional OCT instrument design can be achieved, paving the way for clinical translation. SSADOR promises a fast, objective, and quantifiable functional biomarker for photoreceptor damage in the macula.

Introduction to the Feature Issue on Adaptive Optics for Biomedical Applications

The guest editors introduce a feature issue commemorating the 25th anniversary of adaptive optics in biomedical research.

Repeatability and reciprocity of the cone optoretinogram

Optoretinography has enabled noninvasive visualization of physiological changes in cone photoreceptors exposed to light. Understanding the cone optoretinogram in healthy subjects is essential for establishing it as a biomarker for cone function in disease. Here, we measure the population cone intensity optoretinogram in healthy adults, for multiple irradiance/duration combinations of visible stimuli with equal energy. We study the within and between session repeatability and reciprocity of the ORG in five healthy subjects. We find the cone optoretinogram exhibits equivalent amplitudes for equal-energy stimuli. We also find good within-subject repeatability, which allows us to show differences across the five subjects.